Taking stock of nationally determined contributions: Continued ratcheting of ambition is critical to limit global warming to 1.5°C

Abstract

As countries take stock of progress made in accomplishing their climate goals ahead of COP28 this year, it is increasingly apparent that countries must ratchet ambition in policy areas such as non-CO₂ gases and carbon dioxide removal, while halting deforestation to lead the globe on a path consistent with the goals of the Paris Agreement.

Figure 1. Global CO₂ emissions, and likelihoods of different levels of increase in global mean surface temperature change through the end of the century relative to pre-industrial levels.

The figure is based on results from Fawcett et al. , Ou & Iyer et al. , and Iyer & Ou et al. . The two Paris pledges pathways assume that countries implement their 2015 NDCs through 2025 or 2030. The two Glasgow pledges pathways assume that countries implement revised or new NDCs submitted in 2021. A complete documentation of the implementation of the pledges is available in the supplementary information to the above studies. Beyond 2030, the Continued ambition pathways assume that countries achieve the same level of decarbonization rate (defined as the annual rate of improvement in CO₂ emissions per unit of Gross Domestic Product (GDP)) as the rate to achieve the NDCs through 2030 or a 2% minimum rate if their decarbonization rate is below this minimum rate. The Increased ambition pathways assume a 5% minimum decarbonization rate. See Fawcett et al. and Ou & Iyer et al. for more details about these assumptions. The quantitative estimates presented in this figure are based on two modeling studies that used a consistent assessment methodology to understand the aggregate impact of these nationally determined actions in 2015 and 2021, and therefore provide a robust way to track improvement in overall global climate ambition through NDCs.^, Nevertheless, these findings are broadly consistent with other studies in the literature.^-

Figure 2. Global GHG emissions, CO₂ emissions, and temperature outcomes under a CO₂-only mitigation strategy and Comprehensive GHG mitigation strategy.

Compared to a mitigation strategy that is built only around CO₂ emission reductions and includes only synergistic non-CO₂ reductions resulting from switching away from fossil energy to meet CO₂ reduction goals, a comprehensive strategy that includes targeted non-CO₂ abatement measures across all sectors including industrial processes, agriculture, and waste management in addition to CO₂ mitigation measures could result in an earlier peak in global temperature change, a reduction in peak warming, and a reduction in end-of-century warming.