A new study by researchers from the University of California, Irvine and Utrecht University in the Netherlands has revealed that the surface ice melt of the Greenland and Antarctic ice sheets is not following the same pattern.
While Greenland is experiencing an accelerating rate of surface melt due to warm, dry, downslope winds and increasing air temperatures, Antarctica is showing a slowing trend due to the recovery of the ozone layer and less wind-driven melt on the Antarctic Peninsula.
The study, published in Geophysical Research Letters, used regional climate model simulations to analyze the role of Foehn and katabatic winds, which are gusts that bring warm, dry air into contact with the tops of glaciers.
Greenland: A hotspot of surface ice melt
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The researchers found that the surface ice melt of Greenland has increased by more than 10% in the past 20 years due to the combined effects of downslope winds and global warming.
The winds are responsible for a significant amount of surface melt, as they transfer heat and moisture from lower altitudes to higher elevations.
The study also showed that Greenland has become so warm that sunlight alone (without wind) is enough to melt its surface ice. The increase in air temperature has resulted in a 34% increase in total surface ice melt since 2000.
The researchers attributed this outcome in part to the influence of global warming on the North Atlantic Oscillation (NAO), an index of sea level pressure difference.
The shifting of NAO to a positive phase has led to below-normal pressure across high latitudes, ushering warm air over Greenland and other Arctic areas.
"The ice sheets in Greenland and Antarctica keep over 200 feet of water out of the ocean, and their melt has raised global sea level by about three-quarters of an inch since 1992," said co-author Charlie Zender, UCI professor of Earth System Science.
In contrast with Greenland, the researchers found that the total Antarctic surface melt has decreased by about 15% since 2000.
However, this reduction is largely due to 32% less downslope wind-generated melt on the Antarctic Peninsula, where two vulnerable ice shelves have already collapsed.
The study suggested that the recovery of the Antarctic stratospheric ozone hole discovered in the 1980s has temporarily helped to insulate the surface from further melting.
The ozone layer acts as a shield that blocks harmful ultraviolet radiation from reaching the Earth's surface, and its depletion can increase the amount of solar energy absorbed by the ice.
The researchers warned that this situation may not last long, as the ozone hole is expected to close by mid-century due to international efforts to reduce ozone-depleting substances.
This could lead to more surface ice melt in Antarctica, as well as changes in atmospheric circulation and precipitation patterns.
"Surface melt leads to runoff and ice shelf hydrofracture that increase freshwater flow to oceans-causing sea level rise," Zender said.
The study highlighted the importance of understanding the regional differences in surface ice melt of the Greenland and Antarctic ice sheets, as they have significant implications for global sea level rise and climate change.
The researchers also called for more observations and modeling studies to improve the accuracy and reliability of future projections.
