Bibliography - Climate

This report provides an assessment of the effects of climate change on U.S. agriculture, land resources, water resources, and biodiversity. It is one of a series of 21 Synthesis and Assess¬ment Products (SAP) that are being produced under the auspices of the U.S. Climate Change Science Program (CCSP).This SAP builds on an extensive scientific literature and series of recent assessments of the historical and potential impacts of climate change and climate variability on managed and unmanaged ecosystems and their constituent biota and processes. It discusses the nation’s ability to identify, observe, and monitor the stresses that influence agriculture, land resources, water resources, and biodiversity, and evaluates the relative importance of these stresses and how they are likely to change in the future. It identifies changes in resource conditions that are now being observed, and examines whether these changes can be attributed in whole or part to climate change. The general time horizon for this report is from the recent past through the period 2030-2050, although longer-term results out to 2100 are also considered. There is robust scientific consensus that human-induced climate change is occurring. Records of temperature and precipitation in the United States show trends consistent with the current state of global-scale understanding and observations of change. Observations also show that climate change is currently impacting the nation’s ecosystems and services in significant ways, and those alterations are very likely to accelerate in the future, in some cases dramati¬cally. Current observational capabilities are considered inadequate to fully understand and address the future scope and rate of change in all ecological sectors. Additionally, the complex interactions between change agents such as climate, land use alteration, and species invasion create dynamics that confound simple causal relationships and will severely complicate the development and assessment of mitigation and adaptation strategies. Even under the most optimistic CO2 emission scenarios, important changes in sea level, regional and super-regional temperatures, and precipitation patterns will have profound effects. Management of water resources will become more challenging. Increased incidence of disturbances such as forest fires, insect outbreaks, severe storms, and drought will command public attention and place increasing demands on management resources. Ecosystems are likely to be pushed increasingly into alternate states with the possible breakdown of traditional species relationships, such as pollinator/plant and predator/prey interactions, adding additional stresses and potential for system failures. Some agricultural and forest systems may experience near-term productivity increases, but over the long term, many such systems are likely to experience overall decreases in productivity that could result in economic losses, diminished ecosystem services, and the need for new, and in many cases significant, changes to management regimes.

This paper addresses a number of issues related to current and future climatic change and its impacts on mountain environments and economies, focusing on the ‘Mountain Regions’ Chapter 13 of Agenda 21, a basis document presented at the 1992 United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro, and the International Year of the Mountains (IYM) 2002. The awareness that mountain regions are an important component of the earth’s ecosystems, in terms of the resources and services that they provide to both mountain communities and lowland residents, has risen in the intervening decade. Based upon the themes outlined in the supporting documents for IYM, this paper will provide a succinct review of a number of sectors that warrant particular attention, according to IYM. These sectors include water resources, ecosystems and biological diversity, natural hazards, health issues, and tourism. A portfolio of research and policy options are discussed in the concluding section, as a summary of what the IYM and other concerned international networks consider to be the priority for mountain environmental protection, capacity building, and response strategies in the face of climatic change in the short to medium term future.

Rather than simply enhancing invasion risk, climate change may also reduce invasive plant competitiveness if conditions become climatically unsuitable. Using bioclimatic envelope modeling, we show that climate change could result in both range expansion and contraction for five widespread and dominant invasive plants in the western United States. Yellow starthistle (Centaurea solstitialis) and tamarisk (Tamarix spp.) are likely to expand with climate change. Cheatgrass (Bromus tectorum) and spotted knapweed (Centaurea biebersteinii) are likely to shift in range, leading to both expansion and contraction. Leafy spurge (Euphorbia esula) is likely to contract. The retreat of once-intractable invasive species could create restoration opportunities across millions of hectares. Identifying and establishing native or novel species in places where invasive species contract will pose a considerable challenge for ecologists and land managers. This challenge must be addressed before other undesirable species invade and eliminate restoration opportunities.

Interactions between climate change and non-native invasive species may combine to increase invasion risk to native ecosystems. Changing climate creates risk as new terrain becomes climatically suitable for invasion. However, climate change may also create opportunities for ecosystem restoration on invaded lands that become climatically unsuitable for invasive species. Here, I develop a bioclimatic envelope model for cheatgrass (Bromus tectorum), a non-native invasive grass in the western US, based on its invaded distribution. The bioclimatic envelope model is based on the Mahalanobis distance using the climate variables that best constrain the species' distribution. Of the precipitation and temperature variables measured, the best predictors of cheatgrass are summer, annual, and spring precipitation, followed by winter temperature. I perform a sensitivity analysis on potential cheatgrass distributions using the projections of 10 commonly used atmosphere-ocean general circulation models (AOGCMs) for 2100. The AOGCM projections for precipitation vary considerably, increasing uncertainty in the assessment of invasion risk. Decreased precipitation, particularly in the summer, causes an expansion of suitable land area by up to 45%, elevating invasion risk in parts of Montana, Wyoming, Utah, and Colorado. Conversely, increased precipitation reduces habitat by as much as 70%, decreasing invasion risk. The strong influence of precipitation conditions on this species' distribution suggests that relying on temperature change alone to project future change in plant distributions may be inadequate. A sensitivity analysis provides a framework for identifying key climate variables that may limit invasion, and for assessing invasion risk and restoration opportunities with climate change.

The objective of this study was to simulate dynamically the response of a complex landscape, containing forests, savannas, and grasslands, to potential climate change. Thus, it was essential to simulate accurately the competition for light and water between trees and grasses. Accurate representation of water competition requires simulating the appropriate vertical root distribution and soil water content. The importance of different rooting depths in structuring savannas has long been debated. In simulating this complex landscape, we examined alternative hypotheses of tree and grass vertical root distribution and the importance of fire as a disturbance, as they influence savanna dynamics under historical and changing climates. MC1, a new dynamic vegetation model, was used to estimate the distribution of vegetation and associated carbon and nutrient fluxes for Wind Cave National Park, South Dakota, USA. MC1 consists of three linked modules simulating biogeography, biogeochemistry, and fire disturbance. This new tool allows us to document how changes in rooting patterns may affect production, fire frequency, and whether or not current vegetation types and life-form mixtures can be sustained at the same location or would be replaced by others. Because climate change may intensify resource deficiencies, it will probably affect allocation of resources to roots and their distribution through the soil profile. We manipulated the rooting depth of two life-forms, trees and grasses, that are competing for water. We then assessed the importance of variable rooting depth on ecosystem processes and vegetation distribution by running MC1 for historical climate (1895– 1994) and a GCM-simulated future scenario (1995–2094). Deeply rooted trees caused higher tree productivity, lower grass productivity, and longer fire return intervals. When trees were shallowly rooted, grass productivity exceeded that of trees even if total grass biomass was only one-third to one-fourth that of trees. Deeply rooted grasses developed extensive root systems that increased N uptake and the input of litter into soil organic matter pools. Shallowly rooted grasses produced smaller soil carbon pools. Under the climate change scenario, NPP and live biomass increased for grasses and decreased for trees, and total soil organic matter decreased. Changes in the size of biogeochemical pools produced by the climate change scenario were overwhelmed by the range of responses across the four rooting configurations. Deeply rooted grasses grew larger than shallowly rooted ones, and deeply rooted trees outcompeted grasses for resources. In both historical and future scenarios, fire was required for the coexistence of trees and grasses when deep soil water was available to trees. Consistent changes in fire frequency and intensity were simulated during the climate change scenario: more fires occurred because higher temperatures resulted in decreased fuel moisture. Fire also increased in the deeply rooted grass configurations because grass biomass, which serves as a fine fuel source, was relatively high.

Stationarity of rainfall statistical parameters is a fundamental assumption in hydraulic infrastructure design that may not be valid in an era of changing climate. This study develops a framework for examining the possible impacts of climate change on the urban infrastructure and natural ecosystems of small watersheds, and demonstrates this approach for the Mission/Wagg Creek watershed in British Columbia, Canada. Non-stationarities in rainfall records are first analyzed with linear regression analysis, and the detected trends are extrapolated to build future rainfall scenarios. The Storm Water Management Model (SWMM) is used to analyze the effects of increased rainfall intensity on design peak flows and to assess future drainage infrastructure capacity. Peak design discharges are projected to increase by in excess of 100% by 2050. In terms of impacts on the drainage infrastructure, the results of this study indicate that climate change would not create severe impacts in the Mission/Wagg Creek system.

To date, the majority of states and hundreds of cities have adopted local climate change initiatives, while the federal government has been anything from passive to hostile with respect to climate change issues. State and city climate change initiatives pose a puzzle: Why are citizens and politicians willing to shoulder the entire cost of local climate change initiatives when they must share the benefits with others planet-wide? In this Essay, we address this puzzle by analyzing the potential incentives for supporters of local climate change initiatives. Our analysis indicates that some of the support stems from informed, utility-maximizing decisions and some is derived from various biases affecting individual decision making. Furthermore, the analysis suggests that state and city climate change initiatives could affect incentives of elected and non-elected federal officials in ways that could lead to effective federal action on climate change.

Poverty and hunger are long-standing items on international and national policy makers’ agendas and strategies to overcome both are now once again being intensively discussed in the context of the Millennium Development Goals. Both are largely interlinked since poverty is recognized today both as the cause and the outcome of hunger. Poor people are likely to have less access to healthy, nutritious food, which results in a poor health status and lower labour productivity. These two factors then contribute to perpetuating the vicious cycle of poverty and malnutrition. Despite considerable improvements in food production over the last 50 years, food security still remains a problem in many parts of the world. FAO’s latest estimates for the period 2000 to 2002 show that 852 million people were undernourished. An overwhelming majority of these hungry people is to be found in developing countries (815 million) while, in transition countries, 28 million and, in developed countries, an estimated 9 million people are caloric deficient. The food security situation of a household is determined by four factors: food availability, access to food, stability of supply and accessibility, and the degree to which food is nutritious and safe and can therefore be utilized. Food availability depends, first and foremost, on the actual production of food, which is influenced by agro-ecological production potential as well as by available production technologies and input and output markets. Food aid and food stocks further determine the supply of food within a region or country. Whether a household or a person is able to access food is determined by the income level, unless the household produces the food itself. Also, the structure of the food supply chain, together with market and transport infrastructure, is an important additional factor. The stability of access to food depends on a number of political and economic factors, such as the stability of the political system and overall poverty levels. But measures to reduce food production variability also contribute to stability in access to food. All of these diverse key determinants of the food security situation of a household or a nation are influenced by a wide set of socio-economic and bio-physical driving forces. This paper focuses on three of these, namely climate change, animal disease and plant pests. We have concentrated on their implications for food security, but have also given consideration to their impact on human health, as this is another important factor determining human wellbeing/poverty levels.

Spatial analyses of global vegetation identify the ecoregions where climate change could cause the most extensive shifts in terrestrial vegetation. Because climate change alters the spatial and temporal patterns of temperature and precipitation, climate change will cause geographical shifts in the ranges of individual species and vegetation zones. Climate change has already combined with other factors to shift vegetation zones in West Africa, the Southwestern United States, and Spain. Previous analyses used the MAPSS global vegetation equilibrium model to represent potential current vegetation distributions based on 1961-1990 climatology and to model potential future vegetation distributions based on the HADCM2SUL general circulation model of a doubling of 1990 atmospheric CO2 by 2100 AD. The authors have re-examined those results using the ecoregion as the unit of analysis. The authors re-projected the MAPSS current and future global vegetation distributions to Lambert Azimuthal Equal Area projection for each continent at 50 km resolution and classified vegetation into one of nine biomes: arid land, boreal forest and taiga, grassland, savanna and woodlands, shrub steppe, temperate evergreen forest, temperate mixed forest, tropical broadleaf, tundra. For the 567 of 867 WWF ecoregions of area ≥ 25 000 km2, the authors calculated the fraction of ecoregion area where the biome would change. Results indicate potential vegetation changes on 34% of global non-ice areas in the period 1990-2100 AD. Changes vary from an average of 24% of non-ice area in Africa to 46% in Europe. Thirty-four ecoregions representing 4% of global terrestrial area showed a 1990-2100 potential vegetation change ≥ 0.75. The five ecoregions projected to experience the highest fractional change were: Flint Hills tall grasslands (North America), Western Siberian hemiboreal forests (Asia), Yukon Interior dry forests (North America), Carnarvon xeric shrublands (Australia), Altai alpine meadow and tundra (Asia).

