ND: The Atlantic article and Vice News segment got me really excited about Pleistocene Park. Can you give our readers an overview of the project?
Guy Lomax: Pleistocene Park is a large-scale ecological experiment sitting on a remote stretch of tundra in the northern Siberian Arctic. Dr. Sergey Zimov and his son Nikita, the principle researchers on the project, are attempting to recreate a thriving grassland ecosystem in the tundra not seen since the last ice age in order to help curb the melting of permafrost as the climate warms. Such northern grasslands, known as the Mammoth Steppe, were actually once the world’s largest terrestrial biome, stretching from France to modern China, and across the Bering Strait (then a land bridge) into Canada. At its peak around 25,000 years ago, the Mammoth Steppe supported vast herds of bison, musk ox, wild horses and, of course, woolly mammoths.
Over many thousands of years, the grasslands and grazers of the Mammoth Steppe were responsible for drawing down much of the 1,330-1,580 billion tonnes carbon from the atmosphere that is preserved in the northern permafrost across the Eurasian and North American Arctic. The fast-growing grasses absorbed a lot of carbon from the air and buried it deep in the soil as root biomass and other organic compounds. Cold and permafrost in deeper soil layers then protected the carbon from decay by microbes. Helped by a steady influx of wind-blown glacial dust across Siberia, this soil carbon grew into deposits tens of metres thick in places.
ND: How could restoring the Mammoth Steppe be a climate solution?
GL: There are two halves to how this project could help avert climate change.
The first is the effect that restoring the Mammoth Steppe could have in keeping the permafrost frozen, thus preventing the massive greenhouse gas (GHG) emissions expected from a thawing of the Arctic tundra (which is warming on average twice as fast as the planet overall). As permafrost thaws, Ice Age microbes wake up and begin consuming the trillion tonnes of Ice Age organic carbon in the soil, converting it quickly into carbon dioxide and a little methane. The result is a feedback loop where permafrost melting accelerates warming, which thaws more permafrost, releasing more greenhouse gases (GHGs).
A single hectare of thawing permafrost soil can emit about 400 tonnes of carbon in the first century after melting begins, about twice that emitted by clearing the same area of tropical rainforest. When the Ice Age ended, Sergey has estimated that melting permafrost across Europe and Siberia released more than a trillion tonnes of carbon to the atmosphere. By 2100, our current warming trajectory could melt the equivalent of between 100 and 300 billion tonnes of carbon out of the tundra as both carbon dioxide and methane.
What the Zimov’s results are starting to show, however, is that grassland soils stay several degrees colder than those of the tundra – meaning less thawing and thus more carbon storage. Arctic grasslands would keep the tundra cooler than today’s forests do for a number of reasons. First, grasses reflect more sunlight in summer than mosses, preventing the ground from warming as much in these snow-free periods. In addition, animal herds compact the thick layers of snow that build up in the winter, reducing the insulating effect of that snow on the soil. When January air temperatures routinely fall below -25°C and can reach -50°C, snow acts like an insulating blanket, so when grazers compact the snow and expose soils to the winter air, the cold penetrates deeper into the soil. This deep freeze then protects the soils from thawing when temperatures rise in summer.
ND: Gotcha, so that’s the GHG abatement half of the story. Would restoring this ecosystem also sequester additional carbon from the atmosphere on top of protecting the carbon that’s already there?
GL: On average, Mammoth Steppe soils of the past seem to have accumulated carbon at around 0.1 tonnes of carbon per hectare per year, slightly slower than in the northern peatlands today. And like peatlands, some of the soils once covered by the mammoth steppe now hold thousands of tonnes of carbon per hectare in preserved peat.
The current tundra landscape in Siberia is dominated by unproductive mosses, which have almost no roots, and sparse shrubs. By transiting tundra back to the deep-rooted and productive grasses of the Mammoth Steppe, you’d likely see a surge in net carbon sequestration in the first few decades as the grasses pumped extra carbon below the soil surface, where temperatures and thus rates of decay are lower. Unsurprisingly, there are few data specific to boreal grasslands yet, but in temperate soils the return of grasses to bare or cultivated soil can drive sequestration of 0.3-0.6 tonnes of carbon per hectare per year.
