26 December 2014

Case Studies for Initialized Decadal Hindcasts and Predictions for the Pacific Region


In the new field of decadal climate prediction, it is of interest to determine whether major climate shifts we have previously observed can be simulated by initialized predictions (or hindcasts) of these past conditions. If they can, this builds credibility for the skill and usefulness of initialized decadal climate predictions for future near-term climate. Case studies are analyzed for two such periods, the mid-1970s climate shift, when the eastern tropical Pacific warmed over a decade and globally averaged temperature rapidly increased, and the early 2000s hiatus when the eastern tropical Pacific cooled over a decade and global temperatures warmed little. Ten year hindcasts follow the CMIP5 decadal climate prediction experiment design for those periods using two different initialization techniques in a global coupled climate model, the CCSM4. There is additional skill in the initialized hindcasts for surface temperature patterns over the Pacific region for those two case studies over and above that in free-running historical simulations with the same model. A 30 year hindcast also shows added skill over the Pacific compared to the historical simulations. A 30 year prediction from the initialized model simulations show about 20% less global warming for the 2016-2035 period than the free-running model projection for that same time period. Thus, there is evidence for added utility of initialized decadal climate predictions for near-term climate change that is an improvement over traditional uninitialized climate change projections.

G. A. Meehl
National Center for Atmospheric Research (NCAR)