Climate Science Documents
Ramification of stream networks
The geometric complexity of stream networks has been a source of fascination for centuries. However, a comprehensive understanding of ramification—the mechanism of branching by which such networks grow—remains elusive. Here we show that streams incised by groundwater seepage branch at a characteristic angle of 2π/5 = 72°. Our theory represents streams as a collection of paths growing and bifurcating in a diffusing field. Our observations of nearly 5,000 bifurcated streams growing in a 100 km2 groundwater field on the Florida Panhandle yield a mean bifurcation angle of 71.9° ± 0.8°. This good accord between theory and observation suggests that the network geometry is determined by the external flow field but not, as classical theories imply, by the flow within the streams themselves. river networks | network growth | Laplacian growth
Perception of climate change
“Climate dice,” describing the chance of unusually warm or cool seasons, have become more and more “loaded” in the past 30 y, coincident with rapid global warming. The distribution of seasonal mean temperature anomalies has shifted toward higher temperatures and the range of anomalies has increased. An important change is the emergence of a category of summertime extremely hot outliers, more than three standard deviations (3σ) warmer than the climatology of the 1951–1980 base period. This hot extreme, which covered much less than 1% of Earth’s surface during the base period, now typically covers about 10% of the land area. It follows that we can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming because their likelihood in the absence of global warming was exceedingly small. We discuss practical implications of this substantial, growing, climate change. climate impacts ∣ climate anomalies ∣ heat waves
Resource diversity and landscape-level homogeneity drive native bee foraging
Given widespread declines in pollinator communities and increas- ing global reliance on pollinator-dependent crops, there is an acute need to develop a mechanistic understanding of native pollinator population and foraging biology. Using a population genetics approach, we determine the impact of habitat and floral resource distributions on nesting and foraging patterns of a critical native pollinator, Bombus vosnesenskii. Our findings demonstrate that native bee foraging is far more plastic and extensive than previ- ously believed and does not follow a simple optimal foraging strat- egy. Rather, bumble bees forage further in pursuit of species-rich floral patches and in landscapes where patch-to-patch variation in floral resources is less, regardless of habitat composition. Thus, our results reveal extreme foraging plasticity and demonstrate that floral diversity, not density, drives bee foraging distance. Further- more, we find a negative impact of paved habitat and a positive impact of natural woodland on bumble bee nesting densities. Over- all, this study reveals that natural and human-altered landscapes can be managed for increased native bee nesting and extended foraging, dually enhancing biodiversity and the spatial extent of pollination services. dispersal | ecosystem services | resource dynamics | spatial ecology | urban
Transformational adaptation when incremental adaptations to climate change are insufficient
All human–environment systems adapt to climate and its natural variation. Adaptation to human-induced change in climate has largely been envisioned as increments of these adaptations intended to avoid disruptions of systems at their current locations. In some places, for some systems, however, vulnerabilities and risks may be so sizeable that they require transformational rather than incremental adaptations. Three classes of transformational adaptations are those that are adopted at a much larger scale, that are truly new to a particular region or resource system, and that transform places and shift locations. We illustrate these with examples drawn from Africa, Europe, and North America. Two conditions set the stage for transformational adaptation to climate change: large vulnerability in certain regions, populations, or resource systems; and severe climate change that overwhelms even robust human use systems. However, anticipatory transformational adaptation may be difficult to implement because of uncertainties about climate change risks and adaptation benefits, the high costs of transformational actions, and institutional and behavioral actions that tend to maintain existing resource systems and policies. Implementing transformational adaptation requires effort to initiate it and then to sustain the effort over time. In initiating transformational adaptation focusing events and multiple stresses are important, combined with local leadership. In sustaining transformational adaptation, it seems likely that supportive social contexts and the availability of acceptable options and resources for actions are key enabling factors. Early steps would include incorporating transformation adaptation into risk management and initiating research to expand the menu of innovative transformational adaptations.
Economic growth and the human lot
1st paragraph: In 1974, Richard A. Easterlin, a coauthor of the work by Easterlin et al. (1) in PNAS, published a seminal article (2) that has generated a huge literature. It sought to explain why the happiness score in the United States (and elsewhere) had stayed roughly constant, whereas income per capita had trended up. This evidence has come to be known as the Easterlin Paradox. His explanation was that economic growth has a positive effect on happiness with other things being equal; however, it also raises aspirations, and aspirations have a negative effect. Aspirations are determined by society, particularly reference group income. The combination of these two effects gives rise to a Hedonic Treadmill.
Developing a broader scientific foundation for river restoration: Columbia River food webs
Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure—without explicitly considering food webs—has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.
Quantitative global analysis of the role of climate and people in explaining late Quaternary megafaunal extinctions
The late Quaternary period saw the rapid extinction of the majority of the world’s terrestrial megafauna. The cause of these dramatic losses, especially the relative importance of climatic change and the impacts of newly arrived people, remains highly controversial, with geographically restricted analyses generating conflicting conclusions. By analyzing the distribution and timing of all megafaunal extinctions in relation to climatic variables and human arrival on five landmasses, we demonstrate that the ob- served pattern of extinctions is best explained by models that combine both human arrival and climatic variables. Our conclusions are robust to uncertainties in climate data and in the dates of megafaunal extinctions and human arrival on different land- masses, and strongly suggest that these extinctions were driven by both anthropogenic and climatic factors.
Identifying human influences on atmospheric temperature
We perform a multimodel detection and attribution study with climate model simulation output and satellite-based measurements of tropospheric and stratospheric temperature change. We use simulation output from 20 climate models participating in phase 5 of the Coupled Model Intercomparison Project. This multimodel archive provides estimates of the signal pattern in response to combined anthropogenic and natural external forcing (the finger- print) and the noise of internally generated variability. Using these estimates, we calculate signal-to-noise (S/N) ratios to quantify the strength of the fingerprint in the observations relative to fingerprint strength in natural climate noise. For changes in lower stratospheric temperature between 1979 and 2011, S/N ratios vary from 26 to 36, depending on the choice of observational dataset. In the lower troposphere, the fingerprint strength in observations is smaller, but S/N ratios are still significant at the 1% level or better, and range from three to eight. We find no evidence that these ratios are spuriously inflated by model variability errors. After removing all global mean signals, model fingerprints remain identifiable in 70% of the tests involving tropospheric temperature changes. Despite such agreement in the large-scale features of model and observed geographical patterns of atmospheric temperature change, most models do not replicate the size of the observed changes. On average, the models analyzed underestimate the observed cooling of the lower stratosphere and overestimate the warming of the troposphere. Although the precise causes of such differences are unclear, model biases in lower stratospheric temperature trends are likely to be reduced by more realistic treatment of stratospheric ozone depletion and volcanic aerosol forcing. climate change detection and attribution | climate modeling | multimodel analysis
Groundwater depletion and sustainability of irrigation in the US High Plains and Central Valley
Aquifer overexploitation could significantly impact crop production in the United States because 60% of irrigation relies on groundwater. Groundwater depletion in the irrigated High Plains and California Central Valley accounts for ∼50% of groundwater depletion in the United States since 1900. A newly developed High Plains recharge map shows that high recharge in the northern High Plains results in sustainable pumpage, whereas lower recharge in the central and southern High Plains has resulted in focused depletion of 330 km3 of fossil groundwater, mostly recharged during the past 13,000 y. Depletion is highly localized with about a third of depletion occurring in 4% of the High Plains land area. Extrapolation of the current depletion rate suggests that 35% of the southern High Plains will be unable to support irrigation within the next 30 y. Reducing irrigation withdrawals could extend the lifespan of the aquifer but would not result in sustainable management of this fossil groundwater. The Central Valley is a more dynamic, engineered system, with north/south diversions of surface water since the 1950s contributing to ∼7× higher recharge. However, these diversions are regulated because of impacts on endangered species. A newly developed Central Valley Hydrologic Model shows that groundwater depletion since the 1960s, totaling 80 km3, occurs mostly in the south (Tulare Basin) and primarily during droughts. Increasing water storage through artificial recharge of excess surface water in aquifers by up to 3 km3 shows promise for coping with droughts and improv- ing sustainability of groundwater resources in the Central Valley. Gravity Recovery and Climate Experiment satellite | irrigated agriculture | managed aquifer recharge
Urban land teleconnections and sustainability
This paper introduces urban land teleconnections as a conceptual framework that explicitly links land changes to underlying urbanization dynamics. We illustrate how three key themes that are currently addressed separately in the urban sustainability and land change literatures can lead to incorrect conclusions and misleading results when they are not examined jointly: the traditional system of land classification that is based on discrete categories and reinforces the false idea of a rural–urban dichotomy; the spatial quantification of land change that is based on place-based relationships, ignoring the connections between distant places, especially between urban functions and rural land uses; and the implicit assumptions about path dependency and sequential land changes that underlie current conceptualizations of land transitions. We then examine several environmental “grand challenges” and discuss how urban land teleconnections could help research communities frame scientific inquiries. Finally, we point to existing analytical approaches that can be used to advance development and application of the concept. coupled human–natural systems | land change science
Multidecadal to multicentury scale collapses of Northern Hemisphere monsoons over the past millennium
Late Holocene climate in western North America was punctuated by periods of extended aridity called megadroughts. These droughts have been linked to cool eastern tropical Pacific sea surface temperatures (SSTs). Here, we show both short-term and long-term climate variability over the last 1,500 y from annual band thickness and stable isotope speleothem data. Several megadroughts are evident, including a multicentury one, AD 1350–1650, herein referred to as Super Drought, which corresponds to the coldest period of the Little Ice Age. Synchronicity between southwestern North American, Chi- nese, and West African monsoon precipitation suggests the mega- droughts were hemispheric in scale. Northern Hemisphere monsoon strength over the last millennium is positively correlated with North- ern Hemisphere temperature and North Atlantic SST. The mega- droughts are associated with cooler than average SST and Northern Hemisphere temperatures. Furthermore, the megadroughts, including the Super Drought, coincide with solar insolation minima, suggesting that solar forcing of sea surface and atmospheric temperatures may generate variations in the strength of Northern Hemisphere monsoons. Our findings seem to suggest stronger (wetter) Northern Hemisphere monsoons with increased warming.
