Indirect radiative forcing of the ozone layer during the 21st century

Abstract

The response of a coupled two-dimensional radiativechemical-dynamical model to possible 21st century changes of the greenhouse gasses (GHGs) carbon dioxide, nitrous oxide and methane are explored using a range of IPCC marker scenarios of GHG emissions. The changes to the ozone layer caused by these GHGs are found to be relatively large (e.g., up to 5% global mean column ozone changes and 30% local changes for CO2 using the IPCC A2 scenario between 2000 and 2100) and the mechanisms for these changes are discussed. The ozone changes are compared to the recovery of ozone due to expected decreases in chlorine containing compounds. Since carbon dioxide, nitrous oxide, and methane affect ozone they induce an indirect radiative forcing in addition to their direct radiative forcing. These indirect radiative forcings are computed using a combination of accurate line-by-line and band radiative transfer models and are compared to the radiative forcing of ozone during the 1979-2000 time period. Although the changes in ozone are large at some altitudes over the 2000-2100 time horizon, the range of associated future indirect radiative forcings from ozone over the range of IPCC scenarios are found to be -0.1 to 0.1 W m-2,which is small compared with the corresponding range of total direct radiative forcing of 2.2 to 6.2 W m-2 for these GHGs over this time horizon.