Assessing California's progress toward its 2020 greenhouse gas emissions limit

California law requires statewide greenhouse gas (GHG) emissions to return to 1990 levels by 2020—a goal achieved in 2016, four years early. We conduct the first independent retrospective analysis of California's greenhouse gas emissions to assess how the state has achieved faster-than-expected emissions reductions. We analyze the extent to which economic activity, climate policies, and market forces drove California's greenhouse gas emissions trends overall and in two key categories: electricity and light-duty vehicles. We also compare historical trends with business-as-usual and policy expectations from the 2008 Climate Change Scoping Plan, California's official strategy for achieving the 2020 emissions limit. Our analysis, based on data through 2017, indicates that reduced economic activity during the 2008–2009 recession and its aftermath has been a major contributor to early achievement of the 2020 emissions limit. Policies and market forces, however, have played a larger role in reducing emissions in recent years—particularly in the electricity sector, which has decarbonized more rapidly than expected. Meanwhile, GHG emissions from light-duty vehicles in recent years were rising, not falling, in contrast to expectations. Our analysis demonstrates how decomposition methods can be used to track climate policy implementation and inform future policy development.