
Global-mean net downwelling anomalies from the ISCCP-FD observational data set. Results are monthly means (black_ and annual averages (red). The base period used for calculating anomalies is 1983 to 1999. These and other direct observations do not support Johansson et al.'s very small (-1W/m²) posterior best estimate of the net top of atmospheric radiative forcing caused by the June 1991 eruptio nof Mt. Pinatubo in the Phillipines