deep permafrost – Frozen ground across the Northern Hemisphere stores vast carbon, but a new study suggests deeper permafrost could flip from sink to source by 2100—emitting far more than older models predicted and raising the pressure on how the world budgets greenhouse gases.
On some parts of the Arctic landscape, the soil has been locked in ice for thousands of years. But as the planet warms, that lock is starting to fail—and researchers are now warning that what lies deeper than most models have looked at could matter more than anyone expected.
Permafrost, frozen soil, covers some 15 percent of land in the Northern Hemisphere. It acts as a carbon “sink. ” trapping carbon—mostly in the form of frozen organic matter such as dead plant and animal material. Yet human-driven climate change is warming the ground. As the ice melts, scientists say permafrost releases stored carbon into the atmosphere, enhancing warming in a feedback loop.
The scale of what’s stored is enormous. In the Northern Hemisphere. permafrost holds around double the carbon that’s already in the atmosphere. according to the National Oceanic and Atmospheric Administration. For years. researchers have argued about how fast this trapped carbon could escape—and how much the world’s permafrost might actually expel. The new study. however. estimates the tipping point could arrive earlier than past calculations suggested: by 2100. without reductions in global temperatures.
What makes the finding sharper is where the model looks.
While many projections focused on permafrost near the surface—where most of the carbon is stored—this new work accounts for deeper soils. Those deeper layers lie beyond a depth of three meters, or about 10 feet. Yi Xi. the study’s first author and a postdoctoral researcher at the Laboratory for Climate and Environmental Sciences in France. said the results point to deeper soils as an overlooked source of carbon.
In the study. Xi and co-authors constructed the accumulation history of soil carbon below three meters. including peatlands that formed during the Holocene. Then they ran simulations using various global warming scenarios projected by the United Nations’ Intergovernmental Panel on Climate Change (IPCC). The outcome. they report. is that melting northern permafrost could emit much more carbon before the end of the century than previously thought when deep layers are included.
The framing is significant because permafrost isn’t just another climate variable. It is a reservoir that can amplify warming—or damp it—depending on whether it behaves like a sink or a source.
Alberto Reyes. an associate professor at University of Alberta who studies the North American permafrost. was not involved in the new study. He said deep permafrost has been an under-appreciated component of Earth system models and praised the work for giving more explicit treatment to an important carbon reservoir in model simulations. Reyes also added that the study will be a necessary first step as the community tries to better assess the fate of permafrost and associated climate feedbacks during past periods of climate warming during the Pleistocene.
Susan Natali. an Arctic climate scientist at the Woodwell Climate Research Center who was also not involved. described the study as closing an important modeling gap. She said models used to inform climate policy haven’t fully captured permafrost processes. including the deep carbon stores locked in permafrost.
For all the urgency in the numbers, the study’s authors also see a kind of warning that could still be useful.
Xi said there may be “some good news buried in the findings. ” because understanding how “deep carbon” could fuel climate change could help the world be better prepared. She called it “an alarm for us.” She also suggested that the remaining carbon budget may need to be recalculated—referring to the U.N. threshold of greenhouse gases the world can emit before hitting 1.5 or two degrees Celsius of warming above preindustrial levels.
That recalculation isn’t something the modeling community can do overnight. The IPCC is already working on its seventh major report on climate change, including projections on permafrost. It is slated to be released by the end of 2029.
Natali emphasized that fully assessing and accounting for permafrost carbon emissions, which are being amplified by climate change, is critical for effective climate adaptation and mitigation planning and action.
permafrost deep carbon Arctic climate change carbon feedback greenhouse gas budget IPCC Northern Hemisphere soil carbon Holocene Pleistocene