Energy intensity improvements, or declines in the amount of energy consumption per unit of economic output, must play a critical role in efforts to decarbonize the global economy. Global decarbonization scenarios depend on a wide range of energy intensity improvement rates. Several scenarios which rely heavily on renewable energy and exclude other technologies from consideration (i.e. nuclear or carbon capture and storage), depend on a dramatic acceleration in energy intensity improvement compared to historical rates. Policy making has only limited influence over the mechanisms behind changes in energy intensity. Further research is needed to carefully unpack the mechanisms behind historical rates of change in energy intensity in order to benchmark global decarbonization strategies. Until then, scenarios calling for a step-change acceleration in energy intensity rates should be treated with caution. Avoiding extreme or dangerous climate change will likely require the nearly complete decarbonization of the global energy system during this century, […]