PNAS, August 5, 2024<\/p>\n
The center of Greenland \u2013 currently buried under a 3-kilometer-thick sheet of ice \u2013 supported plant life indicating that it was completely ice-free even when CO2 concentrations were far lower than today\u2019s levels, sometime within the past million years. The authors examined ancient remains of soil from the base of an ice core drilled at the summit of today\u2019s Greenland Ice Sheet. They found unmistakable remains of a tundra plant ecosystem that could only have formed in the absence of ice. Projections of future melting of the ice sheet are unambiguous: when the ice is gone at the summit, at least 90% of Greenland\u2019s ice must have melted. This groundbreaking evidence definitively proves that all or nearly all of Greenland\u2019s entire ice sheet disappeared at a point when warming was similar to today\u2019s, yet with CO2 concentrations far below today\u2019s levels \u2013 let alone the concentrations towards which humanity is rapidly heading. This significant loss of ice, when the causes of warming were not even especially extreme, demonstrates the high risk of continued fossil fuel emissions; and the need to return rapidly to lower CO2 levels in the atmosphere.<\/p>\n