First crossings of global warming levels in CMIP6 in light of observed 1.5 °C exceedance

The year 2024 marked the first time global temperatures exceeded 1.5 °C, raising questions about climate projection accuracy and implications for climate goals. We quantify the timing and likelihood of first crossing 1.5 °C and higher global warming levels across CMIP6 models. The observed 2024 crossing occurred 3–7 years earlier than in CMIP6 projections. Models with high present-day warming rates predicted the timing of the 1.5 °C crossing more accurately, while the 2024 timing is likely affected by internal climate variability superimposed on the anthropogenic trend. A pre-mid-century 2 °C crossing is difficult to avoid even under stringent mitigation (75% of models crossing 2 °C under SSP1-2.6). However, while shifting from high (SSP5-8.5) to medium-high (SSP3-7.0) emissions delays a 3 °C crossing by 10 years, low-emission pathways (SSP1-2.6) avoid crossing this threshold in 85% of models. While near-term 2 °C exceedance is a significant risk, immediate mitigation remains critical to enable adaptation and avoid long-term warming.