Radiative signature of increasing atmospheric carbon dioxide in HIRS satellite observations

We examine the cause and implications of decadal trends observed in the High‐Resolution Infrared Radiation Sounder (HIRS) CO 2 channels over the period 1980–1999 in conjunction with Microwave Sounding Unit (MSU) O 2 channel measurements and climate model simulations. Simulated HIRS brightness temperatures (TBs) from the climate model with constant carbon dioxide indicate a global warming trend (∼0.2 K/decade) consistent with the corresponding MSU observations. By contrast, simulations with observed time‐varying CO 2 concentration result in a global decreasing TB trend (∼−0.3 K/decade), indicating a greater influence of increased CO 2 on the HIRS radiances compared to the tropospheric warming. Moreover, comparison between observation and simulations suggests that there may be important regional variations in the CO 2 trends, particularly over the northern hemisphere midlatitudes downstream from major CO 2 sources (U.S. and China). Thus the HIRS CO 2 radiances may provide one opportunity to supplement existing surface networks by constraining regional patterns of decadal CO 2 variability.