Scientists have improved a climate model that previously overestimated the reflectivity of ice, leading to more accurate predictions of ice melt and the impacts of climate change.
Their revision includes the impact of previously neglected physical properties of ice.
As global temperatures rise due to human-induced climate change, accurate computer climate models will be critical to shedding light on how our climate will evolve 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.
Albedo is a measure of surface reflectance, expressed as the proportion of incoming solar radiation that is reflected by that surface back into space. It is a critical factor in determining the Earth’s climate and energy balance. High-albedo surfaces such as snow and ice can reflect much of the incoming solar energy, while darker surfaces such as forests or oceans absorb more solar energy.
“We found that with the old versions of the models, the ice is about five percent 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.
Analysis using satellite data
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 the 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.”
Reference: “Impact of Physically Based Ice Radiative Processes on Greenland Ice Sheet Albedo and Surface Mass Balance in E3SM” by CA Whicker-Clarke, R. Antwerpen, MG Flanner, A. Schneider, M. Tedesco, and CS Zender, 8 Apr 2024 . Journal of Geophysical Research: Atmospheres.
DOI: 10.1029/2023JD040241
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). Funding information is provided in the study.