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Stocker B.D.,University of Bern | Roth R.,University of Bern | Joos F.,University of Bern | Spahni R.,University of Bern | And 7 more authors.
Nature Climate Change | Year: 2013

Atmospheric concentrations of the three important greenhouse gases (GHGs) CO2, CH4 and N2 O are mediated by processes in the terrestrial biosphere that are sensitive to climate and CO2. This leads to feedbacks between climate and land and has contributed to the sharp rise in atmospheric GHG concentrations since pre-industrial times. Here, we apply a process-based model to reproduce the historical atmospheric N 2 O and CH4 budgets within their uncertainties and apply future scenarios for climate, land-use change and reactive nitrogen (Nr) inputs to investigate future GHG emissions and their feedbacks with climate in a consistent and comprehensive framework. Results suggest that in a business-as-usual scenario, terrestrial N2 O and CH4 emissions increase by 80 and 45%, respectively, and the land becomes a net source of C by AD 2100. N2 O and CH4 feedbacks imply an additional warming of 0.4-0.5C by AD 2300; on top of 0.8-1.0C caused by terrestrial carbon cycle and Albedo feedbacks. The land biosphere represents an increasingly positive feedback to anthropogenic climate change and amplifies equilibrium climate sensitivity by 22-27%. Strong mitigation limits the increase of terrestrial GHG emissions and prevents the land biosphere from acting as an increasingly strong amplifier to anthropogenic climate change. © 2013 Macmillan Publishers Limited. All rights reserved.

Gallego-Sala A.V.,University of Bristol | Gallego-Sala A.V.,Lund University | Gallego-Sala A.V.,University of Exeter | Colin Prentice I.,University of Bristol | And 2 more authors.
Nature Climate Change | Year: 2013

Blanket bog is a highly distinctive biome restricted to disjunct hyperoceanic regions. It is characterized by a landscape covering of peat broken only by the steepest slopes. Plant and microbial life are adapted to anoxia, low pH and low nutrient availability. Plant productivity exceeds soil organic matter decomposition, so carbon is sequestered over time. Unique climatic requirements, including high year-round rainfall and low summer temperatures, make this biome amenable to bioclimatic modelling. However, projections of the fate of peatlands in general, and blanket bogs in particular, under climate change have been contradictory. Here we use a simple, well-founded global bioclimatic model, with climate-change projections from seven climate models, to indicate this biome's fate. We show marked shrinkage of its present bioclimatic space with only a few, restricted areas of persistence. Many blanket bog regions are thus at risk of progressive peat erosion and vegetation changes as a direct consequence of climate change. New areas suitable for blanket bog are also projected, but these are often disjunct from present areas and their location is inconsistently predicted by different climate models. © 2013 Macmillan Publishers Limited. All rights reserved.

Xu-Ri,CAS Institute of Tibetan Plateau Research | Prentice I.C.,Macquarie University | Prentice I.C.,Grantham Institute for Climate Change | Spahni R.,University of Bern | Niu H.S.,University of Chinese Academy of Sciences
New Phytologist | Year: 2012

Ecosystem nitrous oxide (N2O) emissions respond to changes in climate and CO2 concentration as well as anthropogenic nitrogen (N) enhancements. Here, we aimed to quantify the responses of natural ecosystem N2O emissions to multiple environmental drivers using a process-based global vegetation model (DyN-LPJ). We checked that modelled annual N2O emissions from nonagricultural ecosystems could reproduce field measurements worldwide, and experimentally observed responses to step changes in environmental factors. We then simulated global N2O emissions throughout the 20th century and analysed the effects of environmental changes. The model reproduced well the global pattern of N2O emissions and the observed responses of N cycle components to changes in environmental factors. Simulated 20th century global decadal-average soil emissions were c. 8.2-9.5 Tg N yr-1 (or 8.3-10.3 Tg N yr-1 with N deposition). Warming and N deposition contributed 0.85 ± 0.41 and 0.80 ± 0.14 Tg N yr-1, respectively, to an overall upward trend. Rising CO2 also contributed, in part, through a positive interaction with warming. The modelled temperature dependence of N2O emission (c. 1 Tg N yr-1 K-1) implies a positive climate feedback which, over the lifetime of N2O (114 yr), could become as important as the climate-carbon cycle feedback caused by soil CO2 release. See also the Commentary by Del Grosso and Parton. © 2012 New Phytologist Trust.

Ukkola A.M.,Macquarie University | Ukkola A.M.,CSIRO | Prentice I.C.,Macquarie University | Prentice I.C.,Grantham Institute for Climate Change
Hydrology and Earth System Sciences | Year: 2013

Climate change is expected to alter the global hydrological cycle, with inevitable consequences for freshwater availability to people and ecosystems. But the attribution of recent trends in the terrestrial water balance remains disputed. This study attempts to account statistically for both trends and interannual variability in water-balance evapotranspiration (ET), estimated from the annual observed streamflow in 109 river basins during "water years" 1961-1999 and two gridded precipitation data sets. The basins were chosen based on the availability of streamflow time-series data in the Dai et al. (2009) synthesis. They were divided into water-limited "dry" and energy-limited "wet" basins following the Budyko framework. We investigated the potential roles of precipitation, aerosol-corrected solar radiation, land use change, wind speed, air temperature, and atmospheric CO2. Both trends and variability in ET show strong control by precipitation. There is some additional control of ET trends by vegetation processes, but little evidence for control by other factors. Interannual variability in ET was overwhelmingly dominated by precipitation, which accounted on average for 54-55% of the variation in wet basins (ranging from 0 to 100%) and 94-95% in dry basins (ranging from 69 to 100%). Precipitation accounted for 45-46% of ET trends in wet basins and 80-84% in dry basins. Net atmospheric CO2 effects on transpiration, estimated using the Land-surface Processes and eXchanges (LPX) model, did not contribute to observed trends in ET because declining stomatal conductance was counteracted by slightly but significantly increasing foliage cover. © Author(s) 2013.

Mackey B.,Griffith University | Prentice I.C.,Macquarie University | Prentice I.C.,Grantham Institute for Climate Change | Steffen W.,Australian National University | And 4 more authors.
Nature Climate Change | Year: 2013

Depletion of ecosystem carbon stocks is a significant source of atmospheric CO 2 and reducing land-based emissions and maintaining land carbon stocks contributes to climate change mitigation. We summarize current understanding about human perturbation of the global carbon cycle, examine three scientific issues and consider implications for the interpretation of international climate change policy decisions, concluding that considering carbon storage on land as a means to 'offset' CO 2 emissions from burning fossil fuels (an idea with wide currency) is scientifically flawed. The capacity of terrestrial ecosystems to store carbon is finite and the current sequestration potential primarily reflects depletion due to past land use. Avoiding emissions from land carbon stocks and refilling depleted stocks reduces atmospheric CO 2 concentration, but the maximum amount of this reduction is equivalent to only a small fraction of potential fossil fuel emissions. © 2013 Macmillan Publishers Limited. All rights reserved.

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