[A-CG35] Projection and detection of global environmental change

[ACG35-07] Guiding Mother Earth: taking stock of progress to a long-term temperature goal

★Invited Papers

*Myles Robert Allen¹ (1.Environmental Change Institute, School of Geography and the Environment and Department of Physics, University of Oxford)

Keywords:Climate change, Greenhouse-gases, Stocktake, Attribution, Metrics, Forcing

The IPCC Special Report on 1.5°C found that human-induced global warming had reached 1°C ±0.2°C, increasing at 0.2°C per decade, leaving only a few decades for emissions to be reduced to net zero to limit warming to 1.5°C. The Paris Climate Agreement introduced a regime of periodic stocktakes of progress to the long-term temperature goal of limiting warming to well below 2°C, pursuing efforts to 1.5°C. While there is general agreement that these stocktakes are to be informed by science, these is less consensus on how this will be done. I will explain how we can robustly estimate the level of human-induced warming to date, and how this information was used to support a revision in the remaining carbon budget for cumulative future CO₂ emissions consistent with limiting warming to 1.5°C. CO₂ budgets in the IPCC Special Report were contingent on scenarios for non-CO₂ forcing, but the concept of a carbon budget can be generalised if we recognise how other anthropogenic forcing agents affect climate on different timescales, either expressing them as CO₂-forcing-equivalent emissions, or applying the traditional GWP₁₀₀ metric in a new way. Taken together, these insights provide a simple, transparent, scenario-independent and model-independent method of assessing the implications of current and future emissions for progress towards a long-term temperature goal.