Aber, J. D. (2001). “Forest processes and global environmental change: predicting the effects of individual and multiple stressors.” BioScience 51(9): 735-751.
INTRODUCTION: Global change involves the simultaneous and rapid alteration of several key environmental parameters that control the dynamics of forests. We cannot predict with certainty, through direct experimentation, what the responses of forests to global change will be, because we cannot carry out the multisite, multifactorial experiments required for doing so. The physical extent, complexity, and expense of even single-factor experiments at the scale of the whole ecosystem challenge our abilities, although several such experiments have been successfully undertaken (e.g., DeLucia et al. 1999, Wright and Rasmussen 1998). To inform policy decisions, however, the scientific community can offer an interdisciplinary synthesis of existing information. When this synthesis takes the form of a computer model, quantitative predictions can be made that integrate what has been learned from single-factor experiments. The success of such an approach depends on the quality and completeness of the information base and on the rigor of the modeling effort.
The direct and secondary physiological effects of changes in the physical and chemical climate on plants and soils are relatively well known. We also know which primary environmental drivers—precipitation, temperature, and atmospheric concentrations of carbon dioxide (CO2), ozone (O3), and nitrogen (N), for example—are being altered by human activities, and we can directly measure temporal change in these parameters. Despite this relatively rich information base, predictions of future responses of forests to environmental change show significant variation. This is due in part to differences between the models of ecosystem function derived from the existing database and in part to differences in climate scenarios generated by the general circulation models (GCMs) used to predict future climates. Understanding both the trend in predicted futures and the uncertainties surrounding those trends is critical to policy formation. At this time, the major mechanism for determining the degree of uncertainty in predictions is through comparison of results from runs of different models using identical input parameters.
The purpose of this article is to review the state of prediction of forest ecosystem response to envisioned changes in the physical and chemical climate. These results are offered as one part of the forest sector analysis of the National Assessment of the Potential Consequences of Climate Variability and Change; other contributions to this assessment appear in this edition of BioScience. This article has three sections. The first offers a very brief review of the literature on the effects of environmental factors on forest ecosystem function (some references are also made to changes in species composition, but Hansen et al.  provide a more complete discussion). The second and largest part of the article is a summary of results from the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP), an integrated effort to predict ecosystem response to climate change. The third is a brief review of other regional modeling efforts that have addressed climate change or have looked at the possible effects of other components of global change, using tropospheric ozone and nitrogen deposition as examples, or both.
Aber, J. D., et al. (1995). “Predicting the effects of climate change on water yield and forest production in the northeastern United States.” Climate Research 5(3): 207-222.
ABSTRACT: Rapid and simultaneous changes in temperature, precipitation and the atmospheric concentration of CO2 are predicted to occur over the next century. Simple, well-validated models of ecosystem function are required to predict the effects of these changes. This paper describes an improved version of a forest carbon and water balance model (PnET-II) and the application of the model to predict stand- and regional-level effects of changes in temperature, precipitation and atmospheric CO2 concentration. PnET-II is a simple, generalized, monthly time-step model of water and carbon balances (gross and net) driven by nitrogen availability as expressed through foliar N concentration. Improvements from the original model include a complete carbon balance and improvements in the prediction of canopy phenology, as well as in the computation of canopy structure and photosynthesis. The model was parameterized and run for 4 forest/site combinations and validated against available data for water yield, gross and net carbon exchange and biomass production. The validation exercise suggests that the determination of actual water availability to stands and the occurrence or non-occurrence of soil-based water stress are critical to accurate modeling of forest net primary production (NPP) and net ecosystem production (NEP). The model was then run for the entire NewEngland/New York (USA) region using a 1 km resolution geographic information system. Predicted long-term NEP ranged from -85 to +275 g C m-2 yr-1 for the 4 forest/site combinations, and from -150 to 350 g C m-2 yr-2 for the region, with a regional average of 76 g C m-2 yr-1 A combination of increased temperature (+6°C), decreased precipitation (-15%) and increased water use efficiency (2x, due to doubling of CO2) resulted generally in increases in NPP and decreases in water yield over the region.
Acuna-Soto, R., et al. (2002). “Megadrought and megadeath in 16th century Mexico.” Emerging Infectious Diseases 8(4): 360-362.
ABSTRACT: The native population collapse in 16th century Mexico was a demographic catastrophe with one of the highest death rates in history. Recently developed tree-ring evidence has allowed the levels of precipitation to be reconstructed for north central Mexico, adding to the growing body of epidemiologic evidence and indicating that the 1545 and 1576 epidemics of cocoliztli (Nahuatl for “pest”) were indigenous hemorrhagic fevers transmitted by rodent hosts and aggravated by extreme drought conditions.
Adams, K. D. (2003). “Age and paleoclimatic significance of late Holocene lakes in the Carson Sink, NV, USA.” Quaternary Research 60(3): 294-306.
ABSTRACT: New dating in the Carson Sink at the termini of the Humboldt and Carson rivers in the Great Basin of the western United States indicates that lakes reached elevations of 1204 and 1198 m between 915 and 652 and between 1519 and 1308 cal yr B.P., respectively. These dates confirm Morrison’s original interpretation (Lake Lahontan: Geology of the Southern Carson Desert, Professional Paper 40, U.S. Geol. Survey, 1964) that these shorelines are late Holocene features, rather than late Pleistocene as interpreted by later researchers. Paleohydrologic modeling suggests that discharge into the Carson Sink must have been increased by a factor of about four, and maintained for decades, to account for the 1204-m lake stand. The hydrologic effects of diversions of the Walker River to the Carson Sink were probably not sufficient, by themselves, to account for the late Holocene lake-level rises. The decadal-long period of increased runoff represented by the 1204-m lake is also reflected in other lake records and in tree ring records from the western United States.
Adams, R. M., et al. (1990). “Global climate change and US agriculture.” Nature 345(17 May 1990).
ABSTRACT: Agricultural productivity is expected to be sensitive to global climate change. Models from atmospheric science, plant science and agricultural economics are linked to explore this sensitivity. Although the results depend on the severity of climate change and the compensating effects of carbon dioxide on crop yields, the simulation suggests that irrigated acreage will expand and regional patterns of US agriculture will shift. The impact on the US economy strongly depends on which climate model is used.
Alftine, K. J., et al. (2003). “Feedback-driven response to multidecadal climatic variability at an alpine treeline.” Physical Geography 24(6): 520-535.
ABSTRACT: The Pacific Decadal Oscillation (PDO) has significant climatological and ecological effects in northwestern North America. Its possible effects and their modification by feedbacks are examined in the forest-tundra ecotone in Glacier National Park, Montana, USA. Tree ring samples were collected to estimate establishment dates in 10 quadrats. Age-diameter regressions were used to estimate the ages of uncored trees. The temporal pattern of establishment and survival was compared to the pattern of the PDO. A wave of establishment began in the mid-1940s, rose to a peak rate in the mid-1970s, and dropped precipitously beginning ca. 1980 to near zero for the 1990s. The period of establishment primarily coincided with the negative phase of the PDO, but the establishment and survival pattern is not correlated with the PDO index. The pattern indicates a period during which establishment was possible and was augmented by positive feedback from surviving trees. Snow may be the most important factor in the feedback, but studies indicate that its effects vary locally. Spatially differentiated analyses of decadal or longer periodicity may elucidate responses to climatic variation.
Alig, R. J., et al. (2006). “Forest carbon dynamics in the Pacific Northwest (USA) and the St. Petersburg region of Russia: comparisons and policy implications.” Climate Change 79(3-4): 335-360.
ABSTRACT: Forests of the United States and Russia can play a positive role in reducing the extent of global warming caused by greenhouse gases, especially carbon dioxide. To determine the extent of carbon sequestration, physical, ecological, economic, and social issues need to be considered, including different forest management objectives across major forest ownership groups. Private timberlands in the U.S. Pacific Northwest are relatively young, well stocked, and sequestering carbon at relatively high rates. Forests in northwestern Russia are generally less productive than those in the Northwestern U.S. but cover extensive areas. A large increase in carbon storage per hectare in live tree biomass is projected on National Forest timberlands in the U.S. Pacific Northwest for all selected scenarios, with an increase of between 157–175 Mg by 2050 and a near doubling of 1970s levels. On private timberlands in the Pacific Northwest, average carbon in live tree biomass per hectare has been declining historically but began to level off near 65 Mg in 2000; projected levels by 2050 are roughly what they were in 1970 at approximately 80 Mg. In the St. Petersburg region, average carbon stores were similar to those on private lands in the Pacific Northwest: 57 Mg per hectare in 2000 and ranging from 40 to 64 Mg by 2050. Although the projected futures reflect a broad range of policy options, larger differences in projected carbon stores result from the starting conditions determined by ownership, regional environmental conditions, and past changes in forest management. However, an important change of forest management objective, such as the end of all timber harvest on National Forests in the Pacific Northwest or complete elimination of mature timber in the St. Petersburg region, can lead to substantial change in carbon stores over the next 50 years.
Allen, C. D. and D. D. Breshears (1998). “Drought-induced shift of a forest-woodland ecotone: Rapid landscape response to climate variation.” Proceedings of the National Academy of Sciences 95(25): 14839-14842.
ABSTRACT: In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects, particularly those caused by mortality largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and piñon-juniper woodland shifted extensively (2 km or more) and rapidly (<5 years) through mortality of ponderosa pines in response to a severe drought. This shift has persisted for 40 years. Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change. Allen, M. R. and W. J. Ingram (2002). "Constraints on future changes in climate and the hydrologic cycle." Nature 419(6903): 224-232. ABSTRACT: What can we say about changes in the hydrologic cycle on 50-year timescales when we cannot predict rainfall next week? Eventually, perhaps, a great deal: the overall climate response to increasing atmospheric concentrations of greenhouse gases may prove much simpler and more predictable than the chaos of short-term weather. Quantifying the diversity of possible responses is essential for any objective, probability-based climate forecast, and this task will require a new generation of climate modelling experiments, systematically exploring the range of model behaviour that is consistent with observations. It will be substantially harder to quantify the range of possible changes in the hydrologic cycle than in global-mean temperature, both because the observations are less complete and because the physical constraints are weaker. Alley, R. B., et al. (2003). "Abrupt climate change." Science 299: 2005-2010. ABSTRACT: Large, abrupt, and widespread climate changes with major impacts have occurred repeatedly in the past, when the Earth system was forced across thresholds. Although abrupt climate changes can occur for many reasons, it is conceivable that human forcing of climate change is increasing the probability of large, abrupt events. Were such an event to recur, the economic and ecological impacts could be large and potentially serious. Unpredictability exhibited near climate thresholds in simple models shows that some uncertainty will always be associated with projections. In light of these uncertainties, policy-makers should consider expanding research into abrupt climate change, improving monitoring systems, and taking actions designed to enhance the adaptability and resilience of ecosystems and economies. Anderson, J. J. (1997). Decadal climate cycles and declining Columbia River salmon. Proceedings Sustainable Fisheries Conference, Victoria, B.C. ABSTRACT: This paper explores the effects of the interaction of anthropogenic trends and climate cycles on salmon declines in the Columbia and Snake river basins. A basic population model, including anthropogenic and environmental factors, is discussed and literature relating decadal scale climate patterns and the response of the North Pacific ecosystem is reviewed. From this background a ratchet-like decline in Columbia and Snake river salmon production resulted from the interactions of human activities and climatic regime shifts. These interactions are illustrated using hundred year patterns in spring chinook salmon (Oncorhynchus tshawytscha) catch, the Columbia River hydroelectric generating capacity, and a climate index characterizing the shifts between a cool/wet regime favorable to West Coast salmon and a warm/dry regime unfavorable to West Coast salmon. A half century correlation of the climate index and chinook catch suggest that a favorable climate regime counteracted detrimental impacts of hydrosystem development between 1945 and 1977, while an unfavorable climate regime negated beneficial effects of salmon mitigation efforts after 1977. This hypothesis is elaborated by a comparison of changes in the climate index relative to changes in Snake River salmon survival indicators. Proposed Snake River salmon restoration plans are considered in terms of this counteractive effects hypothesis. The recent declines of salmon stocks have led a number of groups to propose plans that discontinue the present recovery actions, especially transportation of juveniles salmon around the dams. This paper hypothesizes that salmon recovery efforts, in part, have been limited by recent poor climate/ocean conditions. If this hypothesis is true, then eliminating the transportation program could be detrimental to fish. If the hypothesis is false, then eliminating transportation may be a viable recovery measure. In either case resolving the issue of counteracting processes is essential prior to making major changes to the hydrosystem operations. Anderson, J. M. (1991). "The effects of climate change on decomposition processes in grassland and coniferous forests." Ecological Applications 1(3): 326-347. ABSTRACT: Current models of climate change predict a reduction of area covered by northern coniferous forests and tundra, and an increase in grasslands. These scenarios also indicate a northerly shift in agricultural regions, bringing virgin soils under cultivation. The direct effects of man on tundra, boreal forest, and temperate grassland ecosystems are likely to result in less carbon mobilization from soils and vegetation than from tropical forests. However, as a consequence of climate change, carbon mineralization rates from arctic and sub-arctic soils could be very rapid under warmer and drier conditions because of low stabilization of soil organic matter (SOM) and enhanced microbial responses to small changes in soil moisture and temperature. Predicting the response of these systems to climate change is complicated where the edaphic environment regulating SOM dynamics is not a direct function of macroclimatic conditions. Grasslands contain a greater proportion of highly stabilized SOM than coniferous forests, distributed over greater depth in the soil profile, which is less susceptible to changes in mineralization rates. It is concluded that short-term responses of soil processes to climate change are more predictable in well-drained grassland and forest soils than in waterlogged soils of the tundra and boreal region. Over longer periods of time, however, plant species and soil types will alter in response to new temperature and moisture regimes above- and belowground interacting with the effects of carbon enrichment and changes in nutrient availability. The dynamics of these plant-soil interactions and the future status of soils in different life zones as sources or sinks of carbon is poorly understood. More data are also needed on the distribution of waterlogged forest soils in the boreal zone and responses to warming, which include the production of methane as well as CO2. The primary recommendation for future research is for integrated studies on plant and soil processes. Anderson, M. L., et al. (2001). "Probabilistic/ensemble forecasting: a case study using hydrologic response distributions associated with El Niño/Southern Oscillation (ENSO)." Journal of Hydrology 249(1-4): 134-147. ABSTRACT: Due to the non-linear processes and interactions of the hydroclimatic system, a given hydroclimatic event such as the El Niño/Southern Oscillation (ENSO) can lead to a range of possible hydrologic system responses described by a probability distribution. This