Carbon dioxide: we're already over the safe limit

Concentrations passed the limit in 1987, says Geoffrey Lean.

By Geoffrey LeanPublished: 6:58PM BST 23 Oct 2009
Something else unprecedented is happening today, and again it has to do with climate change. It marks the first worldwide campaign for a data point, one that has spread randomly and virally – particularly among the young – through internet and mobile phone networks.
More than 4,200 events and rallies are to take place in 170 countries, including 1,500 across the US, 300 in China and 240 in Britain. It's named after a number, 350 – for the 350 parts per million increasingly being seen as the safe limit for carbon dioxide in the atmosphere. Last month, a batch of the world's leading climate scientists, writing in Nature, concluded that it should not be exceeded.

There's rather a big snag, however. We are already well over that limit, at 387 ppm. Concentrations passed the 350 point in 1987, and international negotiations are bogged down over plans that would eventually stabilise them at 450ppm. So the world would not only have to cut emissions back far faster than anyone has thought possible, but would actually have to develop ways of taking the gas out of the atmosphere – the biggest ask in history.
The campaign is undaunted. "We know better than anybody exactly how difficult this is and how politically unrealistic it is at the moment," says author Bill McKibben, its founder." Our job is to change the political reality, because the physical and chemical reality is not going to change."