Model projections of atmospheric steering of Sandy-like superstorms
Superstorm Sandy ravaged the eastern seaboard of the United States, costing a great number of lives and billions of dollars in damage. Whether events like Sandy will become more frequent as anthropogenic greenhouse gases continue to increase remains an open and complex question. Here we consider whether the persistent large-scale atmospheric patterns that steered Sandy onto the coast will become more frequent in the coming decades. Using the Coupled Model Intercomparison Project, phase 5 multi- model ensemble, we demonstrate that climate models consistently project a decrease in the frequency and persistence of the westward flow that led to Sandy’s unprecedented track, implying that future atmospheric conditions are less likely than at present to propel storms westward into the coast. climate change | Hurricane Sandy | global climate models | blocking
Sagebrush carrying out hydraulic lift enhances surface soil nitrogen cycling and nitrogen uptake into inflorescences
Plant roots serve as conduits for water flow not only from soil to leaves but also from wetter to drier soil. This hydraulic redistribution through root systems occurs in soils worldwide and can enhance stomatal opening, transpiration, and plant carbon gain. For decades, upward hydraulic lift (HL) of deep water through roots into dry, litter-rich, surface soil also has been hypothesized to enhance nutrient availability to plants by stimulating microbially controlled nutrient cycling. This link has not been demonstrated in the field. Working in sagebrush-steppe, where water and nitrogen limit plant growth and reproduction and where HL occurs naturally during summer drought, we slightly augmented deep soil water availability to 14 HL+ treatment plants throughout the summer growing season. The HL+ sagebrush lifted greater amounts of water than control plants and had slightly less negative predawn and midday leaf water potentials. Soil respiration was also aug- mented under HL+ plants. At summer’s end, application of a gas- based 15N isotopic labeling technique revealed increased rates of nitrogen cycling in surface soil layers around HL+ plants and increased uptake of nitrogen into HL+ plants’ inflorescences as sagebrush set seed. These treatment effects persisted even though unexpected monsoon rainstorms arrived during assays and increased surface soil moisture around all plants. Simulation models from ecosystem to global scales have just begun to include effects of hydraulic redistribution on water and surface energy fluxes. Results from this field study indicate that plants carrying out HL can also substantially enhance decomposition and nitrogen cycling in surface soils. rhizosphere | flowering | seed production
Microclimate moderates plant responses to macroclimate warming
Recent global warming is acting across marine, freshwater, and terrestrial ecosystems to favor species adapted to warmer conditions and/or reduce the abundance of cold-adapted organisms (i.e., “thermophilization” of communities). Lack of community responses to increased temperature, however, has also been re-ported for several taxa and regions, suggesting that “climatic lags” may be frequent. Here we show that microclimatic effects brought about by forest canopy closure can buffer biotic re- sponses to macroclimate warming, thus explaining an apparent climatic lag. Using data from 1,409 vegetation plots in European and North American temperate forests, each surveyed at least twice over an interval of 12–67 y, we document significant thermophilization of ground-layer plant communities. These changes reflect concurrent declines in species adapted to cooler conditions and increases in species adapted to warmer conditions. However, thermophilization, particularly the increase of warm-adapted species, is attenuated in forests whose canopies have become denser, probably reflecting cooler growing-season ground temperatures via increased shading. As standing stocks of trees have increased in many temperate forests in recent decades, local microclimatic effects may commonly be moderating the impacts of macroclimate warming on forest understories. Conversely, increases in harvesting woody biomass—e.g., for bioenergy—may open forest canopies and accelerate thermophilization of temperate forest biodiversity. climate change | forest management | understory | climatic debt | range shifts
Soil food web properties explain ecosystem services across European land use systems
Intensive land use reduces the diversity and abundance of many soil biota, with consequences for the processes that they govern and the ecosystem services that these processes underpin. Relationships between soil biota and ecosystem processes have mostly been found in laboratory experiments and rarely are found in the field. Here, we quantified, across four countries of contrasting climatic and soil conditions in Europe, how differences in soil food web composition resulting from land use systems (intensive wheat rotation, extensive rotation, and permanent grassland) influence the functioning of soils and the ecosystem services that they deliver. Intensive wheat rotation consistently reduced the biomass of all components of the soil food web across all countries. Soil food web properties strongly and consistently predicted processes of C and N cycling across land use systems and geographic loca- tions, and they were a better predictor of these processes than land use. Processes of carbon loss increased with soil food web properties that correlated with soil C content, such as earthworm biomass and fungal/bacterial energy channel ratio, and were greatest in permanent grassland. In contrast, processes of N cycling were explained by soil food web properties independent of land use, such as arbuscular mycorrhizal fungi and bacterial channel biomass. Our quantification of the contribution of soil organisms to processes of C and N cycling across land use systems and geographic locations shows that soil biota need to be included in C and N cycling models and highlights the need to map and conserve soil biodiversity across the world. soil fauna | modeling | soil microbes | nitrogen
Evolution of natural and social science interactions in global change research programs
Efforts to develop a global understanding of the functioning of the Earth as a system began in the mid-1980s. This effort necessitated linking knowledge from both the physical and biological realms. A motivation for this development was the growing impact of humans on the Earth system and need to provide solutions, but the study of the social drivers and their consequences for the changes that were occurring was not incorporated into the Earth System Science movement, despite early attempts to do so. The impediments to integration were many, but they are gradually being overcome, which can be seen in many trends for assessments, such as the Intergovernmental Platform on Biodiversity and Ecosystem Services, as well as both basic and applied science programs. In this development, particular people and events have shaped the trajectories that have occurred. The lessons learned should be considered in such emerging research programs as Future Earth, the new global program for sustainability research. The transitioning process to this new program will take time as scientists adjust to new colleagues with different ideologies, methods, and tools and a new way of doing science.
Gas production in the Barnett Shale obeys a simple scaling theory
Natural gas from tight shale formations will provide the United States with a major source of energy over the next several decades. Estimates of gas production from these formations have mainly relied on formulas designed for wells with a different geometry. We consider the simplest model of gas production consistent with the basic physics and geometry of the extraction process. In principle, solutions of the model depend upon many parameters, but in practice and within a given gas field, all but two can be fixed at typical values, leading to a nonlinear diffusion problem we solve exactly with a scaling curve. The scaling curve production rate declines as 1 over the square root of time early on, and it later declines exponentially. This simple model provides a surprisingly accurate description of gas extraction from 8,294 wells in the United States’ oldest shale play, the Barnett Shale. There is good agreement with the scaling theory for 2,057 horizontal wells in which production started to decline exponentially in less than 10 y. The remaining 6,237 horizontal wells in our analysis are too young for us to predict when exponential decline will set in, but the model can nevertheless be used to establish lower and upper bounds on well lifetime. Finally, we obtain upper and lower bounds on the gas that will be produced by the wells in our sample, in- dividually and in total. The estimated ultimate recovery from our sample of 8,294 wells is between 10 and 20 trillion standard cubic feet. hydrofracturing | shale gas | scaling laws | energy resources | fracking
Hot climates, high sensitivity
Concluding paragraph: One sure solution to the problem posed by uncertainty of climate sensitivity in hot climates is simply not to go there. Unfortunately, it looks increasingly like Nature will step in to answer some of our questions for us, and I doubt we’ll like the answer. The highest emission scenario currently being considered by the Intergovernmental Panel on Climate Change is Representative Concentration Pathway 8.5 (8), which would bring CO2 concentrations up to 2,000 ppm, which is in the upper reaches of the range considered in ref. 2. Even this scenario can be considered somewhat optimistic, in that it assumes that the annual growth in CO emissions rate (which has been hovering around 3% for decades) will tail off by 2060 and that the emissions rate will cease growing altogether by 2100, whereafter emissions will trend to zero; unrestrained growth could eas- ily dump twice as much carbon into the atmosphere. It is not known if there are actually enough recoverable fossil fuels to emit that much CO2. Hoping that we run out of fossil fuels before bringing on a climate catastrophe does not seem like sound climate policy, but at present it seems to be the only one we have.
The elephant, the blind, and the intersectoral intercomparison of climate impacts
1st paragraph: When decision makers discuss anthropogenic climate change, they often ignore the mighty elephant in the room, namely the question of what global warming really means on the ground. By all accounts, the impacts on our physical environment and society would be starkly different if our planet warmed by “just” 2 °C (1, 2), by a “dangerous” 4 °C (3), or by a “mind-boggling” 6–8 °C (4). However, the pictures of those sweltering worlds that are emerging from scientific research are still regrettably vague, blurred, and fragmentary (see, for example, refs. 5–7). The main reason for this vagueness is as obvious as it is tantalizing: the sheer diversity and complexity of potential climate-change effects on the existing multitude of regions, sectors, and cultures make the swift advancement of robust knowl- edge in this field extremely challenging.
Water-controlled wealth of nations
Population growth is in general constrained by food production, which in turn depends on the access to water resources. At a country level, some populations use more water than they control because of their ability to import food and the virtual water required for its production. Here, we investigate the dependence of demographic growth on available water resources for exporting and importing nations. By quantifying the carrying capacity of nations on the basis of calculations of the virtual water available through the food trade network, we point to the existence of a global water unbalance. We suggest that current export rates will not be maintained and consequently we question the long-term sustainability of the food trade system as a whole. Water-rich regions are likely to soon reduce the amount of virtual water they export, thus leaving import-dependent regions without enough water to sustain their populations. We also investigate the potential impact of possible scenarios that might mitigate these effects through (i) cooperative interactions among nations whereby water-rich countries main- tain a tiny fraction of their food production available for export, (ii ) changes in consumption patterns, and (iii ) a positive feedback between demographic growth and technological innovations. We find that these strategies may indeed reduce the vulnerability of water-controlled societies.
Delayed detection of climate mitigation benefits due to climate inertia and variability
Climate change mitigation acts by reducing greenhouse gas emissions, and thus curbing, or even reversing, the increase in their atmospheric concentration. This reduces the associated anthropogenic radiative forcing, and hence the size of the warming. Because of the inertia and internal variability affecting the climate system and the global carbon cycle, it is unlikely that a reduction in warming would be immediately discernible. Here we use 21st century simulations from the latest ensemble of Earth System Model experiments to investigate and quantify when mitigation becomes clearly discernible. We use one of the scenarios as a reference for a strong mitigation strategy, Representative Concentration Pathway (RCP) 2.6 and compare its outcome with either RCP4.5 or RCP8.5, both of which are less severe mitigation pathways. We analyze global mean atmospheric CO2, and changes in annually and seasonally averaged surface temperature at global and regional scales. For global mean surface temperature, the median detection time of mitigation is about 25–30 y after RCP2.6 emissions depart from the higher emission trajectories. This translates into detection of a mitigation signal by 2035 or 2045, depending on whether the comparison is with RCP8.5 or RCP4.5, respectively. The detection of climate benefits of emission mitigation occurs later at regional scales, with a median detection time between 30 and 45 y after emission paths separate. Requiring a 95% confidence level induces a delay of several decades, bringing detection time toward the end of the 21st century. regional climate change | climate variability | signal detection
The material footprint of nations
Metrics on resource productivity currently used by governments suggest that some developed countries have increased the use of natural resources at a slower rate than economic growth (relative decoupling) or have even managed to use fewer resources over time (absolute decoupling). Using the material footprint (MF), a consumption-based indicator of resource use, we find the contrary: Achievements in decoupling in advanced economies are smaller than reported or even nonexistent. We present a time series analysis of the MF of 186 countries and identify material flows associated with global production and consumption networks in unprecedented specificity. By calculating raw material equivalents of international trade, we demonstrate that countries’ use of nondomestic resources is, on average, about threefold larger than the physical quantity of traded goods. As wealth grows, countries tend to reduce their domestic portion of materials extraction through international trade, whereas the overall mass of material consumption generally increases. With every 10% increase in gross domestic product, the average national MF increases by 6%. Our findings call into question the sole use of current resource productivity indicators in policy making and suggest the necessity of an additional focus on consumption- based accounting for natural resource use. raw material consumption | multiregion input–output analysis | sustainable resource management
Green-up dates in the Tibetan Plateau have continuously advanced from 1982 to 2011
As the Earth’s third pole, the Tibetan Plateau has experienced a pronounced warming in the past decades. Recent studies reported that the start of the vegetation growing season (SOS) in the Plateau showed an advancing trend from 1982 to the late 1990s and a delay from the late 1990s to 2006. However, the findings regard- ing the SOS delay in the later period have been questioned, and the reasons causing the delay remain unknown. Here we explored the alpine vegetation SOS in the Plateau from 1982 to 2011 by integrating three long-term time-series datasets of Normalized Difference Vegetation Index (NDVI): Global Inventory Modeling and Mapping Studies (GIMMS, 1982–2006), SPOT VEGETATION (SPOT-VGT, 1998–2011), and Moderate Resolution Imaging Spec- troradiometer (MODIS, 2000–2011). We found GIMMS NDVI in 2001–2006 differed substantially from SPOT-VGT and MODIS NDVIs and may have severe data quality issues in most parts of the western Plateau. By merging GIMMS-based SOSs from 1982 to 2000 with SPOT-VGT–based SOSs from 2001 to 2011 we found the alpine vegetation SOS in the Plateau experienced a continuous advancing trend at a rate of ∼1.04 d·y−1 from 1982 to 2011, which was consistent with observed warming in springs and winters. The satellite-derived SOSs were proven to be reliable with observed phenology data at 18 sites from 2003 to 2011; however, comparison of their trends was inconclusive due to the limited temporal coverage of the observed data. Longer-term observed data are still needed to validate the phenology trend in the future.
