Will 2026 be the hottest calendar year on record for global average surface temperature?

probability: 30%

rationale:

Current Standings and Year-to-Date Deficit The bar to beat remains 2024, which currently holds the calendar-year temperature record across all major datasets 2 sources. Through the first seven months of the year, 2026 is exceptionally warm but still trailing 2024's record pace. Data from January to July 2026 marks the third-warmest start to a year, running roughly 0.09°C to 0.13°C cooler than the same period in 2024 2 sources. For example, NASA GISTEMP shows the first seven months of 2026 averaging ~1.19°C above the 1951–1980 baseline, compared to 1.28°C for the same period in 2024 data.giss.nasa.gov. NOAA similarly reports January–July 2026 as the third-highest in its 177-year record, at +1.14°C versus +1.25°C for 2024 ncei.noaa.gov. Overcoming this seven-month deficit requires August–December anomalies to run at sustained, all-time record highs.

The ENSO Outlook and Temporal Lag The primary catalyst that could drive late-2026 temperatures to record highs is a rapidly intensifying El Niño. An El Niño Advisory is currently in effect, with a >90% probability of a "very strong" event during the Northern Hemisphere fall and winter of 2026–27 cpc.ncep.noaa.gov. Multi-model ensembles project a potentially historic peak anomaly around November 2026, with some projections reaching near +4.0°C 2 sources. However, global surface temperatures typically lag the ENSO state by 3 to 5 months. Consequently, the vast majority of this extreme El Niño's warming impact will materialize in early 2027 rather than late 2026 theclimatebrink.com.

Dataset Divergence and Structural Hurdles Dataset mechanics present a significant structural hurdle. There is a sharp divergence between agencies—not on how warm 2026 will be, but on how high the 2024 record sits. Reanalysis datasets like ERA5 posted unusually high values for 2024 that sit far above their long-term trend lines, making them exceptionally difficult to beat. Statistical projections utilizing July data indicate a ~65–69% chance of a 2026 record in NASA GISTEMP and Berkeley Earth, but only ~24% in NOAA GlobalTemp and ~13% in Copernicus ERA5 44 sources.

Synthesis and Consensus Requirements The strict resolution criteria necessitate a consensus or majority view, placing primary weight on NASA, NOAA, and ERA5. Because two of these three heavily weighted arbiters (NOAA and ERA5) are strongly bearish on a 2026 record, a split verdict is the most plausible scenario. Even if NASA and Berkeley Earth eventually confirm 2026 as the hottest year, a lack of consensus from NOAA and ERA5 would cause this to fail the multi-agency requirement. Weighing the aggressive late-year El Niño boost against the substantial year-to-date deficit, aligning this overall consensus expectation with individual agency projections—such as the notably lower probability for NOAA—reflects the distinct difficulty of reaching a multi-agency consensus. This structural constraint limits the probability of 2026 securing the overall record to 30%.