A Musing Environment

The Stern Review on the Economics of Climate Change was released February 12.

Go to page 5 of the executive summary.

Currently, atmospheric levels of greenhouse gases (GHG) are 450 parts per million (ppm). This includes 382 ppm CO2. Relative to pre-industrial times, the temperature of the Earth has increased 0.8 C. The authors of the Stern Review feel that keeping atmospheric levels of greenhouse gases to 450 ppm is almost out of reach, and that it will cost 1% of the worldwide Gross Domestic Product to keep GHG levels to levels between 500 and 550 ppm.

Stabilization Levels and Probability Ranges for Temperature Increases

At 450 ppm carbon dioxide equivalent (CO2e), there is a 50% chance that the temperature increase relative to pre-industrial times will be 2 C or more, a 5% chance that it will anywhere from 3.8 C to more than 5 C. At 550 ppm CO2e, there is a 50% chance that temperature increase will be greater than 2.9 C, and a 5% chance that it will be grater than 3.8, perhaps much greater than 5 C. Notice that these probability models show asymmetric results — the 50% or 5% highest temperature increases are spread over a much larger range than the lowest counterparts.

On the same graph, there are burning embers: relative risks at different temperature increases of consequences for food, water, ecosystems, extreme weather events, and risks of rapid climate change and major irreversible impacts (weakening of currents or melting of the world’s large ice sheets).

These yellow to red give a sense of the results of studies and models — by the red region, large numbers of studies or models give a certain prediction. This does not mean that the collapse of the West Antarctic Ice Sheet is unlikely to happen (or be committed to) before the orange region, say.

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