Wednesday, December 09, 2009

Urban heat island effect

In its enthusiasm to convince us of the rectitude of the climate science trade, the Met Office has released data "from 1300 weather stations around the world which show that the globe is getting warmer." The Guardian, very helpfully, has extracted all the UK and US temperature change data and posted links on its site.

What is not said is whether these data are adjusted or not, but we've had a look at the British Isles (not the UK). What is immediately apparent from the 48 stations listed is the large number of airfield sites – at least 15.

Finding the exact location of the Stevenson screens is not easy, but we managed to locate the one at Bournemouth Hurn Airport, pictured above (click the pic to enlarge – centre of red rectangle). This is not my expert field, but doubtless the likes of Anthony Watts might readily assert that this particular station is somewhat prone to what is known as urban heat island effect.

Interestingly, the Met Office is claiming a continuous temperature record right back to 1850, but by no means all of the stations were in place then. Records for Hurn, for instance, are only shown from 1961, in common with London Gatwick Airport.

Aberdeen/Dyce is another of the weather stations, for which records are listed from 1871 – although the site only became an airfield in 1934. It is now the world's busiest commercial heliport. Discerning readers might be able to detect a slight difference between the conditions pre-war and currently (pic above right and below left).

By contrast, the Met Office list includes such sites as Plymouth/Mount Batte, for which records are listed from 1865, Ross-on-Wye, where records start in 1877 and Fort William which has listings from 1884.

Most of these sites were and are still in undeveloped rural areas, when there were very few recording stations in use. But most of the more modern sites, which came into use very much later, are in highly developed sites – and some (as with Aberdeen - weather station shown below) were intensively developed through their history.

What effect that might have had on the temperature record for the British Isles is impossible for us to say – and we have no information as to what adjustments the Met Office have made, if any, to regularise the record and eliminate what at first sight could be a very significant warming bias.

From what we know, however, and what is evident, it would be unwise to accept the record as is, unless and until the Met Office can supply satisfactory information on how the very real possibility of urban heat island effect has been eliminated.