Madrid. A temperature reconstruction from ice cores from the past thousand years reveals that the current warming in north-central Greenland is surprisingly pronounced.
The most recent decade analyzed in a study, from 2001 to 2011, was the warmest in the past thousand years, and the region is now 1.5 degrees Celsius warmer than during the 20th century, researchers from the Alfred Wegener Institute report in the journal Nature. Using a set of ice cores unprecedented in length and quality, they reconstructed temperatures in north-central Greenland and ice sheet melt rates.
The latter has a fundamental role in the global climate system. With enormous amounts of water stored in the ice (about 3 million cubic kilometers), the melting ice and the consequent rise in sea levels are considered a possible tipping point. If global emissions are not reduced, the ice sheet is projected to contribute up to 50 centimeters to global mean sea level by 2100.
Weather stations on the coast have been registering an increase in temperatures for many years, but the influence of global warming in the highest parts of the ice sheet, up to 3,000 meters in altitude, remains unclear due to the lack of of long-term observations.
In the new study, experts from the Alfred Wegener Institute, in collaboration with the Helmholtz Center for Polar and Marine Research (AWI), present clear evidence that the effects of global warming have reached remote and elevated areas of north-central Greenland. .
“The time series we recovered from the ice cores now spans continuously over a millennium, from the year 1000 to 2011. These data show that the warming from 2001 to 2011 differs from natural variations over the past thousand years. Although expected, we were surprised by how apparent this difference was,” Maria Hörhold, a glaciologist at AWI and lead author of the study, said in a statement.
composition analysis
Together with colleagues from that center and from the Niels Bohr Institute, University of Copenhagen, Denmark, he analyzed the isotopic composition of shallow ice cores collected in north-central Greenland during specific Helmholtz expeditions.
Previous ice cores, obtained at the same locations since the 1990s, did not indicate a clear warming of the site, despite the increase in global mean temperature. This is due, in part, to the great natural variability of the climate in the region.
AWI researchers have extended previous data sets through the winter of 2011-2012 through a dedicated drilling effort, retrieving time series of unprecedented length and quality. Temperatures were reconstructed using a systematic method for the entire laboratory record: measurement of stable oxygen isotope concentrations within the ice, which vary with the temperatures at the times of ice formation.
In addition to temperature, the team reconstructed snowmelt production, which has increased substantially in Greenland since the 2000s and is now a significant contributor to global sea level rise. “We were surprised to see how much inland temperatures are related to island-wide meltwater runoff, which, after all, occurs in low-lying areas along the edge of the ice cap. ice, near the coast,” Hörhold explained.
To quantify the connection between highland temperatures and melting along the edges of the ice sheet, the authors used data from a regional climate model for the years 1871 to 2011 and satellite observations of changes in the ice sheet. ice mass for 2002 to 2021 from the Grace/Grace-Fo gravimetry missions. This allowed them to convert the temperature variations identified in the ice cores into melt rates and provide estimates for the past thousand years.
This represents an important data set for climate research: better understanding of past ice sheet melt dynamics improves projections of future sea level rise; Reducing uncertainties in projections is one step to help optimize adaptation measures.
The study also concludes that the climate of the Greenland ice sheet is highly dissociated from the rest of the Arctic. This can be demonstrated in comparison with the reconstruction of the temperature of that entire area. Arctic 2k. Although this is an accurate representation of the circumpolar region, it does not reflect conditions in central Greenland.
“Our reconstruction now offers a robust representation of the evolution of temperature in the center of the island, which has been shown to have its own dynamics,” said Thomas Laepple, AWI climate researcher and co-author of the study. He added: “Actually, we expected the time series to vary strongly with warming of the Arctic region.”
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