Document summary
This paper seeks to explore how conservative is our current estimate of Climate Sentitivity. Climate Sensitivity is a measure of the way the feedback dynamics of the natural world amplify the effects of the greenhouse gasses added to the atmosphere by human activity. A conservative value for Climate Sensitivity underlies all current approaches to the mitigation of climate change, be they international negotiations, pledge-making, target setting, risk assessment, emissions control, energy scenarios, economic implications, etc. Known as the Charney Sensitivity, it is still endorsed by the current ensemble of computer models on which the IPCC 4th Assessment Report is based. It stands at a figure of 3ºC as the increase in average surface temperature of the earth resulting (at equilibrium) from a doubling of the concentration of atmospheric CO2. That represents an Amplification Factor of 2.5 times the effect of the CO2 on its own.