Joel Norris - Are Cloud Changes Over Recent Decades a Response to Global Warming?

April 19, 2017 3:30pm to 4:30pm
MSA 7124

Clouds have long been considered one of the greatest uncertainties of climate change. They have a large impact on Earth’s radiation budget, but global climate models have disagreed over the cloud response to global warming, and a stable long-term observational record of clouds has previously not been available. Recent work that has empirically removed artifacts from several satellite cloud records enables a comparison of cloud changes over the past several decades with those simulated by global climate models with historical external radiative forcing for the same time period. Some robust cloud changes are seen. The majority of climate models and satellite records agree that the subtropical dry zone has expanded poleward and the tops of the highest clouds have risen higher. Both of these are consistent with theories of the atmospheric response to global warming and act as a positive feedback on the climate system. Satellite records exhibit agreement concerning tropical low-level cloud changes, but these are not consistent with any expected global warming pattern. Climate model simulations suggest that changes in low-level clouds instead result from multidecadal atmosphere-ocean variability rather than as an equilibrium response to global warming.