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Tuesday, March 17, 2009

Re: Elmar Kriegler et al. -- Climate roulette by James Dacey of

Climate roulette

By James Dacey

Mankind is playing a Russian roulette with the climate, according to a study published today in the Proceedings of the National Academy of Sciences.

Elmar Kriegler of the Potsdam Institute for Climate Impact Research and his colleagues sought to find out what leading scientists really think will happen to the climate.

So Kriegler surveyed 43 scientists to gauge the impact of rising temperatures on five major components of the global climate system.

They calculate a one in six chance that a “tipping event” will occur if the temperature increases by two to four degrees in the next two hundred years.

The five systems concerned are:

Major changes in the North Atlantic Ocean circulation
The Greenland and West Antarctic ice sheets
The Amazon rainforests and El Nino.

They define a tipping point as “the event of initiating the transition, or making its future initiation inevitable.” Essentially they are saying that beyond these points the climate will reach a kind of elastic limit -- beyond which, we will feel the wrath of the climate and there’ll be nothing we can do about it.

Realising that previous surveys have been met with a fair degree of apathy they used “imprecise probabilities” -- a part of Bayesian statistics.

This new mathematics has been controversial but advocates say it can weigh up a given hypothesis in a more rounded way than classical statistics.

Developed in the 1980s and 1990s Bayesian statistics seem to have gained most traction in the field of operations research and economic decision making.

“The currently discussed long-term targets of 50% reduction globally by 2050 (and 80% reduction for the industrial countries), with a continuing reduction after 2050 is an important step in this direction, but does not guarantee the reaching of the 2 degree target,” Kriegler told

This may sound like a very gloomy forecast, but Kriegler was a bit more pragmatic about taking co-ordinated international action:

“Nevertheless, these [targeted reductions] are a useful benchmark to focus the minds of politicians and society. Reaching this goal requires at least the following -- in the order of importance:

1) A massive decarbonisation of the energy system, starting in the electricity sector;
2) A strong increase in energy efficiency;
3) A stop to tropical deforestation, and an increase of the forest area in the tropics in the long run;
4) A massive reduction of CH4 and N2O emissions from the agricultural sector.”


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