Science, 20 July 2023
Ancient sediments trapped beneath the northwestern portion of Greenland’s ice sheet confirm ice-free conditions existed for around 16,000 years there, during a period of only 1°C-2°C of warming. That sustained warmer period occurred 400,000 years ago, for about 30,000 years total, when sea levels were 6-13 meters higher than today. Modeling of these conditions in this study show that Greenland would have contributed at least 1.4 meters of that global sea-level rise; and perhaps as much as 6 meters, meaning that nearly the entire ice sheet had melted. The site of the ice and sediment core used in this study is today buried beneath nearly 2km of ice. These findings make clear the danger of exposing Earth’s ice sheets to sustained warming even below the 2°C Paris Agreement limit, with temperature of 1.5°C or lower carrying far less risk to low-lying coastal communities. It stresses the importance of urgent emissions reductions consistent with the lower 1.5°C Paris limit, such as the “very low” (SSP1) emissions pathway outlined by the IPCC in its Sixth Assessment earlier this year.