Will 2027 be the hottest calendar year on record for global average surface temperature?

probability: 89%

rationale:

The final estimated probability is 89% that 2027 will be the confirmed warmest calendar year on record for global mean surface temperature.

Initial logic and parameters regarding climatological baseline data and the ENSO cycle's historical lag impacts are validated. Current records establish 2024 as the incumbent high 2 sources, with 2025 ranking slightly lower climate.copernicus.eu. Atmospheric anomalies confirm the development of a historically significant El Nino event extending through late 2026 cpc.ncep.noaa.gov.

Because global average surface temperatures trail the ENSO peak by 3 to 6 months 2 sources, the most intense warming pulse directly targets 2027. Evidence suggests a peak Nino3.4 anomaly near +3.6C theclimatebrink.com, with near-unanimous expectation of persistence through early 2027 wmo.int. Consequently, central estimates jump to approximately 1.71C above pre-industrial levels carbonbrief.org, decisively surpassing the anticipated 2026 baseline.

There are arguments in both directions regarding the absolute threshold 2026 might establish dashboard.theclimatebrink.com. Standard processing of tail risks accounts for an atypically rapid transition to a strong La Nina depressing late-2027 averages, or unforeseen exogenous cooling shocks such as volcanic aerosols. Incorporating these final constraints yields the definitive 89% likelihood of a new global record.