Ten years out -- a decadal prediction system

From the Met Office in the UK: DePreSys is the Met Office decadal climate prediction system (Smith et al., 2007). Although climate is expected to warm over the next century in response to increasing levels of greenhouse gases, regional changes over the coming seasons to a decade or more are likely to be dominated by unforced natural variability of the climate system. Some of this natural variability is potentially predictable months or even years in advance because it is related to relatively slow processes in the ocean, such as El Niño, fluctuations in the thermohaline circulation, and large-scale anomalies of ocean heat content.

Decadal forecasts therefore attempt to predict natural variability in addition to externally forced changes. This is achieved by starting a climate model from the current observed state of the climate system, as well as specifying changes in anthropogenic sources of greenhouse gases and aerosol concentrations and projected changes in solar irradiance and volcanic aerosol.

DePreSys uses the Hadley Centre Coupled Model version 3, HadCM3. Initialisation is achieved by relaxing to full-depth analyses of ocean temperature and salinity (Smith and Murphy, 2007), and atmosphere analyses of winds, temperature and surface pressure. Tests for past cases show that initialisation improves the forecast skill of globally-averaged surface temperature throughout the decade (Smith et al., 2007). Updated decadal forecasts, along with verification of previous forecasts, are available from the experimental seasonal to decadal predictions web page.

John William Waterhouse, "The Crystal Ball," from 1902