Climate Science PDFs
Climate Science PDFs Collection
- Landscape-scale carbon storage associated with beaver dams
- Beaver meadows form when beaver dams promote prolonged overbank flooding and floodplain retention of sediment and organic matter. Extensive beaver meadows form in broad, low-gradient valley segments upstream from glacial terminal moraines. Surveyed sediment volume and total organic carbon content in beaver meadows on the eastern side of Rocky Mountain National Park are extrapolated to create a first-order approximation of landscape-scale carbon storage in these meadows relative to adjacent uplands. Differences in total organic carbon between abandoned and active beaver meadows suggest that valley-bottom carbon storage has declined substantially as beaver have disappeared and meadows have dried. Relict beaver meadows represent ~8% of total carbon storage within the landscape, but the value was closer to 23% when beaver actively maintained wet meadows. These changes reflect the general magnitude of cumulative effects in heterotrophic respiration and organic matter oxidation associated with historical declines in beaver populations across the continent
- Carbon sequestration in the U.S. forest sector from 1990 to 2010
- From 1990 through 2005, the forest sector (including forests and wood products) sequestered an average 162 Tg C year1 . In 2005, 49% of the total forest sector sequestration was in live and dead trees, 27% was in wood products in landfills, with the remainder in down dead wood, wood products in use, and forest floor and soil. The pools with the largest carbon stocks were not the same as those with the largest sequestration rates, except for the tree pool. For example, landfilled wood products comprise only 3% of total stocks but account for 27% of carbon sequestration. Conversely, forest soils comprise 48% of total stocks but account for only 2% of carbon sequestration. For the tree pool, the spatial pattern of carbon stocks was dissimilar to that of carbon flux. On an area basis, tree carbon stocks were highest in the Pacific Northwest, while changes were generally greatest in the upper Midwest and the Northeast. Net carbon sequestration in the forest sector in 2005 offset 10% of U.S. CO2 emissions. In the near future, we project that U.S. forests will continue to sequester carbon at a rate similar to that in recent years. Based on a comparison of our estimates to a compilation of land-based estimates of non-forest carbon sinks from the literature, we estimate that the conterminous U.S. annually sequesters 149–330 Tg C year1. Forests, urban trees, and wood products are responsible for 65–91% of this sink.
- A new, global, multi-annual (2000–2007) burnt area product at 1 km resolution Vol. 35
- This paper reports on the development and validation of a new, global, burnt area product. Burnt areas are reported at a resolution of 1 km for seven fire years (2000 to 2007). A modified version of a Global Burnt Area (GBA) 2000 algorithm is used to compute global burnt area. The total area burnt each year (2000– 2007) is estimated to be between 3.5 million km2 and 4.5 million km2 . The total amount of vegetation burnt by cover type according to the Global Land Cover (GLC) 2000 product is reported. Validation was undertaken using 72 Landsat TM scenes was undertaken. Correlation statistics between estimated burnt areas are reported for major vegetation types. The accuracy of this new global data set depends on vegetation type.
- Animal migration amid shifting patterns of phenology and predation: lessons from a Yellowstone elk herd
- Migration is a striking behavioral strategy by which many animals enhance resource acquisition while reducing predation risk. Historically, the demographic benefits of such movements made migration common, but in many taxa the phenomenon is considered globally threatened. Here we describe a long-term decline in the productivity of elk (Cervus elaphus) that migrate through intact wilderness areas to protected summer ranges inside Yellowstone National Park, USA. We attribute this decline to a long-term reduction in the demographic benefits that ungulates typically gain from migration. Among migratory elk, we observed a 21-year, 70% reduction in recruitment and a 4-year, 19% depression in their pregnancy rate largely caused by infrequent reproduction of females that were young or lactating. In contrast, among resident elk, we have recently observed increasing recruitment and a high rate of pregnancy. Landscape-level changes in habitat quality and predation appear to be responsible for the declining productivity of Yellowstone migrants. From 1989 to 2009, migratory elk experienced an increasing rate and shorter duration of green-up coincident with warmer spring–summer temperatures and reduced spring precipitation, also consistent with observations of an unusually severe drought in the region. Migrants are also now exposed to four times as many grizzly bears (Ursus arctos) and wolves (Canis lupus) as resident elk. Both of these restored predators consume migratory elk calves at high rates in the Yellowstone wilderness but are maintained at low densities via lethal management and human disturbance in the year-round habitats of resident elk. Our findings suggest that large-carnivore recovery and drought, operating simultaneously along an elevation gradient, have disproportionately influenced the demography of migratory elk. Many migratory animals travel large geographic distances between their seasonal ranges. Changes in land use and climate that disparately influence such seasonal ranges may alter the ecological basis of migratory behavior, representing an important challenge.
