Humanity's carbon budget set at one trillion tonnes
18:00 29 April 2009 by Catherine Brahic
No more than one-quarter: that's the proportion of existing reserves of oil, gas and coal that we can burn if we are serious about keeping the planet from warming by 2°C or more.
These are the conclusions of the most comprehensive efforts yet to pin down just how much carbon dioxide can be emitted into the atmosphere.
If governments are to stick to their pledge to avoid "dangerous" global warming – which most politicians and many scientists take to be no more than 2°C – the models come up with roughly the same answer. Humans must not inject more than 1 trillion tonnes of carbon into the atmosphere in total.
That, say teams led by Myles Allen of the University of Oxford and Malte Meinshausen of the Potsdam Institute for Climate Impact Research in Germany, will give us a 50:50 chance of limiting global warming to 2°C.
To improve the chances that the planet remains this side of 2°C, Meinshausen's study suggests we should emit no more than 750 billion tonnes of carbon in total. The risk of exceeding 2°C would then drop from 50% to 25%.
If no climate policies are implemented (red) global warming will cross 2°C by the middle of the century. Making sure we don;t emit more than 1 trillion (1000 gigatons) of CO2 in total (blue) would limit the risk of exceeding 2°C to 25% (Image: M. Meinshausen)
http://www.newscientist.com/article/dn17051-humanitys-carbon-budget-set-at-one-trillion-tonnes.html