Land, irrigation water, greenhouse gas, and reactive nitrogen burdens of meat, eggs, and dairy production in the United States
Livestock production impacts air and water quality, ocean health, and greenhouse gas (GHG) emissions on regional to global scales and it is the largest use of land globally. Quantifying the environ- mental impacts of the various livestock categories, mostly arising from feed production, is thus a grand challenge of sustainability science. Here, we quantify land, irrigation water, and reactive nitrogen (Nr) impacts due to feed production, and recast published full life cycle GHG emission estimates, for each of the major animal- based categories in the US diet. Our calculations reveal that the environmental costs per consumed calorie of dairy, poultry, pork, and eggs are mutually comparable (to within a factor of 2), but strikingly lower than the impacts of beef. Beef production requires 28, 11, 5, and 6 times more land, irrigation water, GHG, and Nr, respectively, than the average of the other livestock categories. Preliminary analysis of three staple plant foods shows two- to sixfold lower land, GHG, and Nr requirements than those of the nonbeef animal-derived calories, whereas irrigation requirements are comparable. Our analysis is based on the best data currently available, but follow-up studies are necessary to improve parameter estimates and fill remaining knowledge gaps. Data imperfections notwithstanding, the key conclusion—that beef production demands about 1 order of magnitude more resources than alternative livestock categories—is robust under existing uncertainties. The study thus elu- cidates the multiple environmental benefits of potential, easy-to- implement dietary changes, and highlights the uniquely high re- source demands of beef. food impact | foodprint | geophysics of agriculture | multimetric analysis
Global water resources affected by human interventions and climate change
Humans directly change the dynamics of the water cycle through dams constructed for water storage, and through water withdrawals for industrial, agricultural, or domestic purposes. Climate change is expected to additionally affect water supply and demand. Here, analyses of climate change and direct human impacts on the terrestrial water cycle are presented and compared using a multi- model approach. Seven global hydrological models have been forced with multiple climate projections, and with and without taking into account impacts of human interventions such as dams and water withdrawals on the hydrological cycle. Model results are analyzed for different levels of global warming, allowing for analyses in line with temperature targets for climate change mitigation. The results indicate that direct human impacts on the water cycle in some regions, e.g., parts of Asia and in the western United States, are of the same order of magnitude, or even exceed impacts to be expected for moderate levels of global warming (+2 K). Despite some spread in model projections, irrigation water consumption is generally projected to increase with higher global mean temperatures. Irrigation water scarcity is particularly large in parts of southern and eastern Asia, and is expected to become even larger in the future. ISI-MIP | WaterMIP
Satellite methods underestimate indirect climate forcing by aerosols
Satellite-based estimates of the aerosol indirect effect (AIE) are consistently smaller than the estimates from global aerosol models, and, partly as a result of these differences, the assessment of this climate forcing includes large uncertainties. Satellite estimates typically use the present-day (PD) relationship between observed cloud drop number concentrations (Nc) and aerosol optical depths (AODs) to determine the preindustrial (PI) values of Nc. These values are then used to determine the PD and PI cloud albedos and, thus, the effect of anthropogenic aerosols on top of the atmo- sphere radiative fluxes. Here, we use a model with realistic aerosol and cloud processes to show that empirical relationships for lnðNc Þ versus lnðAODÞ derived from PD results do not represent the atmo- spheric perturbation caused by the addition of anthropogenic aerosols to the preindustrial atmosphere. As a result, the model estimates based on satellite methods of the AIE are between a factor of 3 to more than a factor of 6 smaller than model estimates based on actual PD and PI values for Nc. Using lnðNcÞ versus lnðAIÞ (Aerosol Index, or the optical depth times angstrom exponent) to estimate preindustrial values for Nc provides estimates for Nc and forcing that are closer to the values predicted by the model. Never- theless, the AIE using lnðNcÞ versus lnðAIÞ may be substantially incorrect on a regional basis and may underestimate or overesti- mate the global average forcing by 25 to 35%.
Assessing the impacts of livestock production on biodiversity in rangeland ecosystems
Biodiversity in rangelands is decreasing, due to intense utilization for livestock production and conversion of rangeland into cropland; yet the outlook of rangeland biodiversity has not been considered in view of future global demand for food. Here we assess the impact of future livestock production on the global rangelands area and their biodiversity. First we formalized exist- ing knowledge about livestock grazing impacts on biodiversity, expressed in mean species abundance (MSA) of the original rangeland native species assemblages, through metaanalysis of peer-reviewed literature. MSA values, ranging from 1 in natural rangelands to 0.3 in man-made grasslands, were entered in the IMAGE-GLOBIO model. This model was used to assess the impact of change in food demand and livestock production on future rangeland biodiversity. The model revealed remarkable regional variation in impact on rangeland area and MSA between two agricultural production scenarios. The area of used rangelands slightly increases globally between 2000 and 2050 in the baseline scenario and reduces under a scenario of enhanced uptake of resource-efficient production technologies increasing production [high levels of agricultural knowledge, science, and technology (high-AKST)], particularly in Africa. Both scenarios suggest a global decrease in MSA for rangelands until 2050. The contribution of livestock grazing to MSA loss is, however, expected to diminish after 2030, in particular in Africa under the high-AKST scenario. Policies fostering agricultural intensification can reduce the overall pressure on rangeland biodiversity, but additional measures, addressing factors such as climate change and infrastructural development, are necessary to totally halt biodiversity loss. dose-response model | intactness | land use
Carbon debt of Conservation Reserve Program (CRP) grasslands converted to bioenergy production
Over 13 million ha of former cropland are enrolled in the US Conservation Reserve Program (CRP), providing well-recognized biodiversity, water quality, and carbon (C) sequestration benefits that could be lost on conversion back to agricultural production. Here we provide measurements of the greenhouse gas consequences of converting CRP land to continuous corn, corn–soybean, or perennial grass for biofuel production. No-till soybeans preceded the annual crops and created an initial carbon debt of 10.6 Mg CO2 equivalents (CO2e)·ha−1 that included agronomic inputs, changes in C stocks, altered N2O and CH4 fluxes, and foregone C sequestration less a fossil fuel offset credit. Total debt, which includes future debt created by additional changes in soil C stocks and the loss of substantial future soil C sequestration, can be constrained to 68 Mg CO2e·ha−1 if subsequent crops are under permanent no-till management. If tilled, however, total debt triples to 222 Mg CO2e·ha−1 on account of further soil C loss. Projected C debt repayment periods under no-till management range from 29 to 40 y for corn– soybean and continuous corn, respectively. Under conventional tillage repayment periods are three times longer, from 89 to 123 y, respectively. Alternatively, the direct use of existing CRP grasslands for cellulosic feedstock production would avoid C debt entirely and provide modest climate change mitigation immediately. Incentives for permanent no till and especially permission to harvest CRP biomass for cellulosic biofuel would help to blunt the climate impact of future CRP conversion. land-use change | renewable energy | carbon balance | agriculture | nitrous oxide
Widespread crown condition decline, food web disruption, and amplified tree mortality with increased climate change-type drought
Climate change is progressively increasing severe drought events in the Northern Hemisphere, causing regional tree die-off events and contributing to the global reduction of the carbon sink efficiency of forests. There is a critical lack of integrated community- wide assessments of drought-induced responses in forests at the macroecological scale, including defoliation, mortality, and food web responses. Here we report a generalized increase in crown defoliation in southern European forests occurring during 1987– 2007. Forest tree species have consistently and significantly altered their crown leaf structures, with increased percentages of defolia- tion in the drier parts of their distributions in response to increased water deficit. We assessed the demographic responses of trees associated with increased defoliation in southern European forests, specifically in the Iberian Peninsula region. We found that defolia- tion trends are paralleled by significant increases in tree mortality rates in drier areas that are related to tree density and temperature effects. Furthermore, we show that severe drought impacts are associated with sudden changes in insect and fungal defoliation dynamics, creating long-term disruptive effects of drought on food webs. Our results reveal a complex geographical mosaic of species- specific responses to climate change–driven drought pressures on the Iberian Peninsula, with an overwhelmingly predominant trend toward increased drought damage. extreme events | earth system feedbacks | ecological networks | global change | Mediterranean biome
Fluvial landscapes of the Harappan civilization
The collapse of the Bronze Age Harappan, one of the earliest urban civilizations, remains an enigma. Urbanism flourished in the western region of the Indo-Gangetic Plain for approximately 600 y, but since approximately 3,900 y ago, the total settled area and settlement sizes declined, many sites were abandoned, and a significant shift in site numbers and density towards the east is recorded. We report morphologic and chronologic evidence indicating that flu- vial landscapes in Harappan territory became remarkably stable during the late Holocene as aridification intensified in the region after approximately 5,000 BP. Upstream on the alluvial plain, the large Himalayan rivers in Punjab stopped incising, while down- stream, sedimentation slowed on the distinctive mega-fluvial ridge, which the Indus built in Sindh. This fluvial quiescence suggests a gradual decrease in flood intensity that probably stimulated intensive agriculture initially and encouraged urbanization around 4,500 BP. However, further decline in monsoon precipitation led to conditions adverse to both inundation- and rain-based farming. Contrary to earlier assumptions that a large glacier-fed Himalayan river, identi- fied by some with the mythical Sarasvati, watered the Harappan heartland on the interfluve between the Indus and Ganges basins, we show that only monsoonal-fed rivers were active there during the Holocene. As the monsoon weakened, monsoonal rivers gradu- ally dried or became seasonal, affecting habitability along their courses. Hydroclimatic stress increased the vulnerability of agricultural production supporting Harappan urbanism, leading to settlement downsizing, diversification of crops, and a drastic increase in settlements in the moister monsoon regions of the upper Punjab, Haryana, and Uttar Pradesh. Indus Valley ∣ floods ∣ droughts ∣ climate change ∣ archaeology
Impacts of climate warming on terrestrial ectotherms across latitude
he impact of anthropogenic climate change on terrestrial organ- isms is often predicted to increase with latitude, in parallel with the rate of warming. Yet the biological impact of rising temperatures also depends on the physiological sensitivity of organisms to temperature change. We integrate empirical fitness curves describ- ing the thermal tolerance of terrestrial insects from around the world with the projected geographic distribution of climate change for the next century to estimate the direct impact of warming on insect fitness across latitude. The results show that warming in the tropics, although relatively small in magnitude, is likely to have the most deleterious consequences because tropical insects are rela- tively sensitive to temperature change and are currently living very close to their optimal temperature. In contrast, species at higher latitudes have broader thermal tolerance and are living in climates that are currently cooler than their physiological optima, so that warming may even enhance their fitness. Available thermal toler- ance data for several vertebrate taxa exhibit similar patterns, suggesting that these results are general for terrestrial ectotherms. Our analyses imply that, in the absence of ameliorating factors such as migration and adaptation, the greatest extinction risks from global warming may be in the tropics, where biological diversity is also greatest. biodiversity fitness global warming physiology tropical
Improved probability of detection of ecological “surprises”
Ecological “surprises” are defined as unexpected findings about the natural environment. They are critically important in ecology because they are catalysts for questioning and reformulating views of the natural world, help shape assessments of the veracity of a priori predictions about ecological trends and phenomena, and underpin questioning of effectiveness of resource management. Despite the importance of ecological surprises, major gaps in understanding remain about how studies might be done differently or done better to improve the ability to identify them. We outline the kinds of ecological surprises that have arisen from long-term research programs that we lead in markedly different ecosystems around the world. Based on these case studies, we identify important lessons to guide both existing studies and new investigations to detect ecological surprises more readily, better anticipate unusual ecological phenomena, and take proactive steps to plan for and alleviate “undesirable” ecological surprises. Some of these lessons include: (i) maintain existing, and instigate new, long-term studies; (ii) conduct a range of kinds of parallel and concurrent research in a given target area; (iii) better use past literature and conceptual models of the target ecosystem in posing good questions and developing hypotheses and alternative hypotheses; and (iv) increase the capacity for ecological research to take advantage of opportunities arising from major natural disturbances. We argue that the increased anticipatory capability resulting from these lessons is critical given that ecological surprises may become more prevalent because of climate change and multiple and interacting environmental stressors.
