Arctic Permafrost Thaw and Methane Release | A Vicious Cycle Accelerating Warming

What Is Happening in the Arctic: Warming Far Above the Global Average

The Phenomenon of Arctic Amplification

The Arctic is warming faster than the global average. This is called "Arctic amplification," and recent studies report that Arctic temperatures have risen about four times faster than the global average over roughly 40 years since 1979. As sea ice shrinks, the white surface that reflected sunlight is replaced by dark open water, which absorbs more heat. This "ice-albedo feedback" is one of the main drivers of amplification.

Changes in the Arctic are not distant events. Sea ice loss, permafrost thaw and the opening of Arctic shipping routes are linked, and their effects reach Japan's weather, fisheries and shipping. This article focuses in particular on methane released from permafrost and its positive feedback on warming, organizing the latest observations and estimates.

Sea Ice Today: Observations from 2025

According to the U.S. National Snow and Ice Data Center (NSIDC), Arctic sea ice reached its annual minimum of about 4.6 million square kilometers around September 10, 2025, the 10th lowest in the nearly 47-year satellite record. The winter maximum in March 2025 was the lowest in the satellite record. The 19 lowest September minimums have all occurred in the last 19 years.

NSIDC also notes that there has been no statistically significant trend in September minimums over the past two decades. This does not mean sea ice loss has stopped; it shows that year-to-year natural variability is large. Over the long term, thick old ice (4+ years) has declined by more than 95% since the 1980s, leaving the ice thinner and more fragile.

What Is Permafrost? Vast Carbon Sleeping in Frozen Ground

Definition and Distribution of Permafrost

Permafrost is soil or rock that stays at or below 0°C for two or more consecutive years. It covers about a quarter of Northern Hemisphere land, spreading across Siberia, Alaska, northern Canada and the Tibetan Plateau. The surface "active layer" thaws in summer and refreezes in winter, with frozen ground beneath.

A Huge Carbon Reservoir

Permafrost holds dead plants and animal remains that froze before they could decompose. The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC, 2019) assessed that Northern Hemisphere permafrost stores about 1,460–1,600 gigatons of organic carbon (GtC). This is nearly twice the carbon currently in the atmosphere (about 870 GtC).

When permafrost thaws, microbes begin decomposing the organic matter. Carbon dioxide (CO2) is mainly produced where oxygen is present, and methane (CH4) where waterlogged ground lacks oxygen. Thawing is thus a gateway for carbon to return to the atmosphere.

How Methane Is Released and the "Positive Feedback"

Warming → Thaw → Release → More Warming

Permafrost thaw is a problem because it is both a result and a cause of warming. Warming thaws permafrost → greenhouse gases are released → warming advances → more permafrost thaws. A cycle in which the result strengthens the cause is called a "positive feedback."

• Gradual thaw: the active layer deepens and organic matter decomposes bit by bit
• Abrupt thaw (thermokarst): ground collapses, lakes and wetlands form suddenly, and oxygen-poor conditions spread
• Arctic fires: peat and organic soils burn, releasing stored carbon all at once

Why Abrupt Thaw Matters

Conventional climate models assumed permafrost thaws slowly from the surface. Recent studies, however, point out that "abrupt thaw," in which ground collapses and lakes form, may increase carbon release more than expected. In this process, methane is readily produced in the oxygen-poor environment of lake bottoms.

Changes Shown by the NOAA Arctic Report Card

NOAA's Arctic Report Card marked its 20th anniversary in 2025. According to news coverage, recent reports point out that Arctic tundra is shifting from a carbon "absorber" to a carbon "emitter." Warming and wildfire are the main causes, and the carbon stored in permafrost was described as about 1.5 trillion tons. However, carbon balance differs greatly by region and year, and uncertainty remains in the assessment.

Frozen Ground Under the Sea: Subsea Permafrost and Methane

What Is Subsea Permafrost?

Permafrost exists not only on land but also under the seabed of the shallow Arctic continental shelf. It is land that froze when sea level was low during the ice age and was later submerged as seas rose. The East Siberian Arctic Shelf (ESAS) is a leading example and is known as one of the world's largest shallow shelves.

