Landscape Partnership Resources Library
Impacts of biofuel cultivation on mortality and crop yields
Ground-level ozone is a priority air pollutant, causing ∼22,000 excess deaths per year in Europe1, significant reductions in crop yields2 and loss of biodiversity3. It is produced in the troposphere through photochemical reactions involving oxides of nitrogen (NOx) and volatile organic compounds (VOCs). The biosphere is the main source of VOCs, with an estimated 1,150 TgC yr−1 (∼90% of total VOC emissions) released from vegetation globally4 . Isoprene (2-methyl-1,3-butadiene) is the most significant biogenic VOC in terms of mass (around 500 TgC yr−1 ) and chemical reactivity4 and plays an important role in the mediation of ground-level ozone concentrations5. Concerns about climate change and energy security are driving an aggressive expansion of bioenergy crop production and many of these plant species emit more isoprene than the traditional crops they are replacing. Here we quantify the increases in isoprene emission rates caused by cultivation of 72 Mha of biofuel crops in Europe. We then estimate the resultant changes in ground-level ozone concentrations and the impacts on human mortality and crop yields that these could cause. Our study highlights the need to consider more than simple carbon budgets when considering the cultivation of biofuel feedstock crops for greenhouse-gas mitigation.
Projections of declining surface-water availability for the southwestern United States
Global warming driven by rising greenhouse-gas concentrations is expected to cause wet regions of the tropics and mid to high latitudes to get wetter and subtropical dry regions to get drier and expand polewards 1–4. Over southwest North America, models project a steady drop in precipitation minus evapotranspiration, P − E, the net flux of water at the land surface5–7, leading to, for example, a decline in Colorado River flow8–11. This would cause widespread and important social and ecological consequences12–14. Here, using new simulations from the Coupled Model Intercomparison Project Five, to be assessed in Intergovernmental Panel on Climate Change As- sessment Report Five, we extend previous work by examining changes in P, E, runoff and soil moisture by season and for three different water resource regions. Focusing on the near future, 2021–2040, the new simulations project declines in surface-water availability across the southwest that translate into reduced soil moisture and runoff in California and Nevada, the Colorado River headwaters and Texas.
The challenge to keep global warming below 2 °C
The latest carbon dioxide emissions continue to track the high end of emission scenarios, making it even less likely global warming will stay below 2 °C. A shift to a 2 °C pathway requires immediate significant and sustained global mitigation, with a probable reliance on net negative emissions in the longer term.
Response of snow-dependent hydrologic extremes to continued global warming
Snow accumulation is critical for water availability in the Northern Hemisphere 1,2, raising concern that global warming could have important impacts on natural and human systems in snow-dependent regions1,3. Although regional hydrologic changes have been observed (for example, refs 1,3–5), the time of emergence of extreme changes in snow accumulation and melt remains a key unknown for assessing climate- change impacts3,6,7. We find that the CMIP5 global climate model ensemble exhibits an imminent shift towards low snow years in the Northern Hemisphere, with areas of western North America, northeastern Europe and the Greater Himalaya showing the strongest emergence during the near- term decades and at 2 ◦ C global warming. The occurrence of extremely low snow years becomes widespread by the late twenty-first century, as do the occurrences of extremely high early-season snowmelt and runoff (implying increasing flood risk), and extremely low late-season snowmelt and runoff (implying increasing water stress). Our results suggest that many snow-dependent regions of the Northern Hemisphere are likely to experience increasing stress from low snow years within the next three decades, and from extreme changes in snow-dominated water resources if global warming exceeds 2 ◦ C above the pre-industrial baseline.
Focus on poleward shifts in species’ distribution underestimates the fingerprint of climate change
Species are largely predicted to shift poleward as global temperatures increase, with this fingerprint of climate change being already observed across a range of taxonomic groups and, mostly temperate, geographic locations1–5. However, the assumption of uni-directional distribution shifts does not account for complex interactions among temperature, precipitation and species-specific tolerances 6, all of which shape the direction and magnitude of changes in a species’ climatic niche. We analysed 60 years of past climate change on the Australian continent, assessing the velocity of changes in temperature and precipitation, as well as changes in climatic niche space for 464 Australian birds. We show large magnitude and rapid rates of change in Australian climate over the past 60 years resulting in high-velocity and multi-directional, including equatorial, shifts in suitable climatic space for birds (ranging from 0.1 to 7.6kmyr−1, mean 1.27kmyr−1). Overall, if measured only in terms of poleward distribution shifts, the fingerprint of climate change is underestimated by an average of 26% in temperate regions of the continent and by an average of 95% in tropical regions. We suggest that the velocity of movement required by Australian species to track their climatic niche may be much faster than previously thought and that the interaction between temperature and precipitation changes will result in multi-directional distribution shifts globally.
