From an article in the Sunday London Times about the northern hemisphere’s cold winter:
A period of humility and even silence would be particularly welcome from the Met Office, our leading institutional advocate of the perils of man-made global warming, which had promised a “barbecue summer” in 2009 and one of the “warmest winters on record”. In fact, the Met still asserts we are in the midst of an unusually warm winter — as one of its staffers sniffily protested in an internet posting to a newspaper last week: “This will be the warmest winter in living memory, the data has [sic] already been recorded. For your information, we take the highest 15 readings between November and March and then produce an average. As November was a very seasonally warm month, then all the data will come from those readings.”
So to prove that this is “an unusually warm winter” the British Meteorological Office will take the 15 warmest days from November through April and average those figures to prove the “warmest winter in living memory”.
That doesn’t even give you an average high temperature for the period. You would get that with taking every day’s high temperature and averaging those data. You could do the same to get the average low for the period – take the low temperature for each day and average those data. Your average temperature for the period would be to take the average temperature per day and average those data.
Remember the sentence from the above quote:
This will be the warmest winter in living memory, the data has [sic] already been recorded.
I have put a [sic] after “has” in the above sentence because the word data is plural. The singular form is datum. Data are; data have. Datum is; datum has…