Dispersal will limit ability of mammals to track climate change in the Western Hemisphere
As they have in response to past climatic changes, many species will shift their distributions in response to modern climate change. However, due to the unprecedented rapidity of projected climatic changes, some species may not be able to move their ranges fast enough to track shifts in suitable climates and associated habitats. Here, we investigate the ability of 493 mammals to keep pace with projected climatic changes in the Western Hemisphere. We modeled the velocities at which species will likely need to move to keep pace with projected changes in suitable climates. We compared these velocities with the velocities at which species are able to move as a function of dispersal distances and dispersal frequencies. Across the Western Hemisphere, on average, 9.2% of mammals at a given location will likely be unable to keep pace with climate change. In some places, up to 39% of mammals may be unable to track shifts in suitable climates. Eighty-seven percent of mammalian species are expected to experience reductions in range size and 20% of these range reductions will likely be due to limited dispersal abilities as opposed to reductions in the area of suitable climate. Because climate change will likely outpace the response capacity of many mammals, mammalian vulnerability to climate change may be more extensive than previously anticipated.
Clone history shapes Populus drought responses
Just as animal monozygotic twins can experience different environmental conditions by being reared apart, individual genetically identical trees of the genus Populus can also be exposed to contrasting environmental conditions by being grown in different locations. As such, clonally propagated Populus trees provide an opportunity to interrogate the impact of individual environmental history on current response to environmental stimuli. To test the hypothesis that current responses to an environmental stimulus, drought, are contingent on environmental history, the transcriptome- level drought responses of three economically important hybrid genotypes—DN34 (Populus deltoides × Populus nigra), Walker [P. deltoides var. occidentalis × (Populus laurifolia × P. nigra)], and Okanese [Walker × (P. laurifolia × P. nigra)]—derived from two different locations were compared. Strikingly, differences in transcript abundance patterns in response to drought were based on differences in geographic origin of clones for two of the three genotypes. This observation was most pronounced for the genotypes with the longest time since establishment and last common propagation. Differences in genome-wide DNA methylation paralleled the transcriptome level trends, whereby the clones with the most divergent transcriptomes and clone history had the most marked differences in the extent of total DNA methylation, suggesting an epigenomic basis for the clone history-dependent transcriptome divergence. The data provide insights into the interplay between genotype and environment in the ecologically and economically important Populus genus, with implications for the industrial application of Populus trees and the evolution and persistence of these important tree species and their associated hybrids. epigenetics | forest trees | poplar
Molecular study of worldwide distribution and diversity of soil animals
The global distribution of soil animals and the relationship of below-ground biodiversity to above-ground biodiversity are not well understood. We examined 17,516 environmental 18S rRNA gene sequences representing 20 phyla of soil animals sampled from 11 locations covering a range of biomes and latitudes around the world. No globally cosmopolitan taxa were found and only 14 of 2,259 operational taxonomic units (OTUs) found were common to four or more locations. Half of those were circumpolar and may reflect higher connectivity among circumpolar locations compared with other locations in the study. Even when OTU assembly criteria were relaxed to approximate the family taxo- nomic level, only 34 OTUs were common to four or more locations. A comparison of our diversity and community structure data to environmental factors suggests that below-ground animal diver- sity may be inversely related to above-ground biodiversity. Our data suggest that greater soil inorganic N and lower pH could explain the low below-ground biodiversity found at locations of high above-ground biodiversity. Our locations could also be characterized as being dominated by microarthropods or domi- nated by nematodes. Locations dominated by arthropods were primarily forests with lower soil pH, root biomass, mean annual temperature, low soil inorganic N and higher C:N, litter and moisture compared with nematode-dominated locations, which were mostly grasslands. Overall, our data indicate that small soil animals have distinct biogeographical distributions and provide unique evidence of the link between above-ground and below- ground biodiversity at a global scale. cosmopolitan species | endemism
Housing growth in and near United States protected areas limits their conservation value
Protected areas are crucial for biodiversity conservation because they provide safe havens for species threatened by land-use change and resulting habitat loss. However, protected areas are only effective when they stop habitat loss within their boundaries, and are connected via corridors to other wild areas. The effectiveness of protected areas is threatened by development; however, the extent of this threat is unknown. We compiled spatially-detailed housing growth data from 1940 to 2030, and quantified growth for each wilderness area, national park, and national forest in the contermi- nous United States. Our findings show that housing development in the United States may severely limit the ability of protected areas to function as a modern “Noah’s Ark.” Between 1940 and 2000, 28 mil- lion housing units were built within 50 km of protected areas, and 940,000 were built within national forests. Housing growth rates during the 1990s within 1 km of protected areas (20% per decade) outpaced the national average (13%). If long-term trends continue, another 17 million housing units will be built within 50 km of pro- tected areas by 2030 (1 million within 1 km), greatly diminishing their conservation value. US protected areas are increasingly iso- lated, housing development in their surroundings is decreasing their effective size, and national forests are even threatened by habitat loss within their administrative boundaries. Protected areas in the United States are thus threatened similarly to those in developing countries. However, housing growth poses the main threat to protected areas in the United States whereas deforestation is the main threat in developing countries. conservation threats | effectiveness | parks | reserves
Flow regime, temperature, and biotic interactions drive differential declines of trout species under climate change
Broad-scale studies of climate change effects on freshwater species have focused mainly on temperature, ignoring critical drivers such as flow regime and biotic interactions. We use downscaled outputs from general circulation models coupled with a hydrologic model to forecast the effects of altered flows and increased temperatures on four interacting species of trout across the interior western United States (1.01 million km2), based on empirical statistical models built from fish surveys at 9,890 sites. Projections under the 2080s A1B emissions scenario forecast a mean 47% decline in total suitable habitat for all trout, a group of fishes of major socioeconomic and ecological significance. We project that native cutthroat trout Oncorhynchus clarkii, already excluded from much of its potential range by nonnative species, will lose a further 58% of habitat due to an increase in temper- atures beyond the species’ physiological optima and continued negative biotic interactions. Habitat for nonnative brook trout Salvelinus fontinalis and brown trout Salmo trutta is predicted to decline by 77% and 48%, respectively, driven by increases in temperature and winter flood frequency caused by warmer, rain- ier winters. Habitat for rainbow trout, Oncorhynchus mykiss, is projected to decline the least (35%) because negative temperature effects are partly offset by flow regime shifts that benefit the species. These results illustrate how drivers other than tempera- ture influence species response to climate change. Despite some uncertainty, large declines in trout habitat are likely, but our find- ings point to opportunities for strategic targeting of mitigation efforts to appropriate stressors and locations. global change | hydrology | invasive species | niche model | distribution modeling
Wilderness and biodiversity conservation
Human pressure threatens many species and ecosystems, so con- servation efforts necessarily prioritize saving them. However, conservation should clearly be proactive wherever possible. In this article, we assess the biodiversity conservation value, and specif- ically the irreplaceability in terms of species endemism, of those of the planet’s ecosystems that remain intact. We find that 24 wil- derness areas, all >1 million hectares, are >70% intact and have human densities of less than or equal to five people per km2. This wilderness covers 44% of all land but is inhabited by only 3% of people. Given this sparse population, wilderness conservation is cost-effective, especially if ecosystem service value is incorporated. Soberingly, however, most wilderness is not speciose: only 18% of plants and 10% of terrestrial vertebrates are endemic to individual wildernesses, the majority restricted to Amazonia, Congo, New Guinea, the Miombo–Mopane woodlands, and the North American deserts. Global conservation strategy must target these five wil- dernesses while continuing to prioritize threatened biodiversity hotspots.
Responses of wind erosion to climate-induced vegetation changes on the Colorado Plateau
Projected increases in aridity throughout the southwestern United States due to anthropogenic climate change will likely cause reduc- tions in perennial vegetation cover, which leaves soil surfaces exposed to erosion. Accelerated rates of dust emission from wind erosion have large implications for ecosystems and human well- being, yet there is poor understanding of the sources and magni- tude of dust emission in a hotter and drier climate. Here we use a two-stage approach to compare the susceptibility of grasslands and three different shrublands to wind erosion on the Colorado Plateau and demonstrate how climate can indirectly moderate the magnitude of aeolian sediment flux through different responses of dominant plants in these communities. First, using results from 20 y of vegetation monitoring, we found perennial grass cover in grass- lands declined with increasing mean annual temperature in the previous year, whereas shrub cover in shrublands either showed no change or declined as temperature increased, depending on the species. Second, we used these vegetation monitoring results and measurements of soil stability as inputs into a field-validated wind erosion model and found that declines in perennial vegeta- tion cover coupled with disturbance to biological soil crust resulted in an exponential increase in modeled aeolian sediment flux. Thus the effects of increased temperature on perennial plant cover and the correlation of declining plant cover with increased aeolian flux strongly suggest that sustained drought conditions across the southwest will accelerate the likelihood of dust production in the future on disturbed soil surfaces. arid ∣ horizontal flux ∣ land use ∣ national park ∣ threshold shear velocity
Point of No Return :The massive climate threats we must avoid
The world is quickly reaching a Point of No Return for preventing the worst impacts of climate change. Continuing on the current course will make it difficult, if not impossible, to prevent the widespread and catastrophic impacts of climate change. The costs will be substantial: billions spent to deal with the destruction of extreme weather events, untold human suffering, and the deaths of tens of millions from the impacts by as soon as 2030.
Global imprint of climate change on marine life
Past meta-analyses of the response of marine organisms to climate change have examined a limited range of locations1,2, taxonomic groups2–4 and/or biological responses5,6. This has precluded a robust overview of the effect of climate change in the global ocean. Here, we synthesized all available studies of the consistency of marine ecological observations with expectations under climate change. This yielded a meta- database of 1,735 marine biological responses for which either regional or global climate change was considered as a driver. Included were instances of marine taxa responding as expected, in a manner inconsistent with expectations, and taxa demonstrating no response. From this database, 81–83% of all observations for distribution, phenology, community composition, abundance, demography and calcification across taxa and ocean basins were consistent with the expected impacts of climate change. Of the species responding to climate change, rates of distribution shifts were, on average, consistent with those required to track ocean surface temperature changes. Conversely, we did not find a relationship between regional shifts in spring phenology and the seasonality of temperature. Rates of observed shifts in species’ distributions and phenology are comparable to, or greater, than those for terrestrial systems.
