How not to measure warming February 4, 2010Posted by BlueGreen in Deception, Doesnt Understand, Misrepresentation.
The Urban Heat Island post series via Anthony Watts:
Meteorologist Anthony Watts and his volunteers meticulously checked the siting of most of the 1221 US weather stations that had allegedly recorded a rise in temperatures over the past century. What they found was that a great many temperature gauges (nine out of 10) were in fact in areas increasingly surrounded by heat-trapping concrete and asphalt, or even machinery, which would exaggerate temperature readings over time. (See the MMTS above.)
Do sites subject to the UHI effect generally get used in the compilation of GW statistics or are they not adjusted to take account of the effect? No:
When compiling temperature records, NASA GISS go to great pains to remove any possible influence from Urban Heat Island Effect. They compare urban long term trends to nearby rural trends. They then adjust the urban trend so it matches the rural trend. The process is described in detail on the NASA website (Hansen 2001).
Does the UHI contribute a false warming signal? No:
They found in most cases, urban warming was small and fell within uncertainty ranges. Surprisingly, 42% of city trends are cooler relative to their country surroundings as weather stations are often sited in cool islands (eg – a park within the city). The point is they’re aware of UHI and rigorously adjust for it when analysing temperature records.
Moral: If the US data on warming is so dodgy, how much can we rely on weather stations in vast countries such as China, Russia, Brazil and India? Or even in Italy (above)?
By choosing only high quality sites, that’s how.
And in fact, in recent times in follow up to the issue:
Poor sites show a cooler maximum temperature compared to good sites. For minimum temperature, the poor sites are slightly warmer. The net effect is a cool bias in poorly sited stations. Considering all the air-conditioners, BBQs, car parks and tarmacs, this result is somewhat a surprise. Why are poor sites showing a cooler trend than good sites?