Regional carbon dioxide implications of forest bioenergy production
Strategies for reducing carbon dioxide emissions include substitution of fossil fuel with bioenergy from forests1, where carbon emitted is expected to be recaptured in the growth of new biomass to achieve zero net emissions 2, and forest thinning to reduce wildfire emissions 3. Here, we use forest inventory data to show that fire prevention measures and large-scale bioenergy harvest in US West Coast forests lead to 2–14% (46–405 Tg C) higher emissions compared with current management practices over the next 20 years. We studied 80 forest types in 19 ecoregions, and found that the current carbon sink in 16 of these ecoregions is sufficiently strong that it cannot be matched or exceeded through substitution of fossil fuels by forest bioenergy. If the sink in these ecoregions weakens below its current level by 30–60 g C m−2 yr−1 owing to insect infestations, increased fire emissions or reduced primary production, management schemes including bioenergy production may succeed in jointly reducing fire risk and carbon emissions. In the remaining three ecoregions, immediate implementation of fire prevention and biofuel policies may yield net emission savings. Hence, forest policy should consider current forest carbon balance, local forest conditions and ecosystem sustainability in establishing how to decrease emissions.
Shrinking body size as an ecological response to climate change
Determining how climate change will affect global ecology and ecosystem services is one of the next important frontiers in environmental science. Many species already exhibit smaller sizes as a result of climate change and many others are likely to shrink in response to continued climate change, following fundamental ecological and metabolic rules. This could negatively impact both crop plants and protein sources such as fish that are important for human nutrition. Furthermore, heterogeneity in response is likely to upset ecosystem balances. We discuss future research directions to better understand the trend and help ameliorate the trophic cascades and loss of biodiversity that will probably result from continued decreases in organism size.
The temperature response of soil microbial efficiency and its feedback to climate
Soils are the largest repository of organic carbon (C) in the terrestrial biosphere and represent an important source of carbon dioxide (CO2)totheatmosphere,releasing60–75PgC an- nually through microbial decomposition of organic materials1,2. A primary control on soil CO2 flux is the efficiency with which the microbial community uses C. Despite its critical importance to soil–atmosphere CO2 exchange, relatively few studies have examined the factors controlling soil microbial efficiency. Here, we measured the temperature response of microbial efficiency in soils amended with substrates varying in lability. We also examined the temperature sensitivity of microbial efficiency in response to chronic soil warming in situ. We find that the efficiency with which soil microorganisms use organic matter is dependent on both temperature and substrate quality, with efficiency declining with increasing temperatures for more recalcitrant substrates. However, the utilization efficiency of a more recalcitrant substrate increased at higher temperatures in soils exposed to almost two decades of warming 5 ◦ C above ambient. Our work suggests that climate warming could alter the decay dynamics of more stable organic matter compounds, thereby having a positive feedback to climate that is attenuated by a shift towards a more efficient microbial community in the longer term.
Global diversity of drought tolerance and grassland climate-change resilience
Drought reduces plant productivity, induces widespread plant mortality and limits the geographic distribution of plant species1–7. As climates warm and precipitation patterns shift in the future8,9, understanding the distribution of the diversity of plant drought tolerance is central to predicting future ecosystem function and resilience to climate change10–12 . These questions are especially pressing for the world’s 11,000 grass species13, which dominate a large fraction of the terrestrial biosphere14, yet are poorly characterized with respect to re- sponses to drought. Here, we show that physiological drought tolerance, which varied tenfold among 426 grass species, is well distributed both climatically and phylogenetically, sug- gesting most native grasslands are likely to contain a high diversity of drought tolerance. Consequently, local species may help maintain ecosystem functioning in response to changing drought regimes without requiring long-distance migrations of grass species. Furthermore, physiologically drought-tolerant species had higher rates of water and carbon dioxide exchange than intolerant species, indicating that severe droughts may generate legacies for ecosystem functioning. In all, our findings suggest that diverse grasslands throughout the globe have the potential to be resilient to drought in the face of climate change through the local expansion of drought-tolerant species.
