Solar radiation is the most important source of renewable energy available to reduce fossil CO2 atmospheric emissions and also is an important factor in heating, ventilation, and air conditioning (HVAC) energy considerations. Solar radiation may be affected by climate changes induced by CO2 emissions. In this study, a refined regional climate model was used to generate seasonal global radiation climatologies for the US under the present and mid 21st century enhanced atmospheric CO2 level. Simulated seasonal-mean daily global radiation (direct plus diffuse incident radiation on a horizontal surface) under the present climate showed overall reasonable agreement with observed patterns but with negative biases in most locations. In most of the US, the enhanced CO2 simulation (future climate) showed a trend of decreased seasonal-mean daily global radiation availability in the range of 0-20%. The most noticeable decrease was simulated in the western US during fall, winter, and spring. In small areas in the southern and northwestern US some increase in global radiation was simulated. Changes in global radiation during summer were relatively low. (C) 2003 Published by Elsevier Ltd.