Heathrow Airport WMO 03772 – The common knowledge that the Met Office doesn’t want you to know – and why this site is complete junk.

51.47918 -0.45054 Met Office CIMO Assessed Class 3 Installed 1/1/1947

For the Met Office to claim this site meets any form of acceptable regulations for providing data sufficiently accurate for inclusion into the national historic temperature record is a clear indication of how far they are prepared to go to produce totally unacceptable readings. This site is completely unsatisfactory even for the production of data for the immediate aviation use of the airport (which incidentally it does not, the Airport uses its own instruments) – it is simply meteorological junk. And the Met Office knows that!

Before examining the site in detail, a bit of history. Meteorological temperature observations are taken by thermometers housed in devices known as Stevenson Screens. Scottish civil engineer Thomas Stevenson (father of Robert Louis Stevenson) designed his screen in 1864. By 1884 modifications to the design enabled it to become the adopted design of all UK Met office sites and thence ultimately almost worldwide. 1884 was also the year that a significant flaw in the design was uncovered by someone more qualified in the subject, Scottish meteorologist John Aitken. Under certain weather conditions Aitken proved the screen was found to over-record temperatures often by 1°C and in particular extremes as much as 2°C. This problem was accepted and became known as the Aitken Effect but somewhat surprisingly was completely ignored.

So what is the Aitken effect? The flaw Aitken discovered was that in calmer conditions with wind speeds below 1 metre per second (2.23 miles per hour – Beaufort Scale 1) there was insufficient air flow within the screen. Particularly on sunny days, this static air could warm up above the surrounding ambient air temperature and thus over record. The point was proven, all meteorologists understood it and indeed are still taught about it on university courses. However, it very conveniently was metaphorically swept under the carpet presumably on the basis that such conditions were “rare” events.

The AGW climate promoting website the Conversation even recently highlighted this issue with modern research but preferred to spin the discussion around to the virtues of Victorians rather than emphasising the shortcomings of Stevenson screens. They also opted to promote the solution to this issue referring to “aspirated” instrumentation that uses a small fan to ensure air movement around the screen’s instruments and thus ensures more accurate readings. So far the Met Office has not got this memo and do not use aspirated screens in any of their stations, but other private sites often do – notably at Heathrow Airport.

The main takeaway from the above, however, is this exercise in hand waving stated in the above article.

The only thing more staggering about the level of proven inaccuracy is the casual way it is passed off as “relatively minor”…….says who? Only 1% (i.e a surprisingly large amount) will be MORE than 1°C – So what percentage are, say, between 0.1°C and 1°C? “12% of recorded minimum temperatures” is almost one in eight of every reading. The line “This is relatively minor, and will not affect the important conclusion that globally, air temperatures are increasing.” is a full on bare faced lie. Such levels of inaccuracy (however played down and mis-described) can only ever have a distorting effect. This is allegedly considered a “science” that accepts such levels of inaccuracy and then quotes readings to the tenth of a degree and averages to the hundredth of a degree. Clearly “researchers” at Reading University missed the memo “ every fraction of a degree temperature increase has a real impact on our lives and our planet. Prof. Celeste Saulo, WMO Secretary-General”

So why is this first issue so relevant to Heathrow? A close up image of the station is very revealing.

This photograph is taken from the south looking north to the enclosure and screen. The profiled metal cladding obscures the screen from the road and is in effect a south facing wall in front of the screen. All the extensive wire fencing and heat reflecting cladding is effectively acting as an almost complete wind break and walled garden. To get a degree of scale, the screen is set at 1.5 metres to the base, the cladding is likely 1 metre height in addition. Seen from the Northern Perimeter Road side it looks like this.

There is a solid barrier to wind penetration from the roadside. In any low wind speed events, day or night, the incidence of still air building up inside the screen is hugely increased over natural surroundings. Whilst such Aitken effect events may be rare in natural surroundings, in this enclosed compound they will be much more frequent, furthermore on hot sunny days the effect can readily build to the more extreme effect of 2°C.