Increased soil emissions of potent greenhouse gases under increased atmospheric CO2
Increasing concentrations of atmospheric carbon dioxide (CO2) can affect biotic and abiotic conditions in soil, such as microbial activity and water content 1,2. In turn, these changes might be expected to alter the production and consumption of the important greenhouse gases nitrous oxide (N2O) and methane (CH4) (refs 2, 3). However, studies on fluxes of N2O and CH4 from soil under increased atmo- spheric CO2 have not been quantitatively synthesized. Here we show, using meta-analysis, that increased CO2 (ranging from 463 to 780 parts per million by volume) stimulates both N2O emissions from upland soils and CH4 emissions from rice paddies and natural wetlands. Because enhanced greenhouse-gas emissions add to the radiative forcing of terrestrial ecosystems, these emissions are expected to negate at least 16.6 per cent of the climate change mitigation potential previously predicted from an increase in the terrest- rial carbon sink under increased atmospheric CO2 concentrations4. Our results therefore suggest that the capacity of land ecosystems to slow climate warming has been overestimated.
Shifts in Season
Is the rising heat forcing change on the seasons? To find out, observed data may be superior to model projections.
Natural and anthropogenic variations in methane sources during the past two millennia
Methane is an important greenhouse gas that is emitted from multiple natural and anthropogenic sources. Atmospheric methane concentrations have varied on a number of timescales in the past, but what has caused these variations is not always well understood1–8. The different sources and sinks of methane have specific isotopic signatures, and the isotopic composition of methane can therefore help to identify the environmental drivers of variations in atmo- spheric methane concentrations9. Here we present high-resolution carbon isotope data (d13C content) for methane from two ice cores from Greenland for the past two millennia. We find that the d13C content underwent pronounced centennial-scale variations between 100 BC and AD 1600. With the help of two-box model calculations, we show that the centennial-scale variations in isotope ratios can be attributed to changes in pyrogenic and biogenic sources. We find correlations between these source changes and both natural climate variability—such as the Medieval Climate Anomaly and the Little Ice Age—and changes in human population and land use, such as the decline of the Roman empire and the Han dynasty, and the population expansion during the medieval period.
Has the Earth’s sixth mass extinction already arrived?
Palaeontologists characterize mass extinctions as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540 million years or so. Biologists now suggest that a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia. Here we review how differences between fossil and modern data and the addition of recently available palaeontological information influence our understanding of the current extinction crisis. Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.
The rebound effect is overplayed
Increasing energy efficiency brings emissions savings. Claims that it backfires are a distraction, say Kenneth Gillingham and colleagues.
The Next Dust Bowl
Drought is the most pressing problem caused by climate change. It receives too little attention, says Joseph Romm.
Observed increase in local cooling effect of deforestation at higher latitudes
Deforestation in mid- to high latitudes is hypothesized to have the potential to cool the Earth’s surface by altering biophysical processes1–3. In climate models of continental-scale land clearing, the cooling is triggered by increases in surface albedo and is reinforced by a land albedo–sea ice feedback 4,5. This feedback is crucial in the model predictions; without it other biophysical processes may overwhelm the albedo effect to generate warming instead5. Ongoing land-use activities, such as land management for climate mitigation, are occurring at local scales (hectares) presumably too small to generate the feedback, and it is not known whether the intrinsic biophysical mechanism on its own can change the surface temperature in a consistent manner6,7. Nor has the effect of deforestation on climate been demonstrated over large areas from direct observations. Here we show that surface air temper- ature is lower in open land than in nearby forested land. The effect is 0.85 6 0.44 K (mean 6 one standard deviation) northwards of 456N and 0.2160.53K southwards. Below 356N there is weak evidence that deforestation leads to warming. Results are based on comparisons of temperature at forested eddy covariance towers in the USA and Canada and, as a proxy for small areas of cleared land, nearby surface weather stations. Night-time temperature changes unrelated to changes in surface albedo are an important contributor to the overall cooling effect. The observed latitudinal dependence is consistent with theoretical expectation of changes in energy loss from convection and radiation across latitudes in both the daytime and night-time phase of the diurnal cycle, the latter of which remains uncertain in climate models8.
