Excerpts from: B.J. Mason, 1979

Question, Info, Comment etc are from ‘whatisclimate’ WIC

‘Weather’ is associated with the complete state of the atmosphere at a particular instant of time and with the evolution of this state through the generation, growth and decay of individual atmospheric disturbances.

WIC refers to the collection of weather definitions in section: C-317 but is of the opinion that a science should look for a more specific definition to ensure that misunderstandings are minimised. For example: shall the general public be informed, or physical processes explained?

‘Climate’ is the synthesis of weather over a period long enough to establish its statistical properties (mean values, variances, probabilities of extreme events etc.) and is largely independent of any instantaneous (weather) state.

WIC assumes it confusing to regard any synthesis of weather as largely independent of “the weather”, as any synthesis is a very subjective matter, e.g. what data over which time period have been used and remain statistics. But speaking of weather statistics it would be usually inevitable to identify the data used clearly.

Rapid atmospheric fluctuations with periods of up to a few days, originating largely within the atmosphere itself, are naturally ascribed to weather

WIC suggest to make a test and try to use such explanation and basis to define climate.

the statistical description of a particular January may be described in terms of its departure from the 'average' or 'climatological’ January or the January climate.

Mason’s explanation shows the use of the words ‘climatological’ or ‘climate’ is a useless exercise and grossly superficial. If speaking of ‘average January’, every one would ask: average? What average? Temperatures? Rainfall? Humidity? Wind speed? Wind direction? Just to name only the few of a long list of weather making and describing atmospheric ‘conditions’.

In general, however, we are not so much concerned with the definition of climate per se as with ‘climatic variability and climatic change’. (cont. next box)

But Mason would certainly have agreed that it makes no sense and is extremely confusing to define ‘climatic variability and climatic change’ if climate is not defined, as demonstrated in the UN Framework Convention on Climate Change.

These terms imply departures from a normal regime, the definition of which must be to some extent arbitrary and based on the statistics of a limited past record. We could, for example, specify limits within which mean values, variances or the frequency of values within stated ranges may be regarded as 'normal'.

Mason’s explanation is a convincing demonstration that establishing any ‘departure from normal’ is an arbitrary process, and depends on few or many statistical data and time periods.

Weather is concerned with the evolution of a succession of atmospheric states or individual disturbances; climate with the long-term average behaviour of the atmosphere expressed in statistical terms.

Mason’s explanation makes absolute clear that climate does not exist, but is –on an arbitrary basis- the explanation of average behaviour of the atmosphere based on selective statistical data.

In an operational context, weather is largely of tactical significance whereas climate is a strategic concept of value in forward planning, risk-assessment and decision-making.

Regarding the term ‘climate’ as strategic concept is what makes the climate debate so confusing. If atmospheric conditions can not be explained by physical processes and weather data (short term or long term), with ‘climate’ nothing can be explained any better.