Satellite constraints on the latitudinal distribution and temperature sensitivity of wetland methane emissions

38Wetland methane (CH4) emissions comprise about one-third of the global CH4 source. The 39 latitudinal distribution and climate sensitivity of wetland CH4 fluxes are the key determinants of 40 the global CH4-climate feedback. However, large differences exist between bottom-up estimates, 41 informed by ground-based flux measurements, and top-down estimates derived from spaceborne 42 total column CH4. Despite the extensive coverage of satellite CH4 concentration observations, 43 challenges remain with using top-down estimates to test bottom-up models, mainly because of the 44 uncertainties in the satellite retrievals, the model representation errors, the variable prior emissions, 45 and the confounding role of the posterior error covariance structures. Here, we use satellite-based 46 top-down CH4 flux estimates (2010-2012) to test and refine 42 bottom-up estimates of wetland 47 emissions that use a range of hypothesized wetland extents and process controls. Our comparison 48 between bottom-up models and satellite-based fluxes innovatively accounts for cross-correlations 49 and spatial uncertainties typically found in top-down inverse estimates, such that only the 50 information from satellite observations and the atmospheric transport model is kept as a constraint. 51 We present a satellite-constrained wetland CH4 ensemble product derived from assembling the 52 highest-performance bottom-up models, which estimates global wetland CH4 emissions of 148 53 (117-189, 5th-95th percentile) Tg CH4 yr-1. We find that tropical wetland emissions contribute 54 72% (63-85%) to the global wetland total. We also find that a lower-than-expected temperature 55 sensitivity agrees better with atmospheric CH4 measurements. Overall, our approach demonstrates 56 the potential for using satellites to quantitatively refine bottom-up wetland CH4 emission estimates, 57 their latitudinal distributions, and their sensitivity to climate. 58Keywords: wetland CH4, top-down constraints, terrestrial ecosystem models, climate sensitivity, 59 global budget, latitudinal distribution