It is the world’s largest forest, and it has been soaking up carbon dioxide from the air at an unprecedented rate. So why are climate campaigners growing anxious about it?

Stretching across eleven time zones, Russia has the largest area of forest on the planet, with more than a fifth of the world’s trees. New research has found that, as those trees grow faster in a warmer world and edge northward into the Arctic tundra, they are grabbing carbon dioxide from the atmosphere faster than any previous estimates would suggest.

Most years, it turns out, Russia’s boreal forests take up more carbon than is being lost to deforestation across the whole of the tropics.

It is, of course, good news for the global climate that nature is in overdrive in the great wilderness of Siberia. But climate scientists are increasingly concerned that there is a downside, too. For the government of Vladimir Putin has, in recent months, said that it plans to meet its climate commitments under the 2015 Paris Agreement in large part by counting Siberia’s carbon uptake as an offset against the country’s industrial emissions, which would therefore be allowed to continue largely unchecked.

The new data, collected with the help of several Russian forest research institutes, suggests the scale of the offset that Russia — the world’s fourth-largest emitter of carbon dioxide from fossil-fuel burning — could declare.

Researchers have long known that roughly half of the carbon dioxide put into the air by burning fossil fuels is swiftly absorbed by nature. This carbon “sink” divides roughly equally between ocean and terrestrial ecosystems, mostly forests. The rest stays in the air, accumulating and causing the greenhouse effect that raises temperatures.

This means that the carbon dioxide absorbed by Russia’s forests is already accounted for in climate models. To claim credit for essentially natural processes will undermine the credibility of national targets for carbon emissions aimed at achieving “net zero” by 2050. Yet critics say that this accounting sleight of hand is allowed under rules established by the UN Intergovernmental Panel on Climate Change (IPCC) for measuring national contributions to cutting carbon emissions. Those rules, they say, have inadvertently written a blank check for any forested countries intent on preserving their right to continue burning fossil fuels.

Forests cover roughly half of Russia and contain an estimated 640 billion trees. Most are larch, pine, spruce and birch in Siberia, the vast region of Asia east of the Ural Mountains that was colonized by Russia in the 16^th century. Despite some logging, most of these forests are largely intact. The World Wildlife Fund (WWF) says that 70 to 75 percent of Siberia’s boreal ecosystems “remain close to their natural state” and include “the largest expanse of untouched boreal forest in the world.” And in recent decades they have been thriving.

The new research uses a detailed analysis of satellite images and previously unpublished data from a Russian forest inventory now nearing completion. The study, published last month in Nature, found that “Russian forests play an even more important global role in carbon sequestration than previously thought,” concluded lead author Dmitry Schepaschenko of the International Institute for Applied Systems Analysis (IIASA), an Austria-based intergovernmental research institution.

Since 1988, he calculated, Russia’s boreal forests have been capturing an average of 1.7 billion tons of carbon dioxide each year. Schepaschenko said that is 47 percent higher than reported in Russia’s previous national greenhouse-gas declarations and is enough to offset almost all of the country’s emissions from burning fossil fuels.

“Most of the carbon gains were in areas where both temperature and precipitation increased during recent decades,” Schepaschenko told Yale Environment 360. Besides trees growing faster in a more congenial Siberian climate, extra carbon was absorbed by forests spreading north into the Arctic tundra and onto an estimated 188 million acres of collective farms abandoned since the end of communist rule in 1990.

The findings are controversial, however. “The Russian forest sink is still very uncertain,” Giacomo Grassi of the European Commission’s Joint Research Centre in Ispra, Italy said after reviewing the findings. Another recent study put the Russian forest sink at just 180 million tons of carbon dioxide, barely a tenth as much, he said.

The size of the sink may vary greatly from year to year, said Anatoly Shvidenko of IIASA and the Sukachev Institute of Forest in Krasnoyarsk, a co-author of the IIASA study published in Nature. While some years it exceeds 2 billion tons, extensive fires in the past three years had reduced it to around 400 million tons, he said. By this week, fires had spread across some 3,000 square miles, releasing hundreds of millions of tons of carbon dioxide.

Fire “may lead to substantial decrease of the Russian forest carbon sink,” warned Pekka Leskinen and colleagues in a study of Russian forest and climate change last year for the European Forest Institute. Yet much depends on whether or not the forests are able to regrow, reabsorbing the carbon dioxide.

Despite the long-term concerns, the staggeringly high new estimates of the carbon-capturing role of Russian forests in recent decades are feeding a growing appetite in Moscow for cashing in. “We have the potential to turn them [forests] into a massive carbon capture hub,” Alexey Chekunkov, minister for the development of the Russian Far East and Arctic, told Bloomberg earlier this year.

In statistics submitted to UN climate negotiators, Russia already offsets more than a quarter of its national fossil fuel emissions against its forest sink. The new findings suggest that it could either increase that or sell the carbon absorption as carbon credits to fossil-fuel companies eager to offset their own emissions. It appears set on doing both.

Earlier this year, Putin announced plans for leasing forests in the Russian Far East to corporations that could claim carbon credits equivalent to the carbon captured in them. The scheme, known as lesvostok.rf, will operate on a digital platform using data on the state of forests collected by satellites and drones.

