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New Record Temperature–But How Much Of It Is Due To UHI?

July 30, 2019

By Paul Homewood


h/t Joe Public




Cambridge University Botanic Garden measured 38.7C (101.7F) on Thursday beating the previous UK record of 38.5C (101.3F), set in Kent in 2003.

A Met Office official was sent to check the equipment before verifying the new record on Monday.

Staff working at the garden on Thursday tweeted: "No wonder we all felt as if we’d melted."

Daily temperatures have been measured by the weather station at the site in the south of the city since 1904.

Cambridge University Botanic Garden director, Beverley Glover, said: "We are really pleased that our careful recording of the weather, something that we’ve been doing every day for over 100 years at the Botanic Garden, has been useful to the Met Office in defining the scale of this latest heatwave.

"Our long history of weather recording is very important to researchers analysing climate change.

"However, we can’t help but feel dismay at the high temperature recorded and the implication that our local climate is getting hotter, with inevitable consequences for the plants and animals around us."


In fact, Cambridge’s new record tells us very little about “climate change”, but an awful lot about the Urban Heat Island Effect, or UHI.

Just to recap, the Botanical Gardens are situated in the middle of the city of Cambridge, which at the last count had a population of 123,000. Furthermore, the winds on the day in question were from the south east, meaning that the air reaching the Gardens had blown right across  a heavily built up area.


The claimed new record is only 0.2C higher than the previous one for Faversham, yet the latter is little more than a village. The difference in UHI between the two is certainly likely to be much more than 0.2C.

We might also consider that there is a second official Met Office site in Cambridge, at the National Institute of Agricultural Botany (NIAB). This, as can be seen below, is away from the city, although gradually being encroached upon by developments.


Cambridge NIAB


The NIAB site only registered 38.1C. Given that there is no other significant differences in siting between the two, it can only be the effect of UHI which explains why the Botanical Gardens were so much hotter last week.


To cap it all, there are two large buildings close to the weather station, the Sainsbury Laboratory to the NW, and the Plant Growth Facility to the north. They were built in 2011 and 2004 respectively, and clearly could be influencing the local micro climate.

The Sainsbury lab, for instance, houses 120 staff, so the heat footprint must be significant.





The late Tim Channon took the screenprint below of the Botanical Gardens site back in 2008, for a Tallbloke story. As you can see, the Lab is still under construction.

But note the radius scale which Tim added, set to 100m. Clearly both buildings are well within 100m, probably around 30m.




The World Meteorological Association has strict guidelines for siting classifications of weather stations. They have five classes for thermometers, and Class 1 is reserved for the most reliable sites. These are the criteria:




Both buildings are well within 100m, and certainly occupy much more than 10% of the area.


So we know that the Botanical Gardens site is at best Class 2. Very few sites are perfect, but surely only high quality, Class 1 sites should be used for climatological purposes, particularly of this sort?


Weather station



The BBC have this photo of the Botanical Gardens site, which thee BBC published yesterday.

Note that the Stevenson Screen is on the edge of a wide expanse of bare earth. This is a strict no-no, as the regulations clearly state:

“Ground covered with natural and low vegetation”.

According to the WMO classifications, this would relegate the site to Class 4, which is said to have an uncertainty estimate of 1C. In other words, worthless for climatological purposes.

  1. July 30, 2019 2:46 pm

    Reblogged this on Climate- Science.

  2. Peter Yarnall permalink
    July 30, 2019 3:05 pm

    It would appear that the idea now is to try to achieve a record temperature rather than record a realistic one. To that end, last Thursday I placed my weather station outside on my window sill in my west facing garden in full sunlight. The result; 40.7C (over 105F) in Milnrow, Lancs.
    Does that mean I win???

  3. Jackington permalink
    July 30, 2019 3:20 pm

    It is very irritating to have the “record” temperature at Cambridge last Thursday as the headline on every weather forecast on BBC TV and radio since then. – just in case we forget the Climate Emergency is still with us.

