The CO2 10 Micron Bands Increase 21st Century Radiative Forcing

Abstract:

Future climate change will largely be driven by increases in atmospheric CO2 concentrations. We investigate the radiative effect of incorporating two additional CO2 bands centered at 960 cm-1 and 1060 cm-1 (commonly referred to as the 10 micron bands) into a new version of the GFDL longwave radiation algorithm. We find good agreement between the impact of the 10 micron bands predicted by our new parameterization and that predicted by a line-by-line calculation. The 10 micron bands increase the global instantaneous longwave radiative forcing due to a quadrupling of CO2 by ~16% at the top of the atmosphere (TOA) and by ~45% at the surface. Calculations with an prescribed sea surface temperature version of the GFDL atmospheric GCM show that the global TOA radiative forcing due to quadrupling of CO2 increases from ~7.1 to ~7.8 W/m2 when the 10 micron bands are included. However, no major differences in the fast radiative feedbacks are seen, as the tropospheric divergence changes only slightly. These results highlight the importance of including the effects of the CO2 10 micron bands in coupled models in the prediction of 21^st Century climate change.