Estimates from Expert Assessment

A 2020 assessment by 25 experts estimated that the subsea permafrost domain holds about 560 GtC of organic carbon (90% confidence interval 170–740) and about 45 GtC as methane (10–110). Current annual methane release from the seabed is put at about 18 million tons of carbon (2–34 million tons).

For the future, under the highest-warming scenario (RCP8.5), about 43 billion tons of CO2 equivalent (14–110 billion) could be released by 2100 and about 190 billion tons by 2300. Under the low-emission scenario (RCP2.6), release is expected to be about 30% lower.

Sea Ice Loss and Its Effects on the Arctic Ocean Ecosystem

Life That Depends on Ice

Algae called "ice algae" grow on the underside of sea ice and form the base of the Arctic food web. Zooplankton, Arctic cod, seals and polar bears rely on it in turn. As ice thins and melts earlier, the timing of this production may shift.

• Polar bears and seals: fewer platforms for hunting, giving birth and raising pups
• Walruses: with less resting ice, large groups have been reported crowding onto land
• Phytoplankton: more open water lets in light, changing spring and autumn blooms

Newcomers from the South

As waters warm, fish and plankton from farther south are expanding into the Arctic Ocean, a shift called "borealization." It creates competition with native species but also draws attention as a possible new fishery resource. To avoid overfishing before management frameworks exist, commercial fishing in the central Arctic Ocean is banned for now under an international agreement.

Changes in the Arctic are not unrelated to Japan's coastal waters. For links to marine heatwaves and shifting fish distributions, see also our article on marine heatwaves.

The Northern Sea Route: Opportunities and Risks of an Open Passage

Current Use

As sea ice shrinks, the Northern Sea Route (NSR) between Europe and Asia becomes realistic. Under good conditions it is said to cut sailing distance greatly compared with the Suez Canal route. According to the Centre for High North Logistics (CHNL), there were 103 transit voyages (88 vessels) in 2025, up from 97 the previous year, carrying about 3.2 million tons of cargo. However, ice formed early in the east, and the navigation window was about three weeks shorter than the year before.

Ships are increasing across the whole Arctic. According to the Arctic Council's PAME, 1,812 vessels operated in the Polar Code area in 2025, with activity concentrated in August–October when sea ice is at its minimum.

Risks and Challenges

• Oil spills: hard to recover in cold conditions, and ecosystems recover slowly
• Ship noise and collisions: concern for whales and seals
• Heavy fuel oil and black carbon: deposits on snow and ice reduce reflectivity and speed melting
• Limited rescue capacity: rescue bases are far away in an accident

The International Maritime Organization (IMO) brought the Polar Code for ships operating in polar waters into force in 2017, setting safety and environmental standards. Japan is also engaged in observation and international cooperation, including building an Arctic research vessel.

The Arctic and Japan: Effects on Weather, Fisheries and Shipping

Effects on Weather

Researchers are studying whether Arctic warming is linked to jet stream meandering and cold waves. Causality is still debated among scientists, however, and no firm conclusion has been reached. For the mechanism, see our article on the jet stream.

Relationship with Sea Level Rise

Sea ice already floats on the ocean, so its melting barely raises sea level. What contributes to sea level rise is melting of the Greenland ice sheet and land glaciers, plus thermal expansion of seawater. The IPCC special report assesses the combined impacts. For the big picture, see our article on the IPCC Special Report on the Ocean and Cryosphere.

Japan's Research and International Cooperation

Japan has advanced Arctic observation centered on the National Institute of Polar Research (NIPR) and JAMSTEC. It also takes part in the Arctic Council as an observer state, contributing to scientific data sharing and international rule-making.

What We Can Do: Cutting Emissions Is the Key Response

Not Strengthening the Feedback

Humans cannot directly stop methane from permafrost. But as the expert assessment above shows, scenarios with strong emission cuts see future release about 30% lower. So reducing CO2 and methane emissions is the most reliable way to weaken the permafrost feedback.

• Save energy and use renewables to cut CO2
• Reduce food loss to curb methane from waste
• Learn the science accurately and share it with others
• Take interest in efforts that support ocean and polar research and observation

The role of ocean carbon uptake is explained in our article on the ocean's carbon uptake.