A cloudless future? The mystery at the heart of climate forecasts

Cloud guesswork is hindering climate models, therefore relying heavily on their outputs to decide policies must be risky. A professor commented that we may “need a Manhattan Project level of new federal funding and interagency coordination to actually solve this problem.” This can’t be brushed aside as a minor issue.
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We hear a lot about how climate change will change the land, sea, and ice says Eurekalert.

But how will it affect clouds?

“Low clouds could dry up and shrink like the ice sheets,” says Michael Pritchard, professor of Earth System science at UC Irvine. “Or they could thicken and become more reflective.”

These two scenarios would result in very different future climates. And that, Pritchard says, is part of the problem.

“If you ask two different climate models what the future will be like when we add a lot more CO2, you get two very different answers. And the key reason for this is the way clouds are included in climate models.”

No one denies that clouds and aerosols — bits of soot and dust that nucleate cloud droplets — are an important part of the climate equation. The problem is these phenomena occur on a length- and time-scale that today’s models can’t come close to reproducing. They are therefore included in models through a variety of approximations.

Analyses of global climate models consistently show that clouds constitute the biggest source of uncertainty and instability.


Whereas the most advanced U.S. global climate model are struggling to approach 4 kilometer global resolution, Pritchard estimates that models need a resolution of at least 100 meters to capture the fine-scale turbulent eddies that form shallow cloud systems — 40 times more resolved in every direction.

It could take until 2060, according to Moore’s law, before the computing power is available to capture this level of detail.

Pritchard is working to fix this glaring gap by breaking the climate modeling problem into two parts: a coarse-grained, lower-resolution (100km) planetary model and many small patches with 100 to 200 meter resolution. The two simulations run independently and then exchange data every 30 minutes to make sure that neither simulation goes off-track nor becomes unrealistic.

His team reported the results of these efforts in the Journal of Advances in Modeling Earth Systems in April 2022.

Continued here.

via Tallbloke’s Talkshop


June 1, 2022 at 05:27AM

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