So what of my claim the Met Office already knows this? Well as mentioned earlier modern large airports require much more extensive weather instrumentation than the modern day Met Office supplies. The aviation requirements run to this 37 page document https://imdpune.gov.in/training/surface/installationofami.pdf

As the document points out the impacts of small changes in parameters can have high impacts. A misread of a climate reporting station is likely harmless, an aviation runway misread can prove disastrous.

This is the detail on Heathrow’s own site “Heathrow Airport’s own weather station is not a single fixed point like the Met Office’s but consists of multiple sensors and instruments strategically placed across the airfield. The primary operational weather monitoring is centered around the air traffic control tower, located near the heart of the airport between the two runways, roughly at 51.477° N, -0.461° W. This central location allows it to collect data directly from the runway environment, including wind speed, direction, temperature, and visibility, which are critical for aircraft operations. Additional sensors are also positioned along the runways—specifically near the thresholds of Runway 09L/27R and Runway 09R/27L—to provide localized data for each runway’s conditions.

This setup ensures the airport has precise, immediate weather information beyond what the Met Office station alone can offer, meeting the stringent demands of aviation safety and efficiency.”

In close up the airport main temperature sensors are as below.

The proximity to the runways would be expected to cause higher readings but the sensors are artificially aspirated to avoid stagnation and over reading……..and they typically read LOWER than the official Met Office screen in calm weather conditions.

The Met Office have tacitly acknowledged this Aitken effect problem several times despite trying not to. When Paul Homewood host of Not a Lot of People Know That and Clive Best raised issues regarding the potential of aircraft take offs/landings affecting the official climate screen’s readings, the Met Office press officer, Nicola Maxey, countered the suggestion as follows

“In addition the turbulence generated by passing aircraft would help mix the air close to the ground and so, is more likely to lower the air temperature rather than raise it.”

What Nicola Maxey did not want to admit was that in the calm weather stagnant air in the screen was warming and over recording – the breeze (distant jet blast) from aircraft might possibly dissipate the effect. The point was not lost on Clive Best who retorted  “If they just want mixing – then instal a fan !” which is exactly what the Heathrow private sensors had already done to ensure accuracy.

I have so far been unable to conclusively prove this point but a large body of evidence is forming that on the 19th July 2022 when the Met Office proclaimed 40.2°C at their site, the airport unit only recorded 39°C – a likely Aitken effect discrepancy given the flat calm and intense sun at the time. I will notify if/when I can get final confirmation of this.

However, the overall Heathrow situation is much worse than just atrocious siting and known screen over recording errors. https://www.bbc.co.uk/news/uk-44980493

Firstly “Paul Williams, Professor of Atmospheric Science at the University of Reading” {the organisation that tested aspirated instruments above} applies more hand-waving techniques to the suggestion that aircraft engines could have any notable effect.

“Planes make a negligible difference,” says Professor Williams. “Every time you use energy – whether it’s from a plane’s engine, or even just switching on a light bulb or taking a shower – it’s eventually turned into heat. “But all of that is a minor influence compared to the effect of the urban heat island.”

I am confident that a more measured reply would have been in order from a reputable professor. After all a single Boeing 747-8 can hold over 238,000 litres of fuel and consume up to 10% on a fully laden take off up to cruising height. Heathrow typically handles 1,300 take offs/ landing over an 18 hour operating day of mostly larger aircraft. This amounts to an exceptionally large amount of fuel being combusted and turned into high temperature waste heat. That heat has to go somewhere. The suggestion that planes make a negligible difference is akin to other above Reading University researchers claiming 12% of minimum readings being over recorded due to Aitken effect has no effect – unquestionable nonsense. {If anyone feels they can run a good calculation on the waste heat produced I would be very interested in it}

Our professor (unwittingly it would seem) continues to point out that the whole Heathrow reading is inaccurate for the wider area representation due to the obvious Urban Heat Island Effect. What he actually states in his “defence” of Heathrow is that it only records the massive distortion effect of the London area. This is clearly a man-made effect but nothing even remotely associated with the national “Climate” nor any perceived changes over time. Prior to the airport construction in the 1940s the area was green fields with a “Row” of small houses on the Heath – the area would not have been recording anything like current temperatures in the absence of the airport and London urban area expansion.

