Beneath the tundra of Siberia, Alaska and northern Canada lies a sleeping giant: permafrost, ground that has stayed frozen for thousands of years, locking away twice as much carbon as the entire atmosphere holds. As the Arctic warms nearly four times faster than the global average, that ground is waking up. Thawing permafrost releases carbon dioxide and methane, buckling infrastructure and reshaping landscapes. Scientists call it a feedback loop: warming thaws permafrost, thawing releases greenhouse gases, and those gases cause more warming.

What permafrost actually is

Permafrost is not just frozen dirt; it is a vast frozen archive. It underlies about 15 percent of the exposed land in the Northern Hemisphere, in places extending hundreds of metres deep. Much of it formed during the last ice age, freezing undecayed plant and animal matter into the ground before microbes could break it down. That organic matter, the frozen remains of steppe ecosystems tens of thousands of years old, is the carbon bomb: an estimated 1,500 billion tonnes of carbon, roughly double what currently floats in the atmosphere as CO2. As long as it stays frozen, it stays locked away.

How thaw releases greenhouse gases

When permafrost thaws, ancient microbes wake up and begin digesting the newly available organic matter, exhaling carbon dioxide. Where the ground becomes waterlogged, oxygen-free conditions favour microbes that produce methane, a greenhouse gas dozens of times more potent than CO2 over the short term. The process is uneven: some areas thaw gradually from the top down, while others collapse abruptly as underground ice melts, forming sinkholes and thaw lakes that accelerate the decay. Abrupt thaw affects a smaller area but releases carbon far faster, and current models may underestimate it. Scientists have even revived ancient viruses and bacteria from thawed permafrost in laboratories, a reminder of how much biology the frozen ground preserves.

The damage on the surface

Even before its climate impact, thawing permafrost is an engineering catastrophe. Roads buckle, pipelines strain, and buildings tilt as the ground beneath them softens; entire communities in Alaska and Siberia face relocation as coastlines erode and foundations fail. The thaw also rewrites landscapes: forests drown in new wetlands, lakes drain away overnight, and hillsides slump. For Indigenous communities whose lives and cultures are built on frozen ground, the changes are not abstract projections but present-tense upheaval.

How big is the carbon feedback?

This is the trillion-tonne question. Estimates suggest permafrost could release tens to hundreds of billions of tonnes of CO2-equivalent this century, depending on warming. That is comparable to a major industrial nation’s emissions, and crucially, it is not included in most countries’ climate pledges. The feedback is also partly irreversible on human timescales: once ancient carbon is in the atmosphere, it stays for centuries. Some researchers worry about abrupt releases from subsea permafrost and methane hydrates, though the evidence suggests a chronic leak rather than a sudden burp.

What scientists are doing about it

Understanding permafrost has become an urgent research frontier:

• Monitoring networks of boreholes and satellites track thaw depth and ground subsidence across the Arctic.
• Field experiments artificially warm plots of tundra to measure exactly how much carbon escapes.
• Models are being upgraded to include abrupt thaw and methane, which earlier generations missed.

FAQs

Could permafrost thaw run away on its own? A self-sustaining runaway is considered unlikely this century, but the feedback will amplify human-caused warming significantly, making emission cuts more urgent, not less.

Does India have permafrost? The Himalayas contain mountain permafrost and glaciers, and their thaw threatens water supplies and triggers glacial lake floods, a parallel crisis closer to home.

Can thawing be stopped? Only by limiting warming. Once thawed, permafrost does not refreeze on human timescales, so prevention is the only real lever.

Permafrost is climate change’s hidden accelerant, a feedback buried for millennia that our warming has now switched on. Every tonne of carbon it releases is one we did not budget for, which is why cutting our own emissions fast enough to keep the giant mostly asleep is among the most urgent tasks of this century. The frozen ground kept its carbon locked away for thousands of years; whether it stays that way is now up to us.

Source: National Snow and Ice Data Center