Dr. Nicolaj Krog Larsen, Aarhus University in Denmark and Professor Kurt Kjær, Natural History Museum of Denmark, ventured off to Greenland to investigate how fast the Greenland Ice Sheet reacted to past warming. Over six summers, they cored lakes in the ice-free land surrounding the ice sheet. The lakes act as a valuable archive as they store glacial meltwater sediments in periods where the ice is advanced. That way it is possible to study and precisely date periods in time when the ice was smaller than present.
Evidence has disappeared
The size of the Greenland Ice Sheet has varied since the Ice Age ended around 11,500 years ago, and scientists have long sought to investigate the response to the warmest period 8,000-5,000 years ago where the temperatures were 4 °C warmer than present.
"The glaciers always leave evidence about their presence in the landscape. So far the problem has just been that the evidence is removed by new glacial advances. That is why it is unique that we are now able to quantify the mass loss during past warming by combining the lake sediment records with state-of-the-art modelling," said Kjær.
Their results show that the ice had its smallest extent during the warming between 8,000 and 5,000 years ago, so they reviewed available ice sheet models to choose the ones that best reproduced the reality of the past warming.
The best models show that during this period the ice sheet was losing mass at a rate of 100 Gigatons per year for several thousand years, and delivered the equivalent of 16 centimeters of global sea-level rise when temperatures were 2-4 °C warmer. For comparison, the mass loss in the last 25 years has varied between 0-400 Gigaton per year. In the more speculative estimates it is claimed that the Arctic could warm up to 7 °C by the year 2100.
Published in Geology.