Jan. 18 () –
A reconstruction of the temperature from ice cores from the last 1,000 years reveals that the current warming in north-central Greenland is surprisingly pronounced.
The most recent decade analyzed in a study, the years 2001 to 2011, was the warmest in the last 1,000 years, and the region is now 1.5°C warmer than it was in the 20th century, according to researchers from the Alfred Wegener Institute in the magazine ‘Nature’. Using a set of ice cores unprecedented in length and quality, they reconstructed past temperatures in north-central Greenland and ice sheet melt rates.
The Greenland Ice Sheet plays a critical 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, it is projected that the ice sheet will contribute up to 50 centimeters to global mean sea level in 2100.
Weather stations on the coast have been recording rising 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 a lack of observations. long-term. 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 they have reached the remote and elevated areas of north-central Greenland.
“The time series we recovered from the ice cores now spans more than 1,000 years continuously, from the year 1000 to 2011. These data show that the warming from 2001 to 2011 clearly differs from the natural variations of the last 1,000 years. Although this was to be expected in light of global warming, we were surprised at how apparent this difference was,” he says. it’s a statement Dr. Maria Hörhold, AWI glaciologist and lead author of the study. Together with colleagues from AWI and the Niels Bohr Institute at the University of Copenhagen, Denmark, she analyzed the isotopic composition of shallow ice cores collected in north-central Greenland during specific AWI expeditions.
Previous ice cores, obtained at the same locations starting in the 1990s, did not indicate clear warming in north-central Greenland, despite rising global mean temperatures. This is due, in part, to 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 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. Previous studies had to draw on a number of different climate files and combine the results to reconstruct the temperature, which introduced much larger uncertainties in the assessment of natural variability.
In addition to temperature, the team reconstructed the melt production of the ice sheet. Melt 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 meltwater runoff across Greenland, which, after all, occurs in low-lying areas along the edge of the ice sheet, near the coast,” explains Maria Hörhold.
To quantify this 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 ice mass changes for the years 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 last 1,000 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 it is a 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 to the ‘Arctic 2k’ whole-Arctic temperature reconstruction. Although ‘Arctic 2k’ 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 central Greenland, which has been shown to have a dynamic of its own,” said Professor Thomas Laepple, AWI climate researcher and co-author of the study. Actually, we expected the time series to covary strongly with warming in the Arctic region.”
But the authors have an explanation for these differences: the ice sheet is several kilometers thick; Due to its height, Greenland is more affected by atmospheric circulation patterns than other parts of the Arctic. Regionally resolved Arctic temperature time series are needed, according to Laepple, to reliably describe climate change in the Arctic.
