Parts of Greenland’s ice sheet completely melted about 7,000 years ago at temperatures close to those expected by the end of this century, a new study shows.
Prudhoe Dome, a 1,640-foot-thick (500-meter) ice cap that currently covers 965 square miles (2,500 square kilometers) of northwestern Greenland, melted during warm temperatures during the early Holocene, exposing the sediments beneath.
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“It’s truly humbling to see nothing but ice on all sides, and to think that that ice will disappear again in the recent geological past and future,” lead author Caleb Wolcott George, a geologist at the University of Kentucky, said in a statement.
After the last ice age ended about 11,700 years ago, temperatures in Greenland rose above current averages and widespread ice melted. However, much of the evidence for Holocene ice extent, or lack thereof, is buried beneath today’s existing ice, making it difficult to determine the impact of climate change on ice sheet extent.
In a new study published Monday (January 5) in the journal Nature, scientists excavated Prudhoe Dome to collect sediment from beneath the ice sheet. They then used infrared light to measure how far the sediment was buried beneath the dome without exposure to sunlight.
The researchers found that this deposit last saw the sun about 7,100 years ago. This means that the ice must have completely melted at that point for the dust and rocks underneath to be exposed. Chemical signatures on the icicles suggest that no ice remained from the last Ice Age, and that the dome completely melted and reformed in the years that followed.
Summer temperatures during the early and mid-Holocene were 5.4 to 10.8 degrees Fahrenheit (3 to 6 degrees Celsius) warmer than today. Major climate models, such as CMIP6, predict that summer temperatures could rise to similar values by 2100. That warming could have a major impact on Greenland’s ice sheet, the researchers said in the study.
However, it is not yet clear how long such high temperatures had to be maintained before the ice on Prudhoe Dome completely melted. Limiting the amount of future warming could help limit ice sheet melting, the researchers wrote.
The early Holocene was “an era known for its climate stability, when humans first developed agricultural practices and began the march toward civilization. So if natural, mild climate changes during this period continued to melt the Prudhoe Dome and potentially cause it to recede for thousands of years, it may only be a matter of time before it begins to peel away again from today’s anthropogenic climate changes,” said study co-author Jason Breiner, a geologist and paleoclimatologist at the University at Buffalo. That statement.
Additional ice cores taken from other parts of Greenland will help map how much the ice sheet retreated during the Holocene warming period, potentially providing better insight into how it will respond in the future and how sea levels may rise as a result. “We have very reliable numerical models that can predict melt rates, but we also need actual observational data points that can tell us without a doubt that X amount of warming in the past has led to X amount of ice loss,” Briner said.
Study co-author Jorg Schäfer, a research professor at Columbia University’s Lamont-Doherty Earth Observatory, added that the findings could help show which parts of the Greenland ice sheet are most vulnerable. This is extremely important in predicting local sea level rise. “This new field of science is a game changer in providing this information through direct observation and predicting ice melt,” he said in a statement.
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