probability distribution changes in space and time reflecting the non-stationary behavior of the hydroclimatic system. An initial approach in quantifying the evolving probability distributions of hydrologic system response utilizes a physically based hemispheric hydrologic model, PBHHM, that incorporates the salient physics of the hydroclimatic system for the midlatitudes of the Northern Hemisphere. The state variables of the model include atmospheric temperature, atmospheric water content, quasi-geostrophic potential vorticity, land hydrologic water storage, and land/sea surface temperature. The model is structured in such a way that characteristics (e.g. sea surface temperature, geopotential anomalies, etc.) of a hydroclimatic event such as ENSO can be incorporated into the model as a forcing event. The hydrologic system response probability distribution is quantified, via the land hydrologic water storage state variable. As a case study, the hydrologic system response probability distributions of the western continental United States to both the El Niño and La Niña phases of ENSO have been simulated. One hundred realizations were run for each phase using random initial conditions for the state variables in order to reflect differing hydroclimatic conditions during the initiation and evolution of the forcing event. The probability distributions of hydrologic system response and their evolution in space and time are described using relative frequency histograms, cumulative distribution functions, and contour plots of frequency histogram categories. Simulation results of the hydrologic system response probability distribution associated with each phase of the ENSO phenomenon are presented which show a distinct response that varies in space and time. The influence of the number of realizations upon these distributions will be discussed along with a means of incorporating the distributions into a water resources planning scheme. Andreadis, K. M. and D. P. Lettenmaier (2006). "Trends in 20th century drought over the continental United States." Geophysical Research Letters 33(L10403): doi:10.1029/2006GL025711. ABSTRACT: We used a simulated data set of hydro-climatological variables to examine for 20th century trends in soil moisture, runoff, and drought characteristics over the conterminous United States (U.S.). An increasing trend is apparent in both model soil moisture and runoff over much of the U.S., with a few decreasing trends in parts of the Southwest. The trend patterns were qualitatively similar to those found in streamflow records observed at a station network minimally affected by anthropogenic activities. This wetting trend is consistent with the general increase in precipitation in the latter half of the 20th century. Droughts have, for the most part, become shorter, less frequent, and cover a smaller portion of the country over the last century. The main exception is the Southwest and parts of the interior of the West, where, notwithstanding increased precipitation (and in some cases increased soil moisture and runoff), increased temperature has led to trends in drought characteristics that are mostly opposite to those for the rest of the country especially in the case of drought duration and severity, which have increased. Arnell, N. W. (2005). "Implications of climate change for freshwater inflows to the Arctic Ocean." Journal of Geophysical Research 110(D07105): doi:10.1029/2004JD005348. ABSTRACT: Observational evidence suggests that river inflows to the Arctic Ocean have increased over the last 30 years. Continued increases have the potential to alter the freshwater balance in the Arctic and North Atlantic Oceans and hence the thermohaline circulation. Simulations with a macroscale hydrological model and climate change scenarios derived from six climate models and two emissions scenarios suggest increases of up to 31% in river inflows to the Arctic by the 2080s under high emissions and up to 24% under lower emissions, although there are large differences between climate models. Uncertainty analysis suggests low sensitivity to model form and parameterization but higher sensitivity to the input data used to drive the model. The addition of up to 0.048 sverdrup (Sv, 106 m3 s-1) is a large proportion of the 0.06–0.15 Sv of additional freshwater that may trigger thermohaline collapse. Changes in the spatial distribution of inflows to the Arctic Ocean may influence circulation patterns within the ocean. Arora, V. K. and G. J. Boer (2001). "Effects of simulated climate change on the hydrology of major river basins." Journal of Geophysical Research 106(D4): 3335-3348. ABSTRACT: Changes in the climatology of precipitation, evapotranspiration, and soil moisture lead also to changes in runoff and streamflow. The potential effects of global warming on the hydrology of 23 major rivers are investigated. The runoff simulated by the Canadian Cetre for Climate Modeling and Analysis (CCCma) coupled climate model for the current climate is routed through the river system to the river mouth and compared with results for the warmer climate simulated to occur towards the end of the century. Changes in mean discharge, in the amplitude and phase of the annual streamflow cycle, in the annual maximum discharge (the flood) and its standard deviation, and in flow duration curves are all examined. Changes in flood magnitudes for different return periods are estimated using extreme value analysis. In the warmer climate, there is a general decrease in runoff and 15 out of the 23 rivers considered experience a reduction in annual mean discharge (with a median reduction of 32%). The changes in runoff are not uniform and discharge increases for 8 rivers (with a median increase of 13%). Middle- and high- latitude rivers typically show marked changes in the amplitude and phase of their annual cycle associated with a decrease in snowfall and an earlier spring melt in the warmer climate. Low-latitude rivers exhibit changes in mean discharge but modest changes in their annual cycle. The analysis of annual flood magnitudes show that 17 out of 23 rivers experience a reduction in mean annual flood (a median reduction of 20%). Changes in flow duration curves are used to characterize the different kinds of behavior exhibited by different groups of rivers. Differences in the regional distribution of simulated precipitation and runoff for the control simulation currently limit the application of the approach. The inferred hydrological changes are, nevertheless, plausible and consistent responses to simulated changes in precipitation and evapotranspiration and indicate the kinds of hydrological changes that could occur in a warmer climate. Ashkenazy, Y. and E. Tziperman (2004). "Are the 41 kyr glacial oscillations a linear response to Milankovitch forcing?" Quaternary Science Reviews 23(18-19): 1879-1890. ABSTRACT: The characteristics of glacial oscillations changed drastically ~0.8 Ma ago, at the “mid-Pleistocene transition”. During the past 0.8 Ma the glacial–interglacial oscillations were strongly asymmetric (i.e., long glacial intervals of growth followed by rapid intervals of deglaciation). The 40 kyr oscillations prior to the mid-Pleistocene transition were of a smaller amplitude and less-asymmetrical looking. The smaller amplitude, apparently symmetric form and period that matches that of obliquity, suggests that these oscillations were a linear response to Milankovitch forcing, while the ~100 kyr oscillations are attributed either to some nonlinear self-sustained variability due to a mechanism internal to the climate system itself or to nonlinear amplification of the insolation forcing. The significant strengthening of the ~100 kyr eccentricity power in the past ~800 kyr is one of the intriguing questions of climate history. Here we show that glacial–interglacial oscillations pre-mid-Pleistocene transition are, in fact, significantly asymmetric. This asymmetry may contradict a straight forward linear Milankovitch explanation, and we therefore suggest that the glacial oscillations before and after the transition may both be explained as self-sustained variability (although the possibility of nonlinear response to insolation forcing still exists). The role of Milankovitch forcing is in setting the phase of the oscillations (e.g. time of terminations) and their period, rather in being the main driving force of the oscillations. This is demonstrated using a simple model based on the sea ice switch mechanism of Gildor and Tziperman (Paleoceanography 15 (2000) 605). Bachelet, D. R. and R. P. Neilson (2000). Biome redistribution under climate change. The impact of climate change on America's forests: a technical document supporting the 2000 USDA Forest Service RPA Assessment. General Technical Report RMRS-GTR-59. L. A. Joyce and R. Birdsey. Fort Collins, Colorado, USDA Forest Service, Rocky Mountain Research Station: 18-44. ABSTRACT: General warming in the Northern Hemisphere has been recorded since the end of the 1800s following the Little Ice Age. Records of glacier retreat during the last 100 years over the entire globe independently confirmed the recorded trend in global temperature rise. Several studies have illustrated various responses to this climate forcing, i.e., the recorded changes in temperature and precipitation concurrent with the increase in atmospheric CO2 concentration, increases in density of tree populations, declines in tree populations, treeline displacement or lack thereof, lengthening of the growing season, and enhanced tree growth. It is critical that we identify the tools needed to estimate potential consequences of climate change on forest ecosystems and develop management practices and policies adapted to projected drifts in the geographic distribution of ecosystems. Bachelet, D. R., et al. (2001). "Climate change effects on vegetation distribution and carbon budgets in the United States." Ecosystems 4(3): 164-185. ABSTRACT: The Kyoto protocol has focused the attention of the public and policymarkers on the earth's carbon (C) budget. Previous estimates of the impacts of vegetation change have been limited to equilibrium "snapshots" that could not capture nonlinear or threshold effects along the trajectory of change. New models have been designed to complement equilibrium models and simulate vegetation succession through time while estimating variability in the C budget and responses to episodic events such as drought and fire. In addition, a plethora of future climate scenarios has been used to produce a bewildering variety of simulated ecological responses. Our objectives were to use an equilibrium model (Mapped Atmosphere-Plant-Soil system, or MAPSS) and a dynamic model (MC1) to (a) simulate changes in potential equilibrium vegetation distribution under historical conditions and across a wide gradient of future temperature changes to look for consistencies and trends among the many future scenarios, (b) simulate time-dependent changes in vegetation distribution and its associated C pools to illustrate the possible trajectories of vegetation change near the high and low ends of the temperature gradient, and (c) analyze the extent of the US area supporting a negative C balance. Both models agree that a moderate increase in temperature produces an increase in vegetation density and carbon sequestration across most of the US with small changes in vegetation types. Large increases in temperature cause losses of C with large shifts in vegetation types. In the western states, particularly southern California, precipitation and thus vegetation density increase and forests expand under all but the hottest scenarios. In the eastern US, particularly the Southeast, forests expand under the more moderate scenarios but decline under more severe climate scenarios, with catastrophic fires potentially causing rapid vegetation conversions from forest to savanna. Both models show that there is a potential for either positive or negative feedbacks to the atmosphere depending on the level of warming in the climate change scenarios. Bachuber, F. W. (1989). "The occurence and paleolimnologic significance of cutthroat trout (Oncorhynchus clarki) in pluvial lakes of the Estancia Valley, central New Mexico." Geological Society of America Bulletin 101(12): 1543-1551. ABSTRACT: Cutthroat trout (Oncorhynchus clarki) fossils in the Quaternary-age lacustrine sediment of the Estancia Valley provide insight into the paleolimnologic history of the valley. The presence of fish is evidence that a pluvial system overflowed into the Pecos River watershed. Most likely, the overflow occurred during the expansion of Early Lake Estancia, an Illinoian or pre-Illinoian pluvial lake known only in subcrop. Once established in the Estancia watershed, trout occupied headwater streams and only intermittently migrated and resided in developing lake systems. The headwater streams served as refugia through the Sangamon(?) and early and middle Wisconsin time when a fresh-water lake did not exist in the valley. With the advent of full-pluvial conditions during the late Wisconsin, trout migrated from headwater streams into the first of three fresh-water phases of Late Lake Estancia. On two occasions, climate shifted to warmer and drier conditions, causing significant lake-level drawdown. Salinity increased and trout were eliminated from the lake, only to be reintroduced during the next fresh-water phase. Near the close of the late Wisconsin, Late Lake Estancia waned and desiccated, but headwater streams remained as fish refugia. Following the interpluvial episode, the basin again filled, culminating in Lake Willard, considered to be of latest Wisconsin age. With evolution into a fresh-water body, trout migrated into a lake environment for the last time. Ensuing hot/dry conditions brought about the desiccation of Lake Willard and severely impacted the headwater streams. This factor, in possible combination with human fishing activity, led to the elimination of fish from the Estancia Valley after a continuous occupation of at least 130,000 yr. Baird, M., et al. (1999). "Wildfire effects on carbon and nitrogen in inland coniferous forests." Plant and Soil 209(2): 233-243. ABSTRACT: A ponderosa pine/Douglas-fir forest (Pinus ponderosa Dougl., Pseudotsuga menziesii (Mirb.) Franco; PP/DF) and a lodgepole pine/Engelmann spruce forest (Pinus contorta Loud., Picea engelmannii Parry ex Engelm.; LP/ES) located on the eastern slopes of the Cascade Mountains in Washington state, USA, were examined following severe wildfire to compare total soil carbon and nitrogen capitals with unburned (control) forests. One year after fire, the average C content (60 cm depth) of PP/DF and LP/ES soil was 30% (25 Mg ha-1) and 10% (7 Mg ha-1) lower than control soil. Average N content on the burned PP/DF and LP/ES plots was 46% (3.0 Mg ha-1) and 13% (0.4 Mg ha-1) lower than control soil. The reduction in C and N in the PP/DF soil was largely the result of lower nutrient capitals in the burned Bw horizons (12–60 cm depth) relative to control plots. It is unlikely that the 1994 fire substantially affected nutrient capitals in the Bw horizons; however, natural variability or past fire history could be responsible for the varied nutrient capitals observed in the subsurface soils. Surface erosion (sheet plus rill) removed between 15 and 18 Mg ha-1 of soil from the burned plots. Nutrient losses through surface erosion were 280 kg C ha-1 and 14 kg N ha-1 in the PP/DF, whereas LP/ES losses were 640 and 22 kg ha-1 for C and N, respectively. In both forests, surface erosion of C and N was ~1% to 2% of the A-horizon capital of these elements in unburned soil. A bioassay (with lettuce as an indicator plant) was used to compare soils from low-, moderate- and high-severity burn areas relative to control soil. In both forests, low-severity fire increased lettuce yield by 70–100% of controls. With more severe fire, yield decreased in the LP/ES relative to the low-intensity burn soil; however, only in the high-severity treatment was yield reduced (14%) from the control. Moderate- and high-severity burn areas in the PP/DF were fertilized with ~56 kg ha-1 of N four months prior to soil sampling. In these soils, yield was 70–80% greater than the control. These results suggest that short-term site productivity can be stimulated by low-severity fire, but unaffected or reduced by more severe fire in the types of forests studied. Post-fire fertilization with N could increase soil productivity where other environmental factors do not limit growth. Baker, R. G., et al. (2000). "Holocene environments of the central Great Plains: multi-proxy evidence from alluvial sequences, southeastern Nebraska." Quaternary International 67(1): 75-88. ABSTRACT: Pollen, plant macrofossils, phytoliths, carbon isotopes, and alluvial history from sediments exposed along the South Fork of the Big Nemaha River, southeastern Nebraska, USA, provide an integrated reconstruction of changes in Holocene vegetation, climate, and fluvial activity. From 9000 to 8500 uncalibrated 14C yr BP, climate became more arid and the floodplain and alluvial fans in the main valley aggraded rapidly, upland deciduous forest declined, and prairie attained its Holocene dominance. From 8500 to 5800 yr BP. upland forest elements disappeared, and even riparian trees were sparse under dry climatic conditions. Alluvial fans continued to aggrade but aggradation in the main valley was interrupted by a stable episode 7000 yr BP. From 5800 to 3100 yr BP, riparian forests returned to prominence, and droughts were intermittent. Alluviation was slower and punctuated by two major episodes of channel incision and terrace formation in the main valley. Aggradation on alluvial fans slowed and finally ceased near the end of this period. During a short dry interval from 3100 to 2700 yr BP riparian trees (except elm) disappeared, and prairie and weedy species became more abundant. This interval is represented by the organic Roberts Creek Member, and the alluvial setting was a slightly incised meandering channel belt. Habitats became similar to presettlement conditions during the last 2700 yr BP. Weedy taxa dominate modern samples, reflecting widespread disturbance. Alluvial fans and terrace surfaces were stable during the last 2500 years, but episodes of floodplain aggradation were punctuated by incision of the main channel. Baker, W. L. (1990). "Climatic and hydrologic effects on the regeneration of Populus Angustifolia James along the Animas River, Colorado." Journal of Biogeography 17(1): 59-73. ABSTRACT: I investigated the dates of origin of riparian forests dominated by Populus angustifolia