By Chris Mooney
14 July 2016
(Washington Post) – Every week, there are many new scientific studies published relating to climate change. It is a big field, a multidisciplinary field and a hot field.
But according to leading climate scientist Veerabhadran Ramanathan — credited with discovering that chlorofluorocarbons, or CFCs, are actually a greenhouse gas, among other major findings — a new study this week showing that clouds already are shifting their distributions across the Earth, and in a way predicted by climate change models, stands out. And not in a good way.
The study was led by Ramanathan’s Scripps Institution of Oceanography colleague Joel Norris, though Ramanathan said he was not involved in the work and didn’t know about it until shortly before publication. But Ramanathan said that the study basically confirms that there’s nothing to prevent the world from reaching the high levels of warming that have long been feared — except for our own swift policy actions, that is.
“My reaction was, my goodness,” Ramanathan said. “Maybe the 4 to 5 degree warming, certainly we were all wishing there was some certainty that would make it go away. So I consider the findings of this paper, the data shows major reorganization of the cloud system.”
This matters because clouds are fundamental regulators of how much solar radiation makes it to the Earth’s surface (rather than being reflected back to space by white cloud tops), and how much infrared or “longwave” radiation escapes back to space once again. […]
The shift is expected to exacerbate climate change, as moving clouds toward the poles means they reflect less sunlight back to space — there is less sunlight at the poles than at Equator, so the reflectivity of clouds counts for less there. [more]
ABSTRACT: Clouds substantially affect Earth’s energy budget by reflecting solar radiation back to space and by restricting emission of thermal radiation to space1. They are perhaps the largest uncertainty in our understanding of climate change, owing to disagreement among climate models and observational datasets over what cloud changes have occurred during recent decades and will occur in response to global warming2, 3. This is because observational systems originally designed for monitoring weather have lacked sufficient stability to detect cloud changes reliably over decades unless they have been corrected to remove artefacts4, 5. Here we show that several independent, empirically corrected satellite records exhibit large-scale patterns of cloud change between the 1980s and the 2000s that are similar to those produced by model simulations of climate with recent historical external radiative forcing. Observed and simulated cloud change patterns are consistent with poleward retreat of mid-latitude storm tracks, expansion of subtropical dry zones, and increasing height of the highest cloud tops at all latitudes. The primary drivers of these cloud changes appear to be increasing greenhouse gas concentrations and a recovery from volcanic radiative cooling. These results indicate that the cloud changes most consistently predicted by global climate models are currently occurring in nature.