TIME is running out, and fast. Rising carbon dioxide levels and higher temperatures will soon set in motion potentially catastrophic changes that will take hundreds or even millions of years to reverse.
That was the warning last week from climate scientists attending a conference in Exeter, UK. While sceptics snipe from the sidelines (see 鈥淐limate change: Menace or myth?鈥�) and politicians prevaricate, researchers highlighted evidence that the danger is more pressing than was thought. 鈥淭he sleeping giants are being woken,鈥� several said.
The conference was called by the British government, currently chair of the G8 group of rich nations. It chose to focus discussion on 鈥渄angerous鈥� climate change because all the signatories of a 1992 UN treaty, including the US, have promised to prevent such change. Defining what constitutes 鈥渄angerous鈥� is a job for politicians and wider society, the scientists agreed. But they did identify three distinct types of danger.
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One is the incremental changes in average climate conditions to which people can adapt if given warning or avoid by migrating if they can.
The second is the effect these changing average conditions have on the chance of dangerous extreme events, such as the 2002 heat wave in Europe that killed an estimated 30,000 people. 鈥淩elatives of the heat-wave victims will think we are past the dangerous level already,鈥� said Stephen Schneider of Stanford University in California.
And the third is waking the sleeping giants 鈥� triggering irreversible changes in natural systems, such as the melting of polar ice caps. Once we pass these thresholds there will be no return. And the conference heard that we could be closer to the brink than previously supposed.
While no formal target was adopted, most researchers agreed the world should not be allowed to warm more than 2 掳C above pre-industrial levels. 鈥淚f we go beyond two degrees we will raise hell,鈥� said John Schellnhuber, director of the Tyndall Centre for Climate Change Research in Cambridge, UK.
But how to achieve this is unclear, because of the continuing uncertainty about how sensitive the climate is to extra doses of greenhouse gases. Most estimates are that a doubling of CO2 in the atmosphere from pre-industrial levels (from 275 parts per million of CO2 to 550 ppm) will increase temperatures by between 2 and 4 掳C. Recent studies, however, suggest there is an outside chance of an increase of up to 11 掳C.
Many researchers at the meeting concluded that the world should be aiming to keep CO2 concentrations in the atmosphere below 400 ppm. Atmospheric levels are currently just short of 380 ppm, and could reach 400 ppm within a decade.
Then there is the cost of reducing emissions. Even if greenhouse sceptics are right about the cost, which they claim will run to trillions of dollars, that is not much in terms of the growing world economy and the eventual cost of doing nothing, Schneider said.
The average world citizen will be five times richer by the end of this century, he pointed out. Acting now to prevent climate change would merely delay that a couple of years. 鈥淲e would be five times richer in 2102 rather than 2100. I think that鈥檚 an acceptable price to pay.鈥�
