Sack Lunch Seminar (SLS)

SLS: Carl Wunsch
Date Time Location
April 20th, 2011 12:10pm-1:00pm 54-915
Can One Predict the North Atlantic Circulation?


At the urging of some scientists, governments around the world are funding attempts to predict the climate system on decadal time scales. This talk will focus on the prediction of the unforced (natural) decadal scale changes in the N. Atlantic sea surface temperature and meridional overturning circulation (MOC)---including attempts to build observing systems directed at "early warning". The ECCO state estimates, derived from a least-squares fit of a GCM to global data sets, are used. It will be argued that observed changes (even going back 100+ years) can be characterized as small perturbations, and thus one should begin with a discussion of linear predictability. Useful nonlinear prediction skill is not ruled out, but must compete with the linear approach. Some linear prediction skill is indeed found, but given the intense noisiness of the natural system, it will be very difficult to detect over 10-20 years. The most robust prediction is that the future state will likely be indistinguishable from today, barring major shifts in external disturbances whose prediction is a separate problem. High and low latitudes have radically different adjustment times and mechanisms, and low latitude predictability appears to carry almost no information about the behavior of high latitudes on decadal time scales.