Abstract
Surface and satellite observations of atmospheric methane show smooth
seasonal behavior in the Southern Hemisphere driven by loss from the
hydroxyl (OH) radical. However, observations in the Northern Hemisphere
show a sharp mid-summer increase that is asymmetric with the Southern
Hemisphere and not captured by the default configuration of the
GEOS-Chem chemical transport model. Using an ensemble of 22 OH model
estimates and 24 wetland emission inventories in GEOS-Chem, we show that
the magnitude, latitudinal distribution, and seasonality of Northern
Hemisphere wetland emissions are critical for reproducing the observed
seasonality of methane in that hemisphere, with the interhemispheric OH
ratio playing a lesser role. Reproducing the observed seasonality
requires a wetland emission inventory with ~80 Tg a-1
poleward of 10°N including significant emissions in South Asia, and an
August peak in boreal emissions persisting into autumn. In our 24-member
wetland emission ensemble, only the LPJ-wsl MERRA-2 inventory has these
attributes.