Sergey Zimov: “Thawing permafrost is a direct threat to the climate”

Beyond the Arctic Circle, in the heart of northern Siberia, Russian scientist Sergey Zimov has created Pleistocene Park – to reconstitute the ecosystem of the Ice Age by reintroducing large herbivore species into the former Mammoth steppe, where the soil had become severely depleted. Restoring these ecosystems could also help halt the thawing of the permafrost, a gigantic layer of glacial ice that traps billions of tons of organic carbon. As it melts, the microbes that dwell here quickly convert formerly frozen organic matter into carbon dioxide and methane. The release of these greenhouse gases as a result of climate change is a threat that has long been ignored.
Sergey Zimov

Interview by Katerina Markelova 

Why has the permafrost started to thaw?

The release of greenhouse gases into the atmosphere is warming the planet. To date, its temperature has risen by more than 1 °C. In the northern hemisphere, in Russia for example, the warming observed is even more than 3 °C. This is because the land is warming faster than the ocean. And the land area is larger in the northern hemisphere. 

But the temperature of the permafrost is not just dictated by the air temperature – it also depends on the thickness of the snow cover. When there is a lot of snow, the ground and the permafrost do not get much colder in winter. Today, the snow cover is one and a half times greater than it was several decades ago. With global warming, more water is evaporating from the ocean, and clouds are producing more snow than before. As a result, the ground temperature in Russia has risen by 5 °C to 7° C.

Permafrost temperatures used to range between -6 °C and -8 °C in the north of Siberia and between -2 °C and -3 °C in the south. Now, almost half of Siberia is melting  – the southern part of the region, but also the lower Kolyma, an area of continuous permafrost on the edge of the Arctic Ocean. Near my home, the permafrost has thawed by more than four metres in some places. In the large coastal plains of Kolyma, this phenomenon began three years ago.

As the permafrost melts, the goals of the Paris Agreement become meaningless
A cross-section of the Duvanny Yar on the right bank of the Kolyma River – three hours by boat from Cherskii – provides a lateral view of the thawing permafrost.
A cross-section of the Duvanny Yar on the right bank of the Kolyma River – three hours by boat from Cherskii – provides a lateral view of the thawing permafrost. © The Zimov Hypothesis/Arturo Mio

What are the dangers associated with melting permafrost?

Permafrost covers 11 million square kilometres of Russian territory. These are rich soils that are full of organic matter and dormant bacteria. When the soil thaws, the old microorganisms wake up and attack what they have not had time to consume – releasing carbon dioxide when the soil is dry, and methane when it is saturated with water.

There is twice as much organic matter in our permafrost as there is in all the flora of the planet. Most of it, equivalent to 1,000 gigatons, is concentrated in the first three metres. And three metres thaw very quickly – it only takes three to five years. This is why the thawing of the permafrost is a direct threat to the global climate today. It produces greenhouse gases, and the resulting global warming in turn accelerates the thawing of the permafrost. It’s very difficult to stop this process.

Under these conditions, the goals of the Paris Agreement – adopted in 2015 to move to a low-carbon economy on a global scale – become meaningless. The reduction of greenhouse gas emissions that could be achieved through the Agreement and renewable energy represents only a small part of the permafrost emissions.

The methane released by permafrost is far more dangerous than carbon dioxide...

If it were only carbon dioxide that was released from the melting, permafrost emissions would be equivalent to those generated by humans. But some of the gas released into the atmosphere, about  ten per cent to twenty per cent, is methane. And since the greenhouse effect of methane is eighty  times more powerful than that of CO2 over short periods of time, the climatic consequences of the release of this gas can be up to four times greater than those resulting from the emission of carbon dioxide.

During the first year and a half of the Covid-19 epidemic, anthropogenic greenhouse gas emissions slowed down significantly. One might have expected the overall concentration of greenhouse gases in the atmosphere to decrease. Instead, there has been a historic increase in the concentration of methane. I regularly observe the appearance of new small springs where methane is bubbling up. I cannot see any other explanation for this high concentration.

Why is the thawing of the permafrost not taken into account in the analyses and forecasts of the Intergovernmental Panel on Climate Change (IPCC)?

Thirty years ago, the scientific community thought it knew the carbon cycle well. Nobody thought about permafrost. When I started talking about the effects of melting, it became clear that all the equations had to be rewritten. In the early years, many scientists disputed my conclusions, refusing to believe that the permafrost was melting. Permafrost has long been treated like an unwanted child in the scientific family. According to the latest estimates, it will have shrunk by ten per cent to twenty per cent by the end of the century. Awareness about it will probably come only this year, thanks to the observation of the significant increase in global greenhouse gas concentrations. 

Twenty years ago, you created Pleistocene Park, not imagining that it would one day contribute to climate protection. Could you tell us about it?

I created Pleistocene Park to observe how quickly animals could transform the moss tundra into productive grassland. My main objective at the time was to solve a scientific mystery – why had the natural environment, which had known so many grasslands, horses, bison, mammoths, become so poor?

The park occupies part of the Kolyma River basin, where the vegetation is rich, and the surrounding hills are covered with larch and shrub forests, marshes and mosses. We have fenced off a portion of this land and introduced various animals: bison, musk oxen, reindeer, yaks, Yakutian horses. Today there is a 200-hectare area with a high density and another 2,000 hectares that have not yet been fully populated. In twenty years, the peat bogs have been trampled, the shrubs broken, and the amount of grass – which dries out the marshes – has increased significantly.

Our park is located in a fairly typical region of Siberia, and shows that it is possible to replace peat bogs and sparse forests everywhere with productive grasslands on dry, dense land. Most of the animals that used to live here can adapt to this environment again.

Experiments at Pleistocene Park show that it is possible to reconstruct an ecosystem comparable to that of the Mammoth steppe – that was dominant in Eurasia at the end of the Pleistocene – across Siberia.
Experiments at Pleistocene Park show that it is possible to reconstruct an ecosystem comparable to that of the Mammoth steppe – that was dominant in Eurasia at the end of the Pleistocene – across Siberia. © Sergey Zimov

Why have the ecosystems of the Mammoth steppe disappeared?

Mainly because of humans. The preservation of diverse grassland ecosystems requires a lot of effort. Moss and trees grow everywhere, and it is very difficult for grasses to resist. The maintenance of grasslands requires a lot of “gardeners”. When humans began to colonize Siberia or America, they reduced the number of animals everywhere. They didn’t kill them all, of course, but if there are only half as many animals, trees, shrubs and mosses will invade the grassland. Through excessive hunting, humans have destroyed these large ecosystems.

Your research in Pleistocene Park has shown that grassland ecosystems can slow down the thawing of the permafrost.

Our measurements have not shown anything that is not already known. Take albedo, for example. Scientists have known for a long time that dark forests absorb the sun's rays, while the lighter, snow-covered grasslands reflect them in winter.

It is also well-established that the thickness of the snow cover has a significant influence on ground and permafrost temperatures. The specialist literature indicates that an additional ten centimetres of snow increases these temperatures by more than 1 °C.

In the grassland ecosystem, everything that grew during the summer must be consumed in the winter. The only way to access the grass during the cold season is to dig through the snow. Our animals dig in the snow all winter long. This contributes greatly to the cooling of the soil.

How many animals does it take to make an ecosystem like this work?

It takes tens of millions of animals to affect the climate, about ten tons per square kilometre. Maybe even fifteen tons, with global warming. What do ten tons of animals per square kilometre represent, when a horse weighs 400 kilos and a bison 500 kilos? That's dozens of animals. 

Before the arrival of humans, horses and bison accounted for sixty per cent to seventy per cent  of the zoo mass, and reindeer and mammoths, for ten per cent each. The other animals made up the remaining ten per cent. Similar proportions, in fact, are found in the African savannah. Until recently, the population there consisted mainly of zebras, wildebeest, elephants, and gazelles. Our goal is to give all surviving species a chance, to help them at the beginning. Then we will let them manage their own relationships – with each other, and with their predators.