- The Gift of the Dying: The Tragedy of AIDS and the Welfare of Future African Generations
- This paper simulates the impact of the AIDS epidemic on future living standards in South Africa. I emphasize two competing effects. On the one hand, the epidemic is likely to have a detrimental impact on the human capital accumulation of orphaned children. On the other hand, widespread community infection lowers fertility, both directly, through a reduction in the willingness to engage in unprotected sexual activity, and indirectly, by increasing the scarcity of labor and the value of a woman’s time. I find that even with the most pessimistic assumptions concerning reductions in educational attainment, the fertility effect dominates. The AIDS epidemic, on net, enhances the future per capita consumption possibilities of the South African economy.
- Don't Blame the Beetles
- Bark beetles have devastated western forests, but that may not mean more severe fires.
- Characterizing coal and mineral mines as a regional source of stress to stream fish assemblages
- Mining impacts on stream systems have historically been studied over small spatial scales, yet investigations over large areas may be useful for characterizing mining as a regional source of stress to stream fishes. The associations between co-occurring stream fish assemblages and densities of various “classes” of mining occurring in the same catchments were tested using threshold analysis. Threshold analysis identifies the point at which fish assemblages change substantially from best available habitat conditions with increasing disturbance. As this occurred over large regions, species comprising fish assemblages were represented by various functional traits as well as other measures of interest to management (characterizing reproductive ecology and life history, habitat preferences, trophic ecology, assemblage diversity and evenness, tolerance to anthropogenic disturbance and state-recognized game species). We used two threshold detection methods: change-point analysis with indicator analysis and piecewise linear regression. We accepted only those thresholds that were highly statistically significant (p 0.01) for both techniques and overlapped within 5% error. We found consistent, wedge-shaped declines in multiple fish metrics with increasing levels of mining in catchments, suggesting mines are a regional source of disturbance. Threshold responses were consistent across the three ecoregions occurring at low mine densities. For 47.2% of the significant thresholds, a density of only 0.01 mines/km2 caused a threshold response. In fact, at least 25% of streams in each of our three study ecoregions have mine densities in their catchments with the potential to affect fish assemblages. Compared to other anthropogenic impacts assessed over large areas (agriculture, impervious surface or urban land use), mining had a more pronounced and consistent impact on fish assemblages. Threshold analysis Fish functional traits Landscape influences Game fishes Mining Rivers
- Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest
- Here, we use one of the world’s longest-running, plot-based forest dynamics projects to compare nonrandom outcomes across stage classes. We considered a cohort of 7,977 individuals in 186 species that were alive in 1971 and monitored in 13 mortality censuses over 42 y to 2013. Nonrandom mortality with respect to species identity occurred more often in the smaller rather than the larger size classes. Furthermore, observed nonrandom mortality in the smaller size classes had a diversifying influence; species richness of the survivors was up to 30% greater than expected in the two smallest size classes, but not greater than expected in the larger size classes. These results highlight the importance of early life cycle stages in tropical forest community dynamics. More generally, they add to an accumulating body of evidence for the importance of early-stage nonrandom outcomes to community structure in marine and terrestrial environments. diversity | early life-cycle stages | nonrandom | tropical forest
- Saturation-state sensitivity of marine bivalve larvae to ocean acidification
- Ocean acidification results in co-varying inorganic carbon system variables. Of these, an explicit focus on pH and organismal acid–base regulation has failed to distinguish the mechanism of failure in highly sensitive bivalve larvae. With unique chemical manipulations of seawater we show definitively that larval shell development and growth are dependent on seawater saturation state, and not on carbon dioxide partial pressure or pH. Although other physiological processes are affected by pH, mineral saturation state thresholds will be crossed decades to centuries ahead of pH thresholds owing to nonlinear changes in the carbonate system variables as carbon dioxide is added. Our findings were repeatable for two species of bivalve larvae could resolve discrepancies in experimental results, are consistent with a previous model of ocean acidification impacts due to rapid calcification in bivalve larvae, and suggest a fundamental ocean acidification bottleneck at early life-history for some marine keystone species.
