Image: Katie Orlinksy, National Geographic
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Summary
Permafrost is a combination of soil, sediment, and the remains of dead plants and animals that stay at or below 0°C for at least two years. As thin as <1m and as thick as >1,300m, deeper layers have been frozen for millions of years.
In the Northern Hemisphere it covers ~23 million km² or ~22% of land (Fig. 1).
In the Southern Hemisphere permafrost is found in Patagonia, New Zealand’s Southern Alps and Antarctica, although how much there is in Antarctica is uncertain as most of the continent is covered in ice sheets that because of their basal movement (grinding over the land) prevent permafrost from forming.
In 2019, roughly 1,700 billion metric tons (gigatons) tonnes of organic carbon—more than twice what’s in the atmosphere today—was estimated to be stored in permafrost. Due to polar amplification and record breaking temperatures, the Arctic and mountain regions are warming much faster than expected, accelerating the loss of permafrost, releasing tonnes of carbon dioxide and methane into the atmosphere.
The Arctic and high mountain regions are now warming at 2–4 times the global average – Cryosphere Report 2024
…warming-induced increase in soil CO2 release is ~5.5 times higher in thermokarst features than the adjacent non-thermokarst landforms. – Wang et al 2024
In 2024 researchers found that the Arctic ocean was no longer absorbing as much CO2 because of melting permafrost:
We find that coastal erosion reduces the Arctic Ocean CO2 uptake from the atmosphere in all simulations: by 4.6–13.2 TgC yr−1 by 2100, which is ~7–14% of the Inner Arctic Ocean uptake. We show that coastal permafrost erosion exerts a positive biogeochemical feedback on climate, increasing atmospheric CO2 by 1–2 TgC yr−1 per °C of increase in global surface air temperature. – Neilsen et al 2024
A “Permafrost-Like” Carbon Reservoir: Though the sediment basins beneath these subglacial lakes are not frozen, scientists have found that they act similarly to Arctic permafrost in terms of climate risk. These isolated, low-oxygen lake beds contain massive reservoirs of organic carbon and trapped methane gas. If the ice sheets continue to melt and retreat, these subglacial drainage networks could escape into the ocean and atmosphere, mirroring the greenhouse gas release seen in thawing Arctic tundra. – Robinson et al, Sept. 2026
Flammable ice looks like ice, but it’s methane clathrates (Fig. 5). Once thought to exist only in the outer parts of the Solar System, it turns out to be abundant in permafrost and beneath the ocean floor.
What’s covered in this page:
Permafrost
We managed to put a finger on when exactly when continuous permafrost melt starts…this is probably the tipping point, 1.5°C warming. – Dr Anton Vaks, Oxford University
Unlike ice, permafrost doesn’t ‘melt’ once temperatures rise above 0.5°C. It falls apart and the organic material decomposes, just as frozen meat or vegetables left outside a freezer will decompose if not eaten. If permafrost decomposes in an environment where there’s oxygen, then carbon dioxide is released. If the environment is anaerobic (lacks oxygen), methane, which is 23 times more potent that carbon dioxide as a greehouse gas, is released. This enters the atmosphere either directly or via lakes and ponds (Video 2).
Previously, it had been assumed that a warming climate would enable more plants to grow at higher altitudes and latitudes, absorbing the carbon that’s being released. But that’s not happening. In fact, plant roots can accelerate permafrost decay by as much as four times as fast as permafrost without plants.
..ice sheets overlie extensive, biologically active methan-ogenic wetlands and high rates of methane export to the atmosphere can occur via efficient subglacial drainage pathways. Our findings suggest that such environments have been previously underappreciated and should be considered in Earth’s methane budget…Genomics studies are helping to reveal how bacteria and archaea influence one of Earth’s largest carbon stores as it begins to thaw.
– Lamarche-Gagnon et al 2019
Increasingly, research raised the alarm ithat microbes in permafrost could trigger a massive carbon bomb (Fig. 2) By 2024 it had become clear that the overall rate of carbon dioxide being absorbed by the land had dropped by around 30%. At the same time, the ability of the Arctic ocean to take up CO2 was being reduced.
...anaerobic carbon dioxide and methane production from deep sediments was commensurate with aerobic production on a per gram carbon basis, and had double the global warming potential at warmer temperatures. Carbon release from deep Arctic sediments may thus have a more substantial impact on a changing climate than currently anticipated. – Freitas et al, 2025
Even if we reach net-zero and are able to draw down the excess greenhouse gases from the atmosphere it is now clear that huge volumes of carbon and methane from permafrost will continue to be emitted.
