Radiative signature of increasing atmospheric carbon dioxide in HIRS satellite observations

Abstract

We examine the cause and implications of decadal trends observed in the High‐Resolution Infrared Radiation Sounder (HIRS) CO2 channels over the period 1980–1999 in conjunction with Microwave Sounding Unit (MSU) O2 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 CO2 concentration result in a global decreasing TB trend (∼−0.3 K/decade), indicating a greater influence of increased CO2 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 CO2 trends, particularly over the northern hemisphere midlatitudes downstream from major CO2 sources (U.S. and China). Thus the HIRS CO2 radiances may provide one opportunity to supplement existing surface networks by constraining regional patterns of decadal CO2 variability.