- Microhabitats in the tropics buffer temperature in a globally coherent manner
- Vegetated habitats contain a variety of fine-scale features that can ameliorate temperate extremes. These buffered microhabitats may be used by species to evade extreme weather and novel climates in the future. Yet, the magnitude and extent of this buffering on a global scale remains unknown. Across all tropical continents and using 36 published studies, we assessed temperature buffering from within microhabitats across various habitat strata and structures (e.g. soil, logs, epiphytes and tree holes) and compared them to non-buffered macro-scale ambient temperatures (the thermal control). Microhabitats buf- fered temperature by 3.98C and reduced maximum temperatures by 3.58C. Buffering was most pronounced in tropical lowlands where temperatures were most variable. With the expected increase in extreme weather events, microhabitats should provide species with a local layer of protection that is not captured by traditional climate assessments, which are typically derived from macro-scale temperatures (e.g. satellites). Our data illustrate the need for a next generation of predictive models that account for species’ ability to move within microhabitats to exploit favourable buffered microclimates.
- Managing the whole landscape: historical, hybrid, and novel ecosystems
- The reality confronting ecosystem managers today is one of heterogeneous, rapidly transforming landscapes, particularly in the areas more affected by urban and agricultural development. A landscape management framework that incorporates all systems, across the spectrum of degrees of alteration, provides a fuller set of options for how and when to intervene, uses limited resources more effectively, and increases the chances of achieving management goals. That many ecosystems have departed so substantially from their historical trajectory that they defy conventional restoration is not in dispute. Acknowledging novel ecosystems need not constitute a threat to existing policy and management approaches. Rather, the development of an integrated approach to management interventions can provide options that are in tune with the current reality of rapid ecosystem change.
- Challenges of ecological restoration: Lessons from forests in northern Europe
- The alarming rate of ecosystem degradation has raised the need for ecological restoration throughout different biomes and continents. North European forests may appear as one of the least vulnerable ecosystems from a global perspective, since forest cover is not rapidly decreasing and many ecosystem services remain at high level. However, extensive areas of northern forests are heavily exploited and have lost a major part of their biodiversity value. There is a strong requirement to restore these areas towards a more natural condition in order to meet the targets of the Convention on Biological Diversity. Several northern countries are now taking up this challenge by restoring forest biodiversity with increasing intensity. The ecology and biodiversity of boreal forests are relatively well understood making them a good model for restoration activities in many other forest ecosystems. Here we introduce northern forests as an ecosystem, discuss the historical and recent human impact and provide a brief status report on the ecological restoration projects and research already conducted there. Based on this discussion, we argue that before any restoration actions commence, the ecology of the target ecosystem should be established with the need for restoration carefully assessed and the outcome properly monitored. Finally, we identify the most important challenges that need to be solved in order to carry out efficient restoration with powerful and long-term positive impacts on biodiversity: coping with unpredictability, maintaining connectivity in time and space, assessment of functionality, management of conflicting interests and social restrictions and ensuring adequate funding.
- Rising air and stream-water temperatures in Chesapeake Bay region, USA
- Monthly mean air temperature (AT) at 85 sites and instantaneous stream-water temperature (WT) at 129 sites for 1960–2010 are examined for the mid-Atlantic region, USA. Temperature anomalies for two periods, 1961–1985 and 1985–2010, relative to the climate normal period of 1971–2000, indicate that the latter period was statistically signifi- cantly warmer than the former for both mean AT and WT. Statistically significant temporal trends across the region of 0.023 °C per year for AT and 0.028 °C per year for WT are detected using simple linear regression. Sensitivity analyses show that the irregularly sampled WT data are appropriate for trend analyses, resulting in conservative estimates of trend magnitude. Relations between 190 landscape factors and significant trends in AT-WT relations are examined using principal components analysis. Measures of major dams and deciduous forest are correlated with WT increasing slower than AT, whereas agriculture in the absence of major dams is correlated with WT increasing faster than AT. Increasing WT trends are detected despite increasing trends in streamflow in the northern part of the study area. Continued warming of contributing streams to Chesapeake Bay likely will result in shifts in distributions of aquatic biota and contribute to worsened eutrophic conditions in the bay and its estuaries.
