Chris Huhne, secretary of state for energy and climate change, warns – not for the first time – that the world must act now to avoid “unprecedented environmental and geopolitical catastrophe”. He is, of course, talking once again about the need to ensure that global greenhouse gas emissions peak by 2020, and that global warming is limited to 2C. That means a global agreement to act by 2015: this parliament, he warns, is the last one with a chance to help avert catastrophic climate change. He is hardly a lone voice, and on the latest evidence the global barometer seems set for stormy weather. On Friday a team of researchers in Boston calculated that even with only a 2C rise, summer temperatures now regarded as “extreme” will become normal. This is the second such warning from the US this summer.