Climate Model Cloud Simulations Improving
Climate model predictions of how much the planet is warming because of rising greenhouse gases vary widely due to different simulated responses of clouds to warming. Model cloud predictions are variable because clouds are among the least well simulated components in spite of much effort over many years to improve their simulations by climate models. In this study, U.S. Department of Energy scientists from Lawrence Livermore National Laboratory measured whether or not cloud simulations have improved in the newest generation of climate models being assessed for reports by the Intergovernmental Panel on Climate Change. The team examined the ability of 19 climate models to simulate climatological cloud amount, reflectivity, and altitude in comparison with satellite observations and found that cloud simulations are improving. In the newest models, a bias associated with too many highly reflective clouds has been widely reduced, and the best models have eliminated this bias. With increased amounts of clouds with lesser reflectivity, there is a significant reduction in the “too few – too bright” problem where the time-mean radiation balance is well simulated by having the compensating errors of too few clouds that are too reflective. Improved cloud simulations in climate models is a necessary, but insufficient step towards increased confidence in their predictions.
Klein, S. A., Y. Zhang, M. D. Zelinka, R. Pincus, J. Boyle, and P. J. Gleckler. 2013. “Are Climate Model Simulations of Clouds Improving? An Evaluation Using the ISCCP Simulator,” Journal of Geophysical Research: Atmospheres 118, 1329–42. DOI: 10.1002/jgrd.50141.