IPCC baseline scenarios over-project CO2 emissions and economic growth

Our new paper on IPCC scenarios is now posted as a preprint. Details below and I have summarized it in a new column at Forbes.

Burgess, M. G., Ritchie, J., Shapland, J., & Pielke, R., Jr. (2020, February 18). IPCC baseline scenarios over-project CO2 emissions and economic growth. https://doi.org/10.31235/osf.io/ahsxw SocArXiv

Abstract

Scenarios used by the Intergovernmental Panel on Climate Change (IPCC) are central to climate science and policy. A recent Nature commentary found observed trends and International Energy Agency (IEA) projections of global CO2 emissions substantially diverging from high-emission scenarios such as RCP8.5, which are often treated as equivalent to ‘business as usual’ in climate research and assessment. Here, we quantify the bases for this divergence by comparing “baseline” (or “no policy”) scenario projections of key fossil-fuel CO2 emission drivers to observations from 2005-2017, and also to projections through 2040 from world energy outlooks. We find most of the baseline scenarios used in the Fifth (AR5) and designed for the forthcoming Sixth (AR6) IPCC Assessment Reports have over-projected per-capita GDP growth—severely in most developing regions, and slightly in other regions—and have slightly over-projected carbon intensity (CO2 emissions/primary energy) in most regions. These baseline scenarios will likely continue to over-project carbon intensity through 2040 and beyond, in part due to unrealistic assumptions about fossil-fuel expansion. Long-term economic growth outlooks lack consensus among economists, but we argue that most of these baseline scenarios will likely continue over-projecting per-capita GDP to at least 2040 due to inertia. Our results inform the rapidly evolving discussion on uses of scenarios in climate science and policy.