Range shifts due to climate change may cause species to move out of protected areas. Climate change could therefore result in species range dynamics that reduce the relevance of current fixed protected areas in future conservation strategies. Here, we apply species distribution modeling and conservation planning tools in three regions (Mexico, the Cape Floristic Region of South Africa, and Western Europe) to examine the need for additional protected areas in light of anticipated species range shifts caused by climate change. We set species representation targets and assessed the area required to meet those targets in the present and in the future, under a moderate climate change scenario. Our findings indicate that protected areas can be an important conservation strategy in such a scenario, and that early action may be both more effective and less costly than inaction or delayed action. According to our projections, costs may vary among regions and none of the three areas studied will fully meet all conservation targets, even under a moderate climate change scenario. This suggests that limiting climate change is an essential complement to adding protected areas for conservation of biodiversity.

We developed interpolated climate surfaces for global land areas (excluding Antarctica) at a spatial resolution of 30 arc s (often referred to as 1-km spatial resolution). The climate elements considered were monthly precipitation and mean,minimum, and maximum temperature. Input data were gathered from a variety of sources and, where possible, were restricted to records from the 1950–2000 period. We used the thin-plate smoothing spline algorithm implemented in the ANUSPLIN package for interpolation, using latitude, longitude, and elevation as independent variables. We quantified uncertainty arising from the input data and the interpolation by mapping weather station density, elevation bias in the weather stations, and elevation variation within grid cells and through data partitioning and cross validation. Elevation bias tended to be negative (stations lower than expected) at high latitudes but positive in the tropics. Uncertainty is highest in mountainous and in poorly sampled areas. Data partitioning showed high uncertainty of the surfaces on isolated islands, e.g. in the Pacific. Aggregating the elevation and climate data to 10 arc min resolution showed an enormous variation within grid cells, illustrating the value of high-resolution surfaces. A comparison with an existing data set at 10 arc min resolution showed overall agreement, but with significant variation in some regions. A comparison with two high-resolution data sets for the United States also identified areas with large local differences, particularly in mountainous areas. Compared to previous global climatologies, ours has the following advantages: the data are at a higher spatial resolution (400 times greater or more); more weather station records were used; improved elevation data were used; and more information about spatial patterns of uncertainty in the data is available. Owing to the overall low density of available climate stations, our surfaces do not capture of all variation that may occur at a resolution of 1 km, particularly of precipitation in mountainous areas. In future work, such variation might be captured through knowledgebased methods and inclusion of additional co-variates, particularly layers obtained through remote sensing.

Despite widespread concern, the continuing effectiveness of networks of protected areas under projected 21st century climate change is uncertain. Shifts in species' distributions could mean these resources will cease to afford protection to those species for which they were originally established. Using modelled projected shifts in the distributions of sub-Saharan Africa's entire breeding avifauna, we show that species turnover across the continent's Important Bird Area (IBA) network is likely to vary regionally and will be substantial at many sites (> 50% at 42% of IBAs by 2085 for priority species). Persistence of suitable climate space across the network as a whole, however, is notably high, with 88–92% of priority species retaining suitable climate space in ≥ 1 IBA(s) in which they are currently found. Only 7–8 priority species lose climatic representation from the network. Hence, despite the likelihood of significant community disruption, we demonstrate that rigorously defined networks of protected areas can play a key role in mitigating the worst impacts of climate change on biodiversity.

Global climate change is predicted to result in the decline and/or extinction of a large number of animal populations worldwide, and the risk of extinction is likely to be greatest for those species already vulnerable—i.e. those with limited climatic range and/or restricted habitat requirements. To date, predictive models have failed to take into account the fact that climate change will alter many of the key life history and ecological parameters which determine a species’ inherent risk of extinction, such as body mass, size of geographic range and a suite of reproductive traits. Herein, I review contemporary research on the effects of climate change on extinction risk in mammals, focusing on the capacity of climate change to modify those life history traits that inherently alter species’ extinction risk. This review finds strong evidence that climate change has already had marked effects on key life history traits in many mammals. These changes have resulted in both negative and positive effects on reproductive success and adult and offspring survival, with implications for extinction risk in affected species. While the capacity of climate change to alter life history traits in mammals is clear, there is currently little research to clarify how these changes have influenced population growth and dynamics. Other currently overlooked areas of research are also identified.

Current knowledge of effects of climate change on biodiversity is briefly reviewed, and results are presented of a survey of biological research groups in the Netherlands, aimed at identifying key research issues in this field. In many areas of the world, biodiversity is being reduced by humankind through changes in land cover and use, pollution, invasions of exotic species and possibly climate change. Assessing the impact of climate change on biodiversity is difficult, because changes occur slowly and effects of climate change interact with other stress factors already imposed on the environment. Research issues identified by Dutch scientists can be grouped into: (i) spatial and temporal distributions of taxa; (ii) migration and dispersal potentials of taxa; (iii) genetic diversity and viability of (meta) populations of species; (iv) physiological tolerance of species; (v) disturbance of functional interactions between species; and (vi) ecosystem processes. Additional research should be done on direct effects of greenhouse gases, and on interactions between effects of climate change and habitat fragmentation. There are still many gaps in our knowledge of effects of climate change on biodiversity. An interdisciplinary research programme could possibly focus only on one or few of the identified research issues, and should generate input data for predictive models based on climate change scenarios.

Interactive effects of multiple global change factors on ecosystem processes are complex. It is relatively expensive to explore those interactions in manipulative experiments. We conducted a modeling analysis to identify potentially important interactions and to stimulate hypothesis formulation for experimental research. Four models were used to quantify interactive effects of climate warming (T), altered precipitation amounts [doubled (DP) and halved (HP)] and seasonality (SP, moving precipitation in July and August to January and February to create summer drought), and elevated [CO2] (C) on net primary production (NPP), heterotrophic respiration (Rh), net ecosystem production (NEP), transpiration, and runoff. We examined those responses in seven ecosystems, including forests, grasslands, and heathlands in different climate zones. The modeling analysis showed that none of the three-way interactions among T, C, and altered precipitation was substantial for either carbon or water processes, nor consistent among the seven ecosystems. However, two-way interactive effects on NPP, Rh, and NEP were generally positive (i.e. amplification of one factor's effect by the other factor) between T and C or between T and DP. A negative interaction (i.e. depression of one factor's effect by the other factor) occurred for simulated NPP between T and HP. The interactive effects on runoff were positive between T and HP. Four pairs of two-way interactive effects on plant transpiration were positive and two pairs negative. In addition, wet sites generally had smaller relative changes in NPP, Rh, runoff, and transpiration but larger absolute changes in NEP than dry sites in response to the treatments. The modeling results suggest new hypotheses to be tested in multifactor global change experiments. Likewise, more experimental evidence is needed for the further improvement of ecosystem models in order to adequately simulate complex interactive processes.

Global climate change and its broad spectrum of effects on human and natural systems has become a central research topic in recent years; biodiversity informatics tools—particularly ecological niche modeling (ENM)—have been used extensively to anticipate potential effects on geographic distributions of species. Misuse of these tools, however, is counterproductive, as biased conclusions might be reached. In this paper, I discuss some issues related to niche theory, geographic distributions, data quality, and algorithms, all of which are relevant when using ENM in climate change projections for biodiversity. This assortment of opinions and ideas is presented in the hope that ENM applications to climate change questions can be made more realistic and more predictive.

Climate change will pose new challenges to conserving Earth’s natural ecosystems, due to incremental changes in temperature and weather patterns, and to increased frequency and intensity of extreme climate events. Addressing these challenges will require pragmatic conservation actions informed by sitespecific understanding of susceptibility to climate change and capacity of societies to cope with and adapt to change. Depending on a location’s environmental susceptibility and social adaptive capacity, appropriate conservation actions will require some combination of: (1) large-scale protection of ecosystems; (2) actively transforming and adapting social-ecological systems; (3) building the capacity of communities to cope with change; and (4) government assistance focused on de-coupling communities from dependence on natural resources. We apply a novel analytical framework to examine conservation actions in five western Indian Ocean countries, where climate-mediated disturbance has impacted coral reefs and where adaptive capacity differs markedly. We find that current conservation strategies do not reflect adaptive capacity and are, therefore, ill prepared for climate change. We provide a vision for conservation policies that considers social adaptive capacity that copes with complexities of climate change better than the singular emphasis on government control and the creation of no-take areas.

Anthropogenic changes in tropical rainfall are evaluated in a multimodel ensemble of global warming simulations. Major discrepancies on the spatial distribution of these precipitation changes remain in the latest-generation models analyzed here. Despite this uncertainty, we find a number of measures, both global and local, on which reasonable agreement is obtained, notably for the regions of drying trend (negative precipitation anomalies). Models agree on the overall amplitude of the precipitation decreases that occur at the margins of the convective zones, with percent error bars of magnitude similar to those for the tropical warming. Similar agreement is found on a precipitation climate sensitivity defined here and on differential moisture increase inside and outside convection zones, a step in a hypothesized causal path leading to precipitation changes. A measure of local intermodel agreement on significant trends indicates consistent predictions for particular regions. Observed rainfall trends in several data sets show a significant summer drying trend in a main region of intermodel agreement: the Caribbean/Central-American region.

The Bonn Convention on the Conservation of Migratory Species of Wild Animals adopted a Resolution in 2005 recognising the impacts of climate change on migratory species. It called on Contracting Parties to undertake more research to improve our understanding of these impacts and to implement adaptation measures to reduce foreseeable adverse effects. Given the large diversity of taxa and species affected by climate change, it is impossible to monitor all species and effects thereof. However, it is likely that many of the key ecological and physical processes through which climate change may impact wildlife could be monitored using a suite of indicators, each comprising parameters of species/populations or groups of species as proxies for wider assemblages, habitats and ecosystems. Herein, we identify a suite of 17 indicators whose attributes could reveal negative impacts of climate change on the global status of migratory species: 4 for birds, 4 for marine mammals, 2 for sea turtles, 1 for fish, 3 for land mammals and 3 for bats. A few of these indicators would be relatively straightforward to develop, but most would require additional data collation, and in many cases methodological development. Choosing and developing indicators of the impacts of climate change on migratory species is a challenge, particularly with endangered species, which are subject to many other pressures. To identify and implement conservation measures for these species, indicators must account for the full ensemble of pressures, and link to a system of alerts and triggers for action.

Major rivers worldwide have experienced dramatic changes in flow, reducing their natural ability to adjust to and absorb disturbances. Given expected changes in global climate and water needs, this may create serious problems, including loss of native biodiversity and risks to ecosystems and humans from increased flooding or water shortages. Here, we project river discharge under different climate and water withdrawal scenarios and combine this with data on the impact of dams on large river basins to create global maps illustrating potential changes in discharge and water stress for dam-impacted and free-flowing basins. The projections indicate that every populated basin in the world will experience changes in river discharge and many will experience water stress. The magnitude of these impacts is used to identify basins likely and almost certain to require proactive or reactive management intervention. Our analysis indicates that the area in need of management action to mitigate the impacts of climate change is much greater for basins impacted by dams than for basins with free-flowing rivers. Nearly one billion people live in areas likely to require action and approximately 365 million people live in basins almost certain to require action. Proactive management efforts will minimize risks to ecosystems and people and may be less costly than reactive efforts taken only once problems have arisen.