James, and recent interannual fluctuation in P. angustifolia seedling abundance on a relatively undisturbed 6-mile reach of the Animas River in southwestern Colorado. The goal was to develop plausible hypotheses about the roles of floods and interannual climatic fluctuation in structuring these forests. I determined the year of origin 242 recently-established seedlings and fifty-seven forest stands, and then developed empirical models relating seedling abundance and stand-origin events to climatic and hydrologic fluctuations. Seedlings were most abundant in years with cool winters, wet springs, and cool, wet falls (R2adj=0.98). Both good seedling years and stand-origin years were associated with winter blocking in the North Pacific and a persistent late-summer Arizona Monsoon. Extant stand originated in ten to thirteen discrete periods between 1848 and 1976, in years with both high spring and fall peak discharges. Expected seedling abundance and stand-origin dates since 1914 were reconstructed using climate data, and were extended to 1556 using tree-ring chronologies. Model results suggest good seedling years occurred more frequently (about ever 3.4 years) than stand-origin years (about every 10-15 years). Good seedling years were 2-3 times, and stand-origin years were 5 times more common from 1848 to 1985 than from 1556 to 1848. Recent expansion of P. angustifolia may have been favoured by more frequent cool, wet years since 1848. Balch, D. P., et al. (2005). "Ecosystem and paleohydrological response to Quaternary climate change in the Bonneville Basin, Utah." Paleogeography, Paleoclimatology, Paleoecology 221(1-2): 99-122. ABSTRACT: We report the results of a detailed paleoecological study of the Bonneville basin covering the last ~280,000 yr. Our study used fossil ostracodes and a sedimentological record obtained from the August 2000 GLAD800 drilling operation at Great Salt Lake. We analyzed 125 samples, taken at ~1 m intervals from Site 4 (GSL00-4), for ostracodes and other paleoecologic and sedimentologic indicators of environmental change. Multivariate analyses applied to the ostracode data and qualitative analyses of fossil and sedimentological data indicate an alternation between three major environments at the core site over the cored interval: (1) shallow saline or hypersaline lakes; (2) salt or freshwater marshes; and (3) occasional deep freshwater lakes. These environmental changes are consistent with shoreline studies of regional lake level fluctuations, but provide considerable new detail on both the timing and environmental conditions associated with the various lake phases. Our age model (using 14C, U-series, tephra and biostratigraphic chronologies) allowed us to associate the core's record of regional paleohydrology with the marine oxygen isotope stages of global climate change. The core contains continuous records for the last four glacial/interglacial sequences. Salt/freshwater marshes were common during the interglacials and deep freshwater conditions correspond with maximum global ice volume in OIS 2, and before a maximum in global ice during OIS 6. Immediately following deep lake phases, crashes in lake level from rapid desiccation resulted in the deposition of thick evaporite units. Our study suggests that the climate of the Great Salt Lake catchment appears to have been drier during OIS 6 than during OIS 2.We compare our record of environmental change during OIS 6 glaciation with other records from the western United States and find that the overall pattern of climate was similar throughout the West, but differences in the timing of climate change (i.e. when a region became drier or moister) are common. Balling, R. C., Jr. and G. B. Goodrich (2007). "Analysis of drought determinants for the Colorado River Basin." Climate Change 82(1-2): 179-194. ABSTRACT: Ongoing drought in the Colorado River Basin, unprecedented urban growth in the watershed, and numerical model simulations showing higher temperatures and lower precipitation totals in the future have all combined to heighten interest in drought in this region. In this investigation, we use principal components analysis (PCA) to independently assess the influence of various teleconnections on Basin-wide and sub-regional winter season Palmer Hydrological Drought Index (PHDI) and precipitation variations in the Basin. We find that the Pacific Decadal Oscillation (PDO) explains more variance in PHDI than El Niño-Southern Oscillation (ENSO), the Atlantic Multidecadal Oscillation (AMO), and the planetary temperature combined for the Basin as a whole. When rotated PCA is used to separate the Basin into two regions, the lower portion of the Basin is similar to the Basin as a whole while the upper portion, which contains the high-elevation locations important to hydrologic yield for the watershed, demonstrates poorly defined relationships with the teleconnections. The PHDI for the two portions of the Basin are shown to have been out of synch for much of the twentieth century. In general, teleconnection indices account for 19% of the variance in PHDI leaving large uncertainties in drought forecasting. Balling, R. C., Jr. and S. G. Wells (1990). "Historic rainfall patterns and arroyo activity within the Zuni River drainage basin, New Mexico." Annals of the Association of American Geographers 80(4): 603-617. ABSTRACT: Climate change, grazing practices, timbering activities, and erosional thresholds have been proposed to explain wide-spread accelerated arroyo erosion near the turn of the century in the southwestern United States. We analyze the morphology and potential causes of arroyo activity in the Zuni River drainage basin of New Mexico; our analyses illustrate the linkage between arroyos and changes that occurred through time in local precipitation patterns. Substantial archival and geological evidence confirms dominant downcutting in the intermediate and small-size arroyos within the basin for a 20- to 30-year period beginning near 1905. Historical climatic records reveal a long and severe drought from 1898-1904; this drought ended abruptly with three years dominated by unusually frequent high-intensity summer rainfall events. Daily weather records show the following two to three decades had a high number of intense summer storms, large rainfall totals, and few precipitation days. The results add support for the climate change explanation of periods dominated by arroyo incision and infilling in the southwestern U.S. Band, L. E., et al. (1996). "Ecosystem processes at the watershed scale: sensitivity to potential climate change." Limnology and Oceanography 41(5): 928-938. ABSTRACT: A distributed data and simulation system for forested watersheds was used to investigate the potential changes in watershed hydrological and ecological processes under hypothesized climate change scenarios. RHESSys (Regional HydroEcological Simulation System) incorporates a spatial representation of nested catchment and lake systems in a GIS, along with a set of process submodels to compute local flux and storage of energy, water, carbon, and nutrients. A hierarchy of potential climate change shifts in weather, forest canopy physiological processes, and forest cover were used to operate RHESSys for comparison with control simulations for present-day conditions. Use of projected temperature and precipitation changes alone led to qualitatively different forecasts of watershed climate change impact when compared to simulations that also incorporated adjustment of canopy physiology to elevated concentrations of atmospheric CO2. In addition, ecosystem processes may be more resilient to climate change due to the existence of a series of offsetting effects. Annual net effects on specific processes such as watershed outflow and forest productivity may qualitatively vary from year to year rather than showing consistent increases or decreases relative to current conditions. The model results illustrate the significance of incorporating a reasonable description of terrestrial ecosystem processes within the contributing watershed when assessing the impact of climate change. Bard, E. (2002). "Climate shock: abrupt changes over millennial time scales." Physics Today 55(12): 32-38. INTRODUCTION: What is the natural variability of our climate? This simple question is, in fact, very hard to answer, from either the theoretical or observational point of view. However, it is of utmost importance if we really want to detect and predict the consequences of human activities that have altered several components of the climate system, the most noticeable change being a considerable increase in atmospheric carbon dioxide from the burning of fossil fuels. The climate system is complex because it is made up of several components (such as the atmosphere, oceans, and ice sheets), each of which has its own response times and thermodynamic properties. Those components not only interact nonlinearly with each other, but are connected to other complex systems such as the carbon cycle, which regulates greenhouse gas concentrations in the atmosphere. The climate can be affected by various types of so-called external forcings or influences (such as changes in insolation) that have different spatial and temporal scales of propagation in the system. A further problem is that internal rearrangements and resonances make it difficult to determine a true equilibrium state. Indeed, the steady state is characterized by a significant noise level and oscillations that are not always easy to distinguish from real transient changes of the global climate. Barnes, C. R. (1999). "Paleoceanography and paleoclimatology: an Earth system perspective." Chemical Geology 161(1-3): 17-35. ABSTRACT: The purpose of this paper is to provide an overview of paleoceanography and paleoclimatology as a framework for other papers dealing with The Earth System: Geochemical Perspectives. An introduction to both paleoceanography and paleoclimatology is followed by examples of the temporal changes through the Phanerozoic. The important and interactive role of the biosphere is emphasized. Many important changes in the Earth system have affected the coupled ocean–atmosphere system and many, in turn, have been reflected in biotic events. Many such changes can be tracked through time using geochemical signatures as proxy indicators. Whereas the scale of past paleoceanographic and paleoclimatic changes have been generally appreciated for some time, the recognition of periodic rapid change in the ocean/climate state and the ability to study and measure these precisely is only a recent accomplishment. The potential for such rapid change in the ocean/climate/biosphere of the Earth system raises concerns for events in the near future that may be forced by anthropogenic activities that enhance natural variability. Barnett, T., et al. (1988). "On the prediction of El Niño of 1986-1987." Science 241(4862): 192-196. ABSTRACT: Three different classes of numerical models successfully predicted the occurrence of the El Niño of 1986-87 at lead times of 3 to 9 months. Although the magnitude and timing of predicted ocean surface temperatures were not perfect, these results suggest that routine prediction of moderate to large El Niño events is feasible. The key to the success of the models lies in recognizing or simulating the low-frequency, large-scale changes in the tropical ocean-atmosphere system that give rise to El Niño events. Barnett, T., et al. (2004). "The effects of climate change on water resources in the west: introduction and overview." Climatic Change 62(1-3): 1-11. ABSTRACT: The results of an experimental 'end to end' assessment of the effects of climate change on water resources in the western United States are described. The assessment focuses on the potential effects of climate change over the first half of the 21st century on the Columbia, Sacramento/San Joaquin, and Colorado river basins. The paper describes the methodology used for the assessment, and it summarizes the principal findings of the study. The strengths and weaknesses of this study are discussed, and suggestions are made for improving future climate change assessments. Barnett, T. P., et al. (2005). "Potential impacts of a warming climate on water availability in snow-dominated regions." Nature 438(17 November 2005): 303-309. ABSTRACT: All currently available climate models predict a near-surface warming trend under the influence of rising levels of greenhouse gases in the atmosphere. In addition to the direct effects on climate—for example, on the frequency of heatwaves—this increase in surface temperatures has important consequences for the hydrological cycle, particularly in regions where water supply is currently dominated by melting snow or ice. In a warmer world, less winter precipitation falls as snow and the melting of winter snow occurs earlier in spring. Even without any changes in precipitation intensity, both of these effects lead to a shift in peak river runoff to winter and early spring, away from summer and autumn when demand is highest. Where storage capacities are not sufficient, much of the winter runoff will immediately be lost to the oceans. With more than one-sixth of the Earth's population relying on glaciers and seasonal snow packs for their water supply, the consequences of these hydrological changes for future water availability—predicted with high confidence and already diagnosed in some regions—are likely to be severe. Barron, E. J., et al. (1999). "The hydrologic cycle: A major variable during earth history." Paleogeography, Paleoclimatology, Palaeoecology 75(3): 157-174. ABSTRACT: Water plays a central role in nearly all Earth processes and in the evolution of the planet. However, despite the significance of water, our knowledge of it as part of the global system in meager. In fact, for paleoclimatology the primary focus on planetary evolution is centered on temperature variations and little attention is directed towards the role of the hydrologic cycle. Model analyses presented here based on a series of simulations utilizing the Community Climate Model (CCM) at the National Center for Atmospheric Research demonstrate that the hydrologic cycle is highly sensitive to climate change and to climatic forcing factors such as changes in atmospheric carbon dioxide, plate tectonics, paleogeography, and orbital variations. The implications of the large sensitivity of the hydrologic cycle are of considerable importance. The role of water in explaining much of the Earth's record has probably been underestimated. The importance of water in global change in Earth history may also suggest that the hydrologic cycle should be of primary interest in studies of future global change. Bartlein, P. J. (1982). "Streamflow anomaly patterns in the U.S.A. and southern Canada –– 1951–1970." Journal of Hydrology 57(1-2): 49-63. ABSTRACT: The map patterns of streamflow conditions in the U.S.A. and southern Canada are examined by means of a principal components analysis of the monthly flow records of 102 streams. The analysis reveals the basic anomaly patterns of streamflow, and also describes the variation of these patterns through time. The basic anomaly patterns are of large spatial scale, and vary slowly through time, reflecting the temporal and spatial scale of the controlling climatic anomalies. An extension of the analysis allows the gaging stations to be assigned to homogeneous hydrologic regions. Barton, A. M., et al. (2001). "Arizona pine (Pinus arizonica) stand dynamics: local and regional factors in a fire-prone madrean gallery forest of Southeast Arizona, USA." Landscape Ecology 16(4): 351-369. ABSTRACT: In southwestern North America, large-scale climate patterns appear to exert control on moisture availability, fire occurrence, and tree demography, raising the compelling possibility of regional synchronization of forest dynamics. Such regional signals may be obscured, however, by local, site-specific factors, such as disturbance history and land use. Contiguous sites with similar physical environments, lower and middle Rhyolite Canyon, Arizona, USA, shared nearly the same fire history from 1660-1801, but then diverged. For the next 50 years, fires continued to occur frequently in lower Rhyolite, but, probably as result of flood-induced debris deposition, largely ceased in middle Rhyolite. We related stand dynamics of Arizona pine (Pinus arizonica) to fire history and drought severity and compared the dynamics in the two sites before and after the divergence in fire frequency. Fires occurred during unusually dry years, and possibly following unusually moist years. Arizona pine exhibited three age structure peaks: two (1810–1830 and 1870–1900) shared by the two sites and one (1610–1640) only in middle Rhyolite. The latter two peaks occurred during periods of unusually low fire frequency, suggesting that fire-induced mortality shapes age structure. Evidence was mixed for the role of favorable moisture availability in age structure. As expected, moisture availability had a prominent positive effect on radial growth, but the effect of fire was largely neutral. The two sites differed only moderately in stand dynamics during the period of divergence, exhibiting subtle age structure contrasts and, in middle Rhyolite only, reduced growth during a 50-year fire hiatus followed by fire-induced release. These results suggest that, despite local differences in disturbance history, forest responses to regional fire and climate processes can persist. Battin, J., et al. (2007). "Projected impacts of climate change on salmon habitat restoration." Proceedings of the National Academy of Sciences 104(16): 6720-6725. ABSTRACT: Throughout the world, efforts are under way to restore watersheds, but restoration planning rarely accounts for future climate change. Using a series of linked models of climate, land cover, hydrology, and salmon population dynamics, we investigated the impacts of climate change on the effectiveness of proposed habitat restoration efforts designed to recover depleted Chinook salmon populations in a Pacific Northwest river basin. Model results indicate a large negative impact of climate change on freshwater salmon habitat. Habitat restoration and protection can help to mitigate these effects and may allow populations to increase in the face of climate change. The habitat deterioration associated with climate change will, however, make salmon recovery targets much more difficult to attain. Because the negative impacts of climate change in this basin are projected to be most pronounced in relatively pristine, high-elevation streams where little restoration is possible, climate