This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
Sorry about that. It is the usual deviation from the average during a certain previous period, the exact years of which escape me for the moment, but no doubt I will be rapidly informed, in degrees Celcius. Daft, but much beloved by warmers.
My understanding of the temperature reference level definition for the major average global temperature datasets that temperature differences (or 'anomalies') are given with respect to is:
Satellite temperature measurements:
Mean temperature from 1979 to present day (1979 is when satellite temperature records started)
Surface temperature measurements:
Hadley CRU (Climate Research Unit):
Mean temperature from 1961 to 1990 (possible significance of 1990 is that it was when Hadley Research Centre was opened)
GISS (Goddard Institute for Space Studies, NASA):
Mean temperature from 1951 to 1980
NCDC (National Climatic Data Center of U.S. Department of Commerce):
Mean temperature from 1880 to present day (1880 is the first year of the dataset)
Of the surface temperature datasets, Hadley CRU has the highest 'status' and is most often used by the IPCC. People promoting AGW have an increasing tendency to favour the GISS dataset because it gives 2005 as the hottest year so far whereas the other datasets give 1998 as the hottest year.
thanks for replies, i emailed theClimatic Research Unit.
and was directed to these links which explains it all in gorey detail (mainly the faq)
so, they've created their very own temp scale with the a fundamental interval of 1K but a different zero; strange! why isnt there a name for it?
It does have a name. It's sometimes called the "Global Temperature Anomaly".
And the name itself tries to influence the listener, as if any departure from some arbitrary temperature represents an anomaly and is therefore bad. The alarmists have some idea of a right temperature for the Earth, and express it as some sort of global average. The whole idea is ridiculous. BUT, odds are if you plot that temperature (well, it's not a temperature at all, it's a concept measured in temp units) over 100 years, one end of the line will be higher than the other, so you can have an alarm over cooling or warming. The chances of the global average temp being identical between two times 100 years apart are minimal. Even if the average were identical, would that mean the climate conditions were the same? Well, no, it could be 15C all the time, or -273/+303 every day.