Reactive halogens increase the global methane lifetime and radiative forcing in the 21st century

This increase in CH4 lifetime helps to reduce the gap between models and observations and results in a greater burden and radiative forcing during this century. The increase in CH4 burden due to halogens (up to 700 Tg or 8% by 2100) is equivalent to the observed atmospheric CH4 growth during the last three to four decades. Notably, the halogen-driven enhancement in CH4 radiative forcing is 0.05 W/m(2) at present and is projected to increase in the future (0.06 W/m(2) by 2100); such enhancement equals similar to 10% of present-day CH4 radiative forcing and one-third of N2O radiative forcing, the third-largest well-mixed greenhouse gas.

Both direct (Cl-driven) and indirect (via OH) impacts of halogens should be included in future CH4 projections.