Within a decade, we could populate the Siberian ecosystems with herbivores, and have a significant impact on the climate.
The Northeast Science Station in Cherskii, northern Siberia.
The Northeast Science Station in Cherskii, northern Siberia. © Hypothèse de Zimov / Arturo Mio

Where will we find all these animals?

First of all, you should know that even large animals reproduce relatively quickly. They can multiply a hundred times over every twenty-five years. Today in Russia, there are several million reindeer, half a million Yakutian horses, thousands of musk oxen and snow sheep. It would therefore be easy to obtain tens of millions of animals in Siberia within five to ten years, and their number could reach several hundred million in twenty-five or thirty years. In other words, within a decade, we could populate the Siberian ecosystems with herbivores, and have a significant impact on the climate.

Our family has created two parks [the second, Wild Field, is located in the Tula region, about 250 kilometres south of Moscow] on a small scale, without any state funding. We use expensive means of transportation, we move a few animals, we face many administrative problems related to health regulations and customs – and yet we have succeeded. If one family of scientists could do it, large states could easily do it through international co-operation.

At Harvard Medical School in the United States, a team of scientists led by geneticist George Church is working on genetically resurrecting woolly mammoths thousands of years after they went extinct. What links do they have with Pleistocene Park?

Grassland ecosystems have all had elephants – the African elephant, the Asian elephant, mastodons, steppe mammoths, or mammoths in general. I believe that the main function of the elephant in the Mammoth steppe was to provide water sources. The streams and rivers often dry up in the summer, and the animals have to look for water several dozen kilometres away. Elephants and mammoths can dig holes to collect water in ditches. After they have drunk, other animals can also take advantage of this.

In winter, the animals eat snow and do not need water. But in Siberia, autumn is often cold, and the rivers and lakes freeze over before the first snow. At this time, animals risk dying of thirst. Mammoths could break through any ice, drink, and allow other animals to drink. In our case, we could imagine an Asian elephant with longer hair and increased fat reserves. This is what the Harvard scientists are working on. I plan to experiment this year with the adaptation of Asian elephants to our climate.

Which regions of the planet should be occupied by mammoth steppe ecosystems to stop the permafrost from melting?

The entire extent of the permafrost. With the help of animals, the permafrost could be cooled by 4 °C. This would give humanity a chance to adapt to global warming. These ecosystems must be reconstituted not only where there is permafrost, but more generally, everywhere in Russia, where the territory is not exploited. It is not just permafrost that threatens the climate, but also all the land in the north that is rich in organic matter. The rate of decomposition of organic matter in the soil depends mainly on its temperature. The only way to force the soil to retain carbon is to cool it down. 

We must create parks right now in many parts of Siberia – besides expanding our own, we should open parks in the Indigirka River basin; in Central Yakutia; south of the Taimyr Peninsula; in the northern Urals – and introduce animals in these parks. Then it will be necessary to expand these parks and introduce animals accustomed to the climate, and to each other, into new territories. 

Forest fires in Siberia and the melting permafrost are destroying ecosystems. Every year there are more and more places where grass can grow. These are all ready-made grasslands. If we created wildernesses in these areas, nature would continue to develop on its own. Animals could then, without human intervention, help regulate climate change.

Sergey Zimov

The Russian geophysicist and ecologist Sergey Zimov founded the Northeast Science Station in Cherskii, northern Siberia, which serves as an open-air laboratory today. He is also one of the research directors of the Pacific Geographical Institute of the Far Eastern Branch of the Russian Academy of Sciences. 

Zimov initiated the first experiments to reintroduce mammals into the Kolyma River basin in 1988, and created Pleistocene Park in 1996. Its mission is to restore an ecosystem comparable to the Mammoth steppe which was dominant in Eurasia in the late Pleistocene epoch – between 2.58 million years and 11,700 years ago.

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