Methane (CH4) is a potent greenhouse gas which contributes in second place to anthropogenic climatic warming and influences atmospheric chemistry, but is still short of investigation, especially in its terrestrial source in response to changing global environment. Using a process-based model (Dynamic Land Ecosystem Model), driven by multiple global change factors including climate variability, nitrogen deposition, rising atmospheric CO2, ozone pollution, nitrogen fertilization, and land use conversion, the spatial and temporal variations in the terrestrial ecosystem CH4 flux over North America were attributed to various global change factors.
Results/Conclusions
From 1979 to 2008, the North America accumulatively emitted 440.75 T g CH4-C (1Tg = 1012 g), of which the global change factors contributed 43.05 T g CH4-C and baseline emission contributed 397.7 T g CH4-C. Ozone pollution led to a reduction of CH4 emission by 2.69 T g CH4-C; climate variability, nitrogen deposition, rising atmospheric CO2, nitrogen fertilization, and land conversion increased ecosystem CH4 emission from North America by 40.37 T g CH4-C, 0.42 T g CH4-C, 6.95 T g CH4-C, 0.11 T g CH4-C, and 3.70 T g CH4-C, respectively. The interaction between/among these global change factors led to a decline of CH4 emission by 5.80 T g CH4-C over the 30-year time period. At the country-level, climate variability and ozone pollution suppressed CH4 emission, and other factors increased CH4 emission over the United States of America; climate variability significantly enhanced CH4 emission, while all the other factors exerted minor, positive or negative, effects on CH4 flux over the Canada; Mexico acted as a sink for atmospheric CH4 with major contribution from climate change. Climatic variability dominated the inter-annual variations in terrestrial CH4 flux over North America at both continental and country levels; interactive effects among global change factors also help explaining the inter-annual variations in terrestrial CH4 flux over the United States of America.