Uncertainties around net-zero climate targets have major impact on greenhouse gas emissions projections

Globally, more than 100 countries have adopted net-zero targets. Most studies agree on how this increases the chance of keeping end-of-century global warming below 2°C. However, they typically make assumptions about net-zero targets that do not capture uncertainties related to gas coverage, sector coverage, sinks, and removals. This study aims to analyze the impact of many uncertainty factors on the projected greenhouse gas (GHG) emissions by 2050 for major emitting countries following their net-zero pathways, and their aggregate impact on global GHG emissions. Global emission projections range from 23 to 40 gigatons of CO₂ equivalent (GtCO₂eq), with a median of 31 GtCO₂eq. Our full range corresponds to about 40–75% of 2015 emission levels, which is much wider than the range of 30–45% reported by various integrated assessment models. The main factors contributing to this divergence are the uncertainty in the gas coverage of net-zero targets and uncertainty in the socioeconomic baseline. Countries with net-zero GHG targets by 2050 have a small range of 2050 emissions, while countries with net-zero targets beyond 2050 and unclear coverage, such as China, India, and Indonesia, have a large range of emissions by 2050.