Attribution of spatial and temporal variations in terrestrial methane flux over North America

[摘要] The attribution of spatial and temporal variations in terrestrial methane(CH₄) flux is essential for assessing and mitigating CH₄ emissionfrom terrestrial ecosystems. In this study, we used a process-based model,the Dynamic Land Ecosystem Model (DLEM), in conjunction with spatial data ofsix major environmental factors to attribute the spatial and temporalvariations in the terrestrial methane (CH₄) flux over North Americafrom 1979 to 2008 to six individual driving factors and their interaction.Over the past three decades, our simulations indicate that global changefactors accumulatively contributed 23.51 ± 9.61 T g CH₄-C(1 Tg = 10¹² g) emission over North America, among which ozone (O₃)pollution led to a reduced CH₄ emission by 2.30 ± 0.49 T g CH₄-C.All other factors including climate variability, nitrogen (N)deposition, elevated atmospheric carbon dioxide (CO₂), N fertilizerapplication, and land conversion enhanced terrestrial CH₄ emissions by19.80 ± 12.42 T g CH₄-C, 0.09 ± 0.02 T g CH₄-C, 6.80 ± 0.86 T g CH₄-C,0.01 ± 0.001 T g CH₄-C, and 3.95 ± 0.38 T g CH₄-C,respectively, and interaction between/among theseglobal change factors led to a decline of CH₄ emission by 4.84 ± 7.74 T g CH₄-C.Climate variability and O₃ pollution suppressed,while other factors stimulated CH₄ emission over the USA; climatevariability significantly enhanced, while all the other factors exertedminor effects, positive or negative, on CH₄ emission in Canada; Mexicofunctioned as a sink for atmospheric CH₄ with a major contribution fromclimate change. Climatic variability dominated the inter-annual variationsin terrestrial CH₄ flux at both continental and country levels.Precipitation played an important role in the climate-induced changes interrestrial CH₄ flux at both continental and country-levels. Therelative importance of each environmental factor in determining themagnitude of CH₄ flux showed substantially spatial variation acrossNorth America. This factorial attribution of CH₄ flux in North Americamight benefit policy makers who would like to curb climate warming byreducing CH₄ emission.

[学科分类] 地球化学与岩石