4 October 2023

Superficial permafrost could (almost) disappear by 2100

,

By the end of the century, near-surface permafrost may exist only in the highlands of eastern Siberia, the High Arctic and northern Greenland. As was the case 3 million years ago

by Matteo Cavallito

 

Most of the near-surface permafrost could disappear between now and 2100. This is claimed by a study by a team of scientists from the United States, Russia, the United Kingdom, Germany, Japan, Canada, the Netherlands, France and Sweden. The team, led by Donglin Guo, a researcher at the Chinese Academy of Sciences and Nanjing University, compared the current climate scenario with that of millions of years ago. The results were published in the journal Proceedings of the National Academy of Sciences.

“Our study indicates dramatically smaller-than-present near-surface permafrost extent in the geological past, under climate conditions analogous to those expected if global warming continues unabated,” write the authors quoted in a statement released by the Fairbanks Geophysical Institute at the University of Alaska.

The scenario? Like three million years ago

The term “permafrost” refers to the type of perennially frozen (but not necessarily ice-covered) soil found in some cold regions. Of particular interest to scientists is its surface layer, which is subject to melting in the summertime. According to the authors, in particular, by the end of the century, permafrost located in the first 3-4 meters of soil depth could survive only in the highlands of eastern Siberia, the Canadian High Arctic archipelago and the northernmost part of Greenland,

This would be, the researchers still explain, the same situation found in the warm period of the Middle Pliocene, an epoch about three million years distant from us. The comparison is based on a simulation based on the analysis of several factors, such as vegetation composition and soil characteristics. This leads to assumptions about surface air temperature and the extent of permafrost.

The study

“Studies of how permafrost responded historically during Earth’s past warm periods are helpful in exploring potential future permafrost behavior and to evaluate the uncertainty of future permafrost change projections,” the paper states. “Here, we combine a surface frost index model with outputs from the second phase of the Pliocene Model Intercomparison Project to simulate the near‐surface (~3 to 4 m depth) permafrost state in the Northern Hemisphere during the mid-Pliocene warm period (mPWP, ~3.264 to 3.025 Ma).”

On balance, the researchers explain, the simulations “demonstrate that near‐surface permafrost was highly spatially restricted during the mPWP and was 93 ± 3% smaller than the preindustrial extent“. Esse inoltre “are similar to near‐surface permafrost changes projected for the end of this century under the SSP5-8.5 scenario and provide a perspective on the potential permafrost behavior that may be expected in a warmer world.”

The loss of permafrost will have consequences for the carbon cycle

According to Vladimir Romanovsky, a researcher at the University of Alaska Fairbanks Geophysical Institute and co-author of the study, the loss of permafrost “will have widespread implications for human livelihoods and infrastructure, for the global carbon cycle and for surface and subsurface hydrology.” And the fears, of course, are related to CO2 leakage as a result of thawing.

To date, recalls an estimate quoted  by the University of Arizona, permafrost contains, on a global scale, “a whopping 1,500 trillion grams of carbon (1,5 bn tonnes, ed.),. That’s twice as much as what’s stored in the atmosphere.”

According to research carried out last year by scientists at the University of Arizona, predictive models suggest that under current global warming conditions, thawing would affect 20 percent of the Arctic permafrost’s surface area and 60 percent of Alpine near-surface area in the future (but the time horizon is not defined).