Experts have long expressed concern about the feedback loop between a warming climate and greenhouse gases released as permafrost melts and is decomposed by microbes.

Now a new study in the journal Nature Communications suggests mountain permafrost might melt even faster than frozen ground in northern climes.

"We need to really study these regions, understand how they're changing, what those rates of change are, and whether we can preserve them," said co-author Carmie Garzione, dean of the University of Arizona College of Science.

"Alpine permafrost supports unique ecosystems that don't exist in very many settings on Earth," she said. "However, they also hold a significant quantity of carbon in the form of frozen soil, and that carbon is also vulnerable to release as permafrost warms and thaws out."

Researchers combined climate models with lake sediment evidence from the Tibetan Plateau to reconstruct temperatures affecting alpine permafrost 2.7 to 4 million years ago, when pre-ice-age conditions resembled those expected under climate change.

They found around 60% of alpine permafrost could thaw under current CO2 levels, compared to 20% of permafrost near the arctic.

“When we discovered that the temperature in this region was above freezing at that time period, we began to think about that region as a great analog for the conditions that we are living in today with much higher CO2,” said Garzione.

Around half of the organic carbon stored in soil is trapped in permafrost located in and around the arctic region. That amounts to 1,500 trillion grams of carbon, or twice the amount currently in the atmosphere. Permafrost in mountains and highlands is less well studied, but likely holds around 85 trillion grams of carbon.

That smaller amount could make a sizable difference if it melts more quickly. 

"If you look at temperature maps of the Earth, the poles are warming at a faster rate than equatorial regions, and the same is true over altitude," said Garzione. "When we look at temperature records that are increasingly collected at high altitude, we see that high elevations are warming faster than low elevations."