Biotic Drivers of Stream Planform: Implications for Understanding the Past and Restoring the Future
Traditionally, stream channel planform has been viewed as a function of larger watershed and valley-scale physical variables, including valley slope, the amount of discharge, and sediment size and load. Biotic processes serve a crucial role in transforming channel planform among straight, braided, meandering, and anabranching styles by increasing stream-bank stability and the probability of avulsions, creating stable multithread (anabranching) channels, and affecting sedimentation dynamics. We review the role of riparian vegetation and channel-spanning obstructions—beaver dams and logjams—in altering channel–floodplain dynamics in the southern Rocky Mountains, and we present channel planform scenarios for combinations of vegetation and beaver populations or old-growth forest that control logjam formation. These conceptual models provide understanding of historical planform variability throughout the Holocene and outline the implications for stream restoration or management in broad, low-gradient headwater valleys, which are important for storing sediment, carbon, and nutrients and for supporting a diverse riparian community. Keywords: stream planform, riparian vegetation, beaver, old-growth forest, restoration
The beaver meadow complex revisited – the role of beavers in post-glacial floodplain development
We evaluate the validity of the beaver-meadow complex hypothesis, used to explain the deposition of extensive fine sediment in broad, low-gradient valleys. Previous work establishes that beaver damming forms wet meadows with multi-thread channels and enhanced sediment storage, but the long-term geomorphic effects of beaver are unclear. We focus on two low-gradient broad valleys, Beaver Meadows and Moraine Park, in Rocky Mountain National Park (Colorado, USA). Both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes. We examine the geomorphic significance of beaver-pond sediment by determining the rates and types of sedimentation since the middle Holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition. Sediment analyses from cores and cutbanks indicate that 33–50% of the alluvial sediment in Beaver Meadows is ponded and 28–40% was deposited in-channel; in Moraine Park 32–41% is ponded sediment and 40–52% was deposited in-channel. Radiocar- bon ages spanning 4300 years indicate long-term aggradation rates of ~0.05 cm yr-1. The observed highly variable short-term rates indicate temporal heterogeneity in aggradation, which in turn reflects spatial heterogeneity in processes at any point in time. Channel complexity increases directly downstream of beaver dams. The increased complexity forms a positive feedback for beaver-induced sedimentation; the multi-thread channel increases potential channel length for further damming, which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped. Channel complexity decreased significantly as surveyed beaver population decreased. Beaver Meadows and Moraine Park represent settings where beaver substantially influence post-glacial floodplain aggradation. These findings underscore the importance of understanding the historical range of variability of valley bottom processes, and implications for environmental restoration. Copyright © 2011 John Wiley & Sons, Ltd. KEYWORDS: floodplain; sedimentation; beaver; Holocene
Slow Recovery from Perturbations as a Generic Indicator of a Nearby Catastrophic Shift
The size of the basin of attraction in ecosystems with alternative stable states is often referred to as “ecological resilience.” Ecosystems with a low ecological resilience may easily be tipped into an alternative basin of attraction by a stochastic event. Unfortunately, it is very difficult to measure ecological resilience in practice. Here we show that the rate of recovery from small perturbations (some- times called “engineering resilience”) is a remarkably good indicator of ecological resilience. Such recovery rates decrease as a catastrophic regime shift is approached, a phenomenon known in physics as “crit- ical slowing down.” We demonstrate the robust occurrence of critical slowing down in six ecological models and outline a possible ex- perimental approach to quantify differences in recovery rates. In all the models we analyzed, critical slowing down becomes apparent quite far from a threshold point, suggesting that it may indeed be of practical use as an early warning signal. Despite the fact that critical slowing down could also indicate other critical transitions, such as a stable system becoming oscillatory, the robustness of the phenomenon makes it a promising indicator of loss of resilience and the risk of upcoming regime shifts in a system. Keywords: alternative stable states, catastrophic bifurcations, critical slowing down, early warning signals, resilience, return time.
Rising atmospheric carbon dioxide concentration and the future of C 4 crops for food and fuel
Crops with the C4 photosynthetic pathway are vital to global food supply, particularly in the tropical regions where human well-being and agricultural productivity are most closely linked. While rising atmospheric [CO2 ] is the driving force behind the greater temperatures and water stress, which threaten to reduce future crop yields, it also has the potential to directly benefit crop physiology. The nature of C4 plant responses to elevated [CO2 ] has been controversial. Recent evidence from free-air CO2 enrichment (FACE) experiments suggests that elevated [CO2] does not directly stimulate C4 photosynthesis. Nonetheless, drought stress can be ameliorated at elevated [CO2] as a result of lower stomatal conductance and greater intercellular [CO2]. Therefore, unlike C3 crops for which there is a direct enhancement of photosynthesis by elevated [CO2 ], C4 crops will only benefit from elevated [CO2 ] in times and places of drought stress. Current projections of future crop yields have assumed that rising [CO2] will directly enhance photosynthesis in all situations and, therefore, are likely to be overly optimistic. Additional experiments are needed to evaluate the extent to which amelioration of drought stress by elevated [CO2 ] will improve C4 crop yields for food and fuel over the range of C4 crop growing conditions and genotypes.
Diverse pollinator communities enhance plant reproductive success
Understanding the functional consequences of biodiversity loss is a major goal of ecology. Animal-mediated pollination is an essential ecosystem function and service provided to mankind. However, little is known how pollinator diversity could affect pollination services. Using a substitutive design, we experimentally manipu- lated functional group (FG) and species richness of pollinator communities to investigate their consequences on the reproductive success of an obligate out-crossing model plant species, Raphanus sativus. Both fruit and seed set increased with pollinator FG richness. Furthermore, seed set increased with species richness in pol- linator communities composed of a single FG. However, in multiple-FG communities, highest species richness resulted in slightly reduced pollination services compared with intermediate species richness. Our analysis indicates that the presence of social bees, which showed roughly four times higher visitation rates than solitary bees or hoverflies, was an important factor contributing to the positive pollinator diversity–pollination service relationship, in particular, for fruit set. Visitation rate at different daytimes, and less so among flower heights, varied among social bees, solitary bees and hoverflies, indicating a niche complementarity among these pollinator groups. Our study demonstrates enhanced pollination services of diverse pollinator communities at the plant population level and suggests that both the niche complementarity and the presence of specific taxa in a pollinator community drive this positive relationship.
Genetic consequences of climate change for northern plants
Climate change will lead to loss of range for many species, and thus to loss of genetic diversity crucial for their long-term persistence. We analysed range-wide genetic diversity (amplified fragment length poly- morphisms) in 9581 samples from 1200 populations of 27 northern plant species, to assess genetic consequences of range reduction and potential association with species traits. We used species distri- bution modelling (SDM, eight techniques, two global circulation models and two emission scenarios) to predict loss of range and genetic diversity by 2080. Loss of genetic diversity varied considerably among species, and this variation could be explained by dispersal adaptation (up to 57%) and by genetic differentiation among populations (FST; up to 61%). Herbs lacking adaptations for long-distance disper- sal were estimated to lose genetic diversity at higher rate than dwarf shrubs adapted to long-distance dispersal. The expected range reduction in these 27 northern species was larger than reported for tem- perate plants, and all were predicted to lose genetic diversity according to at least one scenario. SDM combined with FST estimates and/or with species trait information thus allows the prediction of species’ vulnerability to climate change, aiding rational prioritization of conservation efforts. Keywords: conservation genetics; FST; genetic diversity; range reduction; species distribution model; species traits
How does climate change cause extinction?
Anthropogenic climate change is predicted to be a major cause of species extinctions in the next 100 years. But what will actually cause these extinctions? For example, will it be limited physiological tolerance to high temperatures, changing biotic interactions or other factors? Here, we systematically review the proximate causes of climate-change related extinctions and their empirical support. We find 136 case studies of climatic impacts that are potentially relevant to this topic. However, only seven ident- ified proximate causes of demonstrated local extinctions due to anthropogenic climate change. Among these seven studies, the proximate causes vary widely. Surprisingly, none show a straightforward relation- ship between local extinction and limited tolerances to high temperature. Instead, many studies implicate species interactions as an important proximate cause, especially decreases in food availability. We find very similar patterns in studies showing decreases in abundance associated with climate change, and in those studies showing impacts of climatic oscillations. Collectively, these results highlight our disturbingly limited knowledge of this crucial issue but also support the idea that changing species interactions are an important cause of documented population declines and extinctions related to climate change. Finally, we briefly outline general research strategies for identifying these proximate causes in future studies. Keywords: climate change; extinction; physiological tolerances; species interactions
How the type of anthropogenic change alters the consequences of ecological traps
Understanding altered ecological and evolutionary dynamics in novel environments is vital for predicting species responses to rapid environmental change. One fundamental concept relevant to such dynamics is the ecological trap, which arises from rapid anthropogenic change and can facilitate extinction. Ecological traps occur when formerly adaptive habitat preferences become maladaptive because the cues individuals preferentially use in selecting habitats lead to lower fitness than other alternatives. While it has been emphasized that traps can arise from different types of anthropogenic change, the resulting consequences of these different types of traps remain unknown. Using a novel model framework that builds upon the Price equation from evolutionary genetics, we provide the first analysis that contrasts the ecological and evolutionary consequences of ecological traps arising from two general types of perturbations known to trigger traps. Our model suggests that traps arising from degradation of existing habitats are more likely to facilitate extinction than those arising from the addition of novel trap habitat. Importantly, our framework reveals the mechanisms of these outcomes and the substantial scope for persistence via rapid evolution that may buffer many populations from extinction, helping to resolve the paradox of continued persistence of many species in dramatically altered landscapes. Keywords: attractive sink; evolutionary trap; habitat selection; maladaptation; Price equation; rapid evolution
Genetic change for earlier migration timing in a pink salmon population
To predict how climate change will influence populations, it is necessary to understand the mechanisms, particularly microevolution and phenotypic plasticity, that allow populations to persist in novel environmental conditions. Although evidence for climate-induced phenotypic change in populations is widespread, evidence documenting that these phenotypic changes are due to microevolution is exceed- ingly rare. In this study, we use 32 years of genetic data (17 complete generations) to determine whether there has been a genetic change towards earlier migration timing in a population of pink salmon that shows phenotypic change; average migration time occurs nearly two weeks earlier than it did 40 years ago. Experimental genetic data support the hypothesis that there has been directional selection for earlier migration timing, resulting in a substantial decrease in the late-migrating phenotype (from more than 30% to less than 10% of the total abundance). From 1983 to 2011, there was a significant decrease—over threefold—in the frequency of a genetic marker for late-migration timing, but there were minimal changes in allele frequencies at other neutral loci. These results demonstrate that there has been rapid microevolution for earlier migration timing in this population. Circadian rhythm genes, however, did not show any evidence for selective changes from 1993 to 2009. Keywords: microevolution; genetic change; salmon; circadian rhythms; climate change; migration timing
Disturbance−diversity models: what do they really predict and how are they tested?
The intermediate disturbance hypothesis (IDH) and the dynamic equilibrium model (DEM) are influential theories in ecology. The IDH predicts large species numbers at intermediate levels of disturbance and the DEM predicts that the effect of disturbance depends on the level of productivity. However, various indices of diversity are considered more commonly than the predicted number of species in tests of the hypotheses. This issue reaches beyond the scientific community as the predictions of the IDH and the DEM are used in the management of national parks and reserves. In order to compare responses with disturbance among measures of biodiversity, we used two different approaches of mathematical modelling and conducted an extensive meta-analysis. Two-thirds of the surveyed studies present different results for different diversity measures. Accordingly, the meta-analysis showed a narrow range of negative quadratic regression components for richness, but not evenness. Also, the two models support the IDH and the DEM, respectively, when biodiversity is measured as species richness, but predict evenness to increase with increasing disturbance, for all levels of productivity. Consequently, studies that use compound indices of diversity should present logical arguments, a priori, to why a specific index of diversity should peak in response to disturbance.
