At higher elevations of the Greenland Ice Sheet, the years 2001 to 2011 were 1.5°C warmer than in the last 20 years.y century and represents the warmest decade in the past thousand years
Temperature reconstructions from ice core samples over the past 1,000 years reveal that today’s warming in central and northern Greenland is surprisingly pronounced. The last decade surveyed in the study, the years 2001 to 2011, was the warmest in the past 1,000 years, and the region is now 1.5 degrees Celsius warmer than it was during the 2020s.y century, researchers led by the Alfred Wegener Institute write in the journal Nature. Using a collection of ice samples of unprecedented length and quality, they have reconstructed past temperatures in central and northern Greenland and ice sheet melt rates.
The Greenland Ice Sheet plays a pivotal role in the global climate system. With huge amounts of water stored in the ice (about 3 million cubic km), the melting and resulting rise in sea level is seen as a potential tipping point. For unmitigated (“business as usual”) global emissions rates, the ice sheet is expected to contribute up to 50 centimeters to the global mean sea level by 2100. Weather stations along the coast have been recording warming for many years. But the effect of global warming on higher parts of the ice sheet up to 3,000 meters has remained unclear due to the lack of long-term observations. In a study now published in natureExperts from the Alfred Wegener Institute and the Helmholtz Center for Polar and Marine Research (AWI) provide clear evidence that the effects of global warming have reached the remote, upland regions of central north Greenland.
“The time series that we have recovered from the ice core now continuously covers more than 1,000 years, from 1,000 to 2011. These data show that the warming from 2001 to 2011 is clearly different from natural changes over the past 1,000 years. Although it is expected Sombre in light about global warming, we were surprised by how pronounced this difference really was,” says AWI glaciologist Dr Maria Horhold, lead author of the study. Together with colleagues from AWI and the Niels Bohr Institute at the University of Copenhagen, she analyzed the isotopic composition of shallow ice cores collected in central and northern Greenland during dedicated AWI flights.
Previous ice core samples obtained at the co-locations beginning in the 1990s did not indicate clear warming in central and northern Greenland, despite rising global mean temperatures. Part of the reason is the great natural variability of the climate in the region.
AWI researchers have now extended previous data sets through winter 2011/2012 through a dedicated re-drilling effort, restoring time series of unprecedented length and quality. The temperatures were reconstructed using one method consistent for the entire record in the laboratory: measuring the concentrations of stable oxygen isotopes within the ice, which varied with the temperatures prevailing at the times of ice formation. Previous studies had to draw on a range of different climate archives and combine results to reconstruct temperature, introducing greater uncertainty into the assessment of natural variability.
In addition to temperature, the team reconstructed the ice sheet’s melt production. Melting has increased dramatically in Greenland since the 2000s and is now contributing significantly to global sea level rise. “We were amazed to see how closely internal temperatures are linked to Greenland-wide meltwater discharge—which, after all, occurs in low-altitude regions along the edge of the ice sheet near the coast,” says Maria Urhold.
In order to determine this association between temperatures in the high-altitude portions and melting along the edges of the ice sheet, the authors used data from a regional climate model for the years 1871 through 2011 and satellite observations of ice mass changes for the years 2002 through 2021 from the GRACE/GRACE- fo. This allowed them to convert specific temperature changes in the ice core into melting rates and provide estimates for the past thousand years. This represents an important data set for climate research: a better understanding of past ice-sheet melt dynamics improves projections of future sea-level rise; Reducing uncertainty in projections is one step to help improve adaptation measures.
Another exciting finding from the study: The climate of the Greenland ice sheet is largely separate from the rest of the Arctic. This can be shown by comparison with the ‘Arctic 2k’ Arctic-level temperature reconstruction. Although “Arctic 2k” is an accurate representation of the polar region, it does not reflect conditions in central Greenland. “Our reconstruction provides a robust representation of the temperature evolution of Central Greenland, which has proven to have a dynamic of its own,” says Professor Thomas Lebel, climate researcher at AWI and co-author of the study. “In fact, we expected the time series to be strongly proportional to the warming of the Arctic region,” Lebel says. But the authors have an explanation for these differences: the ice sheet is several kilometers thick; Because of its elevation, Greenland is affected by atmospheric circulation patterns more than other parts of the Arctic. Lebel says Arctic temperature time series with regional resolution are needed, in order to reliably describe Arctic climate change.