A new study has left climate scientists more confident that “cloud feedback”—a wickedly complex cycle in which clouds respond to temperature change according to factors like type and altitude—will drive further warming, though perhaps not as much as feared.
“Clouds are a complex part of the climate system, driving a range of processes that can heat up and cool down the planet,” explains Carbon Brief. This new study, recently published in the Proceedings of the National Academy of Sciences, breaks new ground by offering “the first global estimate of cloud feedback,” rather than focusing on specific cloud types or geographic regions.
While clouds are, at present, generally acting to cool things down, researchers believe that warming itself “could trigger subtle changes in cloud properties that either enhance or reduce their cooling effect,” Carbon Brief says. Getting a better handle on this type of cloud feedback is crucial to producing more accurate estimates of equilibrium climate sensitivity (ECS)—the technical term for how much a doubling of atmospheric CO2 will warm the planet.
After accounting for the findings of their cloud feedback research—which used machine learning to analyze 20 years’ worth of global satellite data, including humidity, temperature, and wind—lead author Paulo Ceppi and his team produced a central ECS estimate of 2 to 3.2°C of expected warming. Key factors in the research included surface temperature and tropospheric stability, which is “a lack of mixing in the vertical air column.”
To further explain the interplay between clouds and temperature change, Carbon Brief cites University of Reading climate physicist Ellie Highwood, who, in a 2018 guest post, described the relation between cloud type and global temperature change. “Low, bright clouds have a largely cooling influence because they reflect sunlight [shortwave radiation] away from the Earth’s surface. High, thin clouds composed of ice crystals are more or less transparent to sunlight, but do absorb outgoing infrared [longwave] radiation, re-emitting a small fraction and, thereby, warming the planet.”
What complicates things further, she added, “is that, in most places, there are multiple layers of cloud at any one time.”
Finding a proverbial silver lining in the new research, Tapio Schneider, a professor of environmental science at the California Institute of Technology, told Carbon Brief that while the latest feedback study “rules out that clouds globally dampen global warming,” it also suggests that any amplification is unlikely to be very strong.
“The latter part is good news,” Schneider said. “It is another piece of evidence suggesting that the extremely high climate sensitivities seen in some recent climate models may not be consistent with Earth observations.”