Impact of Increased Methane Emissions on the Atmospheric Composition and Related Radiative Forcing on the Climate System

Abstract

An interactive two-dimensional model of the troposphere, stratosphere, and mesosphere, in which dynamics, radiation, and chemistry are treated interactively, is used to investigate the steady-state atmospheric composition changes and the associated radiative forcings on climate to increased methane surface emissions. Significant perturbations of troposphere and middle atmosphere compositions are predicted. In the case of a CH₄ emission doubling, tropospheric ozone increases by more than 20 % in the northern hemisphere during summer and in the tropical upper troposphere during all the year. In the middle atmosphere, water vapor increase reaches more than 40 % and significant changes in ozone and chlorine species distributions are calculated. The analysis of the associated radiative forcings indicates that the chemically induced forcings contribute for more than 30 % to the total radiative perturbation. Tropospheric ozone infrared forcing plays a dominant role, contributing for more than 20 %. In contrast, the stratospheric water vapor contribution is very weak, as calculated with this model.