None of these factors are included in current climate models.
State of the Cryosphere Report 2025 Summary: Permafrost
More than 210,000 km2 of frozen permafrost land area has thawed each decade on average since current warming began a century ago, accelerating since the 1990s with every fraction of a degree of warming…
This thaw also decreases the global carbon budget. Already today, permafrost thaw releases annual carbon emissions equal to those of a top 10 greenhouse gas emitter such as Japan (about 0.3–0.6Gt CO2-equivalent per year). Emissions will continue at this scale for one to two centuries even with no additional warming; and cannot be halted once initiated, making carbon neutrality more difficult to achieve if temperatures continue to rise.
Permafrost emissions over coming decades and centuries depend on how much carbon countries release into the atmosphere: lower human emissions mean lower permafrost emissions. Growing wildfires and extreme heatwaves leading to abrupt thaw events may increase permafrost emissions even further. NDCs consistent with 1.5°C would lead to annual permafrost emissions around the same level as carbon emissions from India today (about 2.5Gt) for the rest of this century. NDCs causing over- shoot to 2°C would increase annual permafrost emissions to the same scale as current emissions from the 38 countries of the OECD Europe (about 3–4Gt)…
NDCs resulting in 3–4°C would lead to annual permafrost emissions similar to the United States or China’s annual emissions today (about 5Gt or more) for one to two centuries, burdening the next several generations struggling to keep atmospheric CO2 concentrations at manageable levels.
As an aside, in 2024 it was also clear that large volumes of mercury, a potent neurotoxin, is being released from melting Arctic permafrost (it’s unclear if this is happening elsewhere).
The ‘subglacial drainage’ process that’s melting glaciers and ice sheets described in the section on Antarctica, is also waking microbes in ancient swamps and releasing methane from beneath Greenland. Antarctica is many times larger than Greenland and was once covered in lush forests, so is likely to have very, very large areas of permafrost.
Several orders of magnitude more methane has been hypothesized to be capped beneath the Antarctic Ice Sheet than beneath Arctic ice-masses. Like we did in Greenland, it’s time to put more robust numbers on the theory. – Lamarche-Gagnon 2019
An increasing number of wildfires are exacerbating the rate of melting, releasing even more carbon (Fig. 4):
Burning ice: methane clathrates
Methane clathrates, also called methane hydrate, fire ice, hydromethane, methane ice, natural gas hydrate, or gas hydrate, is composed of methane trapped and frozen within a crystal structure of water, forming a solid that looks like ice but is highly flammable (Fig. 5).
Once thought to exist only in the frozen outer parts of the Solar System, it turns out to abundant in permafrost and beneath the ocean floor.
The Arctic is experiencing record breaking temperatures for extended periods. In very deep waters, the melting methane clathrates can dissolve before reaching the surface. On the land and in shallower waters, methane ‘burbs’ are forming large craters, often explosively (Figs. 6 & 7).
The estimated amount of methane is the equivalent of 500 – 2500Gt of CO2. Currently there’s just over just over 3364Gt of CO2 in that atmosphere (430ppm).
A release of methane in this form has been implicated in at least one mass extinction event. But the United States Geological Service estimates regard it as a fossil fuel resource; one cubic metre of methane hydrate produces ~163-180 cubic metres of natural gas , so the explosive potential is also high. Mining it risks:
…gas blowouts, loss of support for pipelines, and sea-floor failure that could lead to underwater landslides and the release of methane from hydrates. – USGS
Still, the prospect of so much cheap gas is hugely appealing, especially as the Arctic is becoming increasingly accessible as more sea ice melts each year.
On March 1, 2025, Beijing officially announced the construction of a deep-sea habitat in these methane-rich “cold seep” zones, where six researchers will live for month-long stretches to study gas hydrates – crystalline formations of methane trapped in ice. With 80 billion tonnes of oil-equivalent reserves – far surpassing the Gulf’s 50 billion-tonne proven oil stocks – these vast hydrate deposits could redefine energy geopolitics. – South China Morning Post
Atmospheric methane
- Mouse over anywhere on the graph to see the changes in global atmospheric methane over the last thousand years.
- To see details for time periods of your choice, hold your mouse button down on one section then drag the mouse across a few years, and release it.
- To see how this compares to the past 771,000 years, click on the ‘time’ icon on the top left.
- Compare this to rising global temperatures by clicking the planet/thermometer icon at the top left corner.
- To return the graph to its original position, double-click the time icon to the left of the thermometer/planet icon