As the Earth warms, many species are likely to disappear, often because of changing disease dynamics. Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming. Seventeen years ago, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufo periglenes). An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated. Analysing the timing of losses in relation to changes in sea surface and air temperatures, we conclude with 'very high confidence' (> 99%, following the Intergovernmental Panel on Climate Change, IPCC) that large-scale warming is a key factor in the disappearances. We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium, thus encouraging outbreaks. With climate change promoting infectious disease and eroding biodiversity, the urgency of reducing greenhouse-gas concentrations is now undeniable.

This paper develops a framework for the study of climate on fish populations based on first principles of physiology, ecology, and available observations. Environmental variables and oceanographic features that are relevant to fish and that are likely to be affected by climate change are reviewed. Working hypotheses are derived from the differences in the expected response of different species groups. A review of published data on Northeast Atlantic fish species representing different biogeographic affinities, habitats, and body size lends support to the hypothesis that global warming results in a shift in abundance and distribution (in patterns of occurrence with latitude and depth) of fish species. Pelagic species exhibit clear changes in seasonal migration patterns related to climate-induced changes in zooplankton productivity. Lusitanian species have increased in recent decades (sprat, anchovy, and horse mackerel), especially at the northern limit of their distribution areas, while Boreal species decreased at the southern limit of their distribution range (cod and plaice), but increased at the northern limit (cod). Although the underlying mechanisms remain uncertain, available evidence suggests climate-related changes in recruitment success to be the key process, stemming from either higher production or survival in the pelagic egg or larval stage, or owing to changes in the quality/quantity of nursery habitats.

Long-distance migrations are among the wonders of the natural world, but this multitaxon review shows that the characteristics of species that undertake such movements appear to make them particularly vulnerable to detrimental impacts of climate change. Migrants are key components of biological systems in high latitude regions, where the speed and magnitude of climate change impacts are greatest. They also rely on highly productive seasonal habitats, including wetlands and ocean upwellings that, with climate change, may become less food-rich and predictable in space and time. While migrants are adapted to adjust their behaviour with annual changes in the weather, the decoupling of climatic variables between geographically separate breeding and nonbreeding grounds is beginning to result in mistimed migration. Furthermore, human land-use and activity patterns will constrain the ability of many species to modify their migratory routes and may increase the stress induced by climate change. Adapting conservation strategies for migrants in the light of climate change will require substantial shifts in site designation policies, flexibility of management strategies and the integration of forward planning for both people and wildlife. While adaptation to changes may be feasible for some terrestrial systems, wildlife in the marine ecosystem may be more dependent on the degree of climate change mitigation that is achievable.

We quantify the risks of climate-induced changes in key ecosystem processes during the 21st century by forcing a dynamic global vegetation model with multiple scenarios from 16 climate models and mapping the proportions of model runs showing forest/nonforest shifts or exceedance of natural variability in wildfire frequency and freshwater supply. Our analysis does not assign probabilities to scenarios or weights to models. Instead, we consider distribution of outcomes within three sets of model runs grouped by the amount of global warming they simulate: <2°C (including simulations in which atmospheric composition is held constant, i.e., in which the only climate change is due to greenhouse gases already emitted), 2–3°C, and >3°C. High risk of forest loss is shown for Eurasia, eastern China, Canada, Central America, and Amazonia, with forest extensions into the Arctic and semiarid savannas; more frequent wildfire in Amazonia, the far north, and many semiarid regions; more runoff north of 50°N and in tropical Africa and northwestern South America; and less runoff in West Africa, Central America, southern Europe, and the eastern U.S. Substantially larger areas are affected for global warming >3°C than for <2°C; some features appear only at higher warming levels. A land carbon sink of ≈1 Pg of C per yr is simulated for the late 20th century, but for >3°C this sink converts to a carbon source during the 21st century (implying a positive climate feedback) in 44% of cases. The risks continue increasing over the following 200 years, even with atmospheric composition held constant.

At least a quarter of the world’s cetaceans were recently confirmed as endangered and the situation may be worse as the status of many others remains unclear. Climate change is affecting the oceans and a number of studies have recently highlighted its potential impact on cetacean species - for example, there are important linkages between sea ice and krill, the primary prey for baleen whales in Antarctica. This paper provides a synthesis of new information available on this theme and considers its implications for the future conservation and management of cetacean populations and species. The more mobile (or otherwise adaptable) cetaceans may be able to respond to climate related changes, although the extent of this adaptability is largely unknown. However, there is broad agreement that certain species and populations are likely to be especially vulnerable to climate related changes, including those with a limited habitat range, or those for which sea ice provides an important habitat for the cetacean population and/or that of their prey. International conservation bodies, such as the Convention for Migratory Species and the International Whaling Commission, are striving to address these issues. The challenges presented by climate change require an innovative, large scale, long term and multinational response from scientists, conservation managers and decision makers. This response that should encompass a precautionary approach, including addressing the detrimental effects of other factors negatively impacting populations and species.

Climate constitutes one of the great determinants of all natural environments. As such, it goes a long way in accounting for the distributions of the plant and animal species that inhabit the Sierra Nevada today. Most land managers are well aware that climate has changed over geologic time—indeed, one needs to look no farther than the polished rock of high Sierra Nevadan canyons to see evidence that a climate conducive to large-scale glaciations existed in the past. And most land managers accept that these past climate changes must have brought about shifts in distributions of the biota. But many still tend to view modern climate (defined, for present purposes, as that of the past 120 years) as being both long established and “normal.” In this view, climates of the pre-modern period are treated as long gone (and thus largely irrelevant to land management) and as mere deviations from “normality.” Two primary factors contribute to this tendency. First, many scientists lack an appreciation for time scales that exceed a few human generations in length, considering 1,000 years ago as the distant past. Second, many assume that the pre-instrumental past cannot be well known or understood and that the inferences drawn from proxy records, such as pollen records in lake sediment cores, therefore constitute an insufficient basis for high-stakes management decisions. Proxy records of Sierra Nevadan climate spanning the past millennium suggest that these views are flawed in ways that have consequences for management and mismanagement of the land. Specifically, proxy records indicate that the Sierra Nevada's modern climate is, by the standards of the past millennium (or the past 2, 3, or 4 millennia, for that matter), abnormally wet and warm; wide, multi-decade-scale fluctuations in moisture availability, unlike any seen in modern time, have characterized the Sierra Nevada over the past millennium; and many such swings—naturally or artificially induced, or both—must be expected to recur within a time period relevant to current land management practices and decisions. This paper summarizes some of the multi-decade to century-scale records, examining first the Sierra Nevadan climate of late Medieval time (from roughly A.D. 900 to 1350) and then the climate of the Little Ice Age (from roughly A.D. 1350 to 1880). The final section considers some of the management implications of the records.

The understanding of climate impacts on tropical rivers and catchments has developed, in part, from models developed for temperate landscapes, and a common rhythm is often apparent when millennial-scale studies are compared. At this level issues arising from the complex response of rivers to internal and external factors appear less important than the climate-driven signal. Understanding the fluvial record, however, depends on the availability and interpretation of other sources of proxy data such as pollen spectra, lake levels and ocean cores. In many rainforest areas few pollen records exist and many of these reveal a hiatus at the time of the Last Glacial Maximum. Examples of fluvial archives from Africa, Indonesia and tropical Queensland, Australia are discussed in relation to independent records of vegetation change and inferences are made concerning critical episodes in fluvial history, focusing on the transitions from Oxygen Isotope Stage (OIS)3 towards ‘glacial’ conditions in OIS2 and the Pleistocene–Holocene transition to modern climates. Links between climate, vegetation change and fluvial activity are presented as descriptive models.

As defined in this Synthesis and Assessment Report, ‘an ecological threshold is the point at which there is an abrupt change in an ecosystem quality, property, or phenomenon, or where small changes in one or more external conditions produce large and persistent responses in an ecosystem’. Ecological thresholds occur when external factors, positive feedbacks, or nonlinear instabilities in a system cause changes to propagate in a domino-like fashion that is potentially irreversible. This report reviews threshold changes in North American ecosystems that are potentially induced by climatic change and addresses the significant challenges these threshold crossings impose on resource and land managers. Sudden changes to ecosystems and the goods and services they provide are not well understood, but they are extremely important if natural resource managers are to succeed in developing adaptation strategies in a changing world. The report provides an overview of what is known about ecological thresholds and where they are likely to occur. It also identifies those areas where research is most needed to improve knowledge and understand the uncertainties regarding them. The report suggests a suite of potential actions that land and resource managers could use to improve the likelihood of success for the resources they manage, even under conditions of incomplete understanding of what drives thresholds of change and when changes will occur. Key examples of climate-induced threshold changes are presented. This synthesis effort identified a suite of potential actions that, taken together or separately, can begin to improve the understanding of thresholds and increase the likelihood of success in developing management and adaptation strategies in a changing climate, before, during, and after thresholds are crossed. In general, it is essential to increase the resilience of ecosystems and thus to slow or prevent the crossing of thresholds; to identify early warning signals of impending threshold changes; and to employ adaptive management strategies to deal with new conditions, new successional trajectories and new combinations of species.

We compare the simulations of three biogeography models (BIOME2, Dynamic Global Phytogeography Model (DOLY)5 and Mapped Atmosphere-Plant Soil System (MAPSS)) and three biogeochemistry models (BIOME-BGC (BioGeochemistry Cycles), CENTURY, and Terrestrial Ecosystem Model (TEM)) for the conterminous United States under contemporary conditions of atmospheric CO2 and climate. We also compare the simulations of these models under doubled CO2 and a range of climate scenarios. For contemporary conditions, the biogeography models successfully simulate the geographic distribution of major vegetation types and have similar estimates of area for forests (42 to 46% of the conterminous United States), grasslands (17 to 27%), savannas (15 to 25%), and shrublands (14 to 18%). The biogeochemistry models estimate similar continental-scale net primary production (NPP; 3125 to 3772 × 1012 gC yr−1) and total carbon storage (108 to 118 × 1015 gC) for contemporary conditions. Among the scenarios of doubled CO2 and associated equilibrium climates produced by the three general circulation models (Oregon State University (OSU), Geophysical Fluid Dynamics Laboratory (GFDL), and United Kingdom Meteorological Office (UKMO)), all three biogeography models show both gains and losses of total forest area depending on the scenario (between 38 and 53% of conterminous United States area). The only consistent gains in forest area with all three models (BIOME2, DOLY, and MAPSS) were under the GFDL scenario due to large increases in precipitation. MAPSS lost forest area under UKMO, DOLY under OSU, and BIOME2 under both UKMO and OSU. The variability in forest area estimates occurs because the hydrologie cycles of the biogeography models have different sensitivities to increases in temperature and CO2. However, in general, the biogeography models produced broadly similar results when incorporating both climate change and elevated CO2 concentrations. For these scenarios, the NPP estimated by the biogeochemistry models increases between 2% (BIOME-BGC with UKMO climate) and 35% (TEM with UKMO climate). Changes in total carbon storage range from losses of 33% (BIOME-BGC with UKMO climate) to gains of 16% (TEM with OSU climate). The CENTURY responses of NPP and carbon storage are positive and intermediate to the responses of BIOME-BGC and TEM. The variability in carbon cycle responses occurs because the hydrologie and nitrogen cycles of the biogeochemistry models have different sensitivities to increases in temperature and CO2. When the biogeochemistry models are run with the vegetation distributions of the biogeography models, NPP ranges from no response (BIOME-BGC with all three biogeography model vegetations for UKMO climate) to increases of 40% (TEM with MAPSS vegetation for OSU climate). The total carbon storage response ranges from a decrease of 39% (BIOME-BGC with MAPSS vegetation for UKMO climate) to an increase of 32% (TEM with MAPSS vegetation for OSU and GFDL climates). The UKMO responses of BIOME-BGC with MAPSS vegetation are primarily caused by decreases in forested area and temperature-induced water stress. The OSU and GFDL responses of TEM with MAPSS vegetations are primarily caused by forest expansion and temperature-enhanced nitrogen cycling.

