Vapour buoyancy flaw leads to inaccurate simulations of cloud distributions in climate models, study finds

Tropical scene

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Tropical scene

The researchers say ‘climate models often differ on the precise degree of future warming, largely due to their representation of clouds.’ For decades we’ve been told to believe variations in carbon dioxide are the key to any future warming, but climate model forecasts have been unable to deliver the hoped-for precision. Predicting future cloud variations looks like a tall order.
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Quick Summary

— Study adds a missing piece to the climate science puzzle of simulating clouds.
— Lightness of water vapor influences the amount of low clouds.
— Some leading climate models don’t include this effect.
— Including vapor buoyancy into climate models helps improve climate forecasting.

Clouds are notoriously hard to pin down, especially in climate science, says UC Davis.

A study from the University of California, Davis, and published in the journal Nature Geoscience shows that air temperature and cloud cover are strongly influenced by the buoyancy effect of water vapor, an effect currently neglected in some leading global climate models.

Global climate models are the primary tools used to study Earth’s climate, predict its future changes and inform climate policymaking. However, climate models often differ on the precise degree of future warming, largely due to their representation of clouds.

“Climate models are the best tool we have to predict future climate change,” said lead author Da Yang, an assistant professor of atmospheric science at UC Davis and faculty scientist at Lawrence Berkeley National Lab. “It’s important that we actively try to improve them.”

Cold air rises?

While conventional wisdom has it that hot air rises, the reverse is true in the tropical atmosphere, the study notes. Previous research by Yang and his colleagues proposed that cold air rises in the tropics because humid air is lighter than dry air. This effect is known as vapor buoyancy, and it regulates the amount of low clouds over the subtropical ocean.

“Vapor buoyancy influences the distribution of low clouds—the kind of clouds we have off the California coast, which contribute greatly to the global energy balance,” said Yang. “The biggest challenge in accurately predicting future climate change is clouds, so we have to get vapor buoyancy right.”

Continued here.
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Talkshop note – the study says:
‘We further show that vapour buoyancy makes cold air rise and increases subtropical stratiform low cloud by up to 70% of its climatological value.’