How Fast Is the Earth Really Heating? Researchers Find Key in the Clouds

December 6, 2022 By Eric Williamson, williamson@virginia.edu Eric Williamson, williamson@virginia.edu

The scientific consensus is that the Earth is heating with the continued addition of greenhouse gases to the atmosphere. But predicting how much the temperature will increase in the future, and how quickly, has been an inexact science.

A new discovery may explain one of the reasons for a roughly 4-degree difference in estimates of warming among leading global climate models.

University of Virginia collaborative research, published Nov. 19 in the journal Nature Communications, has discovered a pivotal relationship between high and low cloud changes in the tropics – a part of the planet that exerts an inordinate influence over the globe’s overall energy balance.

“Our study helps to explain why there is such a large spread in magnitudes of the predicted warming,” said the study’s first author, Kathleen Schiro, an assistant professor in the Department of Environmental Sciences.

Scientists have understood for a long time that low clouds – primarily those layered, stratocumulus formations – are crucial to Earth’s energy balance. They deflect the sun’s radiation so it’s not absorbed by the planet.

That’s especially important over the tropics, which are geographically positioned to bear the brunt of solar intensity.

“If tropical stratocumulus were to disappear, the Earth would warm rather significantly,” Schiro said.

In performing the research, she said, the team started by looking for statistical correlations among comparable data in the latest generation of climate models. When they eventually found a connection between high and low cloudiness, they realized that the “overturning circulation” that pings between the two layers was among the factors that could help account for significant modeling differences.

Unfortunately, that dynamic between high and low – driven by forces of convection – appears to create a positive feedback loop, they discovered.

Schiro said the feedback disturbs air circulation in such a way that it promotes fewer low clouds and decreases the amount of sunlight deflected back to space.

“Our study suggests that the net effect of a decrease in high clouds may actually be to further warm the planet,” she said.

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Previously, leading theories had held that a decrease in high cloudiness would primarily serve as an exhaust-valve function – cooling the planet by allowing more radiation to escape into space.

Schiro added that more research will be needed to fully address the differences in climate models.

Partnering research institutions in the study included California Institute of Technology; Columbia University; Ewha Womans University in Seoul, South Korea; Hong Kong University of Science and Technology; NASA’s Goddard Institute for Space Studies and the NASA Jet Propulsion Laboratory; and the University of California, Los Angeles.

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