Observer: There was a cleverly staged moment during last week’s BBC eco-drama Burn Up, when oil company workers started poking holes in the icy Canadian tundra. To their consternation, flames of burning methane promptly whooshed out of the melting permafrost. It was a striking moment of television that demonstrated, vividly, how our warming world might soon change in uncontrollable ways. Melt our ice-caps and you release forces you cannot control: in this case, permafrost methane that would …