One set of definitions of weather and climate distinguishes these terms in the context of prediction: weather is considered an initial value problem, while climate is assumed to be a boundary value problem (Bryson 1997). Another perspective holds that climate and weather prediction are both initial value problems (Palmer 1998). If climate prediction were a boundary value problem, then the simulations of future climate will ``forget'' the initial values assumed in a model. However, if the ocean surface and/or land surface changes over the same time period as the atmospheric changes, then the nonlinear feedbacks between the air, land, and water eliminate an interpretation of the ocean-atmosphere and land-atmosphere interfaces as boundaries. Rather than ``boundaries'', these interfaces become interactive mediums. The two-way fluxes that occur between the atmosphere and ocean, and the atmosphere and the land surface, must therefore necessarily be considered as part of the predictive system.
To illustrate the dependence of climate prediction on initial conditions, we present results using a regional climate model which illustrates how modeled seasonal weather is dependent on initial conditions and is altered if two-way atmosphere-land surface interactions are included. The land surface model includes both biophysical (short-term) and biogeochemical (medium-term) interactions with the atmosphere. The biogeochemical model uses the CENTURY model (Parton 1996) in which plants grow in response to temperature and precipitation.
An important practical conclusion results if climate prediction is an initial value problem. This means that there are necessarily limits on the time into the future which we can predict climate, since the feedbacks between the ocean, atmosphere, and land surface are nonlinear. These limits have not been determined, yet climate ``predictions'' are routinely communicated to policy makers on time scales of decades and centuries. Second, in the context of predicting what the future climate would be in response to an anthropogenic forcing such as carbon dioxide input, there are as of yet, undefined limits on what aspects of future climate we can forecast even if all the important ocean-atmosphere-land surface feedbacks were included and also accurately represented in the models. This leads to the conclusion that weather prediction is a subset of climate prediction. Societally useful climate prediction requires that all of the feedbacks and other physical processes included in weather prediction be represented in the climate prediction model. In addition, longer-term feedback and physical processes must be included. This makes climate prediction a much more difficult problem than weather prediction.
Bryson, R.A., 1997: The paradigm of climatology: An essay. Bull. Amer. Meteor. Soc., 78, 449-455.
Palmer, T.N. 1998: A nonlinear dynamical perspective on climate prediction. J. Climate, accepted.
Parton, W.J., 1996: The CENTURY model. NATO ASI Series, Vol. I38, Evaluation of Soil Organic Matter Models, D.S. Powlson, P. Smith, and J.U. Smith, Eds., Springer-Verlag, Berlin Heidelberg, 283-291.