Comparisons of observed trends of energy and carbon intensity in the global economy to trends implied by emissions scenarios used in policy analysis suggested that those scenarios were severely over-optimistic about the rate at which the world would spontaneously decarbonize its economy.
I update these analysis, using global emissions since 2005, and find that observed rates of decarbonization are not far behind those implied by the RCP 4.5 policy scenario. This suggests that the policy challenge may not be as difficult as previous work has reported.
Introduction
Background and the Kaya Identity
In 2000, the Intergovernmental Panel on Climate Change published a Special Report on Emissions Scenarios, in which it developed many possible scenarios for the paths that greenhouse gas emissions might follow during the 21st century under b