    • July 30, 2019 4:43 pm

      Exactly. Quote from The Economist for the week July 27 – Aug 2:

      “The goal today is to offer a verdict on the influence of climate change on particular meteorological events more or less as they are happening. Here, the Met Office has been leading the way…”

  4. john cooknell permalink
    July 30, 2019 3:39 pm

    Adjacent Polytunnels

    • July 30, 2019 4:38 pm

      Also, the vegetation in the general area appears to be well over the 10cm height as needed for point (b).

      • July 31, 2019 3:16 pm

        Streetview suggests an a range of crops (including maize) being grown around the station at times.

  5. Broadlands permalink
    July 30, 2019 3:58 pm

    A 0.2°C record! Is that record designed to tell all those living close to one another to move? Or to stop building things humans need…using asphalt and cement? As was pointed out, record high temperatures in the past have taken place where no UHI effects were to blame, nor could record high CO2 be the cause.

    • It doesn't add up... permalink
      July 30, 2019 6:17 pm

      They have to be careful. Exaggerate too much band more people question the record. Also it means a long wait for the next one. Better to inch the record up slowly, and try to repeat more frequently to maximise scare publicity.

  6. July 30, 2019 4:33 pm

    I guess that the Met Office only check that the measurements are plausible for the station in question, with any UHI that it has. But, to do that they must have looked at data from nearby stations, such as Cambridge Marshall Airport, and must have a pretty good feel for the size of UHI at the record station.

    Is it too much to ask that they give a corrected temperature, what would have been measured if the city of Cambridge was not there? It is well known that Oxford Radcliffe has UHI (a book with a way too long google books URL says 0.7C for Tmax in summer), and it gets corrected.

    • July 30, 2019 8:43 pm

      Evidence that Cambridge Botanical Gardens has significant UHI from the horse’s mouth: it was dropped by the Met Office from CET DAILY after 1931:

      ” While retaining three stations, we replaced the Cambridge (Botanical Gardens) station with Rothamsted Observatory in 1931 because of evidence of urban warming at the former by that time” … Page 321 of:

      Click to access Parker_etalIJOC1992_dailyCET.pdf

      • July 31, 2019 7:35 am

        Whoops, looks like standards are slipping. The site was inspected by a Met Office employee, who gave it the all clear, but presumably was not aware that it had been dropped long before it was anything like as bad as it is now.

  7. July 30, 2019 4:33 pm

    It would be nice to see what the temperature reached at Monks Wood (nr Huntingdon, not far from Cambridge – a very rural site). Unfortunately the available data I can find (weathercast) does not begin until 3 a.m. on the Friday after the record (26th July).

  8. July 30, 2019 4:51 pm

    we can’t help but feel dismay at the high temperature recorded and the implication that our local climate is getting hotter

    Another view: either the MetO is using unfit quality control criteria, or it isn’t applying its fit QC criteria properly [see ‘World Meteorological Association has strict guidelines’ – in the blog post].

    In any case, one day doesn’t make anyone’s climate hotter.

  9. MrGrimNasty permalink
    July 30, 2019 5:08 pm

    The problem isn’t the recording of a record temperature – that’s just curiosity value. I think you have to accept UK records from all sites, warts and all – it would be too complicated to compensate for local issues.

    The scandal is holding it up as proof of/insinuating climate change caused it without explaining the shortcomings of the site. The accuracy of the thermometer in question is not the reason the reading is worthless in that respect.

    The BBC has gone full on climate mental. Weather forecasts are now climate change bulletins. Arctic Fires are yesterday. Extraordinary Greenland heat today, which somehow was linked to a suggestion of lowest ever Arctic Ice extent, with the news anchor saying to the weatherman ‘and we all know why’. Greenland is the only significant heatwave in the world at the moment – it wasn’t there ‘yesterday’ and it will soon be gone. It’s ridiculous, they just look around the world for a heatwave (i.e. weather) and imply it’s global when the current global anomaly is +0.1C (1979-200 base).

