by Ken Gregory, July 2005

Energy Balance Climate Sensitivity

The most important parameter in determining the economic impact of climate change is the sensitivity of the climate to greenhouse gas emissions. Climatologist Nicholas Lewis used an energy balance method to calculate the Equilibrium Climate Sensitivity (ECS) best estimate at 1.45 °C. ECS is the global temperature change resulting from a doubling of CO2 in the atmosphere after allowing the oceans to reach temperature equilibrium, which takes about 3000 years in the models.

A more policy-relevant parameter is the Transient Climate Response (TCR) which is the global temperature change at the time of the CO2 doubling. A doubling of CO2 at the current growth rate would take 126 years. The analysis gives the TCR best estimate at 1.21 °C with a likely range [17 – 83% confidence] of 1.05 to 1.45 °C.