I find the whole business of how these temperature measurements are made and recorded quite interesting. One of the UK weather presenters was talking about it on the radio yesterday and saying that while the temperatures in cities are clearly higher than those in rural areas (because of black tarmac roads, buildings with air conditioning, traffic etc) city locations are always discounted when it comes to weather records because no two city sites are the same.
To get in the record books the measurement has to be taken in a very uniform way – using one of those white louvered boxes on legs (we had one at my school), which must be located away from buildings and trees and sources of heat. I remember a couple of years ago a record temperature in Scotland was disqualified when it turned out that the guy taking the reading had parked his vehicle too close to the weather station, so great care must be taken for the reading to be valid.
It seems to me that the weather stations in this country are often located at airfields and airports, for practical and historic reasons, but wouldn't their special circumstances skew the readings too? For example, the air around Heathrow must surely be warmed by all the acreage of asphalt at the airport and the surrounding traffic and industry, not to mention what comes out the back of all the aircraft. Our nearest weather station is at RAF Benson, which seems to have its own (cold) microclimate out there on the Aylesbury Plain – it never gets as cold here in the winter as it does at RAF Benson. So I'm not convinced that airports and airfields are representative of the surrounding area either.
Just seen the news about the record temperature of 40.2C at Heathrow. Now there’s a surprise.
-R