Updated scenarios show 1.5°C overshoot is unavoidable but limitable

A lack of meaningful action in reducing greenhouse gas emissions has fuelled debate on whether global warming can still be limited to 1.5°C. In 2022, the Working Group III contribution to the Sixth Assessment Report found 97 scenarios that could limit global warming to 1.5°C above pre-industrial levels with no or limited overshoot, while 9 kept median warming projections under 1.5°C throughout the 21st century. These pathways relied on emissions reductions by 2025 that have not materialized. We show that updating the emissions and climate model calibrations to 2023, provides additional constraints on the projected warming outcomes. The window to keep warming below 1.5°C with a greater than 50% likelihood has closed. We use several approaches to show that the objective of limiting warming to 1.5°C needs to be pursued from above after a temporary overshoot. Immediate, rapid deep reductions in CO ₂ emissions and non-CO ₂ forcers, can still limit peak warming to around 1.7°C, and returning below 1.5°C before 2100 is attainable. Keeping peak warming as low as possible and pursuing to reverse it below 1.5°C thereafter will contain the adverse consequences of temperature overshoot and limit the scale of negative emissions required.