Climate change has led to shifts in phenology in many species distributed widely across taxonomic groups. It is, however, unclear how we should interpret these shifts without some sort of a yardstick: a measure that will reflect how much a species should be shifting to match the change in its environment caused by climate change. Here, we assume that the shift in the phenology of a species’ food abundance is, by a first approximation, an appropriate yardstick. We review the few examples that are available, ranging from birds to marine plankton. In almost all of these examples, the phenology of the focal species shifts either too little (five out of 11) or too much (three out of 11) compared to the yardstick. Thus, many species are becoming mistimed due to climate change. We urge researchers with long-term datasets on phenology to link their data with those that may serve as a yardstick, because documentation of the incidence of climate change induced mistiming is crucial in assessing the impact of global climate change on the natural world.

Key risks associated with projected climate trends for the 21st century include the prospects of future climate states with no current analog and the disappearance of some extant climates. Because climate is a primary control on species distributions and ecosystem processes, novel 21st-century climates may promote formation of novel species associations and other ecological surprises, whereas the disappearance of some extant climates increases risk of extinction for species with narrow geographic or climatic distributions and disruption of existing communities. Here we analyze multimodel ensembles for the A2 and B1 emission scenarios produced for the fourth assessment report of the Intergovernmental Panel on Climate Change, with the goal of identifying regions projected to experience (i) high magnitudes of local climate change, (ii) development of novel 21st-century climates, and/or (iii) the disappearance of extant climates. Novel climates are projected to develop primarily in the tropics and subtropics, whereas disappearing climates are concentrated in tropical montane regions and the poleward portions of continents. Under the high-end A2 scenario, 12–39% and 10–48% of the Earth's terrestrial surface may respectively experience novel and disappearing climates by 2100 AD. Corresponding projections for the low-end B1 scenario are 4–20% and 4–20%. Dispersal limitations increase the risk that species will experience the loss of extant climates or the occurrence of novel climates. There is a close correspondence between regions with globally disappearing climates and previously identified biodiversity hotspots; for these regions, standard conservation solutions (e.g., assisted migration and networked reserves) may be insufficient to preserve biodiversity.

Rising Waters is a collaborative effort designed to develop adaptive strategies to protect the Hudson Valley's environment, economy and quality of life from threats associated with climate change. Using a formal scenario development process, originally created by Royal Dutch Shell, to model plausible futures in a changing climate, participants consider possible impacts of climate change on Hudson Valley communities and the environment, and how various types of human response over a 20-year period might change them.

The Gulf of California is considered as a key area for conservation worldwide, and has high endemism and diversity of its reef fish fauna. This group might be affected by global warming, because they are ectotherms and temperature may increase several degrees by 2100. This study analyze the latitudinal patterns of abundance of the 20 most abundant reef fishes in the Gulf of California, and evaluate possible changes caused by the temperature increment. Stationary censuses of fishes (N= 147) were done in six regions, from Los Angeles Bay (28°N) to Los Cabos (22°N). For each region we obtained the following information: mean, minimum and maximum surface temperature, photosynthetic pigments, and nitrate, phosphate and silicate concentrations. These factors were included in stepwise regressions to evaluate its influence on each species, and the equations were used to project change in numbers as a result of warming, by changing the coefficients linked to mean temperature in 1°, 2° and 3° C. The results of the models indicated that as temperature increases, four species reduce their abundance, fourteen became very similar in numbers along the gulf, and two were unaffected. Ten species will extend its range to areas where they are currently absent. Finally, richness and diversity (H') of the "future" communities will increase significantly; the highest value occurred in the 1°C increase model, but afterwards the values reduce gradually. Our conclusions are: a) the Gulf of California reef fish fauna will not react homogeneously to temperature increase; b) some species may change their distribution; c) ecological indices reflect the predicted qualitative shift in assemblage composition; and d) the differential responses of the species may cause an ecological imbalance in teleost assemblages of the gulf in following decades.

Based on the Fourth Report of the Intergovernmental Panel on Climate Change (IPCC), the consequences of global warming in Latin America and the Caribbean (LAC) are estimated to be significant. Broadly speaking, it is estimated that the vegetation characteristic of semi-arid areas will be replaced by that of dry areas, that tropical forests of the eastern part of the Amazon will be replaced by savanna, and that many areas will suffer "water stress", among other consequences . Most affected by these changes are the third of the LAC population living under the poverty line. The authors argue that this is reason enough to give first priority and urgency to the generation of decentralized and intersectoral development programmes, and investment in social and economic infrastructure and building capacities for their utilization. In all three plans, mitigation and adaptation objectives need to be considered to cope with climate change.

Spatial climate data sets of 1971-2000 mean monthly precipitation and minimum and maximum temperature were developed for the conterminous United States. These 30-arcsec (800-m) grids are the official spatial climate data sets of the U.S. Department of Agriculture. The PRISM (Parameter-elevation Relationships on Independent Slopes Model) interpolation method was used to develop data sets that reflected, as closely as possible, the current state of knowledge of spatial climate patterns in the United States. PRISM calculates a climate-elevation regression for each digital elevation model (DEM) grid cell, and stations entering the regression are assigned weights based primarily on the physiographic similarity of the station to the grid cell. Factors considered are location, elevation, coastal proximity, topographic facet orientation, vertical atmospheric layer, topographic position, and orographic effectiveness of the terrain. Surface stations used in the analysis numbered nearly 13 000 for precipitation and 10 000 for temperature. Station data were spatially quality controlled, and short-period-of-record averages adjusted to better reflect the 1971-2000 period. PRISM interpolation uncertainties were estimated with cross-validation (C-V) mean absolute error (MAE) and the 70% prediction interval of the climate-elevation regression function. The two measures were not well correlated at the point level, but were similar when averaged over large regions. The PRISM data set was compared with the WorldClim and Daymet spatial climate data sets. The comparison demonstrated that using a relatively dense station data set and the physiographically sensitive PRISM interpolation process resulted in substantially improved climate grids over those of WorldClim and Daymet. The improvement varied, however, depending on the complexity of the region. Mountainous and coastal areas of the western United States, characterized by sparse data coverage, large elevation gradients, rain shadows, inversions, cold air drainage, and coastal effects, showed the greatest improvement. The PRISM data set benefited from a peer review procedure that incorporated local knowledge and data into the development process.

We use a multi-model, multi-scenario climate model ensemble to identify climate change hotspots in the continental United States. Our ensemble consists of the CMIP3 atmosphere-ocean general circulation models, along with a high-resolution nested climate modeling system. We test both high (A2) and low (B1) greenhouse gas emissions trajectories, as well as two different statistical metrics for identifying regional climate change hotspots. We find that the pattern of peak responsiveness in the CMIP3 ensemble is persistent across variations in GHG concentration, GHG trajectory, and identification method. Areas of the southwestern United States and northern Mexico are the most persistent hotspots. The high-resolution climate modeling system produces highly localized hotspots within the basic GCM structure, but with a higher sensitivity to the identification method. Across the ensemble, the pattern of relative climate change hotspots is shaped primarily by changes in interannual variability of the contributing variables rather than by changes in the long-term means.

This report summarizes the science of climate change and the impacts of climate change on the United States, now and in the future. It is largely based on results of the U.S. Global Change Research Program (USGCRP),a and integrates those results with related research from around the world. This report discusses climate-related impacts for various societal and environmental sectors and regions across the nation. It is an authoritative scientific report written in plain language, with the goal of better informing public and private decision making at all levels.

We examined the vulnerability of 34 species of oaks (Quercus) and pines (Pinus) to the effects of global climate change in Mexico. We regionalized the HadCM2 model of climate change with local climatic data (mean annual temperature and rainfall) and downscaled the model with the inverse distance-weighted method. Databases of herbaria specimens, genetic algorithms (GARP), and digital covers of biophysical variables that affect oaks and pines were used to project geographic distributions of the species under a severe and conservative scenario of climate change for the year 2050. Starting with the current average temperature of 20.2°C and average precipitation of 793 mm, under the severe warming scenario mean temperature and precipitation changed to 22.7°C and 660 mm, respectively, in 2050. For the conservative warming scenario, these variables shifted to 21.8°C and 721 mm. Responses to the different scenarios of climate change were predicted to be species-specific and related to each species climate affinity. The current geographic distribution of oaks and pines decreased 7-48% and 0.2-64%, respectively. The more vulnerable pines were Pinus rudis, P. chihuahuana, P. oocarpa, and P. culminicola, and the most vulnerable oaks were Quercus crispipilis, Q. peduncularis, Q. acutifolia, and Q. sideroxyla. In addition to habitat conservation, we think sensitive pine and oak species should be looked at more closely to define ex situ strategies (i.e., seed preservation in germplasm banks) for their long-term conservation. Modeling climatic-change scenarios is important to the development of conservation strategies.

In the anoxic Cariaco Basin of the southern Caribbean, the bulk titanium content of undisturbed sediment reflects variations in riverine input and the hydrological cycle over northern tropical South America. A seasonally resolved record of titanium shows that the collapse of Maya civilization in the Terminal Classic Period occurred during an extended regional dry period, punctuated by more intense multiyear droughts centered at approximately 810, 860, and 910 A.D. These new data suggest that a century-scale decline in rainfall put a general strain on resources in the region, which was then exacerbated by abrupt drought events, contributing to the social stresses that led to the Maya demise.

The magnitude of future climate change depends substantially on the greenhouse gas emission pathways we choose. Here we explore the implications of the highest and lowest Intergovernmental Panel on Climate Change emissions pathways for climate change and associated impacts in California. Based on climate projections from two state-of-the-art climate models with low and medium sensitivity (Parallel Climate Model and Hadley Centre Climate Model, version 3, respectively), we find that annual temperature increases nearly double from the lower B1 to the higher A1fi emissions scenario before 2100. Three of four simulations also show greater increases in summer temperatures as compared with winter. Extreme heat and the associated impacts on a range of temperature-sensitive sectors are substantially greater under the higher emissions scenario, with some interscenario differences apparent before midcentury. By the end of the century under the B1 scenario, heatwaves and extreme heat in Los Angeles quadruple in frequency while heat-related mortality increases two to three times; alpine_subalpine forests are reduced by 50-75%; and Sierra snowpack is reduced 30-70%. Under A1fi, heatwaves in Los Angeles are six to eight times more frequent, with heat-related excess mortality increasing five to seven times; alpine_subalpine forests are reduced by 75-90%; and snowpack declines 73-90%, with cascading impacts on runoff and streamflow that, combined with projected modest declines in winter precipitation, could fundamentally disrupt California's water rights system. Although interscenario differences in climate impacts and costs of adaptation emerge mainly in the second half of the century, they are strongly dependent on emissions from preceding decades.

