How Fast Is the Earth Really Heating? Researchers Find Key in the Clouds
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.
Kathleen Schiro is an assistant professor in the Department of Environmental Sciences. (Department of Environmental Sciences photo)
“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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