Permafrost and tundra: frozen ground in a warming Arctic
Permafrost is ground that stays frozen for at least two years in a row. It underlies about a quarter of the exposed land in the Northern Hemisphere, holds roughly twice as much carbon as the atmosphere, and is warming. As it thaws, the land above it sinks, buckles and changes color.
What permafrost is
The National Snow and Ice Data Center (NSIDC) defines permafrost as soil, sand, sediment or rock that stays at or below 0 °C (32 °F) for at least two years. The definition is about temperature only, so permafrost does not have to contain ice.
On top of permafrost lies the active layer, the part that thaws each summer and refreezes each winter. Since the early 1980s the active layer has grown up to 25 cm (10 inches) thicker in parts of Siberia. Permafrost itself can be less than 1 meter thick or more than 1,500 meters (4,900 feet) thick.
How much there is
Permafrost covers about 23 million square kilometers (about 9 million square miles) of the Northern Hemisphere, roughly a quarter of its exposed land. About 65% of it is in Eurasia and 35% in North America and Greenland. As a quick check: 65% of 23 million is about 15 million square kilometers in Eurasia, leaving about 8 million in North America and Greenland.
Thaw and carbon
Permafrost is a freezer for dead plants and animals that never fully rotted. The IPCC estimates that Arctic and boreal permafrost holds 1,460–1,600 billion tonnes (gigatonnes) of organic carbon, almost twice the carbon in the atmosphere (IPCC Special Report on the Ocean and Cryosphere, 2019).
The ground is warming. The same report found permafrost temperatures at record highs, with an average rise of about 0.29 °C between 2007 and 2016 across polar and high-mountain regions. When permafrost thaws, microbes start breaking down the old carbon and release carbon dioxide and methane, both greenhouse gases. Over 100 years, methane traps 28 to 36 times more heat than the same amount of carbon dioxide, though it lasts only about a decade in the air on average (NSIDC, citing the US EPA).
How much thaw lies ahead depends on emissions. By 2100 the area of near-surface permafrost (the top 3–4 meters) is projected to shrink by about 24% under a low-emissions scenario (RCP2.6) and about 69% under a very high one (RCP8.5). Under the high scenario, permafrost could release tens to hundreds of billions of tonnes of carbon by 2100, which would add to warming. Scientists still disagree on how much extra carbon northern permafrost is releasing today.
Why it is called a feedback. Warming thaws permafrost; thawing releases greenhouse gases; those gases cause more warming. Lower emissions slow the whole loop. See Polar amplification for other polar feedbacks.
When the ground gives way
When the ice in frozen ground melts, the ground can slump and collapse into pits, wobbly slopes and shallow lakes, a pattern called thermokarst. The IPCC estimates that about 20% of Arctic land permafrost is vulnerable to this kind of sudden thaw and sinking.
Roads, pipelines and towns
Thawing permafrost can make buildings tilt and roads buckle, and repairs are costly. NSIDC notes that the Trans-Alaska Pipeline has 676 km (420 miles) of above-ground sections over permafrost. The IPCC reports that most Arctic infrastructure sits where permafrost thaw is projected to intensify by mid-century, and that redesigning and retrofitting could halve the costs of the damage by 2100.
Coasts are eroding too. In Shishmaref, Alaska, a village of about 500 people, roughly 7 meters (23 feet) of land washes into the sea each year, according to NSIDC. Residents voted to relocate in 1973, 2002 and 2016.
Rusting rivers
NOAA’s Arctic Report Card 2025 describes a newer sign of thaw: in more than 200 watersheds in Arctic Alaska, iron and other metals released from thawing permafrost have turned once-clear rivers and streams orange over the past decade.
A greener tundra
Tundra is the treeless land of low shrubs, grasses, mosses and lichens that grows on permafrost. Satellites show it has broadly become greener, often a sign that plants are growing more (IPCC). The tundra’s peak greenness in 2025 was the third highest in the 26-year satellite record (NOAA Arctic Report Card 2025). Some areas are “browning” instead, where plant productivity has dropped, and more wildfire and sudden thaw are disturbing tundra ecosystems.
Greening does not cancel out thaw. The IPCC expects extra plant growth to replace only part of the soil carbon lost from permafrost over the long term.
- 23 million km²Northern Hemisphere permafrost area (NSIDC)
- 1,460–1,600 GtOrganic carbon in Arctic and boreal permafrost
- 24% / 69%Projected loss of near-surface permafrost area by 2100, low vs very high emissions
- 200+Alaska watersheds with rivers turned orange by thaw (2025 report)
Check yourself
Does permafrost have to contain ice?
No. Permafrost is defined by temperature alone: ground that stays at or below 0 °C for at least two years. Some permafrost is dry rock or sediment.
Why does thawing permafrost add to global warming?
It holds old plant and animal remains. Once thawed, microbes break them down and release carbon dioxide and methane, which trap more heat and cause more thaw.
What is thermokarst?
Uneven, collapsed ground with pits, slumps and small lakes that forms when ice-rich permafrost melts and the land surface sinks.