President Bush said Friday the United States and the rest of the world's worst polluters should work together to set a goal for reducing greenhouse gas emissions that have triggered a global increase in temperature.

NPR: Bush Calls for Goal on Reducing Greenhouse Gases

Climate sensitivity is a key parameter for estimating the long-term temperature increase expected from a doubling of the concentration of greenhouse gas emissions in the atmosphere.

FORBES: Climate Sins and the High Priests of Peer Review

Stabilizing greenhouse gas concentrations at 550 ppm -- which would invoke a rise in temperature of about three degrees Celsius -- would require energy emissions to rise no higher than 33 gigatons and would need to fall in the longer term.

CNN: Report urges fuel revolution

That output is known to vary during the course of the 11-year sunspot cycle, as well as over the longer term, and although such changes have not been matched to temperature changes in the way that rises in the level of greenhouse gases have been, they may still be making a contribution.

ECONOMIST: Changing science