Geographic changes in species distributions toward traditionally cooler climes is one hypothesized indicator of recent global climate change. We examined distribution data on 56 bird species. If global warming is affecting species distributions across the temperate northern hemisphere, these data should show the same northward range expansions of birds that have been reported for Great Britain. Because a northward shift of distributions might be due to multidirectional range expansions for multiple species, we also examined the possibility that birds with northern distributions may be expanding their ranges southward. There was no southward expansion of birds with a northern distribution, indicating that there is no evidence of overall range expansion of insectivorous and granivorous birds in North America. As predicted, the northern limit of birds with a southern distribution showed a significant shift northward (2.35 km/year). This northward shift is similar to that observed in previous work conducted in Great Britain: the widespread nature of this shift in species distributions over two distinct geographical regions and its coincidence with a period of global warming suggests a connection with global climate change.

We studied a 5.1-m sediment core from Aguada X'caamal (20° 36.6'N, 89° 42.9'W), a small sinkhole lake in northwest Yucatan, Mexico. Between 1400 and 1500 A.D., oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2.2%25 and the benthic foraminifer Ammonia beccarii parkinsoniana appeared in the sediment profile, indicating a hydrologic change that included increased lake water salinity. Pollen from a core in nearby Cenote San José Chulchacá showed a decrease in mesic forest taxa during the same period. Oxygen isotopes of shell carbonate in sediment cores from Lakes Chichancanab (19° 53.0'N, 88° 46.0'W) and Salpeten (16° 58.6'N, 89° 40.5'W) to the south also increased in the mid-15th century, but less so than in Aguada X'caamal. Climate change in the 15th century is also supported by historical accounts of cold and famine described in Maya and Aztec chronicles. We conclude that climate became drier on the Yucatan Peninsula in the 15th century A.D. near the onset of the Little Ice Age (LIA). Comparison of results from the Yucatan Peninsula with other circum-Caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the LIA. At that time, sea surface temperatures cooled and aridity in the circum-Caribbean region increased.

Global climate change could have profound effects on the Earth's biota, including large redistributions of tree species and forest types. We used DISTRIB, a deterministic regression tree analysis model, to examine environmental drivers related to current forest-species distributions and then model potential suitable habitat under five climate change scenarios associated with a doubling of atmospheric CO2. Potential shifts in suitable habitat for 76 common tree species in the eastern US were evaluated based on more than 100,000 plots and 33 environmental variables related to climate, soils, land use, and elevation. Regression tree analysis was used to devise prediction rules from current species-environment relationships. These rules were used to replicate the current distribution and predict the potential suitable habitat for more than 2100 counties east of the 100th meridian. The calculation of an importance value-weighted area score, averaged across the five climate scenarios, allowed comparison among species for their overall potential to be affected by climate change. When this score was averaged across all five climate scenarios, 34 tree species were projected to expand by at least 10%, while 31 species could decrease by at least 10%. Several species (Populus tremuloides, P. grandidentata, Acer saccharum, Betula papyrifera, Thuja occidentalis) could have their suitable habitat extirpated from US. Depending on the scenario, the optimum latitude of suitable habitat moved north more than 20 km for 38-47 species, including 8-27 species more than 200 km or into Canada. Although the five scenarios were in general agreement with respect to the overall tendencies in potential future suitable habitat, significant variations occurred in the amount of potential movement in many of the species. The five scenarios were ranked for their severity on potential tree habitat changes. Actual species redistributions, within the suitable habitat modeled here, will be controlled by migration rates through fragmented landscapes, as well as human manipulations.

In the coming century, anthropogenic climate change will threaten the persistence of restricted endemic species, complicating conservation planning. Although most efforts to quantify potential shifts in species' ranges use global climate model (GCM) output, regional climate model (RCM) output may be better suited to predicting shifts by restricted species, particularly in regions with complex topography or other regionally important climate-forcing factors. Using a RCM-based future climate scenario, we found that potential ranges of two California endemic oaks, Quercus douglasii and Quercus lobata, shrink considerably (to 59% and 54% of modern potential range sizes, respectively) and shift northward. This result is markedly different from that obtained by using a comparable GCM-based scenario, under which these species retain 81% and 73% of their modern potential range sizes, respectively. The difference between RCM- and GCM-based scenarios is due to greater warming and larger precipitation decreases during the growing season predicted by the RCM in these species' potential ranges. Based on the modeled regional climate change, <50% of protected land area currently containing these species is expected to contain them under a future midrange "business-as-usual" path of greenhouse gas emissions.

Climate change is predicted to be one of the greatest drivers of ecological change in the coming century. Increases in temperature over the last century have clearly been linked to shifts in species distributions. Given the magnitude of projected future climatic changes, we can expect even larger range shifts in the coming century. These changes will, in turn, alter ecological communities and the functioning of ecosystems. Despite the seriousness of predicted climate change, the uncertainty in climate-change projections makes it difficult for conservation managers and planners to proactively respond to climate stresses. To address one aspect of this uncertainty, we identified predictions of faunal change for which a high level of consensus was exhibited by different climate models. Specifically, we assessed the potential effects of 30 coupled atmosphere-ocean general circulation model (AOGCM) future-climate simulations on the geographic ranges of 2954 species of birds, mammals, and amphibians in the Western Hemisphere. Eighty percent of the climate projections based on a relatively low greenhouse-gas emissions scenario result in the local loss of at least 10% of the vertebrate fauna over much of North and South America. The largest changes in fauna are predicted for the tundra, Central America, and the Andes Mountains where, assuming no dispersal constraints, specific areas are likely to experience over 90% turnover, so that faunal distributions in the future will bear little resemblance to those of today.

The flora of California, a global biodiversity hotspot, includes 2387 endemic plant taxa. With anticipated climate change, we project that up to 66% will experience >80% reductions in range size within a century. These results are comparable with other studies of fewer species or just samples of a region's endemics. Projected reductions depend on the magnitude of future emissions and on the ability of species to disperse from their current locations. California's varied terrain could cause species to move in very different directions, breaking up present-day floras. However, our projections also identify regions where species undergoing severe range reductions may persist. Protecting these potential future refugia and facilitating species dispersal will be essential to maintain biodiversity in the face of climate change.

The threat of global warming to rare species is a growing concern, yet few studies have predicted its effects on rare populations. Using demographic data gathered in both drought and nondrought years between 1996-2003 in central Arizona upper Sonoran Desert, we modeled population viability for the federally endangered Purshia subintegra (Kearney) Henrickson (Arizona cliffrose). We used deterministic matrix projection models and stochastic models simulating weather conditions during our study, given historical weather variation and under scenarios of increased aridity. Our models suggest that the P. subintegra population in Verde Valley is slowly declining and will be at greater risk of extinction with increased aridity. Across patches at a fine spatial scale, demographic performance was associated with environmental factors. Moist sites (patches with the highest soil moisture, lowest sand content, and most northern aspects) had the highest densities, highest seedling recruitment, and highest risk of extinction over the shortest time span. Extinction risk in moist sites was exacerbated by higher variance in recruitment and mortality. Dry sites had higher cumulative adult survival and lower extinction risk but negative growth rates. Steps necessary for the conservation of the species include introductions at more northern latitudes and in situ manipulations to enhance seedling recruitment and plant survival. We demonstrate that fine spatial-scale modeling is necessary to predict where patches with highest extinction risk or potential refugia for rare species may occur. Because current climate projections for the 21st century imply range shifts at rates of 300 to 500 km/century, which are beyond even exceptional examples of shifts in the fossil record of 100-150 km, it is likely that preservation of many rare species will require human intervention and a long-term commitment. Global warming conditions are likely to reduce the carrying capacity of many rare species' habitats.

A hydrologic model was driven by the climate projected by 11 GCMs under two emissions scenarios (the higher emission SRES A2 and the lower emission SRES B1) to investigate whether the projected hydrologic changes by 2071-2100 have a high statistical confidence, and to determine the confidence level that the A2 and B1 emissions scenarios produce differing impacts. There are highly significant average temperature increases by 2071-2100 of 3.7°C under A2 and 2.4°C under B1; July increases are 5°C for A2 and 3°C for B1. Two high confidence hydrologic impacts are increasing winter streamflow and decreasing late spring and summer flow. Less snow at the end of winter is a confident projection, as is earlier arrival of the annual flow volume, which has important implications on California water management. The two emissions pathways show some differing impacts with high confidence: the degree of warming expected, the amount of decline in summer low flows, the shift to earlier streamflow timing, and the decline in end-of-winter snow pack, with more extreme impacts under higher emissions in all cases. This indicates that future emissions scenarios play a significant role in the degree of impacts to water resources in California.

Some conclusions on the vulnerability of hydrologic regions in Mexico to future changes in climate can be drawn from the application of regional-scale thermal-hydrological models. Climate changes induced by the doubling of atmospheric CO2 have been predicted for the year 2050 by general circulation models (GCMs) and energy balance models (EBMs). The results obtained suggest that potential changes in air temperature and precipitation may have a dramatic impact on the pattern and magnitude of runoff, on soil moisture and evaporation, as well as on the aridity level of some hydrologic zones of Mexico. However, in other cases climate change is likely to produce a positive effect. Indlces were estimated for quantifying the vulnerability of hydrologic regions and of the country as a whole. These vulnerability indices were defined according to cntena previously established for studies of this type. The indices provide information about both the hydrologic zones which are vulnerable even under current climate conditions and others which may be vulnerable to future climate changes.

Global climates are changing rapidly, with unexpected consequences 1. Because elements of biodiversity respond intimately to climate as an important driving force of distributional limitation 2, distributional shifts and biodiversity losses are expected3,4. Nevertheless, in spite of modelling efforts focused on single species2or entire ecosystems5, a few preliminary surveys of fauna-wide effects6,7, and evidence of climate change-mediated shifts in several species8,9, the likely effects of climate change on species' distributions remain little known, and fauna-wide or community-level effects are almost completely unexplored6. Here, using a genetic algorithm and museum specimen occurrence data, we develop ecological niche models for 1,870 species occurring in Mexico and project them onto two climate surfaces modelled for 2055. Although extinctions and drastic range reductions are predicted to be relatively few, species turnover in some local communities is predicted to be high (>40% of species), suggesting that severe ecological perturbations may result.

Changes in climate during the 20th century differ from region to region across the United States. We provide strong evidence that spatial variations in US temperature trends are linked to the hydrologic cycle, and we also present unique information on the seasonal and latitudinal structure of the linkage. We show that there is a statistically significant inverse relationship between trends in daily temperature and average daily precipitation across regions. This linkage is most pronounced in the southern United States (30-40°N) during the May-June time period and, to a lesser extent, in the northern United States (40-50°N) during the July-August time period. It is strongest in trends in maximum temperatures (Tmax) and 90th percentile exceedance trends (90PET), and less pronounced in the Tmax 10PET and the corresponding Tmin statistics, and it is robust to changes in analysis period. Although previous studies suggest that areas of increased precipitation may have reduced trends in temperature compared with drier regions, a change in sign from positive to negative trends suggests some additional cause. We show that trends in precipitation may account for some, but not likely all, of the cause point to evidence that shows that dynamical patterns (El Niño/Southern Oscillation, North Atlantic Oscillation, etc.) cannot account for the observed effects during May-June. We speculate that changing aerosols, perhaps related to vegetation changes, and increased strength of the aerosol direct and indirect effect may play a role in the observed linkages between these indices of temperature change and the hydrologic cycle.

