Clouds have a surprising effect on surface warming, McGill climate researchers find
Ď㽶ĘÓƵ researchers have that changes in clouds are slightly mitigating global warming. While greenhouse gases continue to cause temperatures to rise, a reduction in low-cloud cover over land has brought about a modest reduction of the amount of heat being trapped close to ground level.
"We started this research to observationally verify the increase of greenhouse effect of the Earth atmosphere," said Yi Huang, Associate Professor in McGill’s Department of Atmospheric and Oceanic Sciences who conceived a recent study published in Nature, "We indeed verified that, although to our surprise we also found an offsetting effect due to changes in clouds."
“Without these cloud changes, the surface would warm even faster,” said Lei Liu, graduate student in McGill's Department of Atmospheric and Oceanic Sciences and the first author of this study. "This work offers observational truth about how clouds affect warming, which can be used to improve climate models and guide environmental policies,” said Liu.
To discover this surprising effect, the team used the measurements of a key radiative instrument, the Atmospheric Emitted Radiance Interferometer (AERI), along with satellite data, climate models and a technique called "optimal spectral fingerprinting" co-designed by Yi Huang and Lei Liu to isolate the effects of clouds from other atmospheric processes.
The researchers focused on longwave radiation, the heat energy Earth emits back into the atmosphere. Usually, clouds trap some of this heat and send it back to the ground. But as the climate warms, there are fewer low clouds in some areas, which means less heat is returned to the surface.
McGill’s Atmospheric and Oceanic Department, which operates three AERI instruments in Montreal, looks to continue using their critical data for understanding regional climate dynamics and enhancing climate modelling, the researchers said.
“Our research emphasizes the value of precise, long-term climate observations,” said John Gyakum, co-author and Professor in the Department of Atmospheric and Oceanic Sciences.Ěý“This is essential for understanding Earth’s response to global warming and making informed decisions for future generations.”
The researchers cautioned that their discovery does not throw doubt on global warming.
“It’s like having a thermostat that adjusts itself a little,” the researchers explained. “But even with this adjustment, the room is still heating up.”
About the study
“ ” by Lei Liu, Yi Huang, and John R. Gyakum was published in Nature.
This research was funded by grants of the Natural Sciences and Engineering Research Council of Canada (RGPIN-2019-04511) and the Environment and Climate Change Canada (EDF-CA-2021i022) awarded to Yi Huang as Principal Investigator.
