http://www.cei.org/gencon/019,04553.cfm
"...
First, global temperature is a contrived concept. There is no magical point in the Earth’s atmosphere to place a thermometer and take the planet’s temperature. Moreover, if you live in a polar or tropical region (or almost anywhere for that matter), a GMT of 62 degrees F is patently meaningless—what matters is what’s going on outside where you are.
Our GMT is based on surface records. But if you look at a map of weather stations around the globe, you’ll readily see the built-in bias of temperature readings from surface-based weather stations.
The overwhelming majority of surface-based weather stations are land-based — relatively few temperature readings come from ocean-based facilities, resulting in a major upward bias in available temperature data since about 75 percent of the Earth’s surface is water.
An additional bias arises from the fact that there is more land mass and, therefore, more surface temperature stations in the Northern Hemisphere than in the Southern Hemisphere.
There’s an even further bias introduced by the tendency of land-based weather stations to be located in more heavily populated areas, which are subject to the urban heat island effect. Relatively speaking, not many temperature readings come from the wilds of northern and central Asia or eastern Africa, for example.
There are alternatives to the JunkScience.com-calculated GMT—none, however, are available in real-time.
The National Climactic Data Center collects temperature data from about 3,000 surface-based weather stations. But researchers often try to statistically adjust these data to account for the urban heat island effect, which produces results that are more statistical mysteries than true averages of global surface temperature readings.
Other researchers calculate GMTs from data collected by satellites and weather balloons. These data measure atmospheric temperatures from all around the Earth and don’t suffer from the same biases as the surface temperature data. It’s important to note that without the upward bias inherent to the surface temperature data, the satellite/balloon temperature measurements show no significant increase since data collection began 30 years ago.
Global warming alarmism is largely based on the notion that global temperatures have increased since the 19th century industrial revolution due to manmade emissions of greenhouse gases, primarily carbon dioxide. The infamous hockey stick graph tries to dramatize the alleged increase in temperature by going back 1,000 years.
But the pre-20th century GMTs in the hockey stick graph for the most part don’t come from thermometer readings. Instead they are guesstimates of GMTS based on geographically and temporally scattered data scavenged from tree rings, ice cores and other dubious proxies for thermometers.
Whether calculated in real-time or two months after-the-fact, surface-based calculations of GMT are inherently and impossibly biased. In this light, the hockey stick’s GMTs over the last 1,000 years are near worthless—yet it is this very data that are being used to drive global warming hysteria.
..."
Look, I agree with you. I've been arguing this corner for years. What riled me about your post is that I come to FR because there is simply no equivalent UK forum, and I've got to know some great, like-minded people here. But tonight I logged in, saw I had a new message from a name I didn't recognise, and in all innocence I clicked on it. Straight off it was brainwashed stubborn greenfreak socialist Poms on the verge of becoming Nazis. The same old tired old lines (apart from the "Poms" bit of course) trotted out ad nauseum by a small but persistent and vociferous number of posters here on FR. Did you reply to me simply to insult and patronise me? If so, knock yourself out, I'll just file you under "Frenchmen and Other Anglophobes" and leave it at that. But I'd prefer it if we could be civil. Just don't try and convert me to Crowded House.