Satellite observations constrain ratio of tropical and high-latitude wetland methane emissions and their climate sensitivity

Abstract:

Wetland methane (CH₄) emissions comprise about one third of the global CH₄ budget, however the magnitude of the emissions and their sensitivity to climate variability remain uncertain. Here we used new satellite-based, inverse estimates of CH₄ fluxes over a 3-year span (2010-2012) to test a range of bottom-up wetland models that use different wetland maps and process controls. Our comparison explicitly accounted for cross-correlations and uncertainties typically found in large scale inverse problems. Here we evaluated these models against inversion results and presented a satellite-informed wetland CH₄ ensemble product derived by assembling the highest-performing models. We further evaluated our fluxes against independent regional scale estimates of wetland fluxes using airborne data. We found that the satellite-informed model ensemble estimated global wetland CH₄ emission to be 120-175 Tg/year, with 82-127 Tg/year from the tropics (52% to 70% of total global wetland emissions). Furthermore, we found that the seasonal and inter-annual variability of precipitation was the primary driver of global wetland emissions, and the highest-performing models had low to medium temperature sensitivities in CH₄ production. Our results provide critical insights into the role of wetland CH₄ emission variability on the atmospheric CH₄ budget.