RealClimate: A recent paper suggested that 'climate sensitivity' derived from a new paleo-CO2 record is around 7.2ºC (for equilibrium climate sensitivity ECS) and ~13.9ºC (Earth System Sensitivity - ESS) for a doubling of CO2. Some press has suggested that this means that "Earth’s Temperature Could Increase by 25 Degrees" (F). Huge if true! Fortunately these numbers
Some good digging - indeed it is hard to understand all the different ways to define and interpret climate sensitivity.