Increases in atmospheric greenhouse gases are driving significant changes in global climate. To project potential vegetation response to future climate change, this study uses response surfaces to describe the relationship between bioclimatic variables and the distribution of tree and shrub taxa in western North America. The response surfaces illustrate the probability of the occurrence of a taxon at particular points in climate space. Climate space was defined using three bioclimatic variables: mean temperature of the coldest month, growing degree days, and a moisture index. Species distributions were simulated under present climate using observed data (1951-80, 30-year mean) and under future climate (2090-99, 10-year mean) using scenarios generated by three general circulation models- HADCM2, CGCM1, and CSIRO. The scenarios assume a 1%per year compound increase in greenhouse gases and changes in sulfate (SO4) aerosols based on the Intergovernmental Panel on Climate Change (IPCC) IS92a scenario. The results indicate that under future climate conditions, potential range changes could be large for many tree and shrub taxa. Shifts in the potential ranges of species are simulated to occur not only northward but in all directions, including southward of the existing ranges of certain species. The simulated potential distributions of some species become increasingly fragmented under the future climate scenarios, while the simulated potential distributions of other species expand. The magnitudes of the simulated range changes imply significant impacts to ecosystems and shifts in patterns of species diversity in western North America.

Spring snowmelt is the most important contribution of many rivers in western North America. If climate changes, this contribution may change. A shift in the timing of springtime snowmelt towards earlier in the year already is observed during 1948-2000 in many western rivers. Streamflow timing changes for the 1995-2099 period are projected using regression relations between observed streamflow-timing responses in each river, measured by the temporal centroid of streamflow (CT) each year, and local temperature (TI) and precipitation (PI) indices. Under 21st century warming trends predicted by the Parallel Climate Model (PCM) under business-as-usual greenhouse-gas emissions, streamflow timing trends across much of western North America suggest even earlier springtime snowmelt than observed to date. Projected CT changes are consistent with observed rates and directions of change during the past five decades, and are strongest in the Pacific Northwest, Sierra Nevada, and Rocky Mountains, where many rivers eventually run 30-40 days earlier. The modest PI changes projected by PCMyield minimal CT changes. The responses of CT to the simultaneous effects of projected TI and PI trends are dominated by the TI changes. Regressionbased CT projections agree with those from physically-based simulations of rivers in the Pacific Northwest and Sierra Nevada.

It has been recently reported that the climate in Monteverde, Tilarán Mountain Range, Costa Rica, is changing rapidly, and that these changes have begun to affect wildlife populations in the region. Anecdotal evidence suggests that the distributions and abundances of hummingbird species are shifting. It is possible that these changes are related to climate. This paper investigates this potential link, examining how climate affects hummingbirds directly and how it affects their resources, namely nectar producing plants. Hummingbirds have complex effects on the plant community through pollination. In turn, nectar and flower production affects hummingbird behavior, population size, and life cycle. Climatic variables including precipitation, temperature, and cloud cover all affect nectar production. Research shows that precipitation also impacts hummingbirds directly. In Monteverde where the climatic trend is one of decreased precipitation, increased temperature, and increased cloud cover, the potential effects on hummingbird populations and the plants that support them are complex. It is possible that there will be a shift in the spatial and temporal distributions of both hummingbirds and plants and a change in the relative abundances of species. A decline in nectar resources resulting in a reduction of hummingbird diversity is possible. Because of the complexity of the potential effects, it is crucial to implement a monitoring program and conduct experiments to deepen our understanding of the relationship between climate change and wildlife biology. Chapter 2 describes a plan for undertaking this research at the Monteverde Cloud Forest Preserve. This includes determining the population sizes and relative abundances of hummingbirds in the region, identifying important flowering plant species, delineating their phenologies, and noting hummingbird visitation rates to these plants. Techniques for measuring nectar are described. Experiments to ascertain the effects of precipitation, temperature, and cloud cover on nectar production are outlined. Baseline data from earlier studies in the region can be compared to new data in order to determine the extent to which climate change has already begun to impact the hummingbirds of Monteverde. Chapter 3 discusses the pros and cons of using hummingbird feeders as a research tool, and recommends that feeders only be used in a limited capacity and in areas of high flower abundance. The ultimate goal of this paper is to facilitate the conservation of biodiversity in an ever-changing Monteverde.

Climate change is proceeding at a rate at which there will be unavoidable impacts to natural systems and fish and wildlife habitat. Even with the most rigorous emissions reductions we need to plan climate adaptation measures to help natural systems persist in the face of changing climate conditions. Such climate change adaptation is a new challenge for natural resource managers who are grappling with what it will entail in the context of conservation. To develop a clear definition and statement of need for adaptation we conducted 68 interviews of federal and state agency staff, non-governmental organization conservationists, and academic scientists who are thinking about or working on climate change adaptation. We asked these experts to define climate change adaptation, to discuss ongoing adaptation planning efforts, to provide us with examples of adaptation techniques and practices, and to list costs associated with these techniques. We also asked participants to discuss the challenges to planning for and implementing adaptation, the metrics associated with adaptation project monitoring, partnership opportunities, and communication strategies. Most participants defined climate change adaptation to encompass anticipating, preparing for, and responding to the expected impacts of climate change in order to promote ecological resilience in natural systems, and to allow these systems to respond to change. A significant minority of participants expressed concern about the use of the term, noting that it could be easily confused with the scientific definition, and some offered alternatives. These concerns provide further support for the need to adopt a widely accessible definition of climate change adaptation. Many participants are involved in adaptation planning, revision of existing conservation and management plans and reprioritization of conservation and restoration efforts based on climate change. Few examples of specific adaptation techniques or strategies, costs associated with strategies or metrics to measure the effect of techniques are available at this time. Participants identified several barriers to planning for and implementing adaptation strategies: a lack of resources and funding, the need for place-based adaptation strategies and available case studies to guide planning efforts, and further development of adaptation tools, models and guidance. Despite these challenges, the survey responses suggest that progress is being made to plan and implement adaptation strategies, develop tools and models for adaptation planning, and to help build capacity in state and federal agencies that do not currently have the resources to take on the challenge alone. In particular, promising partnerships are developing within and among the federal and state agencies, conservation organizations and the academic sector. However, without increased funding to support adaptation efforts these partnerships will not be enough to prevent natural system collapse and biodiversity loss. The survey participants made it clear that the agencies responsible for managing the lands and waters of the United States and the agencies, organizations and institutions that support their work are in desperate need of new funding to fully understand, plan for, and address the challenges ahead.

We tested two consequences of a currently influential theory based on the notion of seeing adaptations to climate change as local adjustments to deal with changing conditions within the constraints of the broader economic-social-political arrangements. The notion leaves no explicit role for the strength of personal beliefs in climate change and adaptive capacity. The consequences were: (i) adaptive action to climate change taken by an individual who is exposed to and sensitive to climate change is not influenced to a considerable degree by their strength of belief in climate change and (ii) adaptive action to climate change taken by an individual who is exposed to and sensitive to climate change is not influenced to a considerable degree by their strength of belief in an adaptive capacity. Data from a 2004 questionnaire of 1950 Swedish private individual forest owners, who were assumed exposed to and sensitive to climate change, were used. Strength of belief in climate change and adaptive capacities were found to be crucial factors for explaining observed differences in adaptation among Swedish forest owners.

his paper presents a short review of the existing literature on climate change impacts and adaptation options for California. At the global scale, there is a scientific consensus that climate is changing and that the increased concentration of greenhouses gases in the atmosphere are responsible for these changes. California will get warmer in the future, but the level of warming is not known. With respect to precipitation, there is no consensus on how California would be affected, but it is clear that the warming would result in increased runoff in the winter season and decreased runoff in the spring and summer. Human adaptation to climate change in the state may be costly. Ecosystems, one of the most precious state resources, could be severely affected not only by climate change, but also by other stressors such as increased urbanization. Because of the thermal inertia of the Earth, our climate will continue to warm and, for this reason, the identification of adaptation options should be a state priority. Finally, this paper suggests that scientific research should be an integral part of the state overall strategy for how to deal with climate change.

Scenario planning should be an effective tool for developing responses to climate change but will depend on ecological assessments of broad enough scope to support decision-making. Using climate projections from an ensemble of 16 models, we conducted an assessment of a midcontinental area of North America (Minnesota) based on a resistance, resilience, and facilitation framework. We assessed likely impacts and proposed options for eight landscape regions within the planning area. Climate change projections suggest that by 2069, average annual temperatures will increase 3 °C with a slight increase in precipitation (6%). Analogous climate locales currently prevail 400-500 km SSW. Although the effects of climate change may be resisted through intensive management of invasive species, herbivores, and disturbance regimes, conservation practices need to shift to facilitation and resilience. Key resilience actions include providing buffers for small reserves, expanding reserves that lack adequate environmental heterogeneity, prioritizing protection of likely climate refuges, and managing forests for multi-species and multi-aged stands. Modifying restoration practices to rely on seeding (not plants), enlarge seed zones, and include common species from nearby southerly or drier locales is a logical low-risk facilitation strategy. Monitoring "trailing edge" populations of rare species should be a high conservation priority to support decision-making related to assisted colonization. Ecological assessments that consider resistance, resilience, and facilitation actions during scenario planning is a productive first step towards effective climate change planning for biodiversity with broad applicability to many regions of the world.

The relationship between tropical forests and global climate change has so far focused on mitigation, while much less emphasis has been placed on how management activities may help forest ecosystems adapt to this change. This paper discusses how tropical forestry practices can contribute to maintaining or enhancing the adaptive capacity of natural and planted forests to global climate change and considers challenges and opportunities for the integration of tropical forest management in broader climate change adaptation. In addition to the use of reduced impact logging to maintain ecosystem integrity, other approaches may be needed, such as fire prevention and management, as well as specific silvicultural options aimed at facilitating genetic adaptation. In the case of planted forests, the normally higher intensity of management (with respect to natural forest) offers additional opportunities for implementing adaptation measures, at both industrial and smallholder levels. Although the integration in forest management of measures aimed at enhancing adaptation to climate change may not involve substantial additional effort with respect to current practice, little action appears to have been taken to date. Tropical foresters and forest-dependent communities appear not to appreciate the risks posed by climate change and, for those who are aware of them, practical guidance on how to respond is largely non-existent. The extent to which forestry research and national policies will promote and adopt management practices in order to assist production forests adapt to climate change is currently uncertain. Mainstreaming adaptation into national development and planning programs may represent an initial step towards the incorporation of climate change considerations into tropical forestry.

Climate change creates new challenges for biodiversity conservation. Species ranges and ecological dynamics are already responding to recent climate shifts, and current reserves will not continue to support all species they were designed to protect. These problems are exacerbated by other global changes. Scholarly articles recommending measures to adapt conservation to climate change have proliferated over the last 22 years. We systematically reviewed this literature to explore what potential solutions it has identified and what consensus and direction it provides to cope with climate change. Several consistent recommendations emerge for action at diverse spatial scales, requiring leadership by diverse actors. Broadly, adaptation requires improved regional institutional coordination, expanded spatial and temporal perspective, incorporation of climate change scenarios into all planning and action, and greater effort to address multiple threats and global change drivers simultaneously in ways that are responsive to and inclusive of human communities. However, in the case of many recommendations the how, by whom, and under what conditions they can be implemented is not specified. We synthesize recommendations with respect to three likely conservation pathways: regional planning; site-scale management; and modification of existing conservation plans. We identify major gaps, including the need for (1) more specific, operational examples of adaptation principles that are consistent with unavoidable uncertainty about the future; (2) a practical adaptation planning process to guide selection and integration of recommendations into existing policies and programs; and (3) greater integration of social science into an endeavor that, although dominated by ecology, increasingly recommends extension beyond reserves and into human-occupied landscapes.

