Clouds reduce downwelling longwave radiation over land in a warming climate, researchers find

Cumuliform cloudscape over Swifts Creek, Australia
[image credit: Wikipedia]

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The paper says ‘the results are not site specific’, and ‘Our findings establish a pivotal observational benchmark of radiative forcing and feedback needed for validating climate model performance over land’. The old saying ‘warm air rises’ springs to mind. The article here claims ‘The researchers cautioned that their discovery does not throw doubt on global warming’, but the rate of warming is an issue on its own. /em>
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McGill University researchers have discovered that changes in clouds are slightly mitigating global warming, says Phys.org.

While greenhouse gases continue to cause temperatures to rise [Talkshop comment – evidence-free assertion of cause], 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.

Full article here.
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Research article: Clouds reduce downwelling longwave radiation over land in a warming climate (Jan. 2025)