Sixty-five trillion dollars. That is the bill a Cambridge group put on one extreme scenario in a 2013 paper in Nature: the floor of the Arctic sea gives up its methane, and the planet warms by two to two and a half degrees. It is a sum, Igor Semiletov says, comparable to a world budget.
Semiletov is a Corresponding Member of the Russian Academy of Sciences. They head the Arctic research laboratory at the V.I. Il'ichev Pacific Oceanological Institute and the international carbon laboratory for Arctic seas at Tomsk Polytechnic University. They have worked in the Arctic for thirty years, and the extreme scenario in that Nature paper was built on their group's estimates, taken from a paper in the Doklady of the Academy of Sciences.
Two and a half degrees is the distance between an ice age and the warm spell that follows it. The timescale matters as much as the size. Semiletov cares about changes inside one human generation: ten, forty, fifty years. Climate models still disagree with each other by fifty to a hundred percent about the world a century from now, and nobody loses sleep over a date that far off. Semiletov's own memory is closer. In the 1980s, travelling from Vladivostok to Moscow or Petersburg without a sheepskin coat was out of the question. Now a raincoat often does.
Why methane? The whole atmosphere holds about five billion tonnes of it. Over twenty years, by the IPCC figures Semiletov cites, one methane molecule traps as much heat as about eighty of carbon dioxide. Today methane adds roughly a third of what CO2 does. Human activity puts 50 to 150 million tonnes of it into the air each year, and it piles up.
Now look at the seabed. Methane sits there frozen into ice-like hydrates, and about ninety percent of the world's hydrate lies on continental shelves, the largest share on the Arctic one. Nobody knows how much. The estimates run across three orders of magnitude, from 30–50 billion tonnes to thousands of billions. Even the middling guess of 300 to 400 billion tonnes dwarfs what people could emit in a short time. Asked whether that was fair to say, Semiletov answered: "Yes, absolutely."
So Semiletov's bet is that the method of the past is the method of the future. Here is the line they draw:
But if the catastrophic scenario develops, and I'll explain what stands behind it, then it could be, well, the main driver of climate change, namely an increase in methane, as happened in the history of our planet.
Но в случае развития катастрофического сценария, о котором я сейчас объясню, что за этим стоит, значит, это может быть основной драйвер климатических изменений именно увеличение метана, что происходило в истории нашей планеты.
— Igor Semiletov, Scientific Russia, 05:41
Paleoclimatologists push back and ask where the spikes are in the ice cores of Antarctica and Greenland. Semiletov points to a few papers in top journals. At some stages of the climb out of the last ice age, lasting hundreds of years, methane rose before temperature did. And the Alaskan shelf, steep and narrow, has already warmed through. Its permafrost is gone, its hydrates have come apart, and in Semiletov's view that methane has long since gone into the air and added to the warming. The Kara and Barents seas have gone the same way.
The East Siberian shelf has not. The Laptev and East Siberian seas form the widest, shallowest shelf in the world's ocean, and the hydrates there are still intact. After major scientific centres in the West were asked which factors could change the climate within a generation, Semiletov says, they put the destabilisation of that Siberian hydrate store first.
Nobody can say when, or whether, it lets go. A 2024 modelling study by Sophie Wittig and colleagues in Atmospheric Chemistry and Physics found that where monitoring stations are dense, a methane burst would show up within two to ten years. Where they are sparse, it could take ten to thirty. And Semiletov's own group reported in Communications Earth & Environment in January 2026 that the methane now escaping in the inner Laptev Sea comes mostly from microbial pools inside the subsea permafrost, identified by isotope signatures.
What decides everything is speed: how fast the permafrost under the sea thaws. Alaska's shelf has already answered that question. Siberia's is still being measured.
