A modeling study of effective radiative forcing and climate response due to increased methane concentration

An atmospheric general circulation model BCC_AGCM2.0 and observation data from ARIS were used to calculate the effective radiative forcing (ERF) due to increased methane concentration since pre-industrial times and its impacts on climate. The ERF of methane from 1750 to 2011 was 0.46 W m−2 by taking it as a well-mixed greenhouse gas, and the inhomogeneity of methane increased its ERF by about 0.02 W m−2. The change of methane concentration since pre-industrial led to an increase of 0.31 °C in global mean surface air temperature and 0.02 mm d−1 in global mean precipitation. The warming was prominent over the middle and high latitudes of the Northern Hemisphere (with a maximum increase exceeding 1.4 °C). The precipitation notably increased (maximum increase of 1.8 mm d−1) over the ocean between 10°N and 20°N and significantly decreased (maximum decrease >–0.6 mm d−1) between 10°S and 10°N. These changes caused a northward movement of precipitation cell in the Intertropical Convergence Zone (ITCZ). Cloud cover significantly increased (by approximately 4%) in the high latitudes in both hemispheres, and sharply decreased (by approximately 3%) in tropical areas.