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Title: Contemporary and projected biogenic fluxes of methane and nitrous oxide in North American terrestrial ecosystems

item TIAN, HANQIN - Auburn University
item LU, CHAOQUN - Auburn University
item CHEN, GUANGSHENG - Auburn University
item TAO, BO - Auburn University
item PAN, SHUFEN - Auburn University
item DELGROSSO, STEPHEN - Natural Resources Conservation Service (NRCS, USDA)
item XU, XIAOFENG - Oak Ridge National Laboratory
item BRUHWILER, LORI - National Oceanic & Atmospheric Administration (NOAA)
item WOFSKY, STEVEN - Harvard University
item KORT, ERIC - National Aeronautics And Space Administration (NASA)
item Prior, Stephen - Steve

Submitted to: Frontiers in Ecology and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2012
Publication Date: 12/3/2012
Citation: Tian, H., Lu, C., Chen, G., Tao, B., Pan, S., Del Grosso, S.J., Xu, X., Bruhwiler, L., Wofsky, S.C., Kort, E.A., Prior, S.A. 2012. Contemporary and projected biogenic fluxes of methane and nitrous oxide in North American terrestrial ecosystems. Frontiers in Ecology and the Environment. 10(10):528-536.

Interpretive Summary: To date, much attention has given to contemporary and future patterns of estimating terrestrial CH4 and N2O budgets. We used a coupled biogeochemical model to generate continental-scale terrestrial CH4 and N2O budget estimates. Simulations showed that CH4 emission totaled 15.5 Tg C/yr for North America during the 2000s, with the US and Canada contributing about the same while Mexico acted as a small CH4 sink. The N2O emission is estimated to be 1.79 Tg N/yr with most coming from the US. Using two climate scenarios, our model suggest that CH4 and N2O emissions will increase but level off after the 2060s under one scenario, while the other scenario projects more efflux of these two GHGs, possibly due to a more rapid warming trend. Areas with higher contemporary CH4 and N2O emission rates would continue to be hotspots through the end the century. Estimate discrepancies may be due to uncertainties in method, mechanisms, or scaling process. To obtain converging estimates from multiple approaches, we need better knowledge of critical biogeochemical processes, and classification and distribution of key vegetative covers.

Technical Abstract: The importance of methane (CH4) and nitrous oxide (N2O) in determining global climate change has been increasingly recognized, but terrestrial CH4 and N2O budgets and the underlying mechanisms remain far from certain. Accurate estimation of terrestrial CH4 and N2O budgets would be a critical step for closing global budgets of these gases and further mitigating climate warming. In this study, we provide an overview of various estimations on contemporary net exchanges of CH4 and N2O between the atmosphere and land ecosystems in North America. Then a coupled biogeochemical model has been used to predict the likely patterns of terrestrial CH4 and N2O fluxes under two distinct future climate change scenarios across North America during 2011-2099. Our analysis indicates that during the 2000s, terrestrial CH4 emission from entire North America totaled 15.54 ± 2.12 Tg C/yr, with the US and Canada contributing approximately the same and Mexico acting as a small CH4 sink. The continental N2O emission is estimated to be 1.79 ± 0.20 Tg N/yr, most of which came from the US. Driven by two future climate scenarios (i.e., A2 and B1), model projections indicate that both CH4 and N2O emission would significantly increase, reaching up to 137%-151% and 157%-227% of the 2000s’ level, respectively, by the end of this century. Large uncertainties in characterizing environmental changes, vegetation properties and key biogeochemical processes can bias estimates. Future research needs to identify the uncertainty sources and diminish discrepancies among estimations based on contrasting approaches.