The Nation's public lands and waters traditionally have been managed using frameworks and objectives that were established under an implicit assumption of stable climate and the potential of achieving specific desirable conditions. Climate change implies that past experience may not apply and that the assumption of a stable climate is in some regions untenable. Previous chapters in this report examine a selected group of management systems (National Forests, National Parks, National Wildlife Refuges, Wild and Scenic Rivers, National Estuaries, and Marine Protected Areas) and assess how these management systems can adapt to climate change. Using these chapters and their case studies, as well as more general scientific literature concerning adaptive management and climate change, this chapter presents a synthesis of suggested principles and management approaches for federal management agencies as well as other resource managers.

To study the impacts of climate change on water resources in the western U.S., global climate simulations were produced using the National Center for Atmospheric Research/Department of Energy (NCAR/DOE) Parallel Climate Model (PCM). The Penn State/NCAR Mesoscale Model (MM5) was used to downscale the PCM control (20 years) and three future(2040-2060) climate simulations to yield ensemble regional climate simulations at 40 km spatial resolution for the western U.S. This paper describes the regional simulations and focuses on the hydroclimate conditions in the Columbia River Basin (CRB) and Sacramento-San Joaquin River (SSJ) Basin. Results based on global and regional simulations show that by mid-century, the average regional warming of 1 to 2.5 °C strongly affects snowpack in the western U.S. Along coastal mountains, reduction in annual snowpack was about70% as indicated by the regional simulations. Besides changes in mean temperature, precipitation, and snowpack, cold season extreme daily precipitation increased by 5 to 15 mm/day (15-20%) along theCascades and the Sierra. The warming resulted in increased rainfall at the expense of reduced snowfall, and reduced snow accumulation (or earlier snowmelt) during the cold season. In the CRB, these changes were accompanied by more frequent rain-on-snow events. Overall, they induced higher likelihood of wintertime flooding and reduced runoff and soil moisture in the summer. Changes in surface water and energy budgets in the CRB and SSJ basin were affected mainly by changes in surface temperature, which were statistically significant at the 0.95 confidence level. Changes in precipitation, while spatially incoherent, were not statistically significant except for the drying trend during summer. Because snow and runoff are highly sensitive tospatial distributions of temperature and precipitation, this study shows that (1) downscaling provides more realistic estimates of hydrologic impacts in mountainous regions such as the western U.S., and (2) despite relatively small changes in temperature and precipitation, changes in snowpack and runoff can be much larger on monthly to seasonal time scales because the effects of temperature and precipitation are integrated over time and space through various surface hydrological and land-atmosphere feedback processes. Although the results reported in this study were derived from an ensemble of regional climate simulations driven by a global climate model that displays low climate sensitivity compared with most other models, climate change was found to significantly affect water resources in the western U.S. by the mid twenty-first century.

In the threshold of the appearance of global warming from theory to reality, extensive research has focused on predicting the impact of potential climate change on water resources using results from Global Circulation Models (GCMs). This research carries this further by statistical analyses of long term meteorological and hydrological data. Seventy years of historical trends in precipitation, temperature, and streamflows in the Great Lakes of North America are developed using long term regression analyses and Mann-Kendall statistics. The results generated by the two statistical procedures are in agreement and demonstrate that many of these variables are experiencing statistically significant increases over a seven-decade period. The trend lines of streamflows in the three rivers of St. Clair, Niagara and St. Lawrence, and precipitation levels over four of the five Great Lakes, show statistically significant increases in flows and precipitation. Further, precipitation rates as predicted using fitted regression lines are compared with scenarios from GCMs and demonstrate similar forecast predictions for Lake Superior. Trend projections from historical data are higher than GCM predictions for Lakes Michigan/Huron. Significant variability in predictions, as developed from alternative GCMs, is noted. Given the general agreement as derived from very different procedures, predictions extrapolated from historical trends and from GCMs, there is evidence that hydrologic changes particularly for the precipitation in the Great Lakes Basin may be demonstrating influences arising from global warming and climate change.

Applied historical ecology is the use of historical knowledge in the management of ecosystems. Historical perspectives increase our understanding of the dynamic nature of landscapes and provide a frame of reference for assessing modern patterns and processes. Historical records, however, are often too brief or fragmentary to be useful, or they are not obtainable for the process or structure of interest. Even where long historical time series can be assembled, selection of appropriate reference conditions may be complicated by the past influence of humans and the many potential reference conditions encompassed by nonequilibrium dynamics. These complications, however, do not lessen the value of history; rather they underscore the need for multiple, comparative histories from many locations for evaluating both cultural and natural causes of variability, as well as for characterizing the overall dynamical properties of ecosystems. Historical knowledge may not simplify the task of setting management goals and making decisions, but 20th century trends, such as increasingly severe wildfires, suggest that disregarding history can be perilous. We describe examples from our research in the southwestern United States to illustrate some of the values and limitations of applied historical ecology. Paleoecological data from packrat middens and other natural archives have been useful for defining baseline conditions of vegetation communities, determining histories and rates of species range expansions and contractions, and discriminating between natural and cultural causes of environmental change. We describe a montane grassland restoration project in northern New Mexico that was justified and guided by an historical sequence of aerial photographs showing progressive tree invasion during the 20th century. Likewise, fire scar chronologies have been widely used to justify and guide fuel reduction and natural fire reintroduction in forests. A southwestern network of fire histories illustrates the power of aggregating historical time series across spatial scales. Regional fire patterns evident in these aggregations point to the key role of interannual lags in responses of fuels and fire regimes to the El Nino-Southern Oscillation (wet/dry cycles), with important implications for long-range fire hazard forecasting. These examples of applied historical ecology emphasize that detection and explanation of historical trends and variability are essential to informed management.

Climate change poses a challenge to the conventional approach to biodiversity conservation, which relies on fixed protected areas, because the changing climate is expected to shift the distribution of suitable areas for many species. Some species will persist only if they can colonize new areas, although in some cases their dispersal abilities may be very limited. To address this problem we devised a quantitative method for identifying multiple corridors of connectivity through shifting habitat suitabilities that seeks to minimize dispersal demands first and then the area of land required. We applied the method to Proteaceae mapped on a 1-minute grid for the western part of the Cape Floristic Region of South Africa, to supplement the existing protected areas, using Worldmap software. Our goal was to represent each species in at least 35 grid cells (approximately 100 km2) at all times between 2000 and 2050 despite climate change. Although it was possible to achieve the goal at reasonable cost, caution will be needed in applying our method to reserves or other conservation investments until there is further information to support or refine the climate-change models and the species' habitat-suitability and dispersal models.

Large-scale biogeographical shifts in vegetation are predicted in response to the altered precipitation and temperature regimes associated with global climate change. Vegetation shifts have profound ecological impacts and are an important climate-ecosystem feedback through their alteration of carbon, water, and energy exchanges of the land surface. Of particular concern is the potential for warmer temperatures to compound the effects of increasingly severe droughts by triggering widespread vegetation shifts via woody plant mortality. The sensitivity of tree mortality to temperature is dependent on which of 2 non-mutually-exclusive mechanisms predominates-temperature-sensitive carbon starvation in response to a period of protracted water stress or temperature- insensitive sudden hydraulic failure under extreme water stress (cavitation). Here we show that experimentally induced warmer temperatures (_4 °C) shortened the time to droughtinduced mortality in Pinus edulis (pin on shortened pine) trees by nearly a third, with temperature-dependent differences in cumulative respiration costs implicating carbon starvation as the primary mechanism of mortality. Extrapolating this temperature effect to the historic frequency of water deficit in the southwestern United States predicts a 5-fold increase in the frequency of regional-scale tree die-off events for this species due to temperature alone. Projected increases in drought frequency due to changes in precipitation and increases in stress from biotic agents (e.g., bark beetles) would further exacerbate mortality. Our results demonstrate the mechanism by which warmer temperatures have exacerbated recent regional die-off events and background mortality rates. Because of pervasive projected increases in temperature, our results portend widespread increases in the extent and frequency of vegetation die-off.

Tropical cyclones during September addect the semi-arid northwestern region of Mexico with a relatively high frequency, bringing much-needed precipitation. This study provided a better understanding of tropical cyclone inter-annual variability, their relationships with other atmospheric-oceanic phenomena, and their inter-decadal occurrences. Daily rain data from 534 meteorological stations were analyzed and used to calculate the percentage of the annual precipitation related to tropical cyclones of the eastern North Pacific Ocean affecting the region from 1949 to 2002. Using interpolation techniques, the stations were grouped in 1 x 1 areas, and the area structure of the tropical cyclone influence was obtained using empirical orthogonal function (EOF) variable analysis to identify five regions. Representative inter-annual variation series from each region were analyzed to identify changes in the influence of tropical cyclones as part of the annual precipitation. A gradient of tropical cyclone influence was found declining from south to north, mainly in the peninsula area. A regime shift in 1976 is coincident with a shift trend in series from areas with larger tropical cyclones influence. The Southern Oscillation Index (SOI) driving is stronger for the northern part of the region, while the southern part has stronger Pacific Decadal Oscillation (PDO) influence.

There is great interest in the climatic variability of Baja California and the Sea of Cortes, but long-term information is limited because instrumental climate records begin in the 1940s or 1960s. The first tree-ring chronology of Pinus lagunae was developed from the southern part of the Baja California Peninsula and the chronology is used to reconstruct the history of precipitation variations. A September-July precipitation reconstruction is developed for the period AD 1862-1996 (R=0.71, p_0.0001, n=56, cross-validation=0.68). This reconstruction is used to assess precipitation variability over the past two centuries, including the relationship with ENSO events. The reconstructed precipitation series indicates a long drought period from 1939 to 1958. It also shows that 1983, one of the strongest El Niño events of the 20th century, is the wettest year. El Niño events during the 20th century are associated with above-normal precipitation, whereas La Niña events are characterized by below-normal precipitation. Four of the most extreme wet years occurred in association with these warm events (1905, 1912, 1919 and 1983). Seventy-one percent of La Niña events are characterized by below-normal precipitation. Sixty-two percent of El Niño events are characterized by above-normal precipitation. Tree-ring growth of P. lagunae is most strongly correlated with winter precipitation in Sonora, Sinaloa and southern Baja California Sur. Precipitation data from meteorological stations in northern Baja California do not correlate well with the tree-ring chronology because this zone has a Mediterranean climate, which differs from the rest of northwest Mexico.

Water balance calculations are becoming increasingly important for earth-system studies. Precipitation is one of the most critical input variables for such calculations because it is the immediate source of water for the land surface hydrological budget. Numerous precipitation datasets have been developed in the last two decades, but these datasets often show marked differences in their spatial and temporal distribution of this key hydrological variable. This paper compares six monthly precipitation datasets-Climate Research Unit of University of East Anglia (CRU), Willmott-Matsuura (WM), Global Precipitation Climate Center (GPCC), Global Precipitation Climatology Project (GPCP), Tropical Rainfall Measuring Mission (TRMM), and NCEP-Department of Energy (DOE) Atmospheric Model Intercomparison Project (AMIP-II) Reanalysis (NCEP-2)-to assess the uncertainties in these datasets and their impact on the terrestrial water balance. The six datasets tested in the present paper were climatologically averaged and compared by calculating various statistics of the differences. The climatologically averaged monthly precipitation estimates were applied as inputs to a water balance model to estimate runoff and the uncertainties in runoff arising directly from the precipitation estimates. The results of this study highlight the need for accurate precipitation inputs for water balance calculations. These results also demonstrate the need to improve precipitation estimates in arid and semiarid regions, where slight changes in precipitation can result in dramatic changes in the runoff response due to the nonlinearity of the runoff-generation processes.

