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In a remote cave in northern Greenland, a research team led by geologists Gina Moseley, Gabriella Koltai, and Jonathan Baker from the University of Innsbruck has discovered evidence of a significantly warmer Arctic. The cave deposits show that the region was free of permafrost millions of years ago and responded sensitively to rising temperatures.

The findings, in Nature Geoscience, provide new insights into past climate conditions and their relevance for today's climate protection efforts.

Understanding Earth's climate during earlier warm periods is key to predicting how it may change in the future. One particularly revealing time is the Late Miocene, which began about 11 million years ago.

During this period, Earth's distribution of land and ocean was similar to today, and both temperatures and atmospheric COâ‚‚ levels were comparable to projections for the coming decades. Although the Arctic is known to be highly sensitive to climate change, its environmental conditions during the Late Miocene have remained poorly understood.

To fill this knowledge gap, Moseley and her team traveled to one of the most remote regions on Earth—Greenland's far northern coast. The cave known as Cove Cave can only be reached by small aircraft and hiking through uninhabited terrain. During the expedition, the researchers discovered calcite deposits that can form only when the ground is unfrozen and water is flowing.

"These deposits are like tiny time capsules," says Moseley from the Quaternary Research Group at the Department of Geology. "They show that northern Greenland was once free of permafrost and much wetter than it is today."

Insights into past warm periods

The analyses revealed several warm and humid phases during the Late Miocene, between about 9.5 and 5.3 million years ago. During these intervals, average annual air temperatures in northern Greenland were about 14°C higher than today, and atmospheric CO₂ concentrations were at 310 parts per million (ppm) or higher. The cave record also shows that between the warm periods, the climate cooled and small glaciers formed.

"From this we can see that the climate reacted strongly and rapidly to changing boundary conditions," explains Moseley. Until now, such detailed insights into the climate history of the High Arctic have only come from marine sediments.

"Normally, climate records of this age come from the ocean," Moseley says. "Our study provides the first high-resolution terrestrial record from this region, and it matches the marine data remarkably well."

The results demonstrate that the climate in the High Arctic could already shift rapidly under relatively moderate COâ‚‚ levels. For Moseley, this is an important clue for the present: "The Arctic has never been a stable system," she says. "It shows how dynamic this region is and how quickly environmental conditions can change."

Relevance for the future

The study underscores that even small changes in atmospheric carbon dioxide can have major effects on the Arctic. "Our results highlight how sensitive the Arctic climate is and that every fraction of a degree matters," Moseley emphasizes.

Today, COâ‚‚ levels are well above the minimum concentrations associated with permafrost absence during the Late Miocene, highlighting an increasing risk of widespread thaw. These permanently frozen soils store vast amounts of carbon, which can be released as carbon dioxide and methane when the ground thaws.

"Every small step we take to limit warming helps to avoid these feedbacks and to reduce the impacts of climate change," Moseley says.