Most of the World's Permafrost Could Be Preserved Until 2100 By Horses, Reindeer and Bison, Study Suggests

Horses, bison and other large herbivores could be used to help save most of the world's remaining permafrost and reduce thaw with their feet, say scientists writing in Scientific Reports.

A preliminary study inspired by experiments in Siberia involving herds of horses, bison and reindeer used computer models to calculate how much permafrost could be saved if the Arctic circle was repopulated with large herbivores. Their research suggests 80 percent of the world's permafrost could be preserved until 2100 with animal intervention.

Herbivores, the researchers say, can help protect permafrost-covered regions because their stamping hooves scatter and compress snow cover. This reduces the insulating effect of the permafrost, reducing warming and preventing further thawing—instead "intensifying the freezing" of the permafrost, the study author's write.

Observational studies have previously shown that the depth of snow cover can be significantly reduced just by having grazing animals present. One hundred herbivores in one square kilometer of land, for example, can slash the average depth of snow in half.

Now scientists at Universität Hamburg have looked at what would happen if that was applied to the entire Arctic circle and not just Pleistocene Park in Chersky, northeast Russia, where two scientists—Sergey and Nikita Zimov—resettled bison, wisents, reindeer and horses more than two decades ago.

Computer models based on these observations as well as data on factors including snow depth, land surface temperature and ground cover were used to calculate how much permafrost could be saved. The researchers found that under a scenario where greenhouse gas emissions remain unchecked (RCP 8.5), permafrost temperatures would be expected to increase 3.8°C. But that number could be reduced 44 percent to 2.1°C if the area is repopulated with large herbivores. That, the study suggests, would be enough to save 80 percent of the permafrost around today.

The scientists considered adverse side effects of introducing grazing animals, including the destruction of cooling moss in the summer. They say the positives outweigh the negatives though point out that as a first model experiment, the study does not necessarily consider all ecological and physical processes and the proposal requires further investigation.

The permafrost has traditionally been a carbon sink, storing vast amounts of carbon. But this could change and temperatures increase and the ice thaws, releasing that carbon into the atmosphere and accelerating climate change.

"At the moment we have a budget of CO2 that we can emit to the atmosphere to stay below 2°C," lead author Christian Beer, Heisenberg-Professor for dynamics of soil processes at the Universität Hamburg in Germany, told Newsweek. The thawing of the permafrost could release a substantial amount of additional greenhouse gasses in addition to those released by human activity, using up large chunks of the carbon budget.

By some estimations, the permafrost has the potential to release 11 to 143 gigatons into the atmosphere by 2100. In comparison, human society generates approximately 10 gigatons of fossil fuel carbon emissions each year.

According to Froese, this is one of the few methods exploring ways to reduce thawing of the permafrost that does not involve reducing emissions and mitigating climate change. "I don't know any other method," he said.

"There are really no solutions to the increasing problem of permafrost thawing in the Arctic other than mitigation and adaptation around communities and infrastructure," Duane Froese. Professor Earth and Atmospheric Sciences at the University of Alberta, told Newsweek. "The present study, and the experiments at Pleistocene Park, are novel ideas about the problem.

"The grand challenge here is how do you scale this to the Arctic as a whole? It works at the plot scale but could it be done over much larger landscape scales?

Froese says the plan would be controversial and it is not known yet exactly how many horses or bison or reindeer will be needed to have a significant effect—but the idea deserves more work and attention.

That is something Beer hopes to find out. "It would be really interesting to investigate on a large scale how many herbivores per square kilometer are needed," he said. "Do we need 15 per square kilometer or 20?"