ENSEMBLES: A new multi-model ensemble for seasonal-to-annual predictions-Skill and progress beyond DEMETER in forecasting tropical Pacific SSTs

A new 46‐year hindcast dataset for seasonal‐to‐annual ensemble predictions has been created using a multi‐model ensemble of 5 state‐of‐the‐art coupled atmosphere‐ocean circulation models. The multi‐model outperforms any of the single‐models in forecasting tropical Pacific SSTs because of reduced RMS errors and enhanced ensemble dispersion at all lead‐times. Systematic errors are considerably reduced over the previous generation (DEMETER). Probabilistic skill scores show higher skill for the new multi‐model ensemble than for DEMETER in the 4–6 month forecast range. However, substantially improved models would be required to achieve strongly statistical significant skill increases. The combination of ENSEMBLES and DEMETER into a grand multi‐model ensemble does not improve the forecast skill further. Annual‐range hindcasts show anomaly correlation skill of ∼0.5 up to 14 months ahead. A wide range of output from the multi‐model simulations is becoming publicly available and the international community is invited to explore the full scientific potential of these data.