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Methane's Solar Radiative Forcing
  • Rachael Emily Byrom,
  • Keith Peter Shine
Rachael Emily Byrom
CICERO Center for International Climate Research
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Keith Peter Shine
University of Reading

Corresponding Author:[email protected]

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Methane (CH4) has significant absorption bands at wavelengths of 1.7, 2.3, 3.3 and 7.6 µm which absorb incoming solar ‘shortwave’ (SW) radiation and cause a radiative forcing (RF) of climate. This letter presents a comprehensive quantification of CH4 SW RF using a narrow-band radiative transfer model to calculate spatially and monthly resolved estimates of the direct CH4 SW effect and its impact on longwave (LW) RF via stratospheric temperature change. This significantly extends previous assessments. Calculations include satellite measurements of CH4 distribution, spectrally-varying surface albedo and absorption of solar mid-infrared radiation by methane’s 7.6 µm band. These factors substantially influence the SW effect; all-sky CH4 SW tropopause instantaneous RF is significantly smaller than previous estimates at 0.002 W m-2 (±25%). In total, the CH4 SW effect enhances CH4 LW-only RF by 7% from 0.574 W m-2 to 0.613 W m-2 for a 750-1800 ppb perturbation.