Thin Mid-Level Clouds Could Help Relieve Global Warming

A new study from Stockholm University and the University of Miami revealed that thin clouds located at approximately five kilometers altitude could have a substantial cooling effect on the climate, potentially relieving global warming.

The study, published in the journal Nature Communications, suggests that thin mid-level clouds (TMLC) formed by detrainment from convective clouds near the zero-degree isotherm could influence cloud feedbacks, heat and moisture transport and climate sensitivity.

"Using the satellite observations and high-resolution numerical modelling, we find that thin mid-level clouds are frequently formed in the tropics in the vicinity of deep convective clouds and that their cooling effect could be as large as the warming induced by high cirrus clouds" explained lead author Quentin Bourgeois, postdoctoral associate at the Department of Meteorology (MISU) and the Bolin Centre for Climate Research, Stockholm University, in a statement.

About 70 percent of the Earth's surface is covered by clouds at any time. High altitude ice clouds, such as the cirrus clouds warm the Earth, while low altitude clouds, such as cumulus clouds, cool it down.

Using radiative transfer model, the researchers calculated that the cooling effect of TMLC could be as large in magnitude as the warming effect of cirrus clouds. Furthermore, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite observations showed that TMLC are more common in the tropics than previously thought.

The Earth receives about 340 W m-2 energy from the sun every day, in addition to the 3 W m-2 warming caused by greenhouse gas emissions. Clouds relieve some of the warming, by about 20 W m-2.

With their findings, the researchers hope that future climate models would factor in the cooling effect of thin mid-level clouds in their predictions. Additionally, future research is needed to better understand the mechanism behind TMLC, which remains to be challenging to study because they are very difficult to detect using remote sensing techniques.