On a collision course: competition and dispersal differences create no-analogue communities and cause extinctions during climate change
Most climate change predictions omit species interactions and interspecific variation in dispersal. Here, we develop a model of multiple competing species along a warming climatic gradient that includes temperature- dependent competition, differences in niche breadth and interspecific differences in dispersal ability. Competition and dispersal differences decreased diversity and produced so-called ‘no-analogue’ commu- nities, defined as a novel combination of species that does not currently co-occur. Climate change altered community richness the most when species had narrow niches, when mean community-wide dispersal rates were low and when species differed in dispersal abilities. With high interspecific dispersal variance, the best dispersers tracked climate change, out-competed slower dispersers and caused their extinction. Overall, competition slowed the advance of colonists into newly suitable habitats, creating lags in climate tracking. We predict that climate change will most threaten communities of species that have narrow niches (e.g. tropics), vary in dispersal (most communities) and compete strongly. Current forecasts probably underestimate climate change impacts on biodiversity by neglecting competition and dispersal differences. Keywords: climate change; competition; dispersal; community ecology; movement ecology; thermal performance breadth
Life history predicts risk of species decline in a stochastic world
Understanding what traits determine the extinction risk of species has been a long-standing challenge. Natural populations increasingly experience reductions in habitat and population size concurrent with increasing novel environmental variation owing to anthropogenic disturbance and climate change. Recent studies show that a species risk of decline towards extinction is often non-random across species with differ- ent life histories. We propose that species with life histories in which all stage-specific vital rates are more evenly important to population growth rate may be less likely to decline towards extinction under these pressures. To test our prediction, we modelled declines in population growth rates under simulated stochas- tic disturbance to the vital rates of 105 species taken from the literature. Populations with more equally important vital rates, determined using elasticity analysis, declined more slowly across a gradient of increas- ing simulated environmental variation. Furthermore, higher evenness of elasticity was significantly correlated with a reduced chance of listing as Threatened on the International Union for Conservation of Nature Red List. The relative importance of life-history traits of diverse species can help us infer how natural assemblages will be affected by novel anthropogenic and climatic disturbances. Keywords: International Union for Conservation of Nature Red List; extinction; life history; stage-based; elasticity; stochasticity
Future collapse: how optimistic should we be?
1st paragraph: Prof. Kelly FRS is optimistic about the chances of avoiding a collapse, but sadly we find his arguments entirely unpersuasive. For example, have Malthus (or we) really been wrong about food security? Roughly 850 million people are seriously undernourished (lacking sufficient calories) today, and perhaps 2 billion are malnourished (lacking one or more essential nutrients) [1]. When Malthus lived, there were only about 1 billion people on the planet. We agree that there are many things that could be done to feed today’s population of 7.1 billion, or even perhaps over 9 billion in 2050. Many of them (e.g. limiting waste) have been discussed for 50 years with little sign of progress. We do not think any serious analyst doubts that, if it were equitably distributed, today’s food production could nourish everyone adequately. Equally, we know of no serious analyst who believes such distribution is likely in the future. The concern is that climate disruption combined with other problems with the agricultural system will make it impossible to feed an ever larger future population, even if equal distribution were achieved. That concern is reinforced by the recent observation that, even before the likely heavy impacts of climate disruption on agriculture appear, production is failing to keep pace with projected needs [2].
Why a collapse of global civilization will be avoided: a comment on Ehrlich & Ehrlich
1st paragraph: Ehrlich FRS & Ehrlich [1] claim that over-population, over-consumption and the future climate mean that ‘preventing a global collapse of civilization is perhaps the foremost challenge confronting humanity’. What is missing from the well- referenced perspective of the potential downsides for the future of humanity is any balancing assessment of the progress being made on these three chal- lenges (and the many others they cite by way of detail) that suggests that the problems are being dealt with in a way that will not require a major disruption to the human condition or society. Earlier dire predictions have been made in the same mode by Malthus FRS [2] on food security, Jevons FRS [3] on coal exhaustion, King FRS & Murray [4] on peak oil, and by many others. They have all been overcome by the exercise of human ingenuity just as the doom was being prophesied with the deployment of steam engines to greatly improve agricultural efficiency, and the discoveries of oil and of fracking oil and gas, respectively, for the three examples given. It is incumbent on those who would continue to predict gloom to learn from history and make a comprehen- sive review of human progress before coming to their conclusions. The problems as perceived today by Ehrlich FRS and Ehrlich will be similarly seen off by work in progress by scientists and engineers. My comment is intended to summarize and reference the potential upsides being produced by today’s human ingenuity, and I leave the reader to weigh the balance for the future, taking into account the lessons of recent history.
Anthropogenic environments exert variable selection on cranial capacity in mammals
It is thought that behaviourally flexible species will be able to cope with novel and rapidly changing environments associated with human activity. However, it is unclear whether such environments are selecting for increases in behavioural plasticity, and whether some species show more pronounced evolutionary changes in plasticity. To test whether anthropogenic environ- ments are selecting for increased behavioural plasticity within species, we measured variation in relative cranial capacity over time and space in 10 species of mammals. We predicted that urban populations would show greater cranial capacity than rural populations and that cranial capacity would increase over time in urban populations. Based on relevant theory, we also predicted that species capable of rapid population growth would show more pronounced evolutionary responses. We found that urban populations of two small mammal species had significantly greater cranial capacity than rural populations. In addition, species with higher fecundity showed more pronounced differentiation between urban and rural populations. Contrary to expectations, we found no increases in cranial capacity over time in urban populations—indeed, two species tended to have a decrease in cranial capacity over time in urban populations. Furthermore, rural populations of all insectivorous species measured showed significant increases in relative cranial capacity over time. Our results provide partial support for the hypothesis that urban environments select for increased behavioural plasticity, although this selection may be most pronounced early during the urban colonization process. Furthermore, these data also suggest that behavioural plasticity may be simultaneously favoured in rural environments, which are also changing because of human activity.
Competitive and demographic leverage points of community shifts under climate warming
Accelerating rates of climate change and a paucity of whole-community studies of climate impacts limit our ability to forecast shifts in ecosystem structure and dynamics, particularly because climate change can lead to idiosyncratic responses via both demographic effects and altered species interactions. We used a multispecies model to predict which processes and species’ responses are likely to drive shifts in the composition of a space- limited benthic marine community. Our model was parametrized from experimental manipulations of the community. Model simulations indicated shifts in species dominance patterns as temperatures increase, with projected shifts in composition primarily owing to the temperature dependence of growth, mortality and competition for three critical species. By contrast, warming impacts on two other species (rendering them weaker competitors for space) and recruitment rates of all species were of lesser importance in determining projected community changes. Our analysis reveals the impor- tance of temperature-dependent competitive interactions for predicting effects of changing climate on such communities. Furthermore, by identify- ing processes and species that could disproportionately leverage shifts in community composition, our results contribute to a mechanistic understand- ing of climate change impacts, thereby allowing more insightful predictions of future biodiversity patterns.
The impact of climate change on the structure of Pleistocene food webs across the mammoth steppe
Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleis- tocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic inter- actions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abun- dance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species inter- actions in Beringian communities before—and possibly after—the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities.
Extreme contagion in global habitat clearance
Habitat clearance remains the major cause of biodiversity loss, with consequences for ecosystem services and for people. In response to this, many global conservation schemes direct funds to regions with high rates of recent habitat destruction, though some also emphasize the conservation of remaining large tracts of intact habitat. If the pattern of habitat clearance is highly contagious, the latter approach will help prevent destructive processes gaining a foothold in areas of contiguous intact habitat. Here, we test the strength of spatial contagion in the pattern of habitat clearance. Using a global dataset of land-cover change at 50 50 km resolution, we discover that intact habitat areas in grid cells are refractory to clearance only when all neighbouring cells are also intact. The likelihood of loss increases dramatically as soon as habitat is cleared in just one neighbouring cell, and remains high thereafter. This effect is consistent for forests and grassland, across biogeographic realms and over centuries, constituting a coherent global pattern. Our results show that landscapes become vulnerable to wholesale clearance as soon as threatening processes begin to penetrate, so actions to prevent any incursions into large, intact blocks of natural habitat are key to their long-term persistence. Keywords: habitat loss; global change biology; conservation; wilderness
Adapting to flood risk under climate change
Flooding is the most common natural hazard and third most damaging globally after storms and earthquakes. Anthropogenic climate change is expected to increase flood risk through more frequent heavy precipitation, increased catchment wetness and sea level rise. This paper reviews steps being taken by actors at international, national, regional and community levels to adapt to flood risk from tidal, fluvial, surface and groundwater sources. We refer to existing inventories, national and sectoral adaptation plans, flood inqui- ries, building and planning codes, city plans, research literature and international policy reviews. We dis- tinguish between the enabling environment for adaptation and specific implementing measures to manage flood risk. Enabling includes routine monitoring, flood forecasting, data exchange, institutional reform, bridging organizations, contingency planning for disasters, insurance and legal incentives to reduce vulner- ability. All such activities are ‘low regret’ in that they yield benefits regardless of the climate scenario but are not cost-free. Implementing includes climate safety factors for new build, upgrading resistance and resilience of existing infrastructure, modifying operating rules, development control, flood forecasting, temporary and permanent retreat from hazardous areas, periodic review and adaptive management. We identify evidence of both types of adaptation following the catastrophic 2010/11 flooding in Victoria, Australia. However, signif- icant challenges remain for managing transboundary flood risk (at all scales), protecting existing property at risk from flooding, and ensuring equitable outcomes in terms of risk reduction for all. Adaptive management also raises questions about the wider preparedness of society to systematically monitor and respond to evol- ving flood risks and vulnerabilities. Keywords adaptation, climate change, flood, natural hazards, risk, Victoria, vulnerability
Importance of matrix habitats in maintaining biological diversity
Matrix management matters because formal reserve systems will never cover more than a small fraction of the globe.
Effect of habitat area and isolation on fragmented animal populations
Habitat destruction has driven many once-contiguous animal populations into remnant patches of varying size and isolation. The underlying framework for the conservation of fragmented popu- lations is founded on the principles of island biogeography, wherein the probability of species occurrence in habitat patches varies as a function of patch size and isolation. Despite decades of research, the general importance of patch area and isolation as predictors of species occupancy in fragmented terrestrial systems remains unknown because of a lack of quantitative synthesis. Here, we compile occupancy data from 1,015 bird, mammal, reptile, amphibian, and invertebrate population networks on 6 continents and show that patch area and isolation are surprisingly poor predictors of occupancy for most species. We examine factors such as improper scaling and biases in species representation as expla- nations and find that the type of land cover separating patches most strongly affects the sensitivity of species to patch area and isolation. Our results indicate that patch area and isolation are indeed important factors affecting the occupancy of many species, but properties of the intervening matrix should not be ignored. Improving matrix quality may lead to higher conservation returns than manipulating the size and configuration of remnant patches for many of the species that persist in the aftermath of habitat destruction. incidence function island biogeography logistic regression metaanalysis occupancy
The impact of climate change on mental health
Climate change will shortly be assuming centre stage when Copenhagen hosts the United Nations Climate Change Conference in early December 2009. In Copenhagen, delegates will discuss the international response to climate change (i.e. the ongoing increase in the Earth’s average surface temperature) and the meeting is widely viewed as the most important of its kind ever held (http://en.cop15.dk/). International agreement will be sought on a treaty to replace the 1997 Kyoto Protocol. At the time of writing it is not known whether agreement will be reached on the main issues of reducing greenhouse gas emissions and financing the impacts of climate change, and it appears that the impact of climate change on mental health is unlikely to be on the agenda. We discuss here how climate change could have consequences for global mental health and consider the implications for future research and policy. Key words : Climate, mental disorder, mental health, global warming.
