2001-2011 warmest decade in the last millennium in central Greenland: Study

Scientists have found that the years 2001 to 2011 were the warmest in the last thousand years at high elevations of the Greenland Ice Sheet.

The scientists also found that the region was 1.5 degrees Celsius warmer than during the 20th century.

The team of scientists led by the Alfred Wegener Institute (AWI), Germany, reconstructed the temperature from a set of ice cores, unprecedented in length and quality, of the past 1,000 years, which revealed that today's warming in central-north Greenland is surprisingly pronounced. They also measured the melt production rate of the ice sheet, the study said.

The Greenland Ice Sheet plays a pivotal part in the global climate system. With enormous amounts of water stored in the ice, about 3 million cubic kilometres, melt and resulting sea-level rise is considered a potential tipping point.

For unmitigated global emissions rates, or business as usual' scenario, the ice sheet is projected to contribute up to 50 centimetres to global mean sea-level by 2100, the study published in the journal Nature said.

Weather stations along the coast have been recording rising temperatures for many years.

In a study now published in the journal Nature, experts from the institute present clear evidence that effects of global warming have reached the remote, high-elevation areas of central-north Greenland.

"The time series we recovered from ice cores now continuously covers more than 1,000 years, from year 1000 to 2011. This data shows that the warming in 2001 to 2011 clearly differs from natural variations during the past 1,000 years.

Although grimly expected in the light of global warming, we were surprised by how evident this difference really was," said AWI glaciologist Maria Hrhold, lead author of the study.

Together with colleagues from AWI and the University of Copenhagen's Niels Bohr Institute, she analysed the isotope composition in shallow ice cores gathered in central-north Greenland during dedicated AWI expeditions, the study said.

Previous ice cores obtained at co-located sites starting in the 1990s, did not indicate clear warming in central-north Greenland, despite rising global mean temperatures. Part of the reason is substantial natural climate variability in the region, the study said.

The AWI researchers have now extended the previous datasets up to winter 2011/2012 by a dedicated redrilling effort, recovering time series of unprecedented length and quality, the study said.

The temperatures were reconstructed by using consistently one single method for the entire record in the lab: measuring concentrations of stable oxygen isotopes within the ice, which vary with the temperatures prevailing at times of ice formation, the study said.

Previous studies had to draw on a range of different climate archives and combine results to reconstruct temperature, introducing much larger uncertainties in the assessment of natural variability, the study said.

In addition to the temperature, the team reconstructed the melt production of the ice sheet, the study said.

Melting has increased substantially in Greenland since the 2000s and now significantly contributes to global sea-level rise.

"We were amazed to see how closely temperatures inland are connected to Greenland-wide meltwater drainage - which, after all, occurs in low-elevation areas along the rim of the ice sheet near the coast," said Hrhold.

In order to quantify this connection between temperatures in high-elevation parts 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 melting rates and provide estimates for the past 1,000 years.

This represents an important dataset for climate research: better understanding of the melt dynamics of the ice sheet in the past improves projections of related future sea-level rise; reduced uncertainties in projections is one step to help optimize adaptation measures.