DePreSys: Met Office decadal prediction system

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 predictions therefore attempt to predict internal 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.

 Initialisation is achieved by relaxing to full-depth analyses of ocean temperature and salinity, 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. Updated decadal forecasts, along with verification of previous forecasts, are available from the Forecast web page.

References

• Smith, D. M., S. Cusack, A. W. Colman, C. K. Folland, G. R. Harris and J. M. Murphy, 2007, Improved surface temperature prediction for the coming decade from a global climate model, Science, 317, 796-799, doi:10.1126/science.1139540
• Smith, D. M. and J. M. Murphy, 2007, An objective ocean temperature and salinity analysis using covariances from a global climate model, Journal of Geophysical Research, 112, C02022, doi:10.1029/2005JC003172