Beneath vast stretches of Alaska, Canada and Siberia lies ground that has stayed frozen solid, some of it for hundreds of thousands of years. As a warming climate pushes that frozen layer to thaw from the top down, it is not just releasing water. It is unlocking carbon that has been locked out of the atmosphere since before the last ice age, along with organisms that have effectively been in cold storage the entire time.
Ground that has been frozen since before human civilization
Permafrost is defined as any soil, rock or sediment that stays at or below the freezing point continuously for two years or longer. It underlies roughly 15 percent of the exposed land surface of the Northern Hemisphere and about 11 percent of Earth’s total land area, a footprint of around 18 million square kilometers spanning Alaska, most of Canada, Greenland and huge portions of Siberia. Its depth varies enormously by location, from less than a meter in the mildest permafrost zones to more than 1,500 meters in parts of Siberia, and the oldest deposits have remained continuously frozen for roughly 700,000 years.
A carbon vault roughly twice the size of the atmosphere’s
According to the global permafrost record, what makes permafrost a climate concern rather than just a geological curiosity is what is frozen inside it. Over tens of thousands of years, dead plants, animal remains and other organic material accumulated in the Arctic’s cold, oxygen-poor soils faster than microbes could break them down, effectively locking that carbon away in frozen storage instead of letting it decompose and release into the atmosphere the way organic matter normally does in warmer climates. Researchers estimate the northern permafrost region now holds somewhere between 1,460 and 1,600 billion metric tons of organic carbon, a total that amounts to roughly twice as much carbon as currently exists in Earth’s entire atmosphere, concentrated in soil that covers less than a tenth of the planet’s land surface.
That imbalance is what worries climate scientists. When permafrost thaws, microbes that had been dormant along with the frozen ground suddenly find themselves surrounded by organic material they can digest again, and they begin converting it into carbon dioxide and methane, both potent greenhouse gases. Because methane traps far more heat in the atmosphere per molecule than carbon dioxide does over short timeframes, even a relatively small share of permafrost carbon escaping as methane can have an outsized warming effect. Some estimates suggest 5 to 15 percent of the carbon currently locked in surface permafrost could be released by the end of this century under current warming trajectories, a self-reinforcing loop in which thawing drives warming, which then drives further thawing.
A feedback loop with no simple off switch
Unlike most sources of greenhouse gas emissions, permafrost thaw is not something governments or companies can directly throttle back once it accelerates. The process is instead driven by regional air and ground temperatures that respond to global warming with a lag, meaning today’s thaw rates reflect warming that has already happened rather than an amount that can be dialed down quickly. Scientists monitoring permafrost temperatures in the High Arctic and other especially cold zones have recorded warming of more than half a degree Celsius since 2007 to 2009 alone, and the active layer, the top section of ground that thaws each summer and refreezes each winter, has been deepening across most monitored sites, exposing progressively older and deeper carbon deposits to microbial breakdown with each passing decade.
The physical landscape itself often changes as a visible symptom of that process. Thawing ground loses structural stability as its ice content melts, producing sudden slumps, sinkholes and slides that can reshape hillsides and riverbanks within a single season, a set of hazards that also threatens roads, pipelines and buildings constructed on ground that engineers once assumed would remain frozen indefinitely.
Dormant life waking up alongside the carbon
Carbon and methane are not the only things preserved in that frozen ground. Because permafrost keeps its contents at sub-freezing temperatures with little oxygen exposure, it can preserve microorganisms in a dormant, suspended state for extraordinarily long stretches, and researchers have shown some of them remain capable of reviving once thawed. A team led by virologist Jean-Michel Claverie at Aix-Marseille University isolated more than a dozen viruses from Siberian permafrost samples and successfully reactivated them in laboratory conditions, including one specimen radiocarbon-dated to roughly 48,500 years old, the oldest virus ever revived in a lab. Every virus in that study infected only amoebas and posed no threat to humans, but the researchers noted the results demonstrate that viable, infectious pathogens of some kind can survive tens of thousands of years in frozen ground, a finding they said justifies closer monitoring of what else might be locked in permafrost that is now thawing at accelerating rates.
Why scientists keep drilling instead of guessing
Because permafrost carbon release does not show up as a single measurable smokestack the way industrial emissions do, researchers rely on networks of monitoring boreholes, satellite surveys and repeated soil sampling across the Arctic to track how quickly the frozen carbon vault is opening. That ongoing measurement effort is also how scientists caught the ancient viruses in the first place, since routine permafrost coring for climate research is what turned up the frozen samples Claverie’s team eventually thawed and tested. The overlapping science, tracking greenhouse gas leakage on one hand and dormant biology on the other, has turned permafrost monitoring into one of the more closely watched corners of Arctic climate research, precisely because both risks scale together with the same thawing ground.
This article was produced with the assistance of AI and reviewed by an editor.
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