Thawing permafrost could inject enough carbon into the atmosphere to cook the planet. But nobody’s quite sure how fast it’s going to happen.

Permafrost is a giant cold-storage compost heap, stuffed full of frozen carbon. Just like you chucked out last night’s potato peelings, the planet has chucked out billions of tonnes of dead plants, trees, mammoths and, yes, polar bears, all of which is now happily interred under the Arctic wastes.

The difference is that while your compost heap ticks over at a nice warm temperature, breaking down the potato peelings into compost, the frozen ground which makes up permafrost stops that organic stew of Arctic flora and fauna from decomposing, safely locking up the carbon stored in it.

I say ‘safely locking up’ because from the point of view of creating human civilisation, permafrost has been pretty handy. While the permafrost has been permanently frozen, we’ve been busy ekeing out human life, discovering fire, developing agriculture, growing our population. While we’ve been busy nurturing the capabilities that ultimately allow the lucky few to participate in Britain’s Got Talent, the planet’s been watching our backs by keeping this massive store of carbon locked up under the frozen parts of the planet’s surface.

The Arctic Sea Ice Outlook has just been updated for July. It’s based on a synthesis of 16 estimates which utilise a range of different projection methods. They note that there is “no indication that a return to historical levels will occur”.

Big surprise!

The full range of estimates range from 4.0-5.2 million square kilometers, the record low in 2007 was around 4.3 million square kilometres (2008 was 4.7). Most estimates therefore fall between the record lows in 2007 and 2008, …