Jovial Monk wrote on Jul 11
th, 2017 at 8:51pm:
It is generally accepted that weather over 30 years is climate.
That is a WMO definition.
"Climate in a narrow sense is usually defined as the ‘average weather’, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system. (IPCC definition).
Note that this well accepted definition raises many questions. Climate is here viewed as a statistical description, not as a dynamical system (We all know that the climate system is a physical system that varies at all time scales under its own intrinsic dynamics as well as under the influence of external forcing, the sun, volcanoes, anthropogenic influence). Why is it 30 years (and not 300 years) ? Of course, there are practical reasons such as the length of homogenized and good quality climate data sets. But there are also more fundamental reasons that relies on a possible separation between fast and slow variations, the fast variations being usually unpredictable climate variability, and the slow ones being deterministic climate change due for instance to external influence.
Although it is not possible to specify exactly where this potential separation lies, there are suggestions that it is somewhere between 10 and 100 years.
Comment at
https://www.researchgate.net/post/What_is_the_best_period_to_define_a_climateI think 30 years too short.
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