“Safe” climate means “no to coal”

About three-quarters of the world’s fossil-fuel reserves must be left unused if dangerous climate change is to be avoided, scientists warn. Writing in the journal Nature, the scientists say that politicians should focus on limiting humanity’s total output of carbon dioxide (CO2) rather than on setting a “safe” level for annual emissions, the BBC reported.

This group of scientists says that the cumulative emissions total provides a better measure of the likely temperature rise and may present an easier target for policymakers. Without major curbs on fossil-fuel use, they say, the widely supported 2º Celsius ceiling on temperature increases probably will be reached by 2050.

An analysis by Myles Allen, of the physics department at Oxford University, suggests that if emissions total more than about one trillion tonnes of carbon, the 2° threshold is likely to be breached, perhaps within a lifetime. The “trillion tonnes” analysis is one of two studies published in Nature by a pool of researchers that includes the Oxford group and scientists from the Potsdam Institute for Climate Change Impact Research in Germany.

The second study, led by Potsdam’s Malte Mainshausen, attempted to work backwards from the 2° goal, to find out what achieving it might mean in practice. It suggests that the target of halving global emissions by 2050 (from 1990 levels) would leave a significant risk of breaching the 2° target. If policymakers decided they were happy to accept a 25% chance of exceeding 2° by 2050, Mainshausen said, they must also accept that this meant cutting emissions by more than 50%.

That would mean burning only about a quarter of the carbon in the world’s known, economically recoverable fossil-fuel reserves – mainly oil and natural gas. Coal would be left alone unless its emissions could be captured and stored.

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