Residual fossil CO₂ emissions in 1.5-2 °c pathways

The Paris Agreement-which is aimed at holding global warming well below 2 °C while pursuing efforts to limit it below 1.5 °C-has initiated a bottom-up process of iteratively updating nationally determined contributions to reach these long-term goals. Achieving these goals implies a tight limit on cumulative net CO₂ emissions, of which residual CO₂ emissions from fossil fuels are the greatest impediment. Here, using an ensemble of seven integrated assessment models (IAMs), we explore the determinants of these residual emissions, focusing on sector-level contributions. Even when strengthened pre-2030 mitigation action is combined with very stringent long-term policies, cumulative residual CO₂ emissions from fossil fuels remain at 850-1,150 GtCO₂ during 2016-2100, despite carbon prices of US$130-420 per tCO₂ by 2030. Thus, 640-950 GtCO₂ removal is required for a likely chance of limiting end-of-century warming to 1.5 °C. In the absence of strengthened pre-2030 pledges, long-term CO₂ commitments are increased by 160-330 GtCO₂, further jeopardizing achievement of the 1.5 °C goal and increasing dependence on CO₂ removal.