Indicate separate contributions of long-lived and short-lived greenhouse gases in emission targets

As researchers who have published over recent years on the issue of comparing the climate effects of different greenhouse gases, we would like to highlight a simple innovation that would enhance the transparency of stocktakes of progress towards achieving any multi-decade-timescale global temperature goal. In addition to specifying targets for total CO 2-equivalent emissions of all greenhouse gases, governments and corporations could also indicate the separate contribution to these totals from greenhouse gases with lifetimes around 100 years or longer, notably CO 2 and nitrous oxide, and the contribution from Short-Lived Climate Forcers (SLCFs), notably methane and some hydrofluorocarbons. This separate indication would support an objective assessment of the implications of aggregated emission targets for global temperature, in alignment with the UNFCCC Parties' Decision (4/ CMA.1) 1 to provide "information necessary for clarity, transparency and understanding" in nationally determined contributions (NDCs) and long-term low-emission development strategies (LT-LEDSs). While differences remain between us regarding how best to set fair yet ambitious targets for individual emitters 2-5 , including how any additional information might be used, and the interpretation of the Paris Agreement, it is important to emphasise the high level of agreement on the underlying science of how different greenhouse gases affect global temperature. The 2018 IPCC Special Report on 1.5 °C (SR1.5) 6 stated "Reaching and sustaining net-zero global anthropogenic CO 2 emissions and declining net non-CO 2 radiative forcing (Planetary energy imbalance resulting directly from human-induced changes.) would halt anthropogenic global warming on multi-decadal timescales (high confidence). The maximum temperature reached is then determined by cumulative net global anthropogenic CO 2 emissions up to the time of net zero CO 2 emissions (high confidence) and the level of non-CO 2 radiative forcing in the decades prior to the time that maximum temperatures are reached (medium confidence)". The IPCC 6th Assessment Report (AR6) 7 confirmed "limiting human-induced global warming to a specific level requires limiting cumulative CO 2 emissions, reaching at least net zero CO 2 emissions, along with strong reductions in other greenhouse gas emissions". Parties to the Paris Agreement agreed in Katowice in 2018 (Decision 18/CMA.1) 1 to report past emissions of individual gases separately and use 100-year Global Warming Potentials (GWP 10