Levers of climate pledges influencing the Paris Agreement target

Countries pledge GHG mitigation goals in form of near-term emissions targets for 2030, long-term net-zero emissions in mid-century (some countries) and targets for methane emission reductions, towards limiting global warming as stipulated in the Paris Agreement. These undergo regular revisions to strengthen the ambition, with the latest set of revisions occurring during COP26 and COP27. As of December 2022, 169 countries have near-term targets, 56 have long-term targets to become carbon neutral and 150 nations have pledged to reduce their methane emissions up to 30% by 2030.  The end-of-century temperature rise is highly sensitive to the pledges but also to actual extent of implementation of these pledges. Using historical emissions from the PRIMAP-Hist dataset, future emissions of CO₂, N₂O and CH₄ are modelled for each country by incorporating their respective near-term, long-term and methane pledges. Emissions for other climate forcers are assumed to follow SSP4-60. These emission profiles are used as input to simple climate model – ACC2 (Tanaka et al., 2021) to estimate the temperature impacts. With the current pledges, the global temperature rise in 2100 is expected to be 2.0 and 2.1 °C, corresponding to the fulfillment of conditional and unconditional near-term pledges, respectively.  We further explore a suite of emissions pathways to identify some key ‘levers’ across the pledges that can strongly influence the projected global temperature in 2100.  We found that these levers can further reduce the temperature by 0.50 °C or increase by 0.25 °C.  The most significant reductions in temperature rise can be achieved by ratcheting up of the current conditional targets by 10%, shifting the net-zero target year to 2050 for all countries currently having a longer-term goal and adding a net-zero target in 2070 for countries with currently no long-term goals. Inclusion of all these levers can increase the likelihood of limiting temperature rise well below 2 °C and bringing it closer to 1.5 °C. Additional, relatively smaller, contributions accrue from inclusion of Russia, China and India in the Global Methane Pledge. On the other hand, failing to meet even the unconditional NDC targets and delaying the current net-zero targets by 10 years contribute to increases in temperature rise of 0.08 and 0.17 °C. Contributions are also evaluated on a country-by-country basis.

Reference

Tanaka K, Boucher O, Ciais P, Johansson DJA, Morfeldt J (2021) Cost-effective implementation of the Paris Agreement using flexible greenhouse gas metrics. Science Advances 7 (22):eabf9020. doi:10.1126/sciadv.abf9020