Fog drip is a crucial water source for plants in many ecosystems, including a number of global biodiversity hotspots. In California, dozens of rare, drought-sensitive plant species are endemic to coastal areas where the dominant summer moisture source is fog. Low clouds that provide water to these semi-arid ecosystems through fog drip can also sharply reduce evaporative water losses by providing shade. We quantified the relative hydrological importance of cloud shading vs. fog drip. We then examined how both factors influence the range dynamics of an apparently fog-dependent plant species spanning a small-scale -šcloud gradient. The study area is on Santa Cruz Island off the coast of southern California. It is near the southern range limit of bishop pine (Pinus muricata D. Don), a tree endemic to the coasts of California and Baja, Mexico. We measured climate across a pine stand along a 7-°km, coastal-inland elevation transect. Short-term (1-5-°years) monitoring and remote sensing data revealed strong climatic gradients driven primarily by cloud cover. Long-term (102-°years) effects of these gradients were estimated using a water balance -šmodel. We found that shade from persistent low clouds near the coast reduced annual drought stress by 22-40% compared with clearer conditions further inland. Fog drip at higher elevations provided sufficient extra water to reduce annual drought stress by 20-36%. Sites located at both high elevation and nearer the coast were subject to both effects. Together, these effects reduced average annual drought stress by 56% and dramatically reduced the frequency of severe drought over the last century. At lower elevation (without appreciable fog drip) and also near the inland edge of the stand (with less cloud shading) severe droughts episodically kill most pine recruits, thereby limiting the local range -šof this species. Persistent cloud shading can influence hydrology as much as fog drip in cloud-affected ecosystems. Understanding the patterns of both cloud shading and fog drip and their respective impacts on ecosystem water budgets is necessary to fully understand past species range shifts and to anticipate future climate change-induced range shifts in fog-dependent ecosystems.

To characterize observed global and hemispheric temperatures, previous studies have proposed two types of data-generating processes, namely, random walk and trend-stationary, offering contrasting views regarding how the climate system works. Here we present an analysis of the time series properties of global and hemispheric temperatures using modern econometric techniques. Results show that: The temperature series can be better described as trend-stationary processes with a one-time permanent shock which cannot be interpreted as part of the natural variability; climate change has affected the mean of the processes but not their variability; it has manifested in two stages in global and Northern Hemisphere temperatures during the last century, while a second stage is yet possible in the Southern Hemisphere; in terms of Article 2 of the Framework Convention on Climate Change it can be argued that significant (dangerous) anthropogenic interference with the climate system has already occurred.

Understanding patterns of plant population mortality during extreme weather events is important to conservation planners because the frequency of such events is expected to increase, creating the need to integrate climatic uncertainty into management. Dominant plants provide habitat and ecosystem structure, so changes in their distribution can be expected to have cascading effects on entire communities. Observing areas that respond quickly to climate fluctuations provides foresight into future ecological changes and will help prioritize conservation efforts. We investigated patterns of mortality in six dominant plant species during a drought in the southwestern United States. We quantified population mortality for each species across its regional distribution and tested hypotheses to identify ecological stress gradients for each species. Our results revealed three major patterns: (1) dominant species from diverse habitat types (i.e., riparian, chaparral, and low- to high-elevation forests) exhibited significant mortality, indicating that the effects of drought were widespread; (2) average mortality differed among dominant species (one-seed juniper [Juniperus monosperma (Engelm.) Sarg.] 3.3%; manzanita [Arctostaphylos pungens Kunth], 14.6%; quaking aspen [Populus tremuloides Michx.], 15.4%; ponderosa pine [Pinus ponderosa P. & C. Lawson], 15.9%; Fremont cottonwood [Populus fremontii S. Wats.], 20.7%; and pinyon pine [Pinus edulis Engelm.], 41.4%); (3) all dominant species showed localized patterns of very high mortality (24-100%) consistent with water stress gradients. Land managers should plan for climatic uncertainty by promoting tree recruitment in rare habitat types, alleviating unnatural levels of competition on dominant plants, and conserving sites across water stress gradients. High-stress sites, such as those we examined, have conservation value as barometers of change and because they may harbor genotypes that are adapted to climatic extremes.

Plant ecologists have long been concerned with a seemingly paradoxical scenario in the relationship between plant growth and climate change: warming may actually increase the risk of plant frost damage. The underlying hypothesis is that mild winters and warm, early springs, which are expected to occur as the climate warms, may induce premature plant development, resulting in exposure of vulnerable plant tissues and organs to subsequent late-season frosts. The 2007 spring freeze in the eastern United States provides an excellent opportunity to evaluate this hypothesis and assess its large-scale consequences. In this article, we contrast the rapid prefreeze phenological advancement caused by unusually warm conditions with the dramatic postfreeze setback, and report complicated patterns of freeze damage to plants. The widespread devastation of crops and natural vegetation occasioned by this event demonstrates the need to consider large fluctuations in spring temperatures a real threat to terrestrial ecosystem structure and functioning in a warming climate.

Drought is the most economically expensive recurring natural disaster to strike North America in modern times. Recently available gridded drought reconstructions have been developed for most of North America from a network of drought-sensitive tree-ring chronologies, many of which span the last 1000 yr. These reconstructions enable the authors to put the famous droughts of the instrumental record (i.e., the 1930s Dust Bowl and the 1950s Southwest droughts) into the context of 1000 yr of natural drought variability on the continent. We can now, with this remarkable new record, examine the severity, persistence, spatial signatures, and frequencies of drought variability over the past milllennium, and how these have changed with time. The gridded drought reconstructions reveal the existence of successive "megadroughts," unprecedented in persistence (20-40 yr), yet similar in year-to-year severity and spatial distribution to the major droughts experienced in today's North America. These megadroughts occurred during a 400-yr-long period in the early to middle second millennium A.D., with a climate varying as today's, but around a drier mean. The implication is that the mechanism forcing persistent drought in the West and the Plains in the instrumental era is analagous to that underlying the megadroughts of the medieval period. The leading spatial mode of drought variability in the recontructions resembles the North American ENSO pattern: widespread drought across the United States, centered on the Southwest, with a hint of the opposite phase in the Pacific Northwest. Recently, climate models forced by the observed history of tropical Pacific SSTs have been able to successfully simulate all of the major North American droughts of the last 150 yr. In each case, cool "La Niña-like" conditions in the tropical Pacific are consistent with North American drought. With ENSO showing a pronounced signal in the gridded drought recontructions of the last millennium, both in terms of its link to the leading spatial mode, and the leading time scales of drought variability (revealed by multitaper spectral analysis and wavelet analysis), it is postulated that, as for the modern day, the medieval megadroughts were forced by protracted La Niña-like tropical Pacific SSTs. Further evidence for this comes from the global hydroclimatic "footprint" of the medieval era revealed by existing paleoclimatic archives from the tropical Pacific and ENSO-sensitive tropical and extratropical land regions. In general, this global pattern matches that observed for modern-day persistent North American drought, whereby a La Niña-like tropical Pacific is accompanied by hemispheric, and in the midlatitudes, zonal, symmetry of hydroclimatic anomalies.

The 1998-2002 droughts spanning the United States, southern Europe, and Southwest Asia were linked through a common oceanic influence. Cold sea surface temperatures (SSTs) in the eastern tropical Pacific and warm SSTs in the western tropical Pacific and Indian oceans were remarkably persistent during this period. Climate models show that the climate signals forced separately by these regions acted synergistically, each contributing to widespread mid-latitude drying: an ideal scenario for spatially expansive, synchronized drought. The warmth of the Indian and west Pacific oceans was unprecedented and consistent with greenhouse gas forcing. Some implications are drawn for future drought.

The water resources of the western United States depend heavily on snowpack to store part of the wintertime precipitation into the drier summer months. A well-documented shift toward earlier runoff in recent decades has been attributed to 1) more precipitation falling as rain instead of snow and 2) earlier snowmelt. The present study addresses the former, documenting a regional trend toward smaller ratios of winter-total snowfall water equivalent (SFE) to winter-total precipitation (P) during the period 1949-2004. The trends toward reduced SFE are a response to warming across the region, with the most significant reductions occurring where winter wet-day minimum temperatures, averaged over the study period, were warmer than _5°C. Most SFE reductions were associated with winter wet-day temperature increases between 0° and _3°C over the study period. Warmings larger than this occurred mainly at sites where the mean temperatures were cool enough that the precipitation form was less susceptible to warming trends. The trends toward reduced SFE/P ratios were most pronounced in March regionwide and in January near the West Coast, corresponding to widespread warming in these months. While mean temperatures in March were sufficiently high to allow the warming trend to produce SFE/P declines across the study region, mean January temperatures were cooler, with the result that January SFE/P impacts were restricted to the lower elevations near the West Coast. Extending the analysis back to 1920 shows that although the trends presented here may be partially attributable to interdecadal climate variability associated with the Pacific decadal oscillation, they also appear to result from still longer-term climate shifts.

Linkages between sea surface temperatures (SSTs) in the Gulf of California and the North American monsoon rainfall were examined using observational data and regional model experiments. SSTs in the Gulf start to increase in late June and reach a maximum in August. Monsoon onset dates in the Southwest were determined from the gridded rainfall analysis. Monsoon onsets can occur before SSTs in the Gulf reach a maximum. There is no relationship between monsoon rainfall onset dates or seasonal total rainfall over the Southwest and SSTs in the Gulf. Regional model experiments were then performed to study the impact of local SSTs on monsoon rainfall using the NCEP regional spectral model (RSM). RSM experiments were performed with the observed SSTs for four summers (July-September 1997-2000). The experiments were repeated with the same initial and boundary conditions but with the climatological SSTs in the Gulf of California and its vicinity. The model is able to capture the general features of monsoon rainfall and the diurnal cycle. Warm (cold) SSTs in the Gulf are responsible for more (less) rainfall along the western slopes of the Sierra Madre Occidental. Over the Southwest, the impact of local SSTs is small. Large-scale flow has more influence on monsoon rainfall than SSTs in the Gulf of California because the SST forcing does not produce significant changes in the low level flow needed to influence rainfall over the Southwest.

A global coupled climate model representative of the current generation of models is shown to simulate most first order aspects of El Niño events, their teleconnections over North America, and the associated observed patterns of extremes in present-day climate. Future El Niño teleconnection patterns over the U.S. are projected to shift eastward and northward due in part to the different midlatitude base state atmospheric circulation in a warmer climate. Consequently, projections for the changes in the patterns of extremes over the U.S. during future El Niño events include: decreases of frost days over the southwestern U.S expand northward and eastward; increases in intense precipitation in the SW U.S. expands eastward and areas in the SE U.S. become stronger; and decreases of heat wave intensity over much of the southern tier of states turn to increases.

One of the most visible and widely felt impacts of climate warming is the change (mostly loss) of low-elevation snow cover in the midlatitudes. Snow cover that accumulates at temperatures close to the ice-water phase transition is at greater risk to climate warming than cold climate snowpacks because it affects both precipitation phase and ablation rates. This study maps areas in the Pacific Northwest region of the United States that are potentially at risk of converting from a snow-dominated to a rain-dominated winter precipitation regime, under a climate-warming scenario. A data-driven, climatological approach of snow cover classification is used to reveal these "at risk" snow zones and also to examine the relative frequency of warm winters for the region. For a rain versus snow temperature threshold of 0°C the at-risk snow class covers an area of about 9200 km2 in the Pacific Northwest region and represents approximately 6.5 km3 of water. Many areas of the Pacific Northwest would see an increase in the number of warm winters, but the impacts would likely be concentrated in the Cascade and Olympic Ranges. A number of lower-elevation ski areas could experience negative impacts because of the shift from winter snows to winter rains. The results of this study point to the potential for using existing datasets to better understand the potential impacts of climate warming.