Robert D. Cess

Cloud-radiative forcing and climate : Results from the Earth Radiation Budget Experiment

The study of climate and climate change is hindered by a lack of information on the effect of clouds on the radiation balance of the earth, referred to as the cloud-radiative forcing. Quantitative estimates of the global distributions of cloud-radiative forcing have been obtained from the spaceborne Earth Radiation Budget Experiment (ERBE) launched in 1984. For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m2)] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m2) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth. This cooling effect is large over the mid-and high-latitude oceans, with values reaching -100 W/m2. The monthly averaged longwave cloud forcing reached maximum values of 50 to 100 W/m2 over the convectively disturbed regions of the tropics. However, this heating effect is nearly canceled by a correspondingly large negative shortwave cloud forcing, which indicates the delicately balanced state of the tropics. The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO2. The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO2 doubling. Hence, small changes in the cloud-radiative forcing fields can play a significant role as a climate feedback mechanism. For example, during past glaciations a migration toward the equator of the field of strong, negative cloud-radiative forcing, in response to a similar migration of cooler waters, could have significantly amplified oceanic cooling and continental glaciation.

Interpretation of Cloud-Climate Feedback as Produced by 14 Atmospheric General Circulation Models

Understanding the cause of differences among general circulation model projections of carbon dioxide-induced climatic change is a necessary step toward improving the models. An intercomparison of 14 atmospheric general circulation models, for which sea surface temperature perturbations were used as a surrogate climate change, showed that there was a roughly threefold variation in global climate sensitivity. Most of this variation is attributable to differences in the models depictions of cloud-climate feedback, a result that emphasizes the need for improvements in the treatment of clouds in these models if they are ultimately to be used as climatic predictors.

Earth Radiation Budget Experiment (ERBE) Archival and April 1985 Results

This paper describes the Earth Radiation Budget Experiment (ERBE) data products being made available to the community. The Science Team used ten validation criteria to judge the acceptability of the data for archival. We list these criteria and present uncertainty estimates based on them for four typical data products. A brief description of the radiation budget for April 1985 from the combined data of ERBE and NOAA-9 concludes this paper.

Enhanced CO2 greenhouse to compensate for reduced solar luminosity on early Earth

CURRENT models for the evolution of the Sun require an increase in solar luminosity by 25% since the formation of the Solar System1. Such an increase in the solar constant should have profound effects on the terrestrial climate, but there is no evidence from the fossil record of a corresponding change in the Earths global mean temperature2. This apparent conflict cannot be explained by the apparent inability of solar models to account for the low observed neutrino flux3. Even models that are forced to fit the neutrino data require a similar increase in the solar luminosity. As Newman and Rood1 state: “a faint young Sun is one of the most unavoidable consequences of stellar structure considerations”. We discuss here whether CO2–H2O in a weakly reducing atmosphere could have caused this change in the early Earths temperature by the so-called greenhouse effect.