change and habitat restoration together are likely to cause a spatial shift in salmon abundance. River basins that span the current snow line appear especially vulnerable to climate change, and salmon recovery plans that enhance lower-elevation habitats are likely to be more successful over the next 50 years than those that target the higher-elevation basins likely to experience the greatest snow–rain transition. Beamish, R. J. and D. R. Bouillon (1993). "Pacific salmon production trends in relation to climate." Canadian Journal of Fisheries and Aquatic Sciences 50(5): 1002-1016. ABSTRACT: Pink (Oncorhynchus gorbuscha), chum (O. keta), and sockeye salmon (O. nerka) represent approximately 90% of the commercial catch of Pacific salmon taken each year by Canada, Japan, the United States, and Russia. Annual all-nation catches of the three species and of each species, from 1925 to 1989, exhibited long-term parallel trends. National catches, in most cases, exhibited similar but weaker trends. The strong similarity of the pattern of the all-nation pink, chum, and sockeye salmon catches suggests that common events over a vast area affect the production of salmon in the North Pacific Ocean. The climate over the northern North Pacific Ocean is dominated in the winter and spring by the Aleutian Low pressure system. The long-term pattern of the Aleutian Low pressure system corresponded to the trends in salmon catch, to copepod production, and to other climate indices, indicating that climate and the marine environment may play an important role in salmon production. Beamish, R. J., et al. (1997). "Production of Fraser River sockeye salmon (Oncorhynchus nerka) in relation to decadal-scale changes in the climate and the ocean." Canadian Journal of Fisheries and Aquatic Sciences 54(3): 543-554. ABSTRACT: The abundance of Fraser River sockeye salmon (Oncorhynchus nerka) stocks was low in the 1960s, increased to high levels in the 1980s, and possibly entered a period of low abundance in recent years. The abundance changes of the combined stocks can be separated into productivity regimes that correspond to changes in climate trends. The most distinct change occurred when there was a major change in the climate over the Pacific Ocean in the winter of 1976-1977. The existence of natural shifts in abundance trends means that the high returns that occur during periods of high productivity would not be expected to occur during the low-productivity periods. The response of Fraser River sockeye to climate changes may be a specific example of a more general response by a number of species of fishes in the Pacific and perhaps in other oceans. Because the shift from one regime to the other occurred quickly in the 1970s, future shifts could also occur quickly. It is necessary to detect natural shifts in productivity when attempting to manage fishing impacts to ensure that economic expectations are sound and that overfishing does not occur. Beamish, R. J., et al. (2004). "The influence of climate on the stock and recruitment of pink and sockeye salmon from the Fraser River, British Columbia, Canada." Transactions of the American Fisheries Society 133(6): 1396-1412. ABSTRACT: The relationships between the spawning stock and the subsequent recruitment of pink salmon Oncorhynchus gorbuscha and sockeye salmon O. nerka from the Fraser River improve significantly when the data are separated by climate and ocean regimes. Our analyses show changes in these relationships as regimes shift, indicating that the trend in marine survival of pink and sockeye salmon changes on a decadal scale. In general, the climate and ocean regime from 1977 to 1988 was productive for pink and sockeye salmon. However, the regime in the 1990s was characterized by reduced productivity for both species. The occurrence of a natural shift in the trend of pink and sockeye salmon production on a decadal scale should be incorporated into the management of Pacific salmon stocks to ensure that annual catches, escapements, and planned stock abundances are consistent with the productivity of a particular regime. Beebee, R. A. and M. Manga (2004). "Variation in the relationship between snowmelt runoff in Oregon and ENSO and PDO." Journal of the American Water Resources Association 40(4): 1011-1024. ABSTRACT: The value of using climate indices such as ENSO or PDO in water resources predictions is dependent on understanding the local relationship between these indices and streamflow over time. This study identifies long term seasonal and spatial variations in the strength of El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) correlations with timing and magnitude of discharge in snowmelt streams in Oregon. ENSO is best correlated with variability in annual discharge, and PDO is best correlated with spring snowmelt timing and magnitude and timing of annual floods. Streams in the Cascades and Wallowa mountains show the strongest correlations, while the southernmost stream is not correlated with ENSO or PDO. ENSO correlations are weaker from 1920 to 1950 and vary significantly depending on whether Southern Oscillation Index (SOI) or Niño 3.4 is used. PDO correlations are strong from 1920 to 1950 and weak or insignificant other years. Although there are not consistent increasing or decreasing trends in annual discharge or spring snowmelt timing, there are significant increases in fractional winter runoff that are independent of precipitation, PDO, or ENSO and may indicate monotonic winter warming. Beechie, T., et al. (2006). "Hydrologic regime and the conservation of salmon life history diversity." Biological Conservation 130(4): 560-572. ABSTRACT: Life history diversity of imperiled Pacific salmon Oncorhynchus spp. substantially contributes to their persistence, and conservation of such diversity is a critical element of recovery efforts. Preserving and restoring diversity of life history traits depends in part on environmental factors affecting their expression. We analyzed relationships between annual hydrograph patterns and life history traits (spawn timing, age at spawning, age at outmigration, and body size) of Puget Sound Chinook salmon (Oncorhynchus tshawytscha) to identify environmental indicators of current and historic diversity. Based on mean monthly flow patterns, we identified three hydrologic regimes: snowmelt-dominated, rainfall-dominated, and transitional. Chinook populations in snowmelt-dominated areas contained higher proportions of the stream-type life history (juvenile residence >1 year in freshwater), had older spawners, and tended to spawn earlier in the year than populations in rainfall-dominated areas. There are few extant Puget Sound populations dominated by the stream-type life history, as several populations with high proportions of stream-type fish have been extirpated by construction of dams that prevent migration into snowmelt-dominated reaches. The few extant populations are thus a high priority for conservation. The low level of genetic distinction between stream-type and ocean-type (juvenile residence <1 year in freshwater) life histories suggests that allowing some portion of extant populations to recolonize habitats above dams might allow re-expression of suppressed life history characteristics, creating a broader spatial distribution of the stream-type life history. Climate change ultimately may limit the effectiveness of some conservation efforts, as stream-type Chinook may be dependent on a diminishing snowmelt-dominated habitat. Beer, J., et al. (2000). "The role of the sun in climate forcing." Quaternary Science Reviews 19(1-5): 403-415. ABSTRACT: The Sun is by far the most important driving force of the climate system. However, only little is known how variable this force is acting on different time scales ranging from minutes to millennia and how the climate system reacts to changes in this forcing. Changes of the global insolation can be related to the nuclear fusion in the core of the Sun, the energy transport through the radiative zone and the convection zone, the emission of radiation from the photosphere, and the distance between Sun and Earth. Satellite based measurements over two decades show a clear correlation between the solar irradiance and the 11-year sunspot cycle. The irradiance amplitude is about 0.1%. This is too small to affect significantly the climate. However, there are indications that, on longer time scales, solar variability could be much larger. The analysis of cosmogenic nuclides stored in natural archives provides a means to extend our knowledge of solar variability over much longer time periods. The response of the climate system to solar forcing depends not only on the amount of radiation, but also on its spectral composition (e.g. UV contribution), seasonal distribution over the globe, and feedback mechanisms connected with clouds, water vapour, ice cover, atmospheric and oceanic transport and other terrestrial processes. It is therefore difficult to establish a quantitative relationship between observed climate changes in the past and reconstructed solar variability. However, there is growing evidence that periods of low solar activity (so called minima) coincide with advances of glaciers, changes in lake levels, and sudden changes of climatic conditions. These findings point to an active role of the Sun in past climate changes beside other geophysical factors, internal variability of the climate system, and greenhouse gases. In fact a non-linear regression model to separate natural and anthropogenic forcing since 1850 is consistent with a solar contribution of about 40% to the global warming during the last 140 years. Benestad, R. E. (2003). "How often can we expect a record-event?" Climate Research 23(1): 3-13. ABSTRACT: This study applies a simple framework for analysing the incidence of record events. A test of this method on the global mean temperature yields results consistent with a global warming, where record-warm events are more frequent than for a stationary series. The record event analysis suggests that the number of record-warm monthly global mean temperatures is higher than expected, and that the number of record events in the absolute monthly maximum and minimum temperatures in the Nordic countries is slightly higher than expected from a null hypothesis of a stationary behaviour. Because the different station series are not strictly independent, it is difficult to resolve whether there is a significant trend in the warmest absolute monthly minimum temperatures in the Nordic countries. The behaviour of the maximum monthly 24 h precipitation is not distinguishable from the null hypothesis that the series consists of independent and identically distributed random variables. Benson, L., et al. (1997). "Nearly synchronous climate change in the Northern Hemisphere during the last glacial termination." Nature 388(6639): 263-265. ABSTRACT: The climate of the North Atlantic region underwent a series of abrupt cold/warm oscillations when the ice sheets of the Northern Hemisphere retreated during the last glacial termination (17.7–11.5kyr ago). Evidence for these oscillations, which are recorded in European terrestrial sediments as the Oldest Dryas/Bølling/Older Dryas/Allerød/Younger Dryas vegetational sequence, has been found in Greenland ice cores. The geographical extent of many of these oscillations is not well known, but the last major cold event (the Younger Dryas) seems to have been global in extent. Here we present evidence of four major oscillations in the hydrological balance of the Owens basin, California, that occurred during the last glacial termination. Dry events in western North America occurred at approximately the same time as cold events recorded in Greenland ice, with transitions between climate regimes in the two regions taking place within a few hundred years of each other. Our observations thus support recent climate simulations which indicate that cooling of the North Atlantic Ocean results in cooling of the North Pacific Ocean which, in turn, leads to a drier climate in western North America. Benson, L., et al. (2003). "Influence of the Pacific Decadal Oscillation on the climate of the Sierra Nevada, California and Nevada." Quaternary Research 59(2): 151-159. ABSTRACT: Mono Lake sediments have recorded five major oscillations in the hydrologic balance between A.D. 1700 and 1941. These oscillations can be correlated with tree-ring-based oscillations in Sierra Nevada snowpack. Comparison of a tree-ring-based reconstruction of the Pacific Decadal Oscillation (PDO) index  with a coral-based reconstruction of Subtropical South Pacific sea-surface temperature  indicates a high degree of correlation between the two records during the past 300 yr. This suggests that the PDO has been a pan-Pacific phenomena for at least the past few hundred years. Major oscillations in the hydrologic balance of the Sierra Nevada correspond to changes in the sign of the PDO with extreme droughts occurring during PDO maxima. Four droughts centered on A.D. 1710, 1770, 1850, and 1930 indicate PDO-related drought reoccurrence intervals ranging from 60 to 80 yr. Benson, L., et al. (2003). "Response of North American Great Basin lakes to Dansgaard–Oeschger oscillations." Quaternary Science Reviews 22(21-22): 2239-2251. ABSTRACT: We correlate oscillations in the hydrologic and/or cryologic balances of four Great Basin surface-water systems with Dansgaard–Oeschger (D–O) events 2–12. This correlation is relatively strong at the location of the magnetic signature used to link the lake records, but becomes less well constrained with distance/time from the signature. Comparison of proxy glacial and hydrologic records from Owens and Pyramid lakes indicates that Sierran glacial advances occurred during times of relative dryness. If our hypothesized correlation between the lake-based records and the GISP2 d18O record is correct, it suggests that North Atlantic D–O stades were associated with relatively cold and dry conditions and that interstades were associated with relatively warm and wet conditions throughout the Great Basin between 50,500 and 27,000 GISP2 yr B.P. The Great Basin lacustrine climate records reinforce the hypothesis that D–O events affected the climate throughout much of the Northern Hemisphere during marine isotope stages 2 and 3. However, the absolute phasing between lake-size and ice-core d18O records remains difficult to determine. Benson, L., et al. (2005). "New data for Late Pleistocene Pinedale alpine glaciation from southwestern Colorado." Quaternary Science Reviews 24(1-2): 49-65. ABSTRACT: New cosmogenic surface-exposure ages of moraine-crest boulders from southwestern Colorado are compared with published surface-exposure ages of boulders from moraine complexes in north-central Colorado and in west-central (Fremont Lake basin) Wyoming. 10Be data sets from the three areas were scaled to a single 10Be production rate of 5.4 at/g/yr at sea level and high latitude (SLHL), which represents the average 10Be production rate for two high-altitude, mid-latitude sites in the western United States (US) and Austria. Multiple nuclide ages on single boulders indicate that this 10Be production rate yields ages comparable to those calculated with a commonly used 36Cl production scheme. The average age and age range of moraine-crest boulders on terminal moraines at the southwestern Colorado and Wyoming sites are similar, indicating a retreat from their positions 16.8 36Cl ka (Cosmogenic ages in this paper are labeled 10Be or 36Cl ka or just ka when both 10Be or 36Cl ages are being discussed; radiocarbon ages are labeled 14C ka, calibrated radiocarbon are labeled cal ka, and calendar ages are labeled calendar ka. Errors (±1s) associated with ages are shown in tables. Radiocarbon ages were calibrated using the data of Hughen et al. (Science 303 (2004) 202). This suggests a near-synchronous retreat of Pinedale glaciers across a 470-km latitudinal range in the Middle and Southern Rocky Mountains. Hypothetical corrections for snow shielding and rock-surface erosion shifts the time of retreat to between 17.2 and 17.5 10Be ka at Pinedale, Wyoming, and between 16.3 and 17.3 36Cl ka at Hogback Mountain, Colorado. Benson, L. B., et al. (2002). "Holocene multidecadal and multicentennial droughts affecting northern California and Nevada." Quaternary Science Reviews 21(4-6): 659-682. ABSTRACT: Continuous, high-resolution d18O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (cal yr). The records are not stationary; during the past 2740 yr, drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200 yr from the Sierra Nevada and the El Malpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820 cal yr BP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650 cal yr BP may have impacted much of the western United States. During the middle Holocene (informally defined in this paper as extending from 8000 to 3000 cal yr BP), magnetic susceptibility values of sediments deposited in Pyramid Lake's deep basin were much larger than late–Holocene (3000–0 cal yr BP) values, indicating the presence of a shallow lake. In addition, the mean d18O value of CaCO3 precipitated between 6500 and 3430 cal yr BP was 1.6‰ less than the mean value of CaCO3 precipitated after 2740 cal yr BP. Numerical calculations indicate that the shift in the d18O baseline probably resulted from a transition to a wetter (>30%) and cooler (3–5°C) climate. The existence of a relatively dry and warm middle-Holocene climate in the Truckee River–Pyramid Lake system is generally consistent with archeological, sedimentological, chemical, physical, and biological records from various sites within the Great Basin of the western United States. Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC and d18O records from Owens Lake indicate that the first interval in the early Holocene (11,600–10,000 cal yr BP) was characterized by a drying trend that was interrupted by a brief (200 yr) wet oscillation centered at 10,300 cal yr BP. This was followed by a second early-Holocene interval (10,000–8000 cal yr BP) during which relatively wet conditions prevailed. During the early part of the middle Holocene (8000–6500 cal yr BP), high-amplitude oscillations in TIC in Owens Lake and d18O in Pyramid Lake indicate the presence of shallow lakes in both basins. During the latter part of the middle Holocene (6500–3800 cal yr BP), drought conditions dominated, Owens Lake desiccated, and Lake Tahoe ceased spilling to the Truckee River, causing Pyramid Lake to decline. At the beginning of the late Holocene (~3000 cal yr BP), Lake Tahoe rose to its sill level and Pyramid Lake increased in volume.
