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Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model
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The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate1. About half of the current emissions are being absorbed by the ocean and by land ecosystems2, but this absorption is sensitive to climate3,4 as well as to atmospheric carbon dioxide concentrations5, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change6. Here we present results from a fully coupled, three-dimensional carbon±climate model, indicating that carbon-cycle feedbacks could signi®cantly accelerate climate change over the twenty-®rst century. We ®nd that under a `business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr-1 is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models2, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.
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CO2 emissions from forest loss
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Deforestation is the second largest anthropogenic source of carbon dioxide to the atmosphere, after fossil fuel combustion. Following a budget reanalysis, the contribution from deforestation is revised downwards, but tropical peatlands emerge as a notable carbon dioxide source.
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Biodiversity and ecosystem multifunctionality
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Biodiversity loss can affect ecosystem functions and services1–4. Individual ecosystem functions generally show a positive asymptotic relationship with increasing biodiversity, suggesting that some species are redundant5–8. However, ecosystems are managed and conserved for multiple functions, which may require greater biodiversity. Here we present an analysis of published data from grassland biodiversity experiments9–11, and show that ecosystem multifunctionality does require greater numbers of species. We analysed each ecosystem function alone to identify species with desirable effects. We then calculated the number of species with positive effects for all possible combinations of functions. Our results show appreciable differences in the sets of species influ- encing different ecosystem functions, with average proportional overlap of about 0.2 to 0.5. Consequently, as more ecosystem pro- cesses were included in our analysis, more species were found to affect overall functioning. Specifically, for all of the analysed experiments, there was a positive saturating relationship between the number of ecosystem processes considered and the number of species influencing overall functioning. We conclude that because different species often influence different functions, studies focus- ing on individual processes in isolation will underestimate levels of biodiversity required to maintain multifunctional ecosystems.
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Attributing physical and biological impacts to anthropogenic climate change
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Significant changes in physical and biological systems are occurring on all continents and in most oceans, with a concentration of available data in Europe and North America. Most of these changes are in the direction expected with warming temperature. Here we show that these changes in natural systems since at least 1970 are occurring in regions of observed temperature increases, and that these temperature increases at continental scales cannot be explained by natural climate variations alone. Given the conclusions from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report that most of the observed increase in global average temperatures since the mid-twentieth century is very likely to be due to the observed increase in anthropogenic greenhouse gas concentrations, and furthermore that it is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica, we conclude that anthropogenic climate change is having a significant impact on physical and biological systems globally and in some continents.
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USGS Geosciences and Environmental Change Science Center
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Geosciences and Environmental Change Science Center (GECSC) researchers conduct multi-purpose geologic mapping and topical scientific studies to address issues concerning geologic, climatic, ecosystem, and land surface changes; human interactions with the environment; and physical, chemical, and biological characterization of the Earth's surface and upper crust.
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U.S. Global Change Research Program
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The U.S. Global Change Research Program (USGCRP) is a federal program mandated by Congress to coordinate federal research and investments in understanding the forces shaping the global environment, both human and natural, and their impacts on society. USGCRP facilitates collaboration and cooperation across its 13 federal member agencies to advance understanding of the changing Earth system and maximize efficiencies in federal global change research.
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Southeast Climate Adaptation Science Center-Science Seminar – Southeast Regional Invasive Species and Climate Change
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Join us for our Fall/Winter virtual science seminar series highlighting SE CASC funded projects supporting resource management actions across the Southeast. Each month a SE CASC researcher will provide an overview of their work and the management implications of their research findings.
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Carbon in idle croplands
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The collapse of the Soviet Union had diverse consequences, not least the abandonment of crop cultivation in many areas. One result has been the vast accumulation of soil organic carbon in the areas affected.
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Carbon respiration from subsurface peat accelerated by climate warming in the subarctic
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Among the largest uncertainties in current projections of future climate is the feedback between the terrestrial carbon cycle and climate1. Northern peatlands contain one-third of the world’s soil organic carbon, equivalent to more than half the amount of carbon in the atmosphere2. Climate-warming-induced acceleration of carbon dioxide (CO2) emissions through enhanced respiration of thick peat deposits, centuries to millennia old, may form a strong positive carbon cycle–climate feedback. The long-term temperature sensitivity of carbon in peatlands, especially at depth, remains uncertain, however, because of the short duration or correlative nature of field studies3–5 and the disturbance associated with respiration measurements below the surface in situ or during laboratory incubations6,7. Here we combine non-disturbing in situ measurements of CO2 respiration rates and isotopic (13C) composition of respired CO2 in two whole-ecosystem climate- manipulation experiments in a subarctic peatland. We show that approximately 1 6C warming accelerated total ecosystem respira- tion rates on average by 60% in spring and by 52% in summer and that this effect was sustained for at least eight years. While warm- ing stimulated both short-term (plant-related) and longer-term (peat soil-related) carbon respiration processes, we find that at least 69% of the increase in respiration rate originated from carbon in peat towards the bottom (25–50 cm) of the active layer above the permafrost. Climate warming therefore accelerates respiration of the extensive, subsurface carbon reservoirs in peat- lands to a much larger extent than was previously thought6,7. Assuming that our data from a single site are indicative of the direct response to warming of northern peatland soils on a global scale, we estimate that climate warming of about 1 6C over the next few decades could induce a global increase in heterotrophic respiration of 38–100 megatonnes of C per year. Our findings suggest a large, long-lasting, positive feedback of carbon stored in northern peatlands to the global climate system.
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Call for a climate culture shift
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A new book describes the rapid reshaping of human priorities needed to save the planet from global warming. Some of that change is already under way at the community level, explains Robert Costanza.
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