In theory, corporations would qualify for the carbon credits by increasing the existing carbon sink through planting trees or preventing fires and illegal logging. There is genuine potential to do this, according to Anna Romanovskaya, director of the Russian government’s Yu. A. Izrael Institute of Global Climate and Ecology in Moscow, one of the co-authors of the IIASA paper. In another paper in 2019, she put this “mitigation potential” across Russia at 545 to 940 million tons of carbon dioxide per year, with the biggest gains from preventing wildfires.

But many climate scientists have severe doubts about such numbers and how feasible it will ever be to identify the impact of direct human mitigation interventions. “Most countries, using direct observations, cannot disentangle the direct anthropogenic effects of forest harvest and regrowth from the indirect anthropogenic effects such as warming and rainfall change,” said Grassi of the European Commission’s Joint Research Centre. As a result, “one cannot say how much of a biomass change is due to better management and how much is due to environmental factors,” Grassi wrote in a recent analysis with other colleagues for Carbon Brief.

This is no side issue. Grassi and colleagues found that declarations by the world’s nations of how much carbon dioxide their forests soak up add up to 5.5 billion tons more each year than estimates from independent scientific models. The gap arises “because governments tend to assign most of this carbon absorption to human intervention, while models consider it natural,” Grassi said.

The difference is equivalent to more than one tenth of global human-caused emissions from fossil fuel burning, making it a major barrier to effective agreements on halting climate change. The problem is well known to climate scientists. To get around it, while keeping governments on board, the IPCC drew up guidelines, revised in 2019, for national declarations that used a crude proxy for human intervention. Rather than asking whether the carbon capture is caused by human activity or not, it instead asks whether the carbon capture happens in forests that are “managed” or not.

The IPCC defined managed forests as those either harvested for timber or actively protected from fire, disease or invasions by people, Grassi said. It ruled that all changes in the carbon content of these “managed” forests should be considered to be a direct or indirect result of human activity, while changes in unmanaged areas were not.

That is great news for climate negotiators in countries with large areas of formally managed forests that are absorbing carbon with little or no human intervention. Those countries can just stand back, do nothing, and count the carbon. Nowhere is that more so than in Russia.

Schepaschenko estimates that more than half the Russian forest carbon sink is within forests long categorized by the Russian government as “managed.” Technically managed or not, most are regarded by ecologists as being, in WWF’s words, “close to their natural state.” Logging and other human activities are minimal in most places, and where they happen, they are largely unchecked. So carbon capture by trees in these forests probably has little directly to do with human intervention to protect them. “Many argue that it should not be accounted towards the climate target,” Grassi said. But what he calls the “IPCC compromise” expressly permits that.

Russia is widely seen as a laggard on fighting climate change. It remains the world’s fourth-largest emitter of CO2 from burning fossil fuels, despite ranking ninth in terms of its population. Its current plans submitted under the Paris Climate Agreement see emissions rising slightly to 2030 before falling slowly afterwards.

In recent years, Russian emissions declarations to the UN have offset around a quarter of its fossil fuel emissions with claimed uptake of carbon by its forests. In 2019, it subtracted a carbon sink of 540 million tons from its overall emissions of 2.12 billion tons to give it net emissions of 1.58 billion tons. Moreover, the country has consistently said it would achieve its targets, “taking into account the maximum possible absorptive capacity of forests and other ecosystems.”

To that end, it recently widened further its definition of managed forests. In February, the Russian environment ministry said its designated managed forests would now include its network of remote little-visited forest reserves. It said this would, at a stroke, add “an additional 270-450 million tons of carbon dioxide” to the national tally, meaning that it could, in the future, include offsets of “up to 1.1 billion tons per year,” enough to offset as much as half of its fossil-fuel emissions.

The new IIASA findings could allow the government to increase that still further. In June, Putin’s deputy prime minister for environment policy, Victoria Abramchenko, reportedly told the St. Petersburg International Economic Forum that Russian forests capture up to 2.5 billion tons of carbon dioxide each year. Greenpeace’s Alexei Yaroshenko told The Moscow Times, “It’s obvious that the authorities want the estimate to be as high as possible.”

There is huge potential for forested countries to game the carbon-accounting system, said Wolfgang Knorr, a climate scientist at Lund University. In a recent blog post, he wrote, “First you declare some natural ecosystem your own because you are a country or political entity and it sits on your territory. Then you claim that because of this or that policy, it is taking up large amounts of carbon. Step three, count it as part of your net zero obligations … Trick done, problem solved.”

Knorr’s focus was on offsetting by the United States and China, but the potential for Russia is even greater. “There is a definite risk that Russia will join in the chorus of countries claiming part of the natural land sink towards their contributions to fighting climate change, creating a situation of double-counting since the sink has already been taken into account by the IPCC,” he said. “I think this is potentially a very big problem, but very few people really understand it.”

This week, U.S. climate envoy John Kerry has been in Moscow to discuss with Russian officials how to improve what he calls “global climate ambition,” ahead of the next UN climate conference in Glasgow, Scotland in November. It was not clear ahead of time whether forests carbon sinks were on the agenda. It would be well if they were.