Benson, L. V., et al. (1990). “Chronology of expansion and contraction of four Great Basin lake systems during the past 35,000 years.” Paleogeography, Paleoclimatology, Paleoecology 78(3-4): 241-286.
ABSTRACT: During the past 35,000 years, Lake Bonneville, Lake Russell, and Lake Searles underwent a major period of lake-level change. The lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15,000 and 13,500 yr B.P. The rise of Lake Lahontan was gradual but not continuous, in part because of topographic constraints (intrabasin spill). Lake Lahontan also had an oscillation in lake level at 15,500 yr B.P. Radiocarbon-age estimations for materials that were deposited in the lake basins indicate that Lake Bonneville rose more or less gradually from 32,000 yr B.P., and had major oscillations in level between 23,000 and 21,000 yr B.P. and between 15,250 and 14,500 yr B.P. Lake Russell and Lake Searles had several major oscillations in lake level between 35,000 and 14,000 yr B.P. The timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states. All four lakes may have had nearly synchronous recessions between about 14,000 and 13,500 yr B.P. After the recessions, the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11,500 and 10,000 yr B.P. These data provide circumstantial evidence that the Younger Dryas Event affected climate on at least a hemispheric scale. During the Holocene, the four lakes remained at low levels, and small oscillations in lake level occurred. An important aspect of the lake-level data is the accompanying expansion of lake-surface area at the time of the last highstand. Lake Bonneville and Lake Lahontan had surface areas about 10 times larger than their mean-historical reconstructed areas whereas Lake Russell and Lake Searles had surface areas about 5 times larger than their mean-historical reconstructed areas. Differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream, or they may have resulted from lake/atmosphere feedback processes.
Benson, L. V., et al. (1998). “Correlation of late-Pleistocene lake-level oscillations in Mono Lake, California, with North Atlantic climate events.” Quaternary Research 49(1): 1-10.
ABSTRACT: Oxygen-18 (18O) values of sediment from the Wilson Creek Formation, Mono Basin, California, indicate three scales of temporal variation (Dansgaard–Oeschger, Heinrich, and Milankovitch) in the hydrologic balance of Mono Lake between 35,400 and 12,90014C yr B.P. During this interval, Mono Lake experienced four lowstands each lasting from 1000 to 2000 yr. The youngest lowstand, which occurred between 15,500 and 14,00014C yr B.P., was nearly synchronous with a desiccation of Owens Lake, California. Paleomagnetic secular variation (PSV) data indicate that three of four persistent lowstands occurred at the same times as Heinrich events H1, H2, and H4.18O data indicate the two highest lake levels occurred ~18,000 and ~13,10014C yr B.P., corresponding to passages of the mean position of the polar jet stream over the Mono Basin. Extremely low values of total inorganic carbon between 26,000 and 14,00014C yr B.P. indicate glacial activity, corresponding to a time when summer insolation was much reduced.
Berger, A. (1988). “Milankovitch theory and climate.” Reviews of Geophysics 26(4): 624-657.
ABSTRACT: Among the longest astrophysical and astronomical cycles that might influence climate (and even among all forcing mechanisms external to the climatic system itself), only those involving variations in the elements of the Earth’s orbit have been found to be significantly related to the long-term climatic data deduced from the geological record. The aim of the astronomical theory of paleoclimates, a particular version of which being due to Milankovitch, is to study this relationship between insolation and climate at the global scale. It comprises four different parts: the orbital elements, the insolation, the climate model, and the geological data. In the nineteenth century, Croll and Pilgrim stressed the importance of severe winters as a cause of ice ages. Later, mainly during the first half of the twentieth century, Köppen, Spitaler, and Milankovitch regarded mild winters and cool summers as favoring glaciation. After Köppen and Wegener related the Milankovitch new radiation curve to Penck and Brückner’s subdivision of the Quaternary, there was a long-lasting debate on whether or not such changes in the insolation can explain the Quaternary glacial-interglacial cycles. In the 1970s, with the improvements in dating, in acquiring, and in interpreting the geological data, with the advent of computers, and with the development of astronomical and climate models, the Milankovitch theory revived. Over the last 5 years it overcame most of the geological, astronomical, and climatological difficulties. The accuracy of the long-term variations of the astronomical elements and of the insolation values and the stability of their spectra have been analyzed by comparing seven different astronomical solutions and four different time spans (0-0.8 million years before present (Myr B.P.), 0.8-1.6 Myr B.P., 1.6-2.4 Myr B.P., and 2.4-3.2 Myr B.P.). For accuracy in the time domain, improvements are necessary for periods earlier than 2 Myr B.P. As for the stability of the frequencies, the fundamental periods (around 40, 23, and 19 kyr) do not deteriorate with time over the last 5 Myr, but their relative importance for each insolation and each astronomical parameter is a function of the period considered. Spectral analysis of paleoclimatic records has provided substantial evidence that, at least near the obliquity and precession frequencies, a considerable fraction of the climatic variance is driven in some way by insolation changes forced by changes in the Earth’s orbit. Not only are the fundamental astronomical and climatic frequencies alike, but also the climatic series are phase-locked and strongly coherent with orbital variations. Provided that monthly insolation (i.e., a detailed seasonal cycle) is considered for the different latitudes, their long-term deviations can be as large as 13% of the long-term average, and sometimes considerable changes between extreme values can occur in less than 10,000 years. Models of different categories of complexity, from conceptual ones to three-dimensional atmospheric general circulation models and two-dimensional time-dependent models of the whole climate system, have now been astronomically forced in order to test the physical reality of the astronomical theory. The output of most recent modeling efforts compares favorably with data of the past 400,000 years. Accordingly, the model predictions for the next 100,000 years are used as a basis for forecasting how climate would evolve when forced by orbital variations in the absence of anthropogenic disturbance. The long-term cooling trend which began some 6,000 years ago will continue for the next 5,000 years; this first temperature minimum will be followed by an amelioration at around 15 kyr A.P. (after present), by a cold interval centered at 23 kyr A.P., and by a major glaciation at around 60 kyr A.P.
Berger, A. and M. F. Loutre (1991). “Insolation values for the climate of the last 10 million years.” Quaternary Science Reviews 10(4): 297-317.
ABSTRACT: New values for the astronomical parameters of the Earth’s orbit and rotation (eccentricity, obliquity and precession) are proposed for paleoclimatic research related to the Late Miocene, the Pliocene and the Quaternary. They have been obtained from a numerical solution of the Lagrangian system of the planetary point masses and from an analytical solution of the Poisson equations of the Earth-Moon system. The analytical expansion developed in this paper allows the direct determination of the main frequencies with their phase and amplitude. Numerical and analytical comparisons with the former astronomical solution BER78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated. The corresponding insolation values have also been computed and compared to the former ones. This analysis leads to the conclusion that the new values are expected to be reliable over the last 5 Ma in the time domain and at least over the last 10 Ma in the frequency domain.
Berger, A. and M. F. Loutre (2002). “An exceptionally long interglacial ahead?” Science 297(5585): 1287-1288.
ABSTRACT: Today’s comparatively warm climate has been the exception more than the rule during the last 500,000 years or more. If recent warm periods (or interglacials) are a guide, then we may soon slip into another glacial period. But Berger and Loutre argue in their Perspective that with or without human perturbations, the current warm climate may last another 50,000 years. The reason is a minimum in the eccentricity of Earth’s orbit around the Sun.
Betancourt, J. L., et al., Eds. (1990). Packrat middens: the last 40,000 years of biotic change. Tucson, Arizona, University of Arizona Press.
ABSTRACT: Over the past thirty years, late Quaternary environments in the arid interior of western North America have been revealed by a unique source of fossils: well-preserved fragments of plants and animals accumulated locally by packrats and quite often encased, amberlike, in large masses of crystallized urine. These packrat middens are ubiquitous in caves and rock crevices throughout the arid West, where they can lie preserved for tens of thousands of years. More than a thousand of these deposits have been dated and analyzed, and middens have supplanted pollen records as a touchstone for studying vegetation dynamics and climatic change in radiocarbon time (the last 40,000 years). Now, similar deposits made by other mammals like hyraxes are being reported from other parts of the world. This book brings together the most recent findings and views of many of the researchers now investigating fossil middens in the United States, Mexico, Africa, the Middle East, and Australia. The contributions serve to open a forum for methodological concerns, update the fossil record of various geographic regions, introduce new applications, and display the vast potential for fossil midden analysis in arid regions worldwide. The findings presented here will serve to foster regional research and to promote general studies devoted to global climate change. Included in the text are more than two hundred charts, photographs, and maps.
Biondi, F., et al. (2001). “North Pacific decadal climate variability since AD 1661.” Journal of Climate 14(1): 5-10.
ABSTRACT: Climate in the North Pacific and North American sectors has experienced interdecadal shifts during the 20th century. A network of recently developed tree-ring chronologies for Southern and Baja California extends the instrumental record, and reveals decadal-scale variability back to AD 1661. The Pacific Decadal Oscillation (PDO) is closely matched by the dominant mode of tree-ring variability, which provides a preliminary view of multi-annual climate fluctuations spanning the past four centuries. The reconstructed PDO index features a prominent bidecadal oscillation, whose amplitude weakened in the late 1700s to mid-1800s. A comparison with proxy records of ENSO suggests that the greatest decadal-scale oscillations in Pacific climate between 1706 and 1977 occurred around 1750, 1905, and 1947.
Blasing, T. J. and H. C. Fritts (1976). “Reconstructing past climatic anomalies in the north Pacific and western North America from tree-ring data.” Quaternary Research 6(4): 563-579.
ABSTRACT: Winter climatic anomalies in the North Pacific sector and western North America are statistically calibrated with tree-ring data in western North America and reconstructed back to AD 1700. The results are verified using climatic data from the last half of the 19th century, which is prior to the calibration period. Climatic conditions reconstructed for 18th and 19th century winters are then summarized and compared with the 20th century record.
Blasing, T. J., et al. (1988). “Tree ring-based reconstruction of annual precipitation in the south-central United States from 1750 to 1980.” Water Resources Research 24(1): 163-171.
ABSTRACT: A 231-year reconstruction of annual precipitation, from 1750 through 1980 A.D., was developed from 10 tree ring chronologies (9 post oak, Quercus stellata, and 1 white oak, Q. alba, series) in the south-central United States. Straight line regression was used to calibrate regionally averaged precipitation with ring width data, and the derived reconstruction was verified with independent climatic data and historical evidence. A variance trend in the tree ring data, which may have resulted from nonclimatic factors, was removed. The reconstructed precipitation series indicates that (1) a drought which appears to have been more severe than any in the instrumental record occurred about 1860 and (2) severe and prolonged droughts comparable to twentieth century events have occurred at roughly 15- to 25-year intervals throughout the past 231 years. It follows that serious droughts in the south-central United States could be expected to recur even in the absence of projected CO2-induced warming.