Genealogy of nature conservation: a political perspective
Modern nature conservation is a product of post-Enlightenment modernity; I explore the heterogeneity of its conceptual and ideological background. The 19th century legacy comprises concern over human-caused extinctions; protests against excessive hunting and cruelty toward animals; utilitarian care for natural resources; and romantic sensibility concerning the value of nature for human health and spirituality. The 20th century added into conservation thinking increasing consciousness about human biospheric dependence; efforts to identify appropriate conservation targets; and most recently concern over the loss of biodiversity. The politics of nature conservation has taken shape within the framework of politics of nature, that is, choices vis-á-vis nature that have been made either as deliberate decisions on resource use or as side-effects of subsistence practices of various types. Because of tensions and conflicts with alternative ways of using nature, formulating realistic conservation policies has been a complicated task. Problems and uncertainties emerge: pursuing material aspirations of the current world society will necessarily bring about damage to ecological systems of the Earth. The way forward is to identify feasible alternatives in the midst of the tensions and ambiguities that arise, and to open up space for carrying through conservation initiatives. Keywords conservation thought, conservation policy, conservation governance, utilitarian conservation, romanticism, genealogy, framing, normativity, normative order, action space
Forests fuel fish growth in freshwater deltas
Aquatic ecosystems are fuelled by biogeochemical inputs from surrounding lands and within- lake primary production. Disturbances that change these inputs may affect how aquatic ecosystems function and deliver services vital to humans. Here we test, using a forest cover gradient across eight separate catchments, whether disturbances that remove terrestrial biomass lower organic matter inputs into freshwater lakes, thereby reducing food web productivity. We focus on deltas formed at the stream-lake interface where terrestrial-derived particulate material is deposited. We find that organic matter export increases from more forested catchments, enhancing bacterial biomass. This transfers energy upwards through communities of heavier zooplankton, leading to a fourfold increase in weights of plankti- vorous young-of-the-year fish. At least 34% of fish biomass is supported by terrestrial primary production, increasing to 66% with greater forest cover. Habitat tracers confirm fish were closely associated with individual catchments, demonstrating that watershed protection and restoration increase biomass in critical life-stages of fish.
Terrestrial water fluxes dominated by transpiration
Renewable fresh water over continents has input from precipitation and losses to the atmosphere through evaporation and transpiration. Global-scale estimates of transpiration from climate models are poorly constrained owing to large uncertainties in stomatal conductance and the lack of catchment-scale measurements required for model calibration, resulting in a range of predictions spanning 20 to 65 per cent of total terrestrial evapotranspiration (14,000 to 41,000 km3 per year) (refs 1–5). Here we use the distinct isotope effects of transpiration and evaporation to show that transpiration is by far the largest water flux from Earth’s continents, representing 80 to 90 per cent of terrestrial evapotranspiration. On the basis of our analysis of a global data set of large lakes and rivers, we conclude that transpiration recycles 62,000 6 8,000 km3 of water per year to the atmosphere, using half of all solar energy absorbed by land surfaces in the process. We also calculate CO2 uptake by terrestrial vegetation by connecting transpiration losses to carbon assimilation using water-use efficiency ratios of plants, and show the global gross primary productivity to be 129 6 32 giga- tonnes of carbon per year, which agrees, within the uncertainty, with previous estimates6. The dominance of transpiration water fluxes in continental evapotranspiration suggests that, from the point of view of water resource forecasting, climate model development should prioritize improvements in simulations of biological fluxes rather than physical (evaporation) fluxes.
Probabilistic cost estimates for climate change mitigation
For more than a decade, the target of keeping global warming below 2 6C has been a key focus of the international climate debate1. In response, the scientific community has published a number of scenario studies that estimate the costs of achieving such a target 2–5. Producing these estimates remains a challenge, particularly because of relatively well known, but poorly quantified, uncertainties, and owing to limited integration of scientific knowledge across disciplines6. The integrated assessment community, on the one hand, has extensively assessed the influence of technological and socio-economic uncertainties on low-carbon scenarios and asso- ciated costs2–4,7. The climate modelling community, on the other hand, has spent years improving its understanding of the geo- physical response of the Earth system to emissions of greenhouse gases8–12. This geophysical response remains a key uncertainty in the cost of mitigation scenarios but has been integrated with assess- ments of other uncertainties in only a rudimentary manner, that is, for equilibrium conditions6,13. Here we bridge this gap between the two research communities by generating distributions of the costs associated with limiting transient global temperature increase to below specific values, taking into account uncertainties in four factors: geophysical, technological, social and political. We find that political choices that delay mitigation have the largest effect on the cost–risk distribution, followed by geophysical uncertainties, social factors influencing future energy demand and, lastly, technological uncertainties surrounding the availability of greenhouse gas miti- gation options. Our information on temperature risk and mitigation costs provides crucial information for policy-making, because it clarifies the relative importance of mitigation costs, energy demand and the timing of global action in reducing the risk of exceeding a global temperature increase of 2 6C, or other limits such as 3 6C or 1.5 6C, across a wide range of scenarios.
