A vast expanse of permafrost in Siberia and Alaska has started to thaw for the first time since it formed 11,000 years ago, marked in dark blue on the map. It is caused by the recent 3+°C rise in local temperature over the past 40 years - more than four times the global average. Peat bogs cover an area of a million square miles (or almost a quarter of the earth's land surface) to a depth of 25 meters. Those in Siberia are the world's largest.
What was until recently a barren expanse of frozen peat is turning into a broken landscape of mud and lakes, some more than a kilometre across. All only in the past 3 or 4 years.
This has the potential to release vast quantities of methane trapped by ice below the surface - billions of tonnes of methane.
It is estimated that the west Siberian bog alone contains some 70 billion tonnes of methane, a quarter of all the methane stored on the land surface of the world. This is equivalent to emitting 1.7 trillion tons of CO2, which is more greenhouse gas than has been emitted by humans in the past 200 years.
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