low cloud over sub-tropical oceans produces a heating effect ?

[Colin Forrest]

From AR6 WG 1 full report ch 7 page 926..........

An assessment of the low-altitude cloud feedback over the subtropical
oceans, which was previously the major source of uncertainty in the
net cloud feedback, is improved owing to a combined use of climate
model simulations, satellite observations, and explicit simulations
of clouds, altogether leading to strong evidence that this type of
cloud amplifies global warming.

How does this square will the modelling of MCB which predicts a cooling effect from increasing this type of cloud cover ?

Best Wishes,  Colin Forrest

PS the reference for my previous post on SSPs and climate forcing was wrong. It's om page 926, not 928

[Michael Diamond]

Hi Colin,

Great question! We are extremely certain that low-altitude subtropical clouds cool the climate by reflecting sunlight but not having a strong impact on the amount of heat escaping to space. Unfortunately for us, this type of cloud is projected to become less common as sea surface temperatures warm — the loss of these clouds leads to additional warming (positive feedback). Marine cloud brightening, on the other hand, is a proposal to use sea salt aerosol to make these clouds more reflective when they do occur, and potentially make them occur more frequently/over larger areas. This would cool the climate by increasing the amount and/or brightness of these clouds (negative forcing).

In short: increasing low-altitude clouds leads to cooling (MCB) and decreasing them leads to warming (positive feedback to global warming).

Cheers,

Michael