- Effect of Risk Aversion on Prioritizing Conservation Projects
- Agencies making decisions about what threat mitigation actions to take to save which species frequently face the dilemma of whether to invest in actions with high probability of success and guaranteed benefits or to choose projects with a greater risk of failure that might provide higher benefits if they succeed. The answer to this dilemma lies in the decision maker’s aversion to risk—their unwillingness to accept uncertain outcomes. Little guidance exists on how risk preferences affect conservation investment priorities. Using a prioritization approach based on cost effectiveness, we compared 2 approaches: a conservative probability threshold approach that excludes investment in projects with a risk of management failure greater than a fixed level, and a variance-discounting heuristic used in economics that explicitly accounts for risk tolerance and the probabilities of management success and failure. We applied both approaches to prioritizing projects for 700 of New Zealand’s threatened species across 8303 management actions. Both decision makers’ risk tolerance and our choice of approach to dealing with risk preferences drove the prioritization solution (i.e., the species selected for management). Use of a probability threshold minimized uncertainty, but more expensive projects were selected than with variance discounting, which maximized expected benefits by selecting the management of species with higher extinction risk and higher conservation value. Explicitly incorporating risk preferences within the decision making process reduced the number of species expected to be safe from extinction because lower risk tolerance resulted in more species being excluded from management, but the approach allowed decision makers to choose a level of acceptable risk that fit with their ability to accommodate failure. We argue for transparency in risk tolerance and recommend that decision makers accept risk in an adaptive management framework to maximize benefits and avoid potential extinctions due to inefficient allocation of limited resources. Keywords: conservation decisionmaking,cost-effectiveness analysis, management effectiveness,Project Prioritization Protocol, risk analysis, risk tolerance, threatened species, uncertainty
- Using and improving the social cost of carbon: Regular, institutionalized updating and review are essential
- The social cost of carbon (SCC) is a crucial tool for economic analysis of climate policies. The SCC estimates the dollar value of reduced climate change damages associated with a one-metric-ton reduction in carbon dioxide (CO2) emissions. Although the con-ceptual basis, challenges, and merits of the SCC are well established, its use in government cost-benefit analysis (CBA) is relatively new. In light of challenges in constructing the SCC, its newness in government regulation, and the importance of updating, we propose an institutional process for regular SCC review and revision when used in government policy-making and suggest how scientists might contribute to improved SCC estimates.
- Ten years of vegetation assembly after a North American mega fire
- Altered fuels and climate change are transforming fire regimes in many of Earth’s biomes. Postfire reassembly of vegetation – paramount to C storage and biodiversity conservation – frequently remains unpredictable and complicated by rapid global change. Using a unique data set of pre and long-term postfire data, combined with long-term data from nearby unburned areas, we examined 10 years of understory vegetation assembly after the 2002 Hayman Fire. This fire was the largest wildfire in recorded history in Colorado, USA. Resistance (initial postfire deviance from pre- fire condition) and resilience (return to prefire condition) declined with increasing fire severity. However, via both resistance and resilience, ‘legacy’ species of the prefire community constituted >75% of total plant cover within 3 years even in severely burned areas. Perseverance of legacy species, coupled with new colonizers, created a persis- tent increase in community species richness and cover over prefire levels. This was driven by a first-year increase (maintained over time) in forbs with short life spans; a 2–3-year delayed surge in long-lived forbs; and a consistent increase in graminoids through the 10th postfire year. Burning increased exotic plant invasion relative to prefire and unburned areas, but burned communities always were >89% native. This study informs debate in the literature regarding whether these increasingly large fires are ‘ecological catastrophes.’ Landscape-scale severe burning was catastrophic from a tree overstory perspective, but from an understory perspective, burning promoted rich and productive native understories, despite the entire 10-year postfire period receiving below-average precipitation. Keywords: disturbance, exotic species, fire severity, Hayman Fire, Pinus ponderosa, resilience, resistance, succession, vegetation change
- Untangling human and environmental effects on geographical gradients of mammal species richness: a global and regional evaluation