The New Era Of Climate Risk Disclosure
In February of this year, the U.S. Securities and Exchange Commission made clear in no uncertain terms that corporations have a duty to disclose risks faced through poten- tial climate change. Yet many boards remain unaware of what constitutes a “material” climate risk, or just how broad the scope and potential impact truly are.
Effects of Urbanization and Climate Change on Stream Health
Estimation of stream health involves the analysis of changes in aquatic species, riparian vegetation, microinvertebrates, and channel degradation due to hydrologic changes occurring from anthropogenic activities. In this study, we quantified stream health changes arising from urbanization and climate change using a combination of the widely accepted Indicators of Hydrologic Alteration (IHA) and Dundee Hydrologic Regime Assessment Method (DHRAM) on a rapidly urbanized watershed in the Dallas-Fort Worth metropolitan area in Texas. Historical flow data were split into pre-alteration and post-alteration periods. The influence of climate change on stream health was analyzed by dividing the precipitation data into three groups of dry, average, and wet conditions based on recorded annual precipitation. Hydrologic indicators were evaluated for all three of the climate scenarios to estimate the stream health changes brought about by climate change. The effect of urbanization on stream health was analyzed for a specific subwatershed where urbanization occurred dramatically but no stream flow data were available using the widely used watershed-scale Soil and Water Assessment Tool (SWAT) model. The results of this study identify negative impacts to stream health with increasing urbanization and indicate that dry weather has more impact on stream health than wet weather. The IHA-DHRAM approach and SWAT model prove to be useful tools to estimate stream health at the watershed scale.
Can a collapse of global civilization be avoided?
Environmental problems have contributed to numerous collapses of civilizations in the past. ... But today, for the first time, humanity’s global civilization—the worldwide,increasingly interconnected, highly technological society in which we all are to one degree or another, embedded—is threatened with collapse by an array of environmental problems. Humankind finds itself engaged in what Prince Charles described as ‘an act of suicide on a grand scale’ [4], facing what the UK’s Chief Scientific Advisor John Beddington called a ‘perfect storm’ of environmental problems [5]. The most serious of these problems show signsof rapidly escalating severity, especially climate disruption.
Climate Change and Existing Law: A Survey of Legal Issues Past, Present, and Future
Summary: This report surveys existing law for legal issues that have arisen, or may arise in the future, on account of climate change and government responses thereto. At the threshold of many climate-change-related lawsuits are two barriers—whether the plaintiff has standing to sue and whether the claim being made presents a political question. Both barriers have forced courts to apply amorphous standards in a new and complex context. Efforts to mitigate climate change—that is, reduce greenhouse gas (GHG) emissions—have spawned a host of legal issues. The Supreme Court resolved a big one in 2007: the Clean Air Act (CAA), it said, authorizes EPA to regulate GHG emissions. EPA’s subsequent efforts to carry out that authority have been sustained by the D.C. Circuit. Another issue is whether EPA’s “endangerment finding” for GHG emissions from new motor vehicles will compel EPA to move against GHG emissions from other sources, and, if EPA does, whether the CAA authorizes cap- and-trade programs. Still other mitigation issues are (1) the role of the Endangered Species Act in addressing climate change; (2) how climate change must be considered under the National Environmental Policy Act; (3) liability and other questions raised by carbon capture and sequestration; (4) constitutional constraints on land use regulation and state actions to control GHG emissions; and (5) whether the public trust doctrine applies to the atmosphere. Liability for harms allegedly caused by climate change has raised another crop of legal issues. The Supreme Court decision that the CAA bars federal judges from imposing their own limits on GHG emissions from power plants has led observers to ask: Can plaintiffs alleging climate change harms still seek monetary damages, and are state law claims still allowed? The two rulings so far say no to the former, but split on the latter. Questions of insurance policy coverage are also likely to be litigated. Finally, the applicability of international law principles to climate change has yet to be resolved.Water shortages thought to be induced by climate change likely will lead to litigation over the nature of water rights. Shortages have already prompted several lawsuits over whether cutbacks in water delivered from federal projects effect Fifth Amendment takings or breaches of contract. Sea level rise and extreme precipitation linked to climate change raise questions as to (1) the effect of sea level rise on the beachfront owner’s property line; (2) whether public beach access easements migrate with the landward movement of beaches; (3) design and operation of federal levees; and (4) government failure to take preventive measures against climate change harms. Other adaptation responses to climate change raising legal issues, often property rights related, are beach armoring (seawalls, bulkheads, etc.), beach renourishment, and “retreat” measures. Retreat measures seek to move existing development away from areas likely to be affected by floods and sea level rise, and to discourage new development there. Natural disasters to which climate change contributes may prompt questions as to whether response actions taken in an emergency are subject to relaxed requirements and, similarly, as to the rebuilding of structures destroyed by such disasters just as they were before. Finally, immigration and refugee law appear not to cover persons forced to relocate because of climate change impacts such as drought or sea level rise.
Are There Rebound Effects from Energy Efficiency? – An Analysis of Empirical Data, Internal Consistency, and Solutions
Of the rigorously-framed hypotheses claiming that large negative rebounds exist, we measure them against the data, which refute the hypotheses. Rebounds at the end-use level are small and decrease over time. Rebounds at the economy-wide level are trivially small, and might well be a net positive. Jevons himself indicated that the ultimate solution requires a lower standard of living
Identifying refugia from climate change
This article highlights how the loose definition of the term ‘refugia’ has led to discrepancies in methods used to assess the vulnerability of species to the current trend of rising global temperatures. The term ‘refugia’ is commonly used without distinguishing between macrorefugia and microrefugia, ex situ refugia and in situ refugia, glacial and interglacial refugia or refugia based on habitat stability and refugia based on climatic stability. It is not always clear which definition is being used, and this makes it difficult to assess the appropriateness of the methods employed. For example, it is crucial to develop accurate fine-scale climate grids when identifying microrefugia, but coarse-scale macroclimate might be adequate for determining macrorefugia. Similarly, identifying in situ refugia might be more appropriate for species with poor dispersal ability but this may overestimate the extinction risk for good dispersers. More care needs to be taken to properly define the context when referring to refugia from climate change so that the validity of methods and the conservation significance of refugia can be assessed. Keywords Bioclimatic envelope models, climatic stability, conservation biogeography, cryptic refugia, ecological niche models, extinction risk, interglacial refugia, macrorefugia, microclimate, microrefugia.
Refugia: identifying and understanding safe havens for biodiversity under climate change
Identifying and protecting refugia is a priority for conservation under pro- jected anthropogenic climate change, because of their demonstrated ability to facilitate the survival of biota under adverse conditions. Refugia are habitats that components of biodiversity retreat to, persist in and can potentially expand from under changing environmental conditions. However, the study and discussion of refugia has often been ad hoc and descriptive in nature. We therefore: (1) provide a habitat-based concept of refugia, and (2) evaluate methods for the identification of refugia.
Habitat Refugia: A Practical Strategy to Conserve Biodiversity Under Climate Change
As climatic zones shift under climate change, many regions and habitats will slowly become climatically unsuit- able for some of the species that currently inhabit them. The availability of climate refugia - habitats and regions which are buffered from extremes in temperature and fluctuations in water availability, could allow some species to adapt to climate change in-situ, and facilitate dispersal and range shifts for other species. This information sheet explains the concepts behind habitat refugia with specific reference to how refugia can be used to protect and conserve terrestrial biodiversity faced with rapid climate change.
Climate Change Hot Spots Mapped Across the United States
Taking some of the fuzziness out of climate models is revealing the uneven U.S. impact of future global warming; the most severely affected region may be emerging already
Accounting for Environmental Assets
A country can cut down its forests, erode its soils, pollute its aquifers and hunt its wildlife and fisheries to extinction, but its measured income is not affected as these assets disappear. Impoverishment is taken for progress
Carbon Mitigation by Biofuels or by Saving and Restoring Forests?
The carbon sequestered by restoring forests is greater than the emissions avoided by the use of the liquid biofuels.
Large Woody Debris and Salmonid Habitat in the Anchor River Basin, Alaska
A widespread and intense spruce beetle outbreak during the 1990s has killed most of the mature white spruce (Picea glauca) trees across many watersheds in south-central Alaska. To investigate the potential habitat impacts in a salmon stream, we characterized the current abundance and species composition of large woody debris (LWD), examined the linkages between LWD and salmonid habitat, and estimated changes in LWD abundance and associated pool habitat over time. LWD abundance was relatively low (97 pieces/km overall) and varied widely according to riparian vegetation typology, ranging from 15 pieces/km at sites with non- forested riparian zones to 170 pieces/km at sites adjacent to cottonwood forest. LWD provided significant fish cover in pools, especially in cottonwood forest stream reaches. LWD-formed pools were relatively rare (15% of total), but LWD abundance explained much of the variation in pool frequency (r2 = 0.86 in spruce forest reaches) and in the proportion of pool habitats (r2 = 0.85 in cottonwood forest reaches). We project the spruce beetle outbreak to result in a substantial net increase in LWD abundance over a 50-year span, peaking with 243% and 179% increases in LWD abundance for spruce forest and cottonwood forest stream reaches, respectively, in the year 2025. Concurrent with the peak in LWD abundance, our estimates show pool frequency in spruce forest reaches to reach 207% of current levels and the proportion of pools in cottonwood forest reaches to reach 167% of current levels, changes that correspond with substantially increased potential habitat for juvenile salmonids.
Road network density correlated with increased lightning fire incidence in the Canadian western boreal forest
This paper quantifies the influence of anthropogenic linear disturbances on fire ignition frequency in the boreal forests of western Canada. Specifically, we tested if linear features increase the frequency of lightning fires, and whether this relationship is affected by spatial resolution. We considered fires that ignited between 1995 and 2002 within a ∼67 000 km2 region of boreal mixed-wood forest in north-eastern Alberta where linear features are highly abundant and spatially heterogeneous. We constructed Poisson, Negative Binomial and Zero-Inflated Poisson models at two spatial resolutions (∼10 000 and ∼2400 ha), including covariates for linear feature densities, forest composition, weather–lightning indices and geography. We found a positive association between lightning fire frequency and road density; this association was consistent at both spatial resolutions. We suggest this occurs owing to increased availability of flammable fine fuels near roads. The effect was attributable neither to increased detectability of fires proximal to roads by human observers, nor to increased lightning strikes due to metallic infrastructure alongside roads or the topographic characteristics of road location. Our results suggest that, in the face of projected road developments in the region, the potential exists for important changes to the regional fire regime. Further research should elucidate the precise mechanisms in order to develop methods for mitigation.
A holistic approach to climate targets
An assessment of allowable carbon emissions that factors in multiple climate targets finds smaller permissible emission budgets than those inferred from studies that focus on temperature change alone.
Both population size and patch quality affect local extinctions and colonizations
Currently, the habitat of many species is fragmented, resulting in small local populations with individuals occasionally dispersing between the remaining habitat patches. In a solitary bee metapopulation, extinction probability was related to both local bee population sizes and pollen resources measured as host plant population size. Patch size, on the other hand, had no additional predictive power. The turnover rate of local bee populations in 63 habitat patches over 4 years was high, with 72 extinction events and 31 colonization events, but the pollen plant population was stable with no extinctions or colonizations. Both pollen resources and bee populations had strong and independent effects on extinction probability, but connectivity was not of importance. Colonizations occurred more frequently within larger host plant populations. For metapopulation survival of the bee, large pollen plant populations are essential, independent of current bee population size.
