Abstract. Decadal trends and interannual variations in the hydroxyl radical (OH),
while poorly constrained at present, are critical for understanding the
observed evolution of atmospheric methane (CH4). Through analyzing the
OH fields simulated by the model ensemble of the Chemistry–Climate Model
Initiative (CCMI), we find (1) the negative OH anomalies during the El
Niño years mainly corresponding to the enhanced carbon monoxide (CO)
emissions from biomass burning and (2) a positive OH trend during 1980–2010
dominated by the elevated primary production and the reduced loss of OH due
to decreasing CO after 2000. Both two-box model inversions and variational
4D inversions suggest that ignoring the negative anomaly of OH during the El Niño years leads to a large overestimation of the increase in global
CH4 emissions by up to 10 ± 3 Tg yr−1 to match the observed
CH4 increase over these years. Not accounting for the increasing OH
trends given by the CCMI models leads to an underestimation of the CH4
emission increase by 23 ± 9 Tg yr−1 from 1986 to 2010. The
variational-inversion-estimated CH4 emissions show that the tropical
regions contribute most to the uncertainties related to OH. This study
highlights the significant impact of climate and chemical feedbacks related
to OH on the top-down estimates of the global CH4 budget.
Role of the Hudson Bay lowland as a source of atmospheric methane