Arctic alarm: Earth’s frozen carbon stores in the Arctic may stop absorbing CO2 and start releasing it by the 2050s |
The Arctic is warming far faster than the rest of the planet, and a new study published in Science Advances suggests that this warming could transform one of Earth’s biggest natural carbon stores sooner than scientists once thought. Researchers say northern soils above 30°N, including vast areas of permafrost, may switch from absorbing carbon to releasing it around the 2050s when deep frozen carbon is taken into account. The findings challenge a key assumption in many climate models, which currently consider only the upper layers of soil and overlook huge amounts of ancient carbon buried much deeper underground. That hidden carbon, scientists say, could make the Arctic a much stronger contributor to climate change in the decades ahead.
Why Earth’s frozen carbon stores may not absorb CO2 forever
For years, climate models have assumed that northern lands would continue acting as a giant carbon sponge for much of this century. Although warming temperatures can thaw frozen ground and release greenhouse gases, they can also encourage plants to grow faster and absorb more carbon dioxide from the atmosphere. Overall, many models suggested that these regions would remain a net absorber of carbon.But the new study says that picture is incomplete. Researchers argue that current models largely ignore huge stores of ancient carbon buried deep underground in peatlands and Yedoma deposits, a type of ice-rich permafrost found mainly in Siberia, Alaska and parts of Canada.The authors write that these omissions “lead to an underestimation of permafrost extent and high-latitude carbon stocks” and hinder understanding of how thawing affects future carbon release. They note that carbon-rich peat can extend to around 10 metres below the surface, while Yedoma deposits can reach depths of about 20 metres.
What the researchers changed
To address this problem, scientists upgraded the ORCHIDEE-MICT land surface model. In simple terms, they taught the model to reconstruct how carbon accumulated underground over thousands of years.The new version simulates the formation of deep Yedoma deposits since the last ice age and the development of northern peatlands during the Holocene, the geological period that began around 11,700 years ago. It includes more realistic estimates of carbon buried beneath lands north of 30°N.The researchers then ran historical simulations covering the period from 1900 to 2014 and projected future conditions from 2015 to 2100 under three shared socioeconomic pathway scenarios, which are widely used by climate scientists to represent different possible futures. They compared these results with older versions of the model to see how including deep carbon changed the outlook.
The main finding
The updated model showed that northern soils actually stored much more carbon before the industrial era than standard models previously suggested. But that also means there is more carbon available to escape as the Arctic warms.As frozen ground thaws deeper into the soil, microbes begin breaking down organic matter that has remained frozen for thousands of years. This decomposition releases carbon dioxide and other greenhouse gases into the atmosphere.The simulations show that the Arctic’s ability to absorb carbon weakens steadily throughout this century. By around the 2050s, northern lands could start releasing more carbon than they absorb, effectively changing from a climate helper into a climate amplifier.In earlier versions of the model, that shift was projected to occur later, beyond the middle of the century.
What is driving the change
According to the study, much of the additional carbon loss comes from deep permafrost layers, especially Yedoma deposits. As temperatures rise, the “active layer”—the upper soil layer that thaws every summer—gradually becomes thicker.Think of it as slowly opening a giant freezer. The deeper the thaw reaches, the more ancient organic material becomes exposed to microbes, which begin decomposing it and releasing greenhouse gases.Explaining the findings, the researchers wrote:“This higher soil carbon loss in the updated simulations is primarily driven by the gradual degradation of deep permafrost carbon, particularly from Yedoma deposits, which become increasingly exposed as the active layer thickness deepens more rapidly after the mid-21st century.”They also stressed that missing deep deposits “hinder our understanding” of how active layer thickening affects future carbon decomposition.
Why the result may still be conservative
The researchers caution that their estimates may actually understate the problem because several important processes were not fully included in the model.One example is abrupt thaw. Instead of melting gradually, some permafrost can suddenly collapse, exposing large amounts of ancient carbon to decomposition.Another process involves thermokarst lakes. These lakes form when ice-rich ground melts and creates depressions that fill with water. Because water transfers heat more effectively than frozen soil, surrounding permafrost thaws faster, creating a feedback loop that can release even more greenhouse gases.Wildfires, vegetation shifts, nutrient cycles and ground-ice dynamics were also not fully represented. All of these factors could increase future emissions.First author Yi Xi told Scientific American that these vulnerable carbon stores lie “beyond a depth of three meters”, highlighting how much carbon exists below the zone that many climate models currently consider.
Why scientists are worried
Permafrost regions are often described as giant natural freezers preserving dead plants and animals that accumulated over thousands of years. As long as the ground remains frozen, that carbon stays locked away.But once the frozen soil begins to thaw, microbes start breaking down the organic matter and releasing carbon dioxide and methane into the atmosphere.This creates a self-reinforcing cycle. More warming causes more thawing, which releases more greenhouse gases, leading to even more warming. Scientists refer to this as a positive feedback loop.The Arctic is already warming two to four times faster than the global average, and some parts of the region are beginning to show signs of becoming carbon sources rather than carbon sinks.
The study’s bottom line
The authors say realistic climate projections must include deep carbon buried beneath permafrost and peatlands.They write:“These findings are crucial for predicting future permafrost carbon climate feedbacks, as they highlight the importance in including deep carbon dynamics when assessing the northern soil carbon balance.”The researchers add that the approach they developed for the ORCHIDEE-MICT model could also be used in other Earth system models.In other words, scientists may have been overlooking a large part of Earth’s frozen carbon reservoir. Correcting that blind spot suggests that the Arctic could stop helping slow climate change and begin adding to it much sooner than previously thought.
