TO AVOID 鈥渄angerous鈥� climate change, we must not burn more than one-quarter of our remaining reserves of fossil fuels. That鈥檚 the conclusion of the most comprehensive effort yet to work out how much carbon can be pumped into the atmosphere without pushing warming past 2 掳C.
A computer modelling study led by Myles Allen at the University of Oxford and another by Malte Meinshausen of the Potsdam Institute for Climate Impact Research in Germany both point to roughly the same conclusion: humans must not emit more than 1 trillion tonnes of carbon into the atmosphere if we are to have a 50:50 chance of limiting global warming to 2 掳C.
Industrial activity since the mid-18th century has already emitted 500 billion tonnes of carbon, so we are halfway there. 鈥淏ut don鈥檛 let this fool you,鈥� says Allen. 鈥淥n current trends we鈥檒l burn the next 500 billion in less than 40 years.鈥� If we carry on regardless, we will exhaust what Allen calls the 鈥渃arbon budget for the human race鈥� by 2040. Anything beyond that will condemn the planet to more than 2 掳C warming. Meinshausen and colleagues calculate that we could exhaust the carbon budget in as little as 20 years and advise burning less than 500 billion tonnes of carbon.
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鈥淲e can burn less than one-quarter of known economically recoverable fossil fuel reserves between now and 2050,鈥� says Bill Hare of the Potsdam institute. 鈥淲hile a lot of the oil and natural gas can be burned, certainly not much at all of coal reserves can.鈥�
