North American terrestrial CO2 uptake largely offset by CH4 and N2O 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: Dordrecht Springer Netherlands 01.04.2015; Springer Nature B.V; Springer
• Subjects: Atmosphere; Atmospheric Sciences; Biogeochemistry; Carbon; Carbon dioxide; Climate change; Climate Change/Climate Change Impacts; Climate science; CO2; Drought; Earth and Environmental Science; Earth Sciences; Ecosystems; Emissions; ENERGY PLANNING, POLICY, AND ECONOMY; Environmental factors; Environmental policy; ENVIRONMENTAL SCIENCES; Estimates; Extreme drought; Global warming; Greenhouse effect; Greenhouse gas; Greenhouse gases; Methane; Nitrogen; Nitrous oxide; North American terrestrial ecosystems; Terrestrial ecosystems; Terrestrial environments; Multiple Environmental Factor; Global Warming Potential; North American Carbon Program; Terrestrial Ecosystem Model; Extreme Drought Event
• 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 2 though there is no consensus on the magnitude. However, the emissions of non-CO 2 greenhouse gases (CH 4 and N 2 O) may offset or even overturn the climate cooling effect induced by the CO 2 sink. Using a coupled biogeochemical model, in this study, we have estimated the combined global warming potentials (GWP) of CO 2 , CH 4 and N 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 2 , CH 4 and N 2 O fluxes was −0.50 ± 0.27 Pg CO 2 eq/year (1 Pg = 10 15  g) in North American terrestrial ecosystems during 2001–2010. The emissions of CH 4 and N 2 O from terrestrial ecosystems had offset about two thirds (73 %±14 %) of the land CO 2 sink in the North American continent, showing large differences across the three countries, with offset ratios of 57 % ± 8 % in US, 83 % ± 17 % in Canada and 329 % ± 119 % in Mexico. Climate change and elevated tropospheric ozone concentration have contributed the most to GWP increase, while elevated atmospheric CO 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.