Bolin, B., et al. (1986). The greenhouse, climatic change and ecosystems. SCOPE 29. Washington, D.C., Island Press: 574 pp.
EXECUTIVE SUMMARY (partial): The amounts of some trace gases in the atmosphere, notably carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), chlorofluorocarbons and tropospheric ozone, have been increasing. All of these gases are transparent to incoming short-wave radiation, but they absorb and emit long-wave radiation and are thus able to influence the Earth’s climate. They are referred to in this report as greenhouse gases.
Increased concentrations of CO2 and other greenhouse gases lead to a warming of the Earth’s surface and the lower atmosphere. The resulting changes in climate and their impacts (e.g. on sea level, agriculture and forestry) can be estimated without associating the origin of the warming to anyone of these gases specifically. It is, however, necessary to study the effects of these greenhouse gases separately in order to estimate their relative contributions to the warming at any given time and, consequently, to develop strategies for reducing their possible harmful effects.
A review of previous assessments of the CO2 problem shows that there are agreements on some basic issues. The net emissions of CO2 from the biota (due to deforestation and land use changes) in themselves will be insufficient to cause a significant change of climate, while fossil fuel reserves are large enough for climatic changes to occur if these reserves continue to be exploited at a high rate in the future.
Generally it has also been agreed that regional patterns of climatic change cannot yet be predicted. Thus, the ways in which higher CO2 concentrations and given changes in climate would affect ecosystems and human activities cannot be predicted either. This is presumably one of the main reasons why there has been substantial disagreement among previous studies regarding recommendations for future action.
Bond, G., et al. (2001). “Persistent solar influence on North American climate during the Holocene.” Science 294: 2130-2136.
ABSTRACT: Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic’s “1500-year” cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.
Bond, G., et al. (1997). “Pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates.” Science 278(5341): 1257-1266.
INTRODUCTION: Evidence from North Atlantic deep sea cores reveals that abrupt shifts punctuated what is conventionally thought to have been a relatively stable Holocene climate. During each of these episodes, cool, ice-bearing waters from north of Iceland were advected as far south as the latitude of Britain. At about the same times, the atmospheric circulation above Greenland changed abruptly. Pacings of the Holocene events and of abrupt climate shifts during the last glaciation are statistically the same; together, they make up a series of climate shifts with a cyclicity close to 1470 ± 500 years. The Holocene events, therefore, appear to be the most recent manifestation of a pervasive millennial-scale climate cycle operating independently of the glacial-interglacial climate state. Amplification of the cycle during the last glaciation may have been linked to the North Atlantic’s thermohaline circulation.
Bond, N. A. and D. E. Harrison (2000). “The Pacific Decadal Oscillation, air-sea interaction and central north Pacific winter atmospheric regimes.” Geophysical Research Letters 27(5): 731-734.
ABSTRACT: Prominent and persistent anomalies in the atmospheric flow (troughs and ridges) occur sporadically over the central North Pacific, and can have profound consequences for the weather of North America. We have examined how these events are associated with large scale central North Pacific sea surface temperature (SST) anomalies, using an index for the Pacific Decadal Oscillation (PDO). The anomalies in turbulent air-sea heat fluxes and low-level baroclinity associated with the PDO are manifested differently during troughs than during ridges in their effects on the transient eddies (storms). These effects may help explain why prominent troughs (ridges) occur about 3 (2.5) times more frequently during periods when the PDO is significantly positive (negative) than of opposite sign. Our results suggest that the state of the mid-latitude Pacific Ocean more fundamentally affects the atmosphere than has been thought.
Bradford, M. J. and J. R. Irvine (2000). “Land use, fishing, climate change, and the decline of Thompson River, British Columbia, coho salmon.” Canadian Journal of Fisheries and Aquatic Sciences 57(1): 13-16.
ABSTRACT: We investigated a recent, major decline in the abundance of a large aggregate of coho salmon (Oncorhynchus kisutch) spawning in the Thompson River, British Columbia, watershed. We found that the decline could be attributed to a declining trend in productivity likely related to changing ocean conditions, overfishing, and freshwater habitat alteration. Among individual watersheds, rates of decline in adult coho salmon abundance were correlated with agricultural land use, road density, and a qualitative measure of stream habitat status but not with the proportion of land recently logged. The recovery of these populations will require the prudent regulation of fishing, the restoration of salmon producing watersheds, and an improvement in ocean conditions.
Bradley, R. (2000). “One thousand years of climate change.” Science 288(5470): 1353-1355.
INTRODUCTION: It has long been believed that the 20th warming was preceded by the “Little Ice Age” and the “Medieval Warm Period” as a result of the natural variability of climate. But as Bradley explains in this Perspective, recent research has shown that these climate patterns may not have been global, and are much more variable in time and space than previously assumed. However, one fact remains indisputable, namely that end-20th century temperatures were higher than at any time during the last millenium.
Bratcher, A. J. and B. S. Giese (2002). “Tropical Pacific decadal variability and global warming.” Geophysical Research Letters 29(19): 1918, doi:1910.1029/2002GL015191.
ABSTRACT: An analysis of ocean surface temperature records show that low frequency changes of tropical Pacific temperature lead global surface air temperature changes by about 4 years. Anomalies of tropical Pacific surface temperature are in turn preceded by subsurface temperature anomalies in the southern tropical Pacific by approximately 7 years. The results suggest that much of the decade to decade variations in global air temperature may be attributed to tropical Pacific decadal variability. The results also suggest that subsurface temperature anomalies in the southern tropical Pacific can be used as a predictor for decadal variations of global surface air temperature. Since the southern tropical Pacific temperature shows a distinct cooling over the last 8 years, the possibility exists that the warming trend in global surface air temperature observed since the late 1970’s may soon weaken.
Brereton, R., et al. (1995). “Enhanced greenhouse climate change and its potential effect on selected fauna of south-eastern Australia: A trend analysis.” Biological Conservation 72(3): 339-354.
ABSTRACT: It has been predicted that enhanced greenhouse climate change will modify the global climate and consequently cause large-scale changes to the distribution of flora and fauna. This study examined the potential effect of enhanced greenhouse climate change on the distribution of 42 species of fauna of south-eastern Australia. The best available information regarding faunal distributions and predictive models for bioclimatic ranges was used in conjunction with the accepted enhanced greenhouse climate scenarios for 1990. More recent developments that refine the potential climatic changes are discussed in relation to the analysis.
The 42 species of fauna were selected from the major Victorian bioclimatic regions and ecosystems and from species considered most at risk from enhanced greenhouse climate change. Most were species with a threatened conservation status. The results indicate that 41 undergo a reduction in bioclimatic range in response to climatic warming, the most extreme response being the extinction of bioclimatic range. A broadscale subcontinental analysis of the potential effects on faunal distribution is presented.
Breshears, D. D., et al. (2005). “Regional vegetation die-off in response to global-change-type drought.” Proceedings of the National Academy of Sciences 102(42): 15144-15148.
ABSTRACT: Future drought is projected to occur under warmer temperature conditions as climate change progresses, referred to here as global-change-type drought, yet quantitative assessments of the triggers and potential extent of drought-induced vegetation die-off remain pivotal uncertainties in assessing climate-change impacts. Of particular concern is regional-scale mortality of overstory trees, which rapidly alters ecosystem type, associated ecosystem properties, and land surface conditions for decades. Here, we quantify regional-scale vegetation die-off across southwestern North American woodlands in 2002-2003 in response to drought and associated bark beetle infestations. At an intensively studied site within the region, we quantified that after 15 months of depleted soil water content, >90% of the dominant, overstory tree species (Pinus edulis, a piñon) died. The die-off was reflected in changes in a remotely sensed index of vegetation greenness (Normalized Difference Vegetation Index), not only at the intensively studied site but also across the region, extending over 12,000 km2 or more; aerial and field surveys confirmed the general extent of the die-off. Notably, the recent drought was warmer than the previous subcontinental drought of the 1950s. The limited, available observations suggest that die-off from the recent drought was more extensive than that from the previous drought, extending into wetter sites within the tree species’ distribution. Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions.
Bridgham, S. D., et al. (1995). “Potential feedbacks of northern wetlands on climate change.” BioScience 45(4): 262-274.
ABSTRACT: Changes in wetland ecosystems in the northern latitudes may have feedback effects on greenhouse gases. An approach for predicting the climate-change impact of northern wetlands is outlined.
Bridgham, S. D., et al. (1998). “Carbon, nitrogen, and phosphorus mineralization in northern wetlands.” Ecology 79(5): 1545-1561.
ABSTRACT: We examined rates of C, N, and P mineralization in soils from 16 northern Minnesota wetlands that occur across an ombrotrophic–minerotrophic gradient. Soils were incubated at 30°C under aerobic and anaerobic conditions for 59 wk, and the results were fit with a two-pool kinetic model. Additionally, 39 different soil quality variables were used in a principal components analysis (PCA) to predict mineralization rates.
Mineralization of C, N, and P differed significantly among wetland types, aeration status (aerobic vs. anaerobic), and their interaction term. Despite low total soil N and P, there was a rapid turnover of the nutrient pools in ombrotrophic sites, particularly under aerobic conditions. On a volumetric basis, C and N mineralization increased in a predictable manner across the ombrotrophic–minerotrophic gradient, largely due to increasing soil bulk density. However, P mineralization per cubic centimeter remained relatively high in the bogs. The higher total P content of more minerotrophic soils appears to be offset by greater P immobilization due to geochemical sorption, yielding overall lower availability.
Total C turnover rates were relatively similar among sites, despite large differences in soil quality. We suggest that, over time, the decay rates of organic matter in different wetland communities converge to a common rate. In contrast, CH4 production was extremely low in ombrotrophic peats.
The apparent labile pools of N (N0), P (P0), and C (C0) were generally <10% of their respective total pool sizes, except for P0 in the bogs, which constituted up to 33% of total soil P. From 10% to 87% of the N, P, and C mineralized after 59 wk was derived from their respective labile pools. A simple group of variables describing the physical degree of decomposition of organic matter was often as good as, or superior to, more complicated chemical analyses in predicting C, N, and P mineralization. Because peats are classified and mapped according to these variables, it should make scaling efforts in landscape analyses much more tractable. Large differences in mineralization rates in northern wetland communities demonstrate that climate change models should not consider these areas as homogeneous entities. Our C mineralization results suggest that soil respiratory response to climate change (as CO2 and CH4) will vary considerably in different wetland communities. Our results also suggest that the common perception that more ombrotrophic sites are inherently more nutrient deficient needs to be reassessed. Briffa, K. R. (2000). "Annual climate variability in the Holocene: interpreting the message of ancient trees." Quaternary Science Reviews 19(1-5): 87-105. ABSTRACT: Over vast areas of the world's landmasses, where climate beats out a strong seasonal rhythm, tree growth keeps unerring time. In their rings, trees record many climate melodies, played in different places and different eras. Recent years have seen a consolidation and expansion of tree-ring sample collections across the traditional research areas of North America and Europe, and the start of major developments in many new areas of Eurasia, South America and Australasia. From such collections are produced networks of precisely dated chronologies; records of various aspects of tree growth, registered continuously, year by year across many centuries. Their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space. With their extensive coverage, high temporal resolution and rigid dating control, dendroclimatic reconstructions contribute significantly to our knowledge of late Holocene climates, most importantly on timescales ranging from 1 to 100 years. In special areas of the world, where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved, work building chronologies covering many millennia continues apace. Very recently, trees have provided important new information about major modes of general circulation dynamics linked to the El Niño/Southern Oscillation and the North Atlantic Oscillation, and about the effect of large volcanic eruptions. As for assessing the significance of 20th century global warming, the evidence from dendroclimatology in general, supports the notion that the last 100 years have been unusually warm, at least within a context of the last two millennia. However, this evidence should not be considered equivocal. The activities of humans may well be impacting on the ‘natural’ growth of trees in different ways, making the task of isolating a clear climate message subtly difficult. Briles, C. E., et al. (2005). "Postglacial vegetation, fire, and climate history of the Siskiyou Mountains, Oregon, USA." Quaternary Research 64(1): 44-56. ABSTRACT: The forests of the Siskiyou Mountains are among the most diverse in North America, yet the long-term relationship among climate, diversity, and natural disturbance is not well known. Pollen, plant macrofossils, and high-resolution charcoal data from Bolan Lake, Oregon, were analyzed to reconstruct a 17,000-yr-long environmental history of high-elevation forests in the region. In the late-glacial period, the presence of a subalpine parkland of Artemisia, Poaceae, Pinus, and Tsuga with infrequent fires suggests cool dry conditions. After 14,500 cal yr B.P., a closed forest of Abies, Pseudotsuga, Tsuga, and Alnus rubra with more frequent fires developed which indicates more mesic conditions than before. An open woodland of Pinus, Quercus, and Cupressaceae, with higher fire activity than before, characterized the early Holocene and implies warmer and drier conditions than at present. In the late Holocene, Abies and Picea were more prevalent in the forest, suggesting a return to cool wet conditions, although fire-episode frequency remained relatively high. The modern forest of Abies and Pseudotsuga and the present-day fire regime developed ca. 2100 cal yr B.P. and indicates that conditions had become slightly drier than before. Sub-millennial-scale fluctuations in vegetation and fire activity suggest climatic variations during the Younger Dryas interval and within the early Holocene period. The timing of vegetation changes in the Bolan Lake record is similar to that of other sites in the Pacific Northwest and Klamath region, and indicates that local vegetation communities were responding to regional-scale climate changes. The record implies that climate-driven millennial- to centennial-scale vegetation and fire change should be considered when explaining the high floristic diversity observed at present in the Siskiyou Mountains. Broecker, W. S. (1991). "The great ocean conveyor." Oceanography 4(2): 79-89. No Abstract Available Broecker, W. S. (2001). "Was the Medieval Warm Period global?" Science 291(5508): 1497-1499. INTRODUCTION: During the Medieval Warm Period (800 to 1200 A.D.), the Vikings colonized Greenland. In his Perspective, Broecker discusses whether this warm period was global or regional in extent. He argues that it is the last in a long series of climate fluctuations in the North Atlantic, that it was likely global, and that the present warming should be attributed in part to such an oscillation, upon which