Having admitted that the elevated temperatures are an unnatural London effect and completely dismissed a major heat source from the jet blast, comes the absurdly arrogant claim:

” The Met Office told the BBC that its weather stations are built to very specific standards and any biases that could affect temperature records are taken into account when analysing readings.”

More complete nonsense, the Met Office simply delivers the highest possible recorded number in full knowledge it is corrupted by flawed screen design, from a corrupted site in a massive UHI and makes no assessment or adjustments whatsoever. They are “excellent” simply by their own claim – all evidence clearly shows this is not the case and independent review is not allowed.

Having already compared Heathrow to another wholly unnatural site in the London UHI (Kew) the article further goes on to compare soil structure (Heathland) with yet another wholly unnatural environment of the Royal Horticultural Society Gardens at Wisley.

“Even the soil can be a factor, according to Gareth Harvey from the BBC Weather Centre.”Take another very warm spot, like Wisley – located in the Surrey heathland and typified by sandy soils,” he says.”Sand is a natural insulator and so the heating effect of sunshine is stored in the top layer only, which gets very hot and then warms the air.”

One wonders if Gareth Harvey has ever actually ever been to Heathrow Airport – are we expected to take a BBC Weather Centre spokesman seriously when he comments on the “sandy soils”? Oddly enough there really is not a great deal of exposed soil in the 12.3 square kilometres of surface area that makes up Heathrow Airport……it is almost entirely tarmac, concrete, buildings and jet engined aircraft.

The BBC/Met Office axis sums up the Heathrow weather station with the lines

” In summary, the overall temperature of any particular weather station is likely to be affected by several factors – including: the amount of tarmac, the number of buildings, distance from the sea and even the type of soil.

So, there’s more to Heathrow’s hot spot than its proximity to roaring jet engines.”

Translating the above I arrive at the conclusion that a “Strawman” has been falsely set up, i.e. jet engines distorting temperature, to refute this spurious argument and thereby waive away the obvious point that the Heathrow weather station is totally unacceptable for any meteorological purposes whatsoever.

My summary relates to the real world facts.

1. The Heathrow screen is in an appallingly bad immediate location – it is not Class 3 by any rational measure. It is not suitable for readings to be added to the national historic temperature record. It is also not suitable for aviation purposes.

2. This poor location regularly leads to enhanced Aitken effect and over readings of both minimum and maximum temperatures thus supplying false readings and distorted daily averages in an ever upwards direction over time as the site has been developed.

3. Both London in general and Heathrow in particular display a very large and accepted Urban Heat Island effect also artificially raising both maximum and minimum temperatures. No adjustments nor allowances are made for this in reporting readings.

4. The Met Office do NOT apply rigorous standards nor make any adjustments whatsoever to absolute readings and knowingly produce inaccurate readings. The vast majority of weather station sites are actually classed (by the Met Office themselves) at Classes 4 and 5 thus being inferior to Heathrow.

6. The nearest Class 1 station to Heathrow (at Rothamsted Research) registered over 2 degrees cooler despite being much nearer to the centre of the hot weather event area in 2022.

7. This site should either be removed or ignored as it serves no accurate meteorological function.

I feel this review should be an ongoing discussion document and I would very much welcome views, opinions and further information from readers. I am more than happy to be proved wrong if I am so please feel free to criticise (politely) if warranted. Having previously compared Heathrow with Leuchars I will shortly be reviewing Heathrow’s near neighbour and equally bizarre site at RAF Northholt so there are plenty of options to open up the discussion.

Source: https://tallbloke.wordpress.com/2025/04/04/heathrow-airport-wmo-03772-the-common-knowledge-that-the-met-office-doesnt-want-you-to-know-and-why-this-site-is-complete-junk/