North American terrestrial CO sub(2) uptake largely offset by CH sub(4) and N sub(2)O emissions: toward a full accounting of the greenhouse gas budget

• Published in: Climatic change Vol. 129; no. 3-4; pp. 413 - 426
• Main Authors: Tian, Hanqin, Chen, Guangsheng, Lu, Chaoqun, Xu, Xiaofeng, Hayes, Daniel J, Ren, Wei, Pan, Shufen, Huntzinger, Deborah N, Wofsy, Steven C
• Format: Journal Article
• Language: English
• Published: 01.04.2015
• Subjects: Air pollution; Carbon capture and storage; Carbon dioxide; Ecosystems; Estimates; Global warming; Greenhouse effect; Nitrous oxides; Offsets; Canada; ANW, Canada; Mexico
• ISSN: 0165-0009; 1573-1480
• DOI: 10.1007/s10584-014-1072-9

The terrestrial ecosystems of North America have been identified as a sink of atmospheric CO sub(2) though there is no consensus on the magnitude. However, the emissions of non-CO sub(2) greenhouse gases (CH sub(4) and N sub(2)O) may offset or even overturn the climate cooling effect induced by the CO sub(2) sink. Using a coupled biogeochemical model, in this study, we have estimated the combined global warming potentials (GWP) of CO sub(2), CH sub(4) and N sub(2)O fluxes in North American terrestrial ecosystems and quantified the relative contributions of environmental factors to the GWP changes during 1979-2010. The uncertainty range for contemporary global warming potential has been quantified by synthesizing the existing estimates from inventory, forward modeling, and inverse modeling approaches. Our "best estimate" of net GWP for CO sub(2), CH sub(4) and N sub(2)O fluxes was -0.50 plus or minus 0.27 Pg CO sub(2) eq/year (1 Pg=10 super(15) g) in North American terrestrial ecosystems during 2001-2010. The emissions of CH sub(4) and N sub(2)O from terrestrial ecosystems had offset about two thirds (73 % plus or minus 14 %) of the land CO sub(2) sink in the North American continent, showing large differences across the three countries, with offset ratios of 57 % plus or minus 8 % in US, 83 % plus or minus 17 % in Canada and 329 % plus or minus 119 % in Mexico. Climate change and elevated tropospheric ozone concentration have contributed the most to GWP increase, while elevated atmospheric CO sub(2) concentration have contributed the most to GWP reduction. Extreme drought events over certain periods could result in a positive GWP. By integrating the existing estimates, we have found a wide range of uncertainty for the combined GWP. From both climate change science and policy perspectives, it is necessary to integrate ground and satellite observations with models for a more accurate accounting of these three greenhouse gases in North America.