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As the planet continues to warm due to human-induced climate change, accurate computer climate models will be key to help clarify exactly how the climate will continue to change in the coming years.

In a study published in Journal of Geophysical Research: AtmospheresA team led by researchers from the University of California, Irvine’s Department of Earth System Science and the University of Michigan’s Department of Climate and Space Science and Engineering reveals how a climate model commonly used by geologists currently overestimates a key physical property of the climate system of Earth called albedo, which is the degree to which ice reflects planet-warming sunlight into space.

“We found that in the old versions of the model, the ice was about 5 percent too reflective,” said Chloe Clark, a project scientist in the group of UC Irvine professor Charlie Zender. “The reflectivity of the ice was too high.”

The amount of sunlight a planet receives and reflects is important for estimating exactly how much the planet will warm in the coming years. Previous versions of the model, called the Energy Exascale Earth System Model (E3SM), overestimated albedo because they did not account for what Clark described as the microphysical properties of ice in a warming world.

These properties include the effects of things like algae and dust on albedo. Dark algae and dust can make snow and ice less reflective and less able to reflect sunlight.

To do the analysis, Clark and her team examined satellite data to track the albedo of the Greenland ice sheet. They found that the E3SM reflectivity overestimates the reflectivity of the ice sheet, “which means the model estimates less melting than what would be expected from the microphysical properties of the ice,” Clark said.

But with the new ice reflectivity incorporated into the model, the Greenland ice sheet is melting at a rate about six gigatons faster than in older versions of the model. This is based on albedo measurements that are more consistent with satellite observations.

Clark hopes her team’s research highlights the importance of seemingly minor properties that can have far-reaching consequences for the overall climate. “I think our work will help the models do a much better job of helping us capture the climate feedbacks associated with snow and ice,” she said.

Clarke then wants to study different icy parts of the planet to gauge how widespread the albedo discrepancy is in E3SM.

“Our next steps are to make it work globally, not just for Greenland,” said Clark, who also plans to compare the new melting rates of the Greenland ice sheet with observations to measure how much more – is exactly the new albedo of the ice. “It would be useful to apply it to glaciers in places like the Andes and Alaska.”

Additional authors include Raf Antwerpen (Lamont-Doherty Earth Observatory), Mark G. Flanner (University of Michigan), Adam Schneider (National Oceanic and Atmospheric Administration), Marco Tedesco (Lamont-Doherty Earth Observatory), and Charlie S. Zender (University of California in Irvine).