A remarkable discovery in northern Greenland is reshaping what we know about the Arctic’s ancient climate. Deep inside a remote cave, researchers found calcite formations — speleothems — that could only have formed when the ground above was free of permafrost and liquid water was flowing. Their chemical signatures reveal that between 9.5 and 5.3 million years ago, the High Arctic was far warmer than it is today. By analysing oxygen and carbon isotopes, scientists concluded that mean annual temperatures in the area were roughly 14 °C warmer than today. During these intervals, atmospheric CO₂ hovered around 310 ppm, and local sea temperatures were a few degrees higher than modern levels. Under these conditions, permafrost vanished, vegetation expanded, and ice likely retreated — showing how sensitive the Arctic climate system is to even moderate warming. The study highlights an important point: the Arctic has crossed similar thresholds before, and the consequences were profound. With today’s CO₂ levels already exceeding 420 ppm, the new findings offer a clear warning about the potential pace and extent of future Arctic change.
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