the warming due to greenhouse gases is superimposed. Brown, A. G. (2002). "Learning from the past: palaeohydrology and palaeoecology." Freshwater Biology 47(4): 817-829. ABSTRACT: Attempts to increase European biodiversity by restoring rivers and floodplains are based on inadequate data on natural systems. This is particularly the case for NW European rivers because all catchments have been impacted by agriculture and river engineering. If river restoration is to have an ecological, as opposed to `cosmetic' design basis then baseline models are required. However, this poses three questions; (a) what is the natural river-floodplain state, (b) how can it be defined and modelled and (c) can this state be recreated today? The first two questions can only be addressed by using palaeohydrological and palaeoecological data. A second and equally vital consideration is the stability/instability of any restored system to change in external forcing factors (e.g. climate) and in this context it may not be realistic to expect baseline models to provide equilibrium solutions but instead to define process-form domains. Over the last two decades evidence has accumulated that the natural state of lowland rivers in much of NW Europe was multi rather than single thread-braided, anastomosing or anabranching. Until recently our knowledge of floodplain palaeoecology was generally derived from pollen diagrams, which have source-area of problems and lack of taxonomic specificity. The precision and breadth of palaeoecological reconstruction (including richness and structure) has been greatly increased by the use of multiple palaeo-indicators including macrofossils, diatoms and beetles. The dynamics of small to medium sized, low-energy, predeforestation floodplains were dominated by disturbance (windthrow, beavers, etc.) and large woody debris. In order to compare the hydrogeomorphological basis of floodplain ecology, both temporally and spatially, a simple index of fluvial complexity is presented. Palaeoecological and geomorphological investigations have the potential to provide in-depth models of the natural range of channel conditions and sensitivity to external change that can be used to provide a scientific basis for floodplain restoration. There is also the possibility that floodplain-channel restoration may be a valuable tool in the mitigation of future geomorphological change forced by climatic instability. Brown, K. and W. N. Adger (1994). "Economic and political feasibility of international carbon offsets." Forest Ecology and Management 68(2-3): 217-229. ABSTRACT: Forests are important in the global carbon cycle, forming a major sink for carbon. Deforestation is a significant source of carbon dioxide emitted to the atmosphere. There is some scope to enhance natural carbon sinks, and therefore reduce net emissions of greenhouse gases, through afforestation and conservation of existing forests. Such initiatives may be implemented to “offset” emissions of greenhouse gases from other sources. This may be undertaken by private companies, or by governments as part of bilateral agreements or multilateral arrangements. International carbon offsets may be cost effective in terms of reduction of carbon emissions achieved, and may also be one way to mobilise private capital to fund forest conservation. It is argued here that theoretically the international offset of emissions may lead to a resource saving, and that forest conservation, as opposed to afforestation, may bring about many other benefits. However, such international contracts are unlikely to be feasible or make a major contribution to the control of greenhouse gases. The reasons for this are monitoring, enforcement and scientific uncertainties, and the implicit change in property rights involved in “selling” carbon sequestration rights. Brown, P. M. and C. H. Sieg (1999). "Historical variability in fire at the ponderosa pine - Northern Great Plains prairie ecotone, southeastern Black Hills, South Dakota." Ecoscience 6(4): 539-547. ABSTRACT: Ecotones are boundaries between plant assemblages that can represent a physiological or competitive limit of species’ local distributions, usually through one or more biotic or abiotic constraints on species’ resource requirements. However, ecotones also result from the effects of chronic or episodic disturbances, and changes in disturbance regimes may have profound effects on vegetation patterns in transitional areas. In this study, centuries-long chronologies of surface fire events were reconstructed from fire-scarred ponderosa pine (Pinus ponderosa Dougl. ex Laws.) trees in three sites at the ecotone between ponderosa pine forest and Northern Great Plains mixed grass prairie in the southeastern Black Hills of South Dakota. The fire chronologies provide baseline data to assess the possible role of fire in this transitional area and to document historical variability in fire regimes in this region of the Northern Great Plains. Regular fire events were recorded at all three sites from the beginning of the fire chronologies in the 1500s up to the late 1800s or early 1900s, at which time spreading fires ceased. Fire frequencies derived from the fire chronologies were compared to each other and to four sites from interior ponderosa pine forest in the south-central Black Hills. Mean fire intervals at the savanna sites were between 10 to 12 years, whereas Weibull median probability intervals were one year shorter. Fire frequency at the savanna sites was twice as high as at the interior forest sites, and most likely was due to spatial extent of fires on the mixed-grass prairie coupled with warmer and drier climate regime. Post-settlement shifts in the ponderosa pine savanna during the twentieth century in this area may be largely attributed to lack of fire occurrences, although grazing and other factors also likely contributed to observed changes in forest and grassland margins. Brown, T. J., et al. (2004). "The impact of twenty-first century climate change on wildland fire danger in the western United States: an applications perspective." Climatic Change 62(1-3): 365-388. ABSTRACT: High-temporal resolution meteorological output from the Parallel Climate Model (PCM) is used to assess changes in wildland fire danger across the western United States due to climatic changes projected in the 21st century. A business-as-usual scenario incorporating changing greenhouse gas and aerosol concentrations until the year 2089 is compared to a 1975–1996 base period. Changes in relative humidity, especially drying over much of the West, are projected to increase the number of days of high fire danger (based on the energy release component (ERC) index) at least through the year 2089 in comparison to the base period. The regions most affected are the northern Rockies, Great Basin and the Southwest – regions that have already experienced significant fire activity early this century. In these regions starting around the year 2070, when the model climate CO2 has doubled from present-day, the increase in the number of days that ERC (fuel model G) exceeds a value of 60 is as much as two to three weeks. The Front Range of the Rockies and the High Plains regions do not show a similar change. For regions where change is predicted, new fire and fuels management strategies and policies may be needed to address added climatic risks while also accommodating complex and changing ecosystems subject to human stresses on the region. These results, and their potential impact on fire and land management policy development, demonstrate the value of climate models for important management applications, as encouraged under the Department of Energy Accelerated Climate Prediction Initiative (ACPI), under whose auspices this work was performed. Brunelle, A. and C. Whitlock (2003). "Postglacial fire, vegetation, and climate history in the Clearwater Range, Northern Idaho, USA." Quaternary Research 60(3): 307-318. ABSTRACT: The environmental history of the Northern Rocky Mountains was reconstructed using lake sediments from Burnt Knob Lake, Idaho, and comparing the results with those from other previously published sites in the region to understand how vegetation and fire regimes responded to large-scale climate changes during the Holocene. Vegetation reconstructions indicate parkland or alpine meadow at the end of the glacial period indicating cold-dry conditions. From 14,000 to 12,000 cal yr B.P., abundant Pinus pollen suggests warmer, moister conditions than the previous period. Most sites record the development of a forest with Pseudotsuga ca. 9500 cal yr B.P. indicating warm dry climate coincident with the summer insolation maximum. As the amplification of the seasonal cycle of insolation waned during the middle Holocene, Pseudotsuga was replaced by Pinus and Abies suggesting cool, moist conditions. The fire reconstructions show less synchroneity. In general, the sites west of the continental divide display a fire-frequency maximum around 12,000–8000 cal yr B.P., which coincides with the interval of high summer insolation and stronger-than-present subtropical high. The sites on the east side of the continental divide have the highest fire frequency ca. 6000–3500 cal yr B.P. and may be responding to a decrease in summer precipitation as monsoonal circulation weakened in the middle and late Holocene. This study demonstrated that the fire frequency of the last two decades does not exceed the historical range of variability in that periods of even higher-than-present fire frequency occurred in the past. Butler, V. L. and J. E. O'Connor (2004). "9000 years of salmon fishing on the Columbia River, North America." Quaternary Research 62(1): 1-8. ABSTRACT: A large assemblage of salmon bones excavated 50 yr ago from an ~10,000-yr-old archaeological site near The Dalles, Oregon, USA, has been the primary evidence that early native people along the Columbia River subsisted on salmon. Recent debate about the human role in creating the deposit prompted excavation of additional deposits and analysis of archaeologic, geologic, and hydrologic conditions at the site. Results indicate an anthropogenic source for most of the salmonid remains, which have associated radiocarbon dates indicating that the site was occupied as long ago as 9300 cal yr B.P. The abundance of salmon bone indicates that salmon was a major food item and suggests that migratory salmonids had well-established spawning populations in some parts of the Columbia Basin by 9300–8200 yr ago. Caldeira, K. and G. H. Rau (2000). "Accelerating carbonate dissolution to sequester carbon dioxide in the ocean: Geochemical implications." Geophysical Research Letters 27(2): 225-228. ABSTRACT: Various methods have been proposed for mitigating release of anthropogenic CO2 to the atmosphere, including deep-sea injection of CO2 captured from fossil-fuel fired power plants. Here, we use a schematic model of ocean chemistry and transport to analyze the geochemical consequences of a new method for separating carbon dioxide from a waste gas stream and sequestering it in the ocean. This method involves reacting CO2-rich power-plant gases with seawater to produce a carbonic acid solution which in turn is reacted on site with carbonate mineral (e.g., limestone) to form Ca2+ and bicarbonate in solution, which can then be released and diluted in the ocean. Such a process is similar to carbonate weathering and dissolution which would have otherwise occurred naturally, but over many millennia. Relative to atmospheric release or direct ocean CO2 injection, this method would greatly expand the capacity of the ocean to store anthropogenic carbon while minimizing environmental impacts of this carbon on ocean biota. This carbonate-dissolution technique may be more cost-effective and less environmentally harmful, and than previously proposed CO2 capture and sequestration techniques. Caldeira, K. and M. E. Wickett (2003). "Anthropogenic carbon and ocean pH." Nature 425(6956): 365-365. ABSTRACT: The coming centuries may see more ocean acidification than the past 300 million years. Cane, M. A. (2005). "The evolution of El Niño, past and future." Earth and Planetary Science Letters 230(3-4): 227-240. ABSTRACT: We review forecasts of the future of El Niño and the Southern Oscillation (ENSO), a coupled instability of the ocean–atmosphere system in the tropical Pacific with global impacts. ENSO in the modern world is briefly described, and the physics of the ENSO cycle is discussed. Particular attention is given to the Bjerknes feedback, the instability mechanism which figures prominently in ENSO past and future. Our knowledge of ENSO in the paleoclimate record has expanded rapidly within the last 5 yr. The ENSO cycle is present in all relevant records, going back 130 kyr. It was systematically weaker during the early and middle Holocene, and model studies indicate that this results from reduced amplification in the late summer and early fall, a consequence of the altered mean climate in response to boreal summer perihelion. Data from corals shows substantial decadal and longer variations in the strength of the ENSO cycle within the past 1000 yr; it is suggested that this may be due to solar and volcanic variations in solar insolation, amplified by the Bjerknes feedback. There is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future, but it is very far from conclusive. The comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of ENSO's future. Some predict more ENSO activity, some less, with the highly uncertain consensus forecast indicating little change. Cannariato, K. G., et al. (1999). "Biotic response to late Quaternary rapid climate switches in Santa Barbara Basin: Ecological and evolutionary implications." Geology 27(1): 63-66. ABSTRACT: Benthic foraminiferal assemblages from Santa Barbara Basin exhibit major faunal and ecological switches associated with late Quaternary millennial- to decadal-scale global climate oscillations. Repeated turnovers of entire faunas occurred rapidly (<40–400 yr) without extinction or speciation in conjunction with Dansgaard-Oeschger shifts in thermohaline circulation, ventilation, and climate, confirming evolutionary model predictions of Roy et al. Consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late Quaternary and possibly other transitional intervals in the history of the Earth’s oceanatmosphere-cryosphere system. These data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change. Cao, M. and F. I. Woodward (1998). "Dynamic responses of terrestrial ecosystem carbon cycling to global climate change." Nature 393(21 May): 249-252. ABSTRACT: Terrestrial ecosystems and the climate system are closely coupled, particularly by cycling of carbon between vegetation, soils and the atmosphere. It has been suggested1,2 that changes in climate and in atmospheric carbon dioxide concentrations have modified the carbon cycle so as to render terrestrial ecosystems as substantial carbon sinks3,4; but direct evidence for this is very limited5,6. Changes in ecosystem carbon stocks caused by shifts between stable climate states have been evaluated7,8, but the dynamic responses of ecosystem carbon fluxes to transient climate changes are still poorly understood.Here we use a terrestrial biogeochemical model9, forced by simulations of transient climate change with a general circulation model10, to quantify the dynamic variations in ecosystem carbon fluxes induced by transient changes in atmospheric CO2 and climate from 1861 to 2070. We predict that these changes increase global net ecosystem production significantly, but that this response will decline as the CO2 fertilization effect becomes saturated and is diminished by changes in climatic factors. Thus terrestrial ecosystem carbon fluxes both respond to and strongly influence the atmospheric CO2 increase and climate change. Carleton, A. M., et al. (1990). "Mechanisms of interannual variability of the southwest United States summer rainfall maximum." Journal of Climate 3(9): 999-1015. ABSTRACT: The mid-summer rainfall singularity of the Southwest United States (principally Arizona) exhibits marked variations on interannual and decadal time scales. Examination of the synoptic mechanisms involved in these variations is undertaken here. In particular, associations between the rainfall, the dominant latitude of the summertime mid-tropospheric subtropical ridge (STR) over the southwest United States, and the sea surface temperatures (SSTs) of the equatorial and North Pacific region are documented. The analysis utilizes a composite approach for sets of extreme years chosen on the basis of the rainfall and circulation anomalies. It is found that northward (southward) displaced seasonal STR is associated with wetter (drier) summers in Arizona. Further, these extremes have tended to follow winters characterized by positive (negative) phases of the Pacific-North America (PNA) teleconnection pattern. The latter association arises, at least in part from the “memory” imparted to the atmosphere by the accompanying anomalies of Pacific SSTs. However, during the summer season, more localized anomalies of SST appear important for Arizona rainfall variations. In wet (but not dry) summers, an enhanced longitudinal gradient of SST exists between the west coast of the United States, Baja California, and the Gulf of California. This is accompanied by a steeper gradient of lower tropospheric heights (and implied stronger geostrophic flow) and also a reversal in both the total (850–500 mb) and partial (850–700 mb) thickness gradients across the region compared with dry summers. These results