Recorded during the UK's July heatwave, Sam and Roberta turn their thoughts north to cooler regions...

We tend to think of Arctic regions as harsh, frozen, crisp, cold. But professor Marc Macias Fauria invites us to consider parts of the Arctic landscape differently. In summer, he suggests, it is like a landscape of butter.

In this dynamic environment, the carbon locked up in frozen ground, or permafrost, is vulnerable. In episode 2, we looked at how carbon gets into the ground, and how the freezing temperatures help protect it from being decomposed by microbes, much like how we put food in the freezer to preserve it. Now, we ask, what happens to the carbon when we open that freezer, when permafrost thaws? 

And we’ll be discovering that there are a few surprises hidden down there.