Block’s Indicator of Sustainable Growth

by  Ray Block

Two or three degrees Celsius warmer by 2100 is dangerous enough, as my previous post suggested from the articles in Nature. But what about double that figure – a median probability of 5.2 degrees Celsius, with a 90 per cent probability range of 3.5 to 7.4 degrees Celsius warmer by 2100.   

This is the findings of a climate change study by MIT- the Massachusetts Institute of Technology published in the May 2009 issue of the American Meteorological Society’s Journal of Climate.

Professor Ronald Prinn, study co-author, and co-director of the Joint Program on the Science and Policy of Global Change at MIT, and his collaborators used 400 computer runs of MIT’s sophisticated global systems model, a detailed computer simulation of global economic activity and climate change to project temperature outcomes. Prinn is the director of MIT’s Centre of Global Change.

The lead author of the climate change project was Andrei Sokolov, research scientist in the Joint Program. 

Professor Prinn said that each of the 400 runs of the computer model used slight variations in input parameters, selected so that each run had an equal probability of being correct, based on present observations and knowledge.

Other climate projections have estimated the probabilities of various outcomes, based on variations in the physical response of the climate system itself. But Prinn explains, the MIT model is the only one that looks in great detail at the effects of economic activity, coupled with the effects of atmospheric, oceanic and biological systems. “ In that sense, our work is unique.”

While the outcome on a “no policy” change looks much worse than before, Prinn says that it is not too late to put in place strong policies to dramatically curb greenhouse gas emissions. “Without action, there is significantly more risk than was previously estimated. This increases the urgency for significant policy action.”

 Prinn says that with  motor vehicles lasting for years, and buildings and power plants lasting for decades, it is “essential to start making major changes through adoption of significant national and international policies as soon as possible. “The least cost option to lower the risk is to start now and steadily transform the global energy system over the coming decades to low or zero greenhouse gas-emitting technologies.”

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