G8 emissions pledge is 'scientifically illiterate'

It sounds big, but it just isn't enough. Leaders of the G8 industrial nations meeting in Italy this week are likely to agree that the world must cut greenhouse gas emissions by 50 per cent by 2050. That means cuts of 80 per cent among the rich nations.

They will say that this is essential to keep global warming below 2 °C - widely regarded as the tipping point beyond which scary global feedbacks could wreck the climate system that keeps us fed and watered.

Sorry, guys, but this is scientifically illiterate. We might be lucky: if the atmosphere is less sensitive to those gases than most scientists suppose, it could be enough to keep us below 2 degrees, for a while at least. But the best estimate is that the world needs at least 80 per cent cuts in global emissions, and probably more like 100 per cent, to stay below two degrees.
The smart talk back at the climate lab is about negative emissions. We may need to construct a planetary air-conditioning system to keep us cool by sucking carbon dioxide out of the air.

Now I have been writing about climate change since the mid-1980s, when it was not much more than a scary thought among a few atmospheric chemists. Even at the end of the 80s, insiders say Greenpeace decided not to launch a campaign on climate change because they were not sure about the science.

So I am amazed at how far the world has come since, in admitting the need to control the emissions of gases fundamental to our economies. I know the 1997 Kyoto protocol was a bit of a damp squib, with the US bailing out and everyone else taking their cue. But even to be talking about 50 per cent emissions cuts today is, from the historical perspective, dazzling politics.

The trouble is the science has moved on even faster. The planet is not waiting for the diplomats. Climate chaos is coming down the tracks fast.

Even a decade ago, most scientists figured that we could probably cope with doubling the levels of carbon dioxide in the atmosphere from pre-industrial levels. That is, going from 275 parts per million to 550 ppm. Right now, we are at approaching 390 ppm and pushing up by around 2 ppm a year. So it seemed that we had a bit of time.

But five years ago, with growing concern about climate tipping points, scientists began to see 450 ppm as the threshold we should not exceed. That's a lot closer. We will be there in 30 years.

And more recently the talk has been about 350 ppm. In other words, because of the timelags involved in the whole global warming process, we will need to lower concentrations of greenhouse gases to below where they are now.

Either that or we may face the rapid breakup of the Greenland ice sheet, runaway African droughts, drowned cities and oceans so acid they dissolve coral reefs. As the cover story of New Scientist magazine eloquently put it last week: "It's worse than we thought".

But I won't despair when the G8 leaders walk away basking in the glow of having made a strong statement on climate change. Despair isn't really an option. And there is good news.

The White House is listening to its chief scientist, Nobel prize-winning energy campaigner Steve Chu, who certainly gets it. He tells Americans they will have to abandon California to the desert if they don't act fast. He and Obama believe there can be a worldwide revolution in how we generate energy: a low-carbon revolution within a generation.

I believe that too. There are tipping points in human society, as well as the climate system. But will we reach ours in time to prevent nature going over the edge? That I don't know.