About a quarter of all land in the Northern Hemisphere sits on permanently frozen ground called permafrost. In some parts of Siberia, it's frozen to a depth of over a kilometre. It's been frozen for tens of thousands of years — since the last ice age. And it's now thawing.
What exactly is permafrost?
Permafrost is ground — soil, rock, and sediment — that has remained at or below 0°C for at least two consecutive years. In practice, most permafrost has been frozen for far longer. It underlies vast areas of Russia, Canada, Alaska, Greenland, and the Tibetan Plateau. Above it sits a thin "active layer" that thaws each summer and refreezes each winter. Below that, the permafrost can extend hundreds of metres down.
Permafrost is full of organic material — the remains of plants and animals that died and were frozen before they could fully decompose. It's essentially a massive freezer containing thousands of years of biological material.
🥩 Imagine putting meat in a freezer. It stays preserved indefinitely. Take it out and leave it at room temperature, and bacteria get to work — the meat decomposes and releases gases. Permafrost works the same way. While it stays frozen, the ancient organic matter inside it is locked away. Once it thaws, microbes wake up and start decomposing that material — releasing carbon dioxide and methane into the atmosphere.
Why does thawing permafrost matter?
Methane. Permafrost contains an estimated 1.5 trillion tonnes of carbon — nearly double the amount currently in the atmosphere. As it thaws, microbial decomposition releases some of that carbon as methane, a greenhouse gas roughly 80 times more potent than CO₂ over a 20-year period. This creates a feedback loop: warming causes thawing, which releases methane, which causes more warming, which causes more thawing. Scientists call this a climate tipping point — a self-reinforcing process that, once started, becomes very difficult to stop.
What's already happening?
Parts of Siberia are developing "thermokarst" — a landscape of slumps, sinkholes, and lakes formed as permafrost melts and the ground collapses. Buildings, roads, and pipelines built on permafrost are sinking and cracking. Rivers in Alaska have turned orange as thawing permafrost releases stored minerals. And scientists are finding that permafrost is thawing faster than models predicted. It's one of the most alarming but least discussed aspects of climate change.
About a quarter of all land in the north sits on frozen ground. This frozen ground is called permafrost. In some parts of Siberia, it's frozen over a kilometre deep. It has been frozen for tens of thousands of years. This is since the last ice age. Now it is melting.
What exactly is permafrost?
Permafrost is ground that stays frozen for at least two years. This ground is made of soil, rock and mud. Most permafrost has been frozen for much longer than two years. You can find it under huge areas of Russia and Canada. It is also under Alaska, Greenland and Tibet. Above the permafrost is a thin layer that melts each summer. This layer freezes again each winter. Below this, the permafrost goes hundreds of metres down.
Permafrost is full of old plants and animals. These plants and animals died long ago. They froze before they could rot away completely. It's like a massive freezer full of old living things. This frozen material has been stored for thousands of years.
🥩 Think about putting meat in your freezer at home. The meat stays fresh as long as it's frozen. If you take it out and leave it on the kitchen table, it goes bad. Tiny germs called bacteria start eating the meat. The meat rots and makes smelly gases. Permafrost works the same way. While it stays frozen, the old plants and animals stay locked inside. When it melts, tiny germs wake up and start eating them. This makes gases that go into the air.
Why does melting permafrost matter?
The melting makes a gas called methane. Permafrost has about 1.5 trillion tonnes of carbon stored inside it. That's nearly twice as much as all the carbon in the air now. When permafrost melts, tiny germs eat the old plants and animals. This makes methane gas. Methane is much worse for our planet than other gases. It traps 80 times more heat than carbon dioxide over 20 years. This creates a big problem. Warming melts the permafrost. Melting permafrost makes methane. Methane makes more warming. More warming melts more permafrost. Scientists call this a tipping point. Once it starts, it's very hard to stop.
What's already happening?
Parts of Siberia are changing in scary ways. The ground is sinking and making holes. Lakes are forming where the ground has collapsed. This happens when permafrost melts and the ground falls down. Buildings and roads built on permafrost are cracking and sinking. In Alaska, some rivers have turned orange. This is because melting permafrost lets out stored metals. Scientists are finding that permafrost is melting faster than they thought. This is one of the most worrying parts of climate change. But not many people know about it.