Global warming rate doubled since 2011, pointing to 1.5 °C crossing near 2028

Why it matters

The crossing date depends strongly on which warming rate is assumed. A faster recent rate puts the 1.5 °C crossing years earlier than the early-2030s IPCC estimate. The authors say this narrows the window for limiting warming to 1.5 °C. Climate models also underestimate the recent rate.

What they did

The authors used five global surface temperature records through 2025, rescaled to a 1850–1900 baseline. They computed Theil–Sen trends for 1971–2010, 1971–2025 and 2011–2025, with confidence intervals from a percentile bootstrap. They extrapolated each rate to find when the 20-year average reaches 1.5 °C. They also mapped regional trends and compared the results with 26 CMIP6 models.

Key findings

• The 2011–2025 warming rate is 0.40 °C per decade, against 0.18 °C per decade for 1971–2010 and 0.20 °C per decade for 1971–2025. The difference is significant at the 95% level in all five datasets.
• Extrapolating the 2011–2025 rate gives a 1.5 °C crossing time of 2028 (95% CI: 2026–2031). The 0.20 and 0.18 °C per decade rates give 2037 and 2042.
• The acceleration is tied mainly to East Asia–North Pacific, mid-latitude Eurasia and South Atlantic–Antarctic warming. Removing the trends in all three regions cuts the global rate to about 0.26 °C per decade.
• The 26-model CMIP6 mean gives 0.21 °C per decade for 1971–2010 but only 0.29 °C per decade for 2011–2025.
• The record temperatures of 2024 and 2025 are important to the significance of the acceleration. The 2011–2023 trend is not statistically distinguishable from the 1971–2010 trend.

Limitations

• The crossing time assumes the 2011–2025 rate continues, and the authors say this suits near-term projections better than long-range ones.
• The physical causes of the regional accelerations are incompletely understood, especially for mid-latitude Eurasia and the South Atlantic–Antarctic regions.
• The acceleration rests on a short 15-year window and depends on the exceptional years 2024 and 2025.

Glossary

• Theil–Sen slope: A robust trend estimate, taken as the median of the slopes between all pairs of data points.
• Crossing time: The IPCC definition: the midpoint of the first 20-year period whose average temperature reaches a given level above 1850–1900.
• CMIP6: The sixth round of coordinated climate model simulations used in IPCC assessments.
• Percentile bootstrap: A method that resamples the data many times to get a confidence interval for an estimate.