Lord Stern, the economist who is now a leading voice on climate change, is interviewed at length in The Guardian today. The paper exaggerates and simplifies Stern’s importance when they say he is “The man in charge of saving the world”.

But Stern will be an influential voice in the climate negotiations this year and his language is getting stronger by the day. “We are the first generation that has the power to destroy the planet,” he says. “High carbon growth kills itself. First on very high hydrocarbon prices, but second and, of course, much more fundamentally, on the very hostile physical environment it would create.”

Stern says when his original report came out in 2006, “people thought I’d over- egged the omelette. But all the things people were looking at turned out to be worse than they thought. Doing nothing looks even more reckless than it did even a few years ago.”

He continues: “Recklessness is the only word. I mean, we have to recognise the scale of the risk. If we go on at anything like business as usual, we’ll be at concentration levels by the end of this century which will give us around a 50-50 chance of being above five degrees centigrade relative to, say, the 19th century …  We haven’t seen three degrees centigrade for three million years. The idea that humans can easily adapt to conditions like these …”

“We’ll move. People will move. Why? Because much of southern Europe will be desert. Other places will become underwater. Others will be hit by such severe storms with such frequency that they become almost uninhabitable. So hundreds of millions of people will move.”

He continues: “You’re already seeing people moving in Darfur, where droughts devastated the grazing land of pastoralist people, and they moved, and come into conflict with people in the places they’re moving to. We’re seeing that already on just a 0.8 degree rise. …. So you can only describe as reckless ignoring risks like that.”

Ultimately, he points out, the choice is quite simple: however difficult the challenge of action may be, the alternative is unthinkable. “If you say I’m not going to do that, what’s left? What’s left is you just reach for the suntan lotion and the big hat, and you say it’s all too difficult, I’m signing off on this, and let’s all fry. Why would you want to go there?”

But Stern sees positives in the current recession, which is “an opportunity to bring forward some of those investments, because resources are a bit cheaper at the moment. I’ve been struck that this climate change story has stayed very much on the agenda, the way that the green stimulus has been seen as part of the expansion package. In the next two or three decades, I think low-carbon technologies are going to be like the railways or IT – big drivers of growth.”

I wonder if the G20 is listening?