Vast expanses of Earth’s northern regions are built upon a foundation of frozen ground called permafrost. As global temperatures increase, this historically stable layer is beginning to thaw, releasing powerful greenhouse gases into the atmosphere. This process introduces a significant and quickening variable into the planet’s climate system.
Understanding Permafrost
Permafrost is a layer of soil, rock, or sediment that remains frozen for at least two consecutive years, with a thickness ranging from less than a meter to over 1,500 meters. It underlies about 15% of the Northern Hemisphere’s land, including large areas of Siberia, Canada, Alaska, and Greenland, as well as high-altitude mountain ranges. The geographic continuity of permafrost varies from continuous zones to patchier, sporadic areas.
Permafrost is composed of mineral soils, gravel, ice, and a large amount of organic material from ancient plants and animals. This material was locked in the frozen soil before it could fully decompose. Above the permafrost is an “active layer” that thaws in the summer and refreezes in the winter, supporting plant life.
Trapped Greenhouse Gases Within Permafrost
The northern permafrost region holds an estimated 1,460 to 1,600 billion metric tons of organic carbon, roughly double the amount currently in Earth’s atmosphere. This carbon consists of the remains of ancient life preserved in the frozen ground. The cold, oxygen-poor conditions halted the natural process of decomposition.
As permafrost thaws, microbes decompose this organic matter, releasing carbon into the atmosphere as carbon dioxide (CO2) and methane (CH4). While nitrous oxide (N2O) is also emitted, CO2 and methane are the most significant by volume. For thousands of years, this carbon was locked out of the global carbon cycle, and its reintroduction represents a new source of greenhouse gases.
Mechanisms of Thaw and Gas Emission
Permafrost thaw is a direct consequence of rising global temperatures. The Arctic is warming nearly four times faster than the rest of the world, a phenomenon known as Arctic amplification. A contributing factor is the loss of sea ice, which exposes the darker ocean surface to absorb more solar radiation, further warming the region.
Permafrost degrades through two main processes. The first is a gradual, top-down thaw, where the active layer deepens each year. The second is abrupt thaw, such as thermokarst, where melting ground ice causes the surface to collapse, forming new lakes and wetlands and disturbing deep permafrost quickly.
The type of gas released depends on the thaw conditions. In dry, well-drained areas with plentiful oxygen, microbes use aerobic respiration to decompose organic matter, releasing carbon dioxide. In waterlogged, oxygen-poor environments like new wetlands, anaerobic decomposition occurs, which releases methane.
Climate Consequences of Permafrost Thaw
The release of these gases creates a self-reinforcing cycle known as the permafrost carbon feedback loop. Greenhouse gases from thawing permafrost contribute to global warming, which in turn causes more permafrost to thaw and release even more gases. This cycle can accelerate climate change beyond what is caused by human emissions alone.
Methane is a potent greenhouse gas. Over a 20-year period, it is more than 80 times more powerful at trapping heat in the atmosphere than carbon dioxide. While methane has a shorter atmospheric lifespan, its immediate warming impact is substantial, making it more difficult to achieve international climate goals.
These emissions reduce the world’s remaining carbon budget—the amount of carbon that can be released while keeping warming below specific targets. The introduction of this large carbon source complicates climate predictions. It also increases the risk of crossing irreversible climate tipping points.
Current Observations and Future Outlook
Scientists track permafrost thaw and gas emissions using several methods. Field studies directly measure gas flux from the soil, and remote sensing from satellites monitors changes in ground temperature and landscape. Atmospheric measurements from aircraft and towers quantify greenhouse gas concentrations in the Arctic.
Observations indicate some permafrost regions are already becoming net sources of carbon to the atmosphere. Accurately quantifying the total volume of these emissions remains a challenge. The remote nature of these landscapes and the complex thaw processes create large uncertainties in climate models.
Future projections show that under all warming scenarios, permafrost thaw and associated greenhouse gas emissions will increase. The trajectory of these emissions is directly linked to the extent of future global warming, which will fuel the permafrost carbon feedback loop and amplify climate change.