"Roger Coppock" wrote in message
oups.com...
These globally averaged temperature data come from NASA:
http://www.giss.nasa.gov/data/update/gistemp/GLB.Ts.txt
They represent the results of tens of millions of readings
taken at thousands of stations covering all the lands of the
Earth over the last 125 years. Yes, the data are corrected
for the urban heat island effect. Unlike other weather and
climate data currently coming from the United States, no
government censors added 'spin' to this report.


Satellites to measure temperature evenly across the Earth's surface have
been operational since 1979. Data prior to 1979 relies on surface weather
stations and weather balloons, which are not evenly spread around the world.
Good records exist for North America and Europe over a period of about 100
years, but there have never been many stations for the 70 per cent of the
Earth covered by water, or the 38 per cent of the rest that is desert or
mountains.

This means that scientists cannot say for sure what the average temperature
of the Earth was in 1900 - and the problem gets worse the further back we
go. If the starting point data for a model is wrong, even slightly wrong, it
could have a major impact on the outcome. Worse, it is impossible to test
the model. If you want to see how good a model is, perhaps the best way to
test it is to start it from as long ago as possible, and see if the results
match what really happened. This doesn't work if we don't know what really
happened more than two or three decades back.

As Tim Ball, Kenneth Green and Steven Scroeder, three North American climate
researchers, note: 'Surface temperature records for the world are inadequate
to determine the average annual temperature of the earth. The uncertainty in
the global "normal" surface temperature - estimated to be 13.9 degrees
Celsius...a decrease from an earlier estimate of 15 degrees Celsius... is
almost twice as large as the estimated global warming in the last 100
years.' (3)

Perhaps these models provide us with insights into what we don't know, but
they can't predict the future of our climate - at least, not yet. When we
have more powerful computers, greater understanding of the physical
processes involved and a longer history of good data, it's likely that
models will provide better predictions.

http://www.spiked-online.com/Printable/0000000CA8CF.htm

The UHI effect is cobbled together with a half assed formula based on
population. Not an accurate picture.