Climate versus emission drivers of methane lifetime against loss by tropospheric OH from 1860-2100

Over the last two decades, however, the TCH4_OH declines steadily, coinciding with the most rapid climate warming and observed slow-down in CH₄ growth rates, reflecting a possible negative feedback through the CH₄ sink. Sensitivity simulations with CM3 suggest that the aerosol indirect effect (aerosol-cloud interactions) plays a significant role in cooling the CM3 climate. The projected decline in aerosols under all RCPs contributes to climate warming over the 21st century, which influences the future evolution of OH concentration and TCH4_OH.

Projected changes in TCH4_OH from 2006 to 2100 range from -13% to +4%. The only projected increase occurs in the most extreme warming case (RCP8.5) due to the near-doubling of the CH₄ abundance, reflecting a positive feedback on the climate system. The largest decrease occurs in the RCP4.5 scenario due to changes in short-lived climate forcing agents which reinforce climate warming and enhance OH.

This decrease is more-than-halved in a sensitivity simulation in which only well-mixed greenhouse gas radiative forcing changes along the RCP4.5 scenario (5% vs. 13%).