Earth system scientists have discovered a missing piece in climate models

As the planet continues to warm due to human-induced climate change, accurate computer climate models will be key to helping to 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 UC Irvine Department of Earth System Science and the University of Michigan Department of Climate and Space Sciences and Engineering reveals how a climate model commonly used by geoscientists currently overestimates a key physical property of Earth’s climate system called albedo, which is the degree to which ice it reflects solar radiation warming the planet into space.

“We found that in the old versions of the models, the ice is about 5% too reflective,” said Chloe Clarke, a project scientist in Professor Charlie Zender’s group at UC Irvine. “The reflectivity of the ice was too high.

The amount of sunlight a planet receives and reflects is important for estimating 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 Clarke described as the microphysical properties of ice in a warming world.

These properties include the effects that algae and dust have on albedo. Dark colored algae and dust can make snow and ice less reflective and less able to reflect sunlight.

To perform the analysis, Clarke and her team studied satellite data to track the albedo of the Greenland ice sheet. They found that the E3SM reflectance overestimates the reflectance of the ice sheet, “which means the model is estimating less melting than would be expected from the microphysical properties of the ice,” Clarke said.

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

Clarke hopes her team’s study highlights the importance of seemingly minute features that can have far-reaching consequences for the overall climate. “I think our work will help the models do a much better job by helping us capture feedback related to snow and ice,” she said.

Next, Clarke wants to study different icy parts of the planet to see how widespread the albedo discrepancy is in E3SM.

“Our next steps are to make it work globally and not just in Greenland,” said Clarke, who also intends to compare the melting rate of the new Greenland ice sheet with observations to measure how much more accurate the new albedo of the ice is. “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 (UC Irvine).