Atmospheric CO2 concentration is the world’s leading risk indicator.
As reported in my previous post, details of the December 2012 data release for atmospheric CO2 concentration in parts per million at the Mauna Loa Observatory in Hawaii are as follows:
- December 2012 = 394.39 ppm, +2.60 ppm year-on-year
- Twelve Month Average = 393.84 ppm, +2.19 ppm year-on-year
- Twelve month average over pre–industrial level = +40.7%
The current trajectory in atmospheric CO2 concentration rise coupled with the fact that no global agreement has been reached to reduce CO2 emissions mean that the world’s average temperature is likely to rise within the range described by the left-hand ‘no policy’ roulette-style wheel (click for larger image) as developed by the Massachusetts Institute of Technology (MIT) Joint Program on the Science and Policy of Global Change.
Given uncertainties with respect to climate sensitivity to a doubling of CO2 and other factors, the temperature outcome can only be expressed as a probability (just as with a roulette table). However, as with a roulette table, the outcomes are constrained within a range.
You can get a sense of the likely temperature change outcomes for both a ‘no CO2 emissions reduction policy’ and a ‘with CO2 emissions reduction policy’ situation by spinning MIT’s climate change wheel here (the so-called Greenhouse Gamble). The methodology behind the MIT approach is here.
According to MIT:
The median value of the “no policy” wheel, or the temperature at which there is a 50% chance of falling above or below that level (even odds) is 5.2 °C.
A rise in temperature of 5.2 degrees Celsius would lead to a radical change in global climate. Since 1750, the global mean temperature has risen about 0.8 degrees Celsius.