Extreme climatic event drives range contraction of a habitat-forming species
Species distributions have shifted in response to global warming in all major ecosystems on the Earth. Despite cogent evidence for these changes, the underlying mechanisms are poorly understood and currently imply gradual shifts. Yet there is an increasing appreciation of the role of discrete events in driving ecological change. We show how a marine heat wave (HW) eliminated a prominent habitat-forming seaweed, Scytothalia dorycarpa, at its warm distribution limit, causing a range contraction of approximately 100km (approx. 5% of its global distribution). Seawater temperatures during the HW exceeded the seaweed’s physiological threshold and caused extirpation of marginal populations, which are unlikely to recover owing to life-history traits and oceanographic processes. Scytothalia dorycarpa is an important canopy-forming seaweed in temperate Australia, and loss of the species at its range edge has caused structural changes at the community level and is likely to have ecosystem-level implications. We show that extreme warming events, which are increasing in magnitude and frequency, can force step-wise changes in species distributions in marine ecosystems. As such, return times of these events have major implications for projections of species distributions and ecosystem structure, which have typically been based on gradual warming trends.
Ecosystem Disturbance, Carbon, and Climate
Models of climate change effects should incorporate land-use changes and episodic disturbances such as fires and insect epidemics.
Is Global Warming Causing More, Larger Wildfires?
Higher spring and summer temperatures and earlier snowmelt are extending the wildfire season and increasing the intensity of wildfires in the western United States.
Approaching the Limits: A book review in Science
Excerpts: "In Harvesting the Biosphere, Vaclav Smil traces the historical development of human consumption of biological resources and evaluates whether we could be approaching important global limits. Smil (an economist at the University of Manitoba) has written several books on global energy and other resource issues; here, he focuses on human consumption of the plant and animal life and whether current trends are sustainable." And "Full of recent references and statistics, Harvesting the Biosphere adds to the growing chorus of warnings about the current trajectory of human activity on a finite planet, of which climate change is only one dimension. One can quibble with some assumptions or tweak Smil’s calculations, but the bottom line will not change, only the time it may take humanity to reach a crisis point. Systems ecology teaches that the human population and consumption trajectories need a stronger feedback control than currently exists. Either we are smart enough to craft that feedback mechanism ourselves, or the Earth system will ultimately provide it."
A Measurable Planetary Boundary for the Biosphere
Terrestrial net primary (plant) production provides a measurable boundary for human consumption of Earth’s biological resources.
Southward movement of the Pacific intertropical convergence zone AD 1400–1850
Closing sentence of the abstract : We conclude that small changes in Earth’s radiation budget may profoundly affect tropical rainfall.
Population Dynamical Consequences of Climate Change for a Small Temperate Songbird
Predicting the effects of an expected climatic change requires estimates and modeling of stochastic factors as well as density-dependent effects in the population dynamics. In a population of a small songbird, the dipper (Cinclus cinclus), environmental stochasticity and density dependence both influenced the population growth rate. About half of the environmental variance was explained by variation in mean winter temperature. Including these results in a stochastic model shows that an expected change in climate will strongly affect the dynamics of the population, leading to a nonlinear increase in the carrying capacity and in the expected mean population size.
Contemporary ocean warming and freshwater conditions are related to later sea age at maturity in Atlantic salmon spawning in Norwegian rivers
Atlantic salmon populations are reported to be declining throughout its range, raising major management concerns. Variation in adult fish abundance may be due to variation in survival, growth, and timing of life history decisions. Given the complex life history, utilizing highly divergent habitats, the reasons for declines may be multiple and difficult to disentangle. Using recreational angling data of two sea age groups, one-sea-winter (1SW) and two-sea-winter (2SW) fish originated from the same smolt year class, we show that sea age at maturity of the returns has increased in 59 Norwegian rivers over the cohorts 1991– 2005. By means of linear mixed-effects models we found that the proportion of 1SW fish spawning in Norway has decreased concomitant with the increasing sea surface temperature experienced by the fish in autumn during their first year at sea. Furthermore, the decrease in the proportion of 1SW fish was influenced by freshwater conditions as measured by water discharge during summer months 1 year ahead of seaward migration. These results suggest that part of the variability in age at maturity can be explained by the large-scale changes occurring in the north-eastern Atlantic pelagic food web affecting postsmolt growth, and by differences in river conditions influencing presmolt growth rate and later upstream migration.
Species invasions and extinction: The future of native biodiversity on islands
Predation by exotic species has caused the extinction of many native animal species on islands, whereas competition from exotic plants has caused few native plant extinctions. Exotic plant addition to islands is highly nonrandom, with an almost perfect 1 to 1 match between the number of naturalized and native plant species on oceanic islands. Here, we evaluate several alternative implica- tions of these findings. Does the consistency of increase in plant richness across islands imply that a saturation point in species richness has been reached? If not, should we expect total plant richness to continue to increase as new species are added? Finally, is the rarity of native plant extinctions to date a misleading measure of the impact of past invasions, one that hides an extinction debt that will be paid in the future? By analyzing historical records, we show that the number of naturalized plant species has increased linearly over time on many individual islands. Further, the mean ratio of naturalized to native plant species across islands has changed steadily for nearly two centuries. These patterns suggest that many more species will become naturalized on islands in the future. We also discuss how dynamics of invasion bear upon alternative saturation scenarios and the implications these scenarios have for the future retention or extinction of native plant species. Finally, we identify invasion-motivated research gaps (propagule pressure, time-lags to extinction, abundance shifts, and loss of area) that can aid in forecasting extinction and in developing a more comprehensive theory of species extinctions. birds plants species saturation
Early Warnings of Regime Shifts: A Whole-Ecosystem Experiment
Catastrophic ecological regime shifts may be announced in advance by statistical early warning signals such as slowing return rates from perturbation and rising variance. The theoretical background for these indicators is rich, but real-world tests are rare, especially for whole ecosystems. We tested the hypothesis that these statistics would be early warning signals for an experimentally induced regime shift in an aquatic food web. We gradually added top predators to a lake over 3 years to destabilize its food web. An adjacent lake was monitored simultaneously as a reference ecosystem. Warning signals of a regime shift were evident in the manipulated lake during reorganization of the food web more than a year before the food web transition was complete, corroborating theory for leading indicators of ecological regime shifts. Critical slowing down
Education for a Sustainable Future
Sustainability is being integrated into higher-education institutions’ mission and planning, curricula, research, student life, and operations.
Biodiversity in a Warmer World
A new framework helps to understand how species ranges change under global warming.
Impacts of Climatic Change and Fishing on Pacific Salmon Abundance Over the Past 300 Years
The effects of climate variability on Pacific salmon abundance are uncertain because historical records are short and are complicated by commercial har- vesting and habitat alteration. We use lake sediment records of 15N and biological indicators to reconstruct sockeye salmon abundance in the Bristol Bay and Kodiak Island regions of Alaska over the past 300 years. Marked shifts in populations occurred over decades during this period, and some pronounced changes appear to be related to climatic change. Variations in salmon returns due to climate or harvesting can have strong impacts on sockeye nursery lake productivity in systems where adult salmon carcasses are important nutrient sources.
Global Change and the Ecology of Cities
Urban areas are hot spots that drive environmental change at multiple scales. Material demands of production and human consumption alter land use and cover, biodiversity, and hydrosystems locally to regionally, and urban waste discharge affects local to global biogeochemical cycles and climate. For urbanites, however, global environmental changes are swamped by dramatic changes in the local environment. Urban ecology integrates natural and social sciences to study these radically altered local environments and their regional and global effects. Cities themselves present both the problems and solutions to sustainability challenges of an increasingly urbanized world.
Complexity of Coupled Human and Natural Systems
Integrated studies of coupled human and natural systems reveal new and complex patterns and processes not evident when studied by social or natural scientists separately. Synthesis of six case studies from around the world shows that couplings between human and natural systems vary across space, time, and organizational units. They also exhibit nonlinear dynamics with thresholds, reciprocal feedback loops, time lags, resilience, heterogeneity, and surprises. Furthermore, past couplings have legacy effects on present conditions and future possibilities.
The Technology Path to Deep Greenhouse Gas Emissions Cuts by 2050: The Pivotal Role of Electricity
Several states and countries have adopted targets for deep reductions in greenhouse gas emissions by 2050, but there has been little physically realistic modeling of the energy and economic transformations required. We analyzed the infrastructure and technology path required to meet California’s goal of an 80% reduction below 1990 levels, using detailed modeling of infrastructure stocks, resource constraints, and electricity system operability. We found that technically feasible levels of energy efficiency and decarbonized energy supply alone are not sufficient; widespread electrification of transportation and other sectors is required. Decarbonized electricity would become the dominant form of energy supply, posing challenges and opportunities for economic growth and climate policy. This transformation demands technologies that are not yet commercialized, as well as coordination of investment, technology development, and infrastructure deployment.
Homo economicus Evolves
Economic models can benefit from incorporating insights from psychology, but behavior in the lab might be a poor guide to real-world behavior.
More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century
A global coupled climate model shows that there is a distinct geographic pattern to future changes in heat waves. Model results for areas of Europe and North America, associated with the severe heat waves in Chicago in 1995 and Paris in 2003, show that future heat waves in these areas will become more intense, more frequent, and longer lasting in the second half of the 21st century. Observations and the model show that present-day heat waves over Europe and North America coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases, indicating that it will produce more severe heat waves in those regions in the future.
From Death Comes Life: Recovery and Revolution in the Wake of Epidemic Outbreaks of Mountain Pine Beetle
Excerpt : “Part of the initial increase in nutrients and moisture under dead and dying trees is due to reduced uptake,” Rhoades says. “But the sick and dead trees are also losing needles that fall to the ground and help retain soil moisture. And, as trees decay, they release nutrients back into the system.”
Impacts Research Seen As Next Climate Frontier
Scientists hope the next U.S. president will devote more of the billion-dollar climate change research program to impacts SCIENCE VOL 322
Global Warming, Elevational Range Shifts, and Lowland Biotic Attrition in the Wet Tropics
Many studies suggest that global warming is driving species ranges poleward and toward higher elevations at temperate latitudes, but evidence for range shifts is scarce for the tropics, where the shallow latitudinal temperature gradient makes upslope shifts more likely than poleward shifts. Based on new data for plants and insects on an elevational transect in Costa Rica, we assess the potential for lowland biotic attrition, range-shift gaps, and mountaintop extinctions under projected warming. We conclude that tropical lowland biotas may face a level of net lowland biotic attrition without parallel at higher latitudes (where range shifts may be compensated for by species from lower latitudes) and that a high proportion of tropical species soon faces gaps between current and projected elevational ranges.
Impact of a Century of Climate Change on Small-Mammal Communities in Yosemite National Park, USA
We provide a century-scale view of small-mammal responses to global warming, without confounding effects of land-use change, by repeating Grinnell’s early–20th century survey across a 3000-meter-elevation gradient that spans Yosemite National Park, California, USA. Using occupancy modeling to control for variation in detectability, we show substantial (~500 meters on average) upward changes in elevational limits for half of 28 species monitored, consistent with the observed ~3°C increase in minimum temperatures. Formerly low-elevation species expanded their ranges and high-elevation species contracted theirs, leading to changed community composition at mid- and high elevations. Elevational replacement among congeners changed because species’ responses were idiosyncratic. Though some high-elevation species are threatened, protection of elevation gradients allows other species to respond via migration
