20 September 2006The Guardian
There are three things on which almost all climate scientists are now agreed. The first is that man-made climate change is real. The second is that we need to take action. The third is that, to avert catastrophic effects on both humans and ecosystems, we should seek to prevent global temperatures from rising by more than 2C above pre-industrial levels.
Two degrees is the point at which some of the most dangerous processes catalysed by climate change could become irreversible. This includes the melting of the west Antarctic and Greenland ice sheets, which between them could raise global sea levels by seven metres. It includes the drying out of many parts of Africa, and the inundation by salt water of the aquifers used by cities such as Shanghai, Manila, Jakarta, Bangkok, Kolkata, Mumbai, Karachi, Lagos, Buenos Aires and Lima. It also means runaway positive feedback, as the Arctic tundras begin to release the methane they contain, and the Amazon rainforest dies off, turning trees back into carbon dioxide. In other words, if the planet warms by 2C, 3C or 4C becomes almost inevitable.
So by how much do we need to cut carbon emissions if we are to stop this from happening? The most persuasive analysis I have seen was compiled by a man called Colin Forrest. He is not a professional climate scientist, but the figures he uses have been published in peer-reviewed journals. He argues his case as follows.
Researchers at the Potsdam Institute for Climate Impact in Germany have estimated that holding global temperatures to below 2C means stabilising concentrations of greenhouse gases in the atmosphere at or below the equivalent of 440 parts of carbon dioxide per million. While the carbon dioxide concentration currently stands at 380 parts, the other greenhouse gases raise this to an equivalent of 440 or 450. In other words, if everything else were equal, greenhouse gas concentrations in 2030 would need to be roughly the same as they are today.
Unfortunately, everything else is not equal. By 2030, according to a paper published by scientists at the Met Office, the total capacity of the biosphere to absorb carbon will have reduced from the current 4bn tonnes a year to 2.7bn. To maintain equilibrium at that point, in other words, the world's population can emit no more than 2.7bn tonnes of carbon a year in 2030. As we currently produce around 7bn, this implies a global reduction of 60%. In 2030, the world's people are likely to number around 8.2bn. By dividing the total carbon sink (2.7bn tonnes) by the number of people, we find that to achieve stabilisation the weight of carbon emissions per person should be no greater than 0.33 tonnes. If this problem is to be handled fairly, everyone should have the same entitlement to release carbon, at a rate no greater than 0.33 tonnes per year.
In the rich countries, this means an average cut by 2030 of around 90%. The United Kingdom, for example, currently releases 2.6 tonnes of carbon (9.5 tonnes of carbon dioxide) per capita, so would need to reduce its emissions by 87%. Germany requires a cut of 88%, France of 83%, the United States, Canada and Australia, 94%. By contrast, the Kyoto Protocol - the only international agreement that has been struck so far - commits its signatories to cut their carbon emissions by a total of 5.2% by 2012.
These could be underestimates. The Potsdam Institute calculates that with the equivalent of 440 parts of carbon dioxide per million of air in the atmosphere, there is a 67% chance of holding the temperature rise to below 2C. Another study suggests that to obtain a 90% chance of stabilisation below 2C, you would need to keep the concentration below 400 parts per million - 40 or 50 parts below the current level. Because the carbon released now stays in the atmosphere for some 200 years and causes climate change many years into the future, there is perhaps a 30% chance that we have already blown it. We might already be committed to 2C.
But to use this as an excuse for inaction is like remaining on a railway track while the train is hurtling towards you. We might not have time to jump out of the way, but if we don't attempt it, the disaster is bound to happen. If we in the United Kingdom are to bear our fair share of dealing with climate change, we must cut our emissions by 87% in 24 years.
