Weather And Climate – Well Summarized By On Tomas Milanovic On Climate Etc.

Tomas Milanovic has a accurate succinct summary of the relationship between weather and climate on the weblog post The Uncertainty Monster at Climate Etc.

The comment reads

“Weather is chaotic, nobody disputes that. The “climate” is exactly the same system, obeying to the same laws and described by the same equations like weather. The only difference being that the variables of the system “climate” are space and time averages instead of the instantaneous values. In addition for practical purposes the weather time scale is defined in days so that many slow variables are considered constant what spares computing time. However it is clear that if the system is chaotic with these constant coefficients , it will be chaotic with variable coefficients on longer time scales too.”

The issue of what is climate is discussed further in the article

Pielke, R.A., 1998: Climate prediction as an initial value problem. Bull. Amer. Meteor. Soc., 79, 2743-2746

where I wrote

“….weather prediction is a subset of climate prediction. Societally useful (i.e. reliable, accurate,etc.) 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.”

Indeed, climate models must not only be able to simulate weather features such as high and low pressure systems including tropical cyclones are well as operational numerical weather prediction models, but must be able to accurately simulate a diverse variety of physical, chemical and biological processes. Even then, nonlinear interactions between the many components of the climate system (e.g. as illustrated in Figure 1 in Rial et al 2004) can result in limiting skillful prediction decades into the future.  The Milanovic comment on Climate Etc. effectively summarizes this issue. A subject that is not properly assessed in the 2007 IPCC report.

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