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

Abstract

The attribution of spatial and temporal variations in terrestrial methane (CH₄) flux is essential for assessing and mitigating CH₄ emission from terrestrial ecosystems. In this study, we used a process-based model, the Dynamic Land Ecosystem Model (DLEM), in conjunction with spatial data of six major environmental factors to attribute the spatial and temporal variations in the terrestrial methane (CH₄) flux over North America from 1979 to 2008 to six individual driving factors and their interaction. Over the past three decades, our simulations indicate that global change factors 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 fertilizer application, and land conversion enhanced terrestrial CH₄ emissions by 19.80 ± 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 these global 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; climate variability significantly enhanced, while all the other factors exerted minor effects, positive or negative, on CH₄ emission in Canada; Mexico functioned as a sink for atmospheric CH₄ with a major contribution from climate change. Climatic variability dominated the inter-annual variations in terrestrial CH₄ flux at both continental and country levels. Precipitation played an important role in the climate-induced changes in terrestrial CH₄ flux at both continental and country-levels. The relative importance of each environmental factor in determining the magnitude of CH₄ flux showed substantially spatial variation across North America. This factorial attribution of CH₄ flux in North America might benefit policy makers who would like to curb climate warming by reducing CH₄ emission.