- 1. Different hypotheses (geographical, ecological, evolutionary or a combination of them) have been suggested to account for the spatial variation in species richness. However, the relative importance of environment and human impacts in explaining these patterns, either globally or at the biogeographical region level, remains largely unexplored. 2. Here, we jointly evaluate how current environmental conditions and human impacts shape global and regional gradients of species richness in terrestrial mammals. 3. We processed IUCN global distributional data for 3939 mammal species and a set of seven environmental and two human impact variables at a spatial resolution of 965 9 965 km. We used simple, multiple and partial regression techniques to evaluate environmental and human effects on species richness. 4. Actual evapotranspiration (AET) is the main driver of mammal species richness globally. Together with our results at the biogeographical realm level, this lends strong support for the water-energy hypothesis (i.e. global diversity gradients are best explained by the interaction of water and energy, with a latitudinal shift in the relative importance of ambient energy vs. water availability as we move from the poles to the equator). 5. While human effects on species richness are not easily detected at a global scale due to the large proportion of shared variance with the environment, these effects significantly emerge at the regional level. In the Nearctic, Palearctic and Oriental regions, the independent contribu- tion of human impacts is almost as important as current environmental conditions in explain- ing richness patterns. The intersection of human impacts with climate drives the geographical variation in mammal species richness in the Palearctic, Nearctic and Oriental regions. Using a human accessibility variable, we show, for the first time, that the zones most accessible to humans are often those where we find lower mammal species richness. Key-words: human accessibility, human footprint, macroclimate, macroecology, terrestrial vertebrates, water–energy dynamics
- Physiological plasticity increases resilience of ectothermic animals to climate change
- Understanding how climate change affects natural populations remains one of the greatest challenges for ecology and management of natural resources. Animals can remodel their physiology to compensate for the effects of temperature variation, and this physiological plasticity, or acclimation, can confer resilience to climate change1,2. The current lack of a comprehensive analysis of the capacity for physiological plasticity across taxonomic groups and geographic regions, however, constrains predictions of the impacts of climate change. Here, we assembled the largest database to date to establish the current state of knowledge of physiological plasticity in ectothermic animals. We show that acclimation decreases the sensitivity to temperature and climate change of freshwater and marine animals, but less so in terrestrial animals. Animals from more stable environments have greater capacity for acclimation, and there is a significant trend showing that the capacity for thermal acclimation increases with decreasing latitude. Despite the capacity for acclimation, climate change over the past 20 years has already resulted in increased physiological rates of up to 20%, and we predict further future increases under climate change. The generality of these predictions is limited, however, because much of the world is drastically undersampled in the literature, and these undersampled regions are the areas of greatest need for future research efforts.
- Dramatically increasing chance of extremely hot summers since the 2003 European heatwave
- Socio-economic stress from the unequivocal warming of the global climate system(1)could be mostly felt by societies through weather and climate extremes (2). The vulnerability of European citizens was made evident during the summer heatwave of 2003 (refs 3,4) when the heat-related death toll ran into tens of thousands (5). Human influence at least doubled the chances of the event according to the first formal event attribution study (6), which also made the ominous forecast that severe heatwaves could become commonplace by the 2040s. Here we investigate how the likelihood of having another extremely hot summer in one of the worst affected parts of Europe has changed ten years after the original study was published, given an observed summer temperature increase of 0.81 K since then. Our analysis benefits from the availability of new observations and data from several new models. Using a previously employed temperature threshold to define extremely hot summers, we find that events that would occur twice a century in the early 2000s are now expected to occur twice a decade. For the more extreme threshold observed in 2003, the return time reduces from thousands of years in the late twentieth century to about a hundred years in little over a decade.
- Livelihood resilience in the face of climate change
- The resilience concept requires greater attention to human livelihoods if it is to address the limits to adaptation strategies and the development needs of the planet’s poorest and most vulnerable people. Although the concept of resilience is increasingly informing research and policy, its transfer from ecological theory to social systems leads to weak engagement with normative, social and political dimensions of climate change adaptation. A livelihood perspective helps to strengthen resilience thinking by placing greater emphasis on human needs and their agency, empowerment and human rights, and considering adaptive livelihood systems in the context of wider transformational changes.