That still may seem small compared to the emissions from melting permafrost. Yet over the vast area once covered by grasslands, this could amount to sequestration of tens to hundreds of millions of tonnes per year. But to answer this question fully, we’ll need the data on soil carbon accumulation from Pleistocene Park itself.
ND: If we replace northern forests with grasslands, isn't there a huge biomass carbon deficit that will exacerbate climate change for decades before soils have had a chance to accumulate significant amounts of carbon?
GL: It’s not clear how much the expanding Mammoth Steppe would really replace much true boreal forest, as opposed to tundra and shrubland. At least until humans are able to reintroduce mammoths to the ecosystem!
But if it does, there would likely be some emissions associated with the loss of the forest. Then again, 80% of carbon in the boreal forest is typically below the surface in soils. And tree species adapted to permafrost soils can be damaged or even killed if the permafrost melts, when subsidence or erosion leads to collapse of their foundations.
So, the net climate impact would still depend on the alternative fate of that piece of forest.
ND: What about the balance between soil carbon sequestration and the methane emissions from massive reintroduction of grazers?
GL: Sergey and Nikita have estimated the numbers of animals per square kilometre at the peak of the Mammoth Steppe from the bones they have uncovered in the permafrost: five bison, seven and a half horses, fifteen reindeer and one woolly mammoth!
Based on estimates of typical methane emissions from these species, we can estimate that animals at the ecosystem’s peak were producing 0.3-0.5 tCO2e/ha/year in methane (based on a 100-year global warming potential).
That’s the same order of magnitude as potential carbon sequestration, and a lot lower than the emissions we’d expect if the permafrost started melting, which may be tens of tonnes of CO2-equivalent per year. But it is enough to become a significant new source of methane if the Mammoth Steppe is restored at scale, and needs to be accounted for.
ND: How much do you think it would cost to realize the Zimov’s vision, in terms of dollars per hectare or per tonne of carbon avoided?
GL: Nikita estimates it would take $1 billion to scale up Pleistocene Park over a “continental scale”. The North Siberian plains tundra area covers 100 million hectares. Assuming even 1% of that could be restored and preserved as permafrost with this investment, that would imply a cost of around $1000/ha. Based on Sergey’s estimate of historic emissions from melting permafrost, CO2 and methane emissions could amount to more than 16-20 tCO2e/ha/year. That would conservatively imply costs on the order of $2.5-3/tCO2e avoided just over the first 20 years.
But it all depends now on demonstrating whether the model works, gathering better data and proving whether Pleistocene Park can create an ecosystem that can survive in the wild.
ND: What’s next for Pleistocene Park?
GL: Eventually, they hope to see the restoration of the Mammoth Steppe across hundreds of millions of hectares of tundra. The Zimovs have already returned wild horses, musk ox, reindeer and moose to the park, and seen large areas of grassland return; now they are sourcing populations of bison, yaks, and elk. In the future, once the herbivores are established, Nikita wants to bring back tigers, wolves and, one day, perhaps even woolly mammoths to complete the ancient ecosystem.
It’s not going to be a quick fix: to make an impact on the climate, the Mammoth Steppe will need to spread again across many millions of hectares. Sergey readily admits the project must be a global, intergenerational effort. But the first step to reaching that kind of scale tomorrow is to fully understand the science today.
And to state the obvious for a moment, climate change itself is an issue that will be felt for generations to come. Pleistocene Park, if it can demonstrate that large-scale regeneration of this ecosystem is feasible and effective, could be the seed of unprecedented ecosystem restoration efforts over the coming century.
ND: Where can readers learn more about the project?
GL: Visit the Pleistocene Park website. Learn more about Pleistocene Park in Ross Andersen’s article in The Atlantic. You can also read about the Zimovs’ work in Science. The project’s founders, Sergey and Nikita Zimov are currently running a Kickstarter to take their project to the next level.
ND: as always, thanks Guy!
Guy Lomax is a researcher in the Natural Climate Initiative at The Nature Conservancy, specializing in the science of carbon sequestration and mitigation in soils and ecosystems. Guy also works with the Virgin Earth Challenge – Sir Richard Branson’s $25M innovation prize for scalable and sustainable ways of removing carbon from the atmosphere. Guy has been following Pleistocene Park for several years as part of his work, since he met Sergey Zimov at a megafauna conference in Oxford back in the day.