Clouds and global warming: a surprising effect 🌤️

Scientists from McGill University have discovered that changes in cloud cover slightly mitigate global warming. While greenhouse gases continue to drive temperature increases, a reduction in low-level cloud cover near the ground has nevertheless caused a slight decrease in the amount of heat trapped close to the surface.


"We undertook this research to verify, through observation, the impact of increasing greenhouse gas effects on Earth's atmosphere," explains Yi Huang, associate professor in the Department of Atmospheric and Oceanic Sciences at McGill University and lead author of a study recently published in the journal Nature. "We indeed observed this impact, but, surprisingly, we also detected a compensating effect from changes in cloud cover."

"Without these cloud changes, the Earth's surface would be warming even faster," says Lei Liu, an undergraduate student in the Department of Atmospheric and Oceanic Sciences at McGill University and the study's lead author. "This work provides observation-based evidence of the impact of clouds on warming, which can be used to improve climate models and guide environmental policies," he adds.

The team uncovered this surprising effect using data obtained from a major radiation detection instrument, the Atmospheric Emitted Radiance Interferometer (AERI), combined with satellite information and climate models. The team also applied a technique developed by Yi Huang and Lei Liu. Called "optimal spectral fingerprinting," this technique isolates the impact of clouds from other atmospheric processes.

The research team focused on longwave radiation, the thermal energy emitted by the Earth into the atmosphere. Normally, clouds block some of this energy, causing it to be reflected back toward the surface. However, in some regions, global warming reduces cloud formation, which helps to reduce heat.

The Department of Atmospheric and Oceanic Sciences at McGill operates three automated AERI interferometers in Montreal and plans to continue using their data, which is essential for understanding regional climate dynamics and improving modeling, the researchers say.

"Our research highlights the importance of accurate and long-term climate observations," explains John Gyakum, co-author of the study and professor in the Department of Atmospheric and Oceanic Sciences. "These observations are crucial for understanding Earth's response to global warming and making informed decisions for future generations."

However, the scientists emphasize that their discovery does not in any way challenge the reality of global warming.

"It's a bit like a thermostat that adjusts itself slightly," they illustrate. "But this adjustment does not prevent temperatures from rising."

The study "Clouds reduce downwelling longwave radiation in a warming climate," by Lei Liu, Yi Huang, and John R. Gyakum, was published in the journal Nature.

This study was funded by grants from the Natural Sciences and Engineering Research Council of Canada (RGPIN-2019-04511) and Environment and Climate Change Canada (EDF-CA-2021i022) awarded to Yi Huang as principal investigator.