seem to confirm the importance of lower-level southwesterly flow for moisture transport into the deserts. Recent decadal variations in the singularity involve particularly runs of wetter (drier) summers in the 1950s (1970s). Preliminary analysis of these variations for years that were non-ENSO suggests that they may result from the operation of mechanisms similar to those attending the interannual variability of Arizona summer rainfall (viz., the STR and Pacific SSTs). A contributory mechanism in the longer-term trend of STR between these decades appears to be a change in the tropical–extratropical gradient of Pacific SSTs during the summer and antecedent spring. The gradient evidently strengthened during the period, helping to explain the shift to more frequent southward displacements of STR over the Southwest and, accordingly, reduced summer rainfall in Arizona. Carson, E. C., et al. (2007). "Response of bankfull flood magnitudes to Holocene climate change, Uinta Mountains, northeastern Utah." Geological Society of America Bulletin 119(9): 1066-1078. ABSTRACT: Long-term variations in Holocene flood magnitude were quantified from the bankfull dimensions of abandoned channels preserved on floodplain surfaces in the northern Uinta Mountains of northeastern Utah. Cross-sectional areas of abandoned channels were reconstructed, and relationships derived from the modern gage records were used to estimate bankfull discharges from bankfull cross-section areas. The results indicate systematic (nonrandom) variations of bankfull floods in the northern Uinta Mountains. Large floods, as much as 10%–15% greater than modern, dominated from 8500 to 5000 calendar yr B.P., and again from 2800 to 1000 cal yr B.P. Small floods, as much as 15%–20% less than modern, characterize the periods from 5000 to 2800 cal yr B.P., and from 1000 cal yr B.P. to near present. The middle and late Holocene record of bankfull flood magnitude compares well with independent evidence for climatic variation in the area. The early Holocene record indicates that larger than modern bankfull floods coincide with warmer than modern mean annual temperature. We hypothesize that an increased range of magnitude for seasonal solar radiation during the early Holocene favored the accumulation and rapid melting of deep snowpacks in the high Uinta Mountains, thus producing large floods despite warmer mean annual temperatures. The episode of smaller than modern bank-full floods between 5000 and 2800 cal yr B.P. coincides with records of increased forest fire frequency in the northern Uintas. Larger than modern floods from 2800 to 1000 cal yr B.P. coincide with a local decrease in forest fire frequency and evidence for minor local glacial readvances. The decrease in flood magnitudes following 1000 cal yr B.P. corresponds to numerous local and regional records of warming during the Medieval Climatic Anomaly. Case, R. A. and G. M. MacDonald (2003). "Tree ring reconstructions of streamflow for three Canadian prairie rivers." Journal of the American Water Resources Association 39(3): 703-716. ABSTRACT: Information regarding long term hydrological variability is critical for the effective management of surface water resources. In the Canadian Prairie region, growing dependence on major river systems for irrigation and other consumptive uses has resulted in an increasing vulnerability to hydrological drought and growing interprovincial tension. This study presents the first dendrochronological records of streamflow for Canadian Prairie rivers. We present 1,113-year, 522-year, and 325-year reconstructions of total water year (October to September) streamflow for the North Saskatchewan, South Saskatchewan, and Saskatchewan Rivers, respectively. The reconstructions indicate relatively high flows during the 20th Century and provide evidence of past prolonged droughts. Low flows during the 1840s correspond with aridity that extended over much of the western United States. Similarly, an exceptional period of prolonged low flow conditions, approximately 900 A.D. to 1300 A.D., is coincident with evidence of sustained drought across central and western North America. The 16th Century megadrought of the western United States and Mexico, however, does not appear to have had a major impact on the Canadian rivers. The dendrohydrological records illustrate the risks involved if future water policy and infrastructure development in the Canadian Prairies are based solely on records of streamflow variability over the historical record. Cayan, D. R. (1996). "Interannual climate variability and snowpack in the western United States." Journal of Climate 9(5): 928-948. ABSTRACT: An important part of the water supply in the western United States is derived from runoff fed by mountain snowmelt. Snow accumulation responds to both precipitation and temperature variations, and forms an interesting climatic index, since it integrates these influences over the entire late fall-spring period. Here, effects of cool season climate variability upon snow water equivalent (SWE) over the western part of the conterminous United States are examined. The focus is on measurements on/around 1 April, when snow accumulation is typically greatest. The primary data, from a network of mountainous snow courses, provides a good description of interannual fluctuations in snow accumulations, since many snow courses have records of five decades or more. For any given year, the spring SWE anomaly at a particular snow course is likely to be 25%–60% of its long-term average. Five separate regions of anomalous SWE variability are distinguished, using a rotated principal components analysis. Although effects vary with region and with elevation, in general, the anomalous winter precipitation has the strongest influence on spring SWE fluctuations. Anomalous temperature has a weaker effect overall, but it has great influence in lower elevations such as in the coastal Northwest, and during spring in higher elevations. The regional snow anomaly patterns are associated with precipitation and temperature anomalies in winter and early spring. Patterns of the precipitation, temperature, and snow anomalies extend over broad regional areas, much larger than individual watersheds. These surface anomalies are organized by the atmospheric circulation, with primary anomaly centers over the North Pacific Ocean as well as over western North America. For most of the regions, anomalously low SWE is associated with a winter circulation resembling the PNA pattern. With a strong low in the central North Pacific and high pressure over the Pacific Northwest, this pattern diverts North Pacific storms northward, away from the region. Both warm and cool phases of El Niño-Southern Oscillation tend to produce regional patterns with out-of-phase SWE anomalies in the Northwest and the Southwest. Cayan, D. R., et al. (1998). "Decadal variability of precipitation over western North America." Journal of Climate 11(12): 3148-3166. ABSTRACT: Decadal (>7- yr period) variations of precipitation over western North America account for 20%–50% of the variance of annual precipitation. Spatially, the decadal variability is broken into several regional [O(1000 km)] components. These decadal variations are contributed by fluctuations in precipitation from seasons of the year that vary from region to region and that are not necessarily concentrated in the wettest season(s) alone. The precipitation variations are linked to various decadal atmospheric circulation and SST anomaly patterns where scales range from regional to global scales and that emphasize tropical or extratropical connections, depending upon which precipitation region is considered. Further, wet or dry decades are associated with changes in frequency of at least a few short-period circulation “modes” such as the Pacific–North American pattern. Precipitation fluctuations over the southwestern United States and the Saskatchewan region of western Canada are associated with extensive shifts of sea level pressure and SST anomalies, suggesting that they are components of low-frequency precipitation variability from global-scale climate processes. Consistent with the global scale of its pressure and SST connection, the Southwest decadal precipitation is aligned with opposing precipitation fluctuations in northern Africa.
Cayan, D. R. and K. P. Georgakakos (1995). “Hydroclimatology of continental watersheds, 2, Spatial analyses.” Water Resources Research 31(3): 677-698.
ABSTRACT: We diagnose the spatial patterns and further examine temporal behavior of anomalous monthly-seasonal precipitation, temperature, and atmospheric circulation in relationship to hydrologic (soil water and potential evapotranspiration) fluctuations at two watersheds in the central United States. The bulk hydrologic balance at each of the two watersheds, Boone River, Iowa (BN), and Bird Creek, Oklahoma (BC), was determined from the rainfall-runoff-routing watershed model described in part 1. There are many similarities among the hydroclimatic linkages at the two basins. In both, relationships with precipitation and temperature indicate that the forcing occurs on regional scales, much larger than the individual watersheds. Precipitation exhibits anomaly variability over 500-km scales, and sometimes larger. Anomalous temperature, which is strongly correlated with potential evapotranspiration, often extends from the Great Plains to the Appalachian Mountains. Seasonally, the temperature and precipitation anomalies tend to have greatest spatial coherence in fall and least in summer. The temperature and precipitation tend to have out-of-phase anomalies (e.g., warm associated with dry). Thus low soil water conditions are reinforced by low precipitation and high potential evapotranspiration, and vice versa for high soil water. Soil water anomalies in each basin accumulate over a history of significant large-scale climate forcing that usually appears one or two seasons in advance. These forcing fields are produced by atmospheric circulation anomaly patterns that often take on hemispheric scales. BN and BC have strong similarities in their monthly circulation patterns producing heavy/light monthly precipitation episodes, the primary means of forcing of the watersheds. The patterns exhibit regional high or low geopotential anomalies just upstream over the western United States or near the center of the country. The regional circulation features are often part of a train, with teleconnections upstream over the North Pacific and downstream over the North Atlantic/Eurasia sector. Synoptic scale events exhibit very similar patterns to the monthly circulations, only more intense.
Cayan, D. R., et al. (2001). “Changes in the onset of spring in the western United States.” Bulletin of the American Meteorological Society 82(3): 399-415.
ABSTRACT: Fluctuations in spring climate in the western United States over the last 4–5 decades are described by examining changes in the blooming of plants and the timing of snowmelt–runoff pulses. The two measures of spring’s onset that are employed are the timing of first bloom of lilac and honeysuckle bushes from a long–term cooperative phenological network, and the timing of the first major pulse of snowmelt recorded from high–elevation streams. Both measures contain year–to–year fluctuations, with typical year–to–year fluctuations at a given site of one to three weeks. These fluctuations are spatially coherent, forming regional patterns that cover most of the west. Fluctuations in lilac first bloom dates are highly correlated to those of honeysuckle, and both are significantly correlated with those of the spring snowmelt pulse. Each of these measures, then, probably respond to a common mechanism. Various analyses indicate that anomalous temperature exerts the greatest influence upon both interannual and secular changes in the onset of spring in these networks. Earlier spring onsets since the late 1970s are a remarkable feature of the records, and reflect the unusual spell of warmer–than–normal springs in western North America during this period. The warm episodes are clearly related to larger–scale atmospheric conditions across North America and the North Pacific, but whether this is predominantly an expression of natural variability or also a symptom of global warming is not certain.
Cayan, D. R., et al. (1999). “ENSO and hydrologic extremes in the western United States.” Journal of Climate 12(9): 2881-2993.
ABSTRACT: Frequency distributions of daily precipitation in winter and daily stream flow from late winter to early summer, at several hundred sites in the western United States, exhibit strong and systematic responses to the two phases of ENSO. Most of the stream flows considered are driven by snowmelt. The Southern Oscillation index (SOI) is used as the ENSO phase indicator. Both modest (median) and larger (90th percentile) events were considered. In years with negative SOI values (El Niño), days with high daily precipitation and stream flow are more frequent than average over the Southwest and less frequent over the Northwest. During years with positive SOI values (La Niña), a nearly opposite pattern is seen. A more pronounced increase is seen in the number of days exceeding climatological 90th percentile values than in the number exceeding climatological 50th percentile values, for both precipitation and stream flow. Stream flow responses to ENSO extremes are accentuated over precipitation responses. Evidence suggests that the mechanism for this amplification involves ENSO-phase differences in the persistence and duration of wet episodes, affecting the efficiency of the process by which precipitation is converted to runoff. The SOI leads the precipitation events by several months, and hydrologic lags (mostly through snowmelt) delay the stream flow response by several more months. The combined 6–12-month predictive aspect of this relationship should be of significant benefit in responding to flood (or drought) risk and in improving overall water management in the western states.
Changnon, S. A. (2004). “Present and future economic impacts of climate extremes in the United States.” Global Environmental Change Part B: Environmental Hazards 5(3-4): 47-50.
ABSTRACT: Recent studies have yielded definitive information about the nation’s economic impacts from extreme climates, although some sectoral values rely on educated estimates since hard data does not exist. Review of existing measures of the national impacts from weather–climate conditions reveals annual average losses of $36 billion from extremes and gains averaging $26 billion when conditions are favorable (good growing seasons, mild winters, etc.). Comparison of these values with various measures of the national economy reveals that the impacts are relatively small, typically about 1% of the Gross Domestic Product and less than 2% of the federal budget. The current impact information provides a basis for assessing various estimates of the nation’s financial impacts resulting from a future climate change due to global warming. Most such estimates predict values similar to the magnitude of current climate impacts. Moreover, most economists attempting such estimates express a large degree of uncertainty about their projections.
Chao, Y., et al. (2000). “Pacific interdecadal variability in this century’s sea surface temperatures.” Geophysical Research Letters 27(15): 2261-2264.
ABSTRACT: Analysis of this century’s sea surface temperatures over the Pacific Ocean reveals an interdecadal oscillation with a period of 15-20 years. Our results show that the well-known 1976-77 climate regime shift is not unique, but represents one of several phase transitions associated with this interdecadal oscillation, also found around 1924-25, 1941-42, and 1957-58. The oscillations’s striking north-south symmetry across the equator implies strong interactions between tropics and extratropics. A mode with a period of approximately 70 years and an apparently different spatial pattern is also identified tentatively but has to be evaluated further using longer time series.
Chapman, M. R. and N. J. Shackleton (1999). “Global ice-volume fluctuations, North Atlantic ice-rafting events, and deep-ocean circulation changes between 130 and 70 ka.” Geology 27(9): 795-798.
ABSTRACT: Multiproxy data from North Atlantic deep-sea sediment core NEAP18K provide a detailed record of climate through oxygen isotope stage (OIS) 5. Seven distinct, large-scale episodes of ice rafting (C25–C19) were identified between 126 and 70 ka. Global ice-volume reconstructions, based on high-resolution benthic d18O records, indicate that major ice-rafting events were not confined to ice-volume maxima at OIS 5d and 5b, but also occurred during periods of ice-sheet growth and disintegration. However, iceberg discharges were restricted to times when sea levels were 40–65 m below present values. Ice-rafting episode C25, the first large-scale cooling of mid-Atlantic surface waters after the last interglacial, occurred during the gradual buildup of continental ice sheets at the OIS 5e-5d transition. Major ice-sheet collapses allied to ice-rafting events C24 and C21 were associated with rapid sea-level increases of 20 and 40 m, respectively. Suborbital climatic fluctuations in the NEAP18K sedimentary record, denoted by prominent 7.5, 4.5, and 3 k.y. cyclicities, appear to correlate with both Greenland atmospheric temperatures and changes in thermohaline circulation patterns, inferred from benthic d13C values, and hence provide clear evidence of a highly interconnected North Atlantic climatic regime during OIS 5.