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siberian-horses, Pleistocene Park


To slow permafrost thawing, bring in the horses

New research shows that time-traveling back to the Pleistocene could ensure a cooler future.
March 25, 2020

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Carbon has been accumulating in the world’s permafrost for millions of years. As the Arctic warms and the permafrost melts, it’s seeping out again. Experts warn that thawing permafrost is releasing hundreds of millions of tons of carbon each year, on par with the entire footprint of Japan.

But there may be a way to slow this process down: by bringing in the cavalry. Ongoing experiments in Siberia’s Pleistocene Park have shown that the presence of large herbivores—like horses, bison, and reindeer—decelerates permafrost warming considerably. A recent paper in Scientific Reports builds on this research, suggesting that if we let groups of grazers roam throughout the Arctic, they could keep 80% of the world’s permafrost intact until 2100.

Currently, the only large herbivores found in the Arctic are reindeer and musk ox, and there aren’t very many of them—about 5 individuals per square kilometer. But during the late Pleistocene, woolly mammoths, steppe bison, and other now-extinct giants wandered all over what is now Northern Eurasia. Since 1996, researchers in Siberia have tried to recreate that ecosystem on a small scale, keeping modern-day herbivores, like horses and bison, in a 5000-acre area they call Pleistocene Park. They then investigate soil temperature, moisture, and carbon content in order to investigate what the new study’s authors call the “potential of big herbivores to save permafrost from thawing.” 

So far, they’ve found, it’s working. Without the herbivores, layers of snow insulate the permafrost, even as the air temperature dips far below freezing. But as the quadrupeds wander, tromp and graze, they shred this snow blanket, ensuring the permafrost stays cool. It takes one hundred and fourteen animals per square kilometer—an area about the size of fifty Manhattan blocks—to cut the snowpack height in half, a population density “comparable with the situation during the late Pleistocene,” the new study’s authors write

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For this latest study, researchers asked what would happen if we scaled this strategy up, and brought similarly-sized herds of herbivores to stomp across the Arctic. This involved plugging results from a number of different studies into climate models that simulate land surface temperatures. Left untrampled, the models showed, the permafrost would warm 3.8 degrees Celsius over the next 80 years. 

Apply a Pleistocene-sized dose of hooves, though, and it only warms 2.1 degrees. This will “prevent 37% of permafrost soils from thawing across the entire Arctic,” leaving a total of 80% of soils intact, the authors write. Smaller herds would also have a positive effect. And negative climate-related side effects of the herbivores—like the destruction of moss in summer—would be more than counterbalanced by how much they help the permafrost, the authors found. 

“It may be utopian to imagine resettling wild animal herds in all the permafrost regions of the Northern Hemisphere,” the study’s lead author, Christian Beer, told Science Daily. But animal engineers have always helped to shape our shared world. And as we try to limit future damages, it makes sense to take a cue from this past. 

Source: Beer et. al., “Protection of Permafrost Soils from Thawing by Increasing Herbivore Density.” Scientific Reports, 2020.

Image: ©Nikita Zimov, Pleistocene Park

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