AI-forecast-based Attribution
Daily 6-day AI weather forecasts initialised from ERA5 reanalysis, run under both factual (current climate) and counterfactual (pre-industrial, PGW) conditions. The ACC signal = Factual − PGW, averaged over 13 initializations all verifying at the same target date (lead times 2–5 days). Stippled dots mark grid points not significant at p < 0.05 (paired t-test across initializations). Z500 factual contours are overlaid.
See Jiménez-Esteve et al. (2025) for methodology.
Counterfactual: Present Day (2010–2040, SSP5-8.5) minus Pre-Industrial (1850–1900), a CMIP6 30-model-mean warming delta (+1.5 K global mean) subtracted from ERA5 to build the pseudo-global-warming initial condition — see the table below.
2 m Temperature — Attribution Signal
Last updated: 2026-10-01 00:00 UTC · Counterfactual conditions subtract a CMIP6 multi-model-mean warming delta from ERA5 (pseudo-global-warming approach), defined as Present Day (PD) minus Pre-Industrial (PI, 1850–1900).
| Counterfactual | Definition | Global mean | CMIP6 models |
|---|---|---|---|
| SSP5-8.5, 2010–2040 | PD (2010–2040, SSP5-8.5) − PI (1850–1900) | +1.53 K | 30 modelsAWI-CM-1-1-MR, BCC-CSM2-MR, CAMS-CSM1-0, CIESM, CMCC-CM2-SR5, CMCC-ESM2, CNRM-CM6-1-HR, CNRM-ESM2-1, CanESM5, CanESM5-CanOE, E3SM-1-1, EC-Earth3, EC-Earth3-Veg, EC-Earth3-Veg-LR, FGOALS-g3, GISS-E2-1-G, HadGEM3-GC31-LL, HadGEM3-GC31-MM, INM-CM4-8, INM-CM5-0, IPSL-CM6A-LR, KACE-1-0-G, MIROC6, MPI-ESM1-2-HR, MPI-ESM1-2-LR, NESM3, NorESM2-LM, NorESM2-MM, TaiESM1, UKESM1-0-LL |
AIFS (ECMWF, aifs-single-1.0) also takes skin temperature, soil temperature and 2 m dewpoint as inputs. Its counterfactual therefore shifts them consistently with the 2 m temperature (SST delta over ocean, 2 m-temperature delta over land, 2 m relative humidity kept); otherwise AIFS pulls the 2 m temperature back to the unperturbed surface within its first 6 h. The multi-model mean averages Pangu-Weather, FourCastNet v2 and AIFS. Precipitation is AIFS only: the 6 h or 24 h accumulation ending at each date (24 h windows overlap from one date to the next).