Wednesday, 16 January 2002: 2:00 PM
Measurements of Radiative Forcing Beneath Clouds from Greenhouse Gas
A new technique has been developed to measure the greenhouse radiative fluxes from GHG beneath clouds. It is important to measure the radiative forcing from radiatively active gases beneath clouds because the fluxes in the presence of clouds are not well modelled by GCMs. There are large spatial and temporal variations in some gases which make it difficult to quantify their climate forcing. In particular, tropospheric ozone is currently ignored in the Kyoto agreement as are other prime constituents of smog such as nitric acid or PAN. Measurements of the surface radiative forcing from the gases below the cloud are taken against the cold black body background of the sky. Radiative fluxes from ozone, carbon monoxide, nitrous oxide, nitric acid and aerosols have been measured. A comparison of modelled radiative trapping with the measured surface forcing is conducted. The average of the measured fluxes from 30 days at 45 N is about 0.4 W/m2; this is close to the global forcing estimate for tropospheric ozone reported in the last IPCC report.