Assessing Uncertainties of Current and Future Methane Emissions
Methane is an important greenhouse gas. About half of annual methane emissions to the atmosphere result from terrestrial ecosystem sources that are poorly understood and represented in climate models. To characterize uncertainties, study feedbacks between methane fluxes and climate, and guide future model development and experimentation, DOE-funded researchers developed and tested a new methane biogeochemistry model (CLM4Me) integrated in the land component (Community Land Model; CLM4) of the Community Earth System Model. They compared the seasonality and magnitude of predicted CH4 emissions to observations from 18 sites and three global atmospheric inversions. They also used the model to characterize the sensitivity of regional and global methane emission estimates to uncertainties in model parameterizations. Several parameters critical to realistic prediction of future methane emissions dominated the uncertainty (with up to a factor of four in potential range of methane emissions). Most sensitive parameters include the temperature sensitivity of methane production and the treatment of methane chemistry. In a 21st century scenario, they found that predicted declines in high-latitude inundation may limit increases in high-latitude methane emissions. Finally, to address the high level of remaining uncertainty, the study describes observations and experiments that could improve regional and global methane biogeochemical models and therefore future predictions.
Riley, W. J., Z. M. Subin, D. M. Lawrence, S. C. Swenson, M. S. Torn, L. Meng, N. M. Mahowald, and P. Hess. 2011. “Barriers To Predicting Changes in Global Terrestrial Methane Fluxes: Analyses Using CLM4Me, a Methane Biogeochemistry Model Integrated in CESM,” Biogeosciences 8, 1925-53. (DOI:10.5194/bg-8-1925-2011)