The lecture will begin with a review of the known, the unknown and the unknowable about the predictability of weather. The skill of current operational models for weather prediction will be discussed in the context of predictability estimates based on homogeneous two-dimensional and quasi-geostrophic turbulence theories, and recent observations of the energy spectrum of atmospheric disturbances.

In the second part of the lecture, the evolution of climate models from the Phillip’s two-layer model to current GCMs will be discussed. It will be shown that the estimates of climate predictability depend on the physics of the current generation of models. It took more than 30 years for the various weather prediction models of the world to converge to a comparable estimate of the limits of predictability of synoptic scale weather fluctuations. It is unclear how long it will take before we can make comparable definitive statements about the predictability of climate fluctuations.