HADCRUT5 – Changing Variability Over Time

The Annual Standard Deviation of HADCRUT5 data shows a marked, and Significant (1%), decline over the modelled Mean Global Temperature Data Set.

A key contributor to this reduction in variability would seem to be the availability of weather data, determined by the number of GHCN Stations available over time and the area of the Earth for which data can be regarded as available.

The number of stations has generally increased:

as has the number of model elements containing actual data:

and hence the area of the Earth with weather data;

There is a Significant (1%) Negative Correlation with these changes:

showing that the reduction of variability is significantly influenced by the available data, with recent years showing more consistency in variability within the year. There are clearly 2 periods of effect:

with rapid (Significant (1%)) decrease from 1850 to 1940 and no discernible trend since.