Conventional climate discussions use the targets of 2°C above pre-industrial global mean temperature and 450 ppm CO2 to avoid dangerous climate change This limit of 2°C is not a scientific target.

It is a political one that dates from the mid 1990s and the European Union.

Sophisticated theoretical climate models used by climate scientists, including the IPCC, have shown that 2°C correlated with 450 ppm CO2 and it is the most often cited target of the current international climate negotiations.

These theoretical models are based upon the data that projects (the Charney Effect) a doubling of pre-industrial CO2 (280 ppm to 550 ppm) would result in a 3°C increase in global mean temperature. These models incorporate so-called “fast feedbacks” – interactions that amplify changes in systems – such as annual sea ice and the albedo effect (less white surface area to reflect sun, more dark areas to absorb heat) and water vapor, clouds, and aerosols (particles in the atmosphere).

In their conclusion, the IPPC report also projected a sea-level rise of .18 to .59 meters over the next 100 years based on Alpine glacial runoff and thermal expansion of the ocean. But potential impacts from Greenland and West Antarctica were excluded.

Both the IPCC Report and the Stern Review make compelling cases for action now. Sir Stern recently commented that his review the dynamics of the climate systems were “substantially underestimated.” Nobel Laureate and IPCC Chair Rajenda K. Pachauri said recently, “If there’s no action before 2012, that’s too late. What we do in the next two to three years will determine our future. This is the defining moment.”

The IPCC report and the Stern Review were produced with scientific data that is now 3-4 years old. Much of that knowledge is still valid. But now we know even more.