A cave in Greenland has shown that temperatures in the High Arctic were 25 degrees Fahrenheit higher than those of today.
Minerals in the cave date back to roughly 9.5–5.3 million years ago. Their chemistry points to rapid flips between mild conditions and brief advances of small glaciers, suggesting the region reacted swiftly to climate shifts.
Inside the Greenland cave, calcite could accumulate only when liquid water moved through the ground. That detail alone shows the landscape wasn’t locked in permafrost during the periods when these layers formed.
The sequence captures several episodes of warmth and moisture that were interrupted whenever temperatures cooled enough for small glaciers to reappear. As a result, the cave offers an uncommon land-based record from the far north that lines up with long-studied evidence from ocean cores.
Scientists connected the timing of the cave’s mineral growth to both warmer nearby seas and relatively moderate atmospheric CO? levels. They found that thawed ground and running water occurred whenever carbon dioxide climbed to about 310 ppm or higher. One researcher noted that each cave behaves like its own character, preserving climate history in a distinct and unpredictable way.