Even so, if they really are sincere about acting on global warming, they must follow the example of wartime scientists, and give politicians solutions, not problems.

They must drop the notion that a perfect answer exists out there somewhere - if only enough time was spent dreaming it up. For example, no-one thinks nuclear power is the perfect solution to energy generation – but it beats the hell out of letting the lights go out.

There must also be an acceptance that there's neither the time nor resources to tackle every aspect of climate change. And that means drawing up invidious priority lists and building coalitions of the willing to tackle them. Self-indulgent campaigns aimed at making us all feel guilty – about, say, using cheap air travel, which is of trivial importance for climate change – are no way to do either.

If environmentalists start acting as if there's a war on, they might actually succeed in their self-appointed aim of saving the planet. But they haven't a hope as long as they keep treating the rest of us as the enemy.