SENSITIVITY OF THE EARTHS RADIATION BUDGET TO CHANGES IN LOW CLOUDS

VARIOUS mechanisms have been suggested whereby clouds might take part in or initiate climate change, including changes in cloud amounts, liquid-water paths and droplet sizes1-11. Previous studies of the sensitivity of the Earth's radiation budget to cloud liquid-water path and droplet size were made with one-dimensional or even simpler models1-6,12,13, which cannot represent the real cloud distribution. Here I present the results of a study that uses a three-dimensional general circulation model, which should give more reliable estimates. The top-of-atmosphere radiative forcing by doubled carbdn dioxide concentrations can be balanced by modest relative increases of ∼15-20% in the amount of low clouds and 20-35% in liquid-water path, and by decreases of 15-20% in mean drop radius (depending on the version of the model). This indicates that a minimum relative accuracy of ∼5% is needed, both to simulate these quantities in climate models and to estimate climate response by monitoring them over extended periods from satellite platforms. © 1990 Nature Publishing Group.