  10. Joe Public permalink
    July 30, 2019 5:16 pm

    “But note the radius scale which Tim added, set to 100m. Clearly both buildings are well within 100m, probably around 30m.”

    Google Earth Pro (it’s free BTW) indicates those two buildings may be just under 50m away.

    It seems there are however, a number of tall trees within a 30m radius.

  11. mwhite permalink
    July 30, 2019 5:21 pm

    These are electronic thermometers, they take an unknown(by me) number of temperature readings every hour and then send that data back to the met office.(Sky news reported this from Kew gardens).

    I’ve seen a couple of blog posts claiming that electronic thermometers being several degrees warmer than the mercury max-min thermometers they were replacing.

    • July 31, 2019 2:29 pm

      The Meteorological Office dis run a comparisons between electric and Liquid in Glass thermometers (between July 1996 and June 1998) and concluded electric thermometers were reading slightly lower than LIG (despite some apparent significantly higher readings)..However they had rejected nearly 6% of the comparisons where the difference was >1 oC. I would have thought that these were worthy of study given the Transient Response Bias of the electric thermometers.

      Extracts from the two papers are below.

      OPR Climate Studies
      Memorandum No 10
      Comparison of Conventional and Electronic
      Air Temperature Thermometry
      (Version: 23rd April 1999)
      Tim Allott
      Observation, Plans and Requirement Branch

      3.2 Rejected measurements
      Table 3 shows the number of (SAMOS-LIG) differences of maximum and minimum
      temperature that were rejected for each station and expresses them as a percentage
      of the total for that station. Differences were rejected if they exceeded 1.0 deg C; an
      arbitrary level set to eliminate spurious measurements (as discussed in Section 4.1
      of the stage 1 report). Shading shows stations where more than 5% and 10% were
      rejected: 17 of the 49 stations had at least 5% of their (SAMOS-LIG) differences
      rejected; 7 stations had in excess of 10%. Large daily differences could be due to a
      faulty instrument or a mistake made when taking or entering the LIG reading. The
      mean rejection percentage was 5.8%.

      4.1 Frequency distributions
      The histograms illustrate that the vast majority of pairs of readings (SAMOS and LIG) are within 1.0 degrees Celsius of each other (96.7% for maximum and 97.1% for minimum temperatures). Furthermore most LIG check readings were within 0.1 degrees Celcius of the SAMOS value (71% for maximum temperature, 54% for minimum temperature.

      Differences in excess of 1.0 deg C will be left out of future analysis. This rejects around 3% of the data and helps to ensure that the only values considered in this investigation result from the instruments’ characteristics and not some other malfunction or human error. Large differences also arise if observations are taken when temperatures are changing rapidly and 2 observers are not available to take simultaneous readings.

      A selection of statistics have been calculated for the frequency distributions, after exclusion of absolute differences >1.0 deg C. These are shown in Table 2.

      The means confirm the tendency towards negative differences (SAMOS readings tend to be slightly lower than LIG readings), although only by 1 or 2 hundredths of a degree C on average, which is less than the uncertainty of the LIG check thermometer.

      6 Discussion and Conclusions
      At the majority of sites the observed average (SAMOS-LIG) differences were small (<0.1 deg C). Only four of the 49 stations studied had mean differences for maximum temperature exceeding 0.15 deg C and 12 exceeding 0.10 deg C. The numbers for minimum temperature were 14 and 23 respectively. The largest absolute mean differences were 0.22 deg C for maximum temperature and 0.32 deg C for minimum temperature.

  12. Joe Public permalink
    July 30, 2019 5:32 pm

    “The Sainsbury lab, for instance, houses 120 staff, so the heat footprint must be significant.”

    1. There’s a massive number of (dark) solar panels on that roof. All absorbing a significant amount of solar heat, especially that day.

    2. In the centre of that roof are 3x banks of 12x air conditioning fans dumping what must on that particular day, have been a record amount of heat from inside the building to outside into its little own micro climate.

    There are another 3x banks of 6x air conditioning fans in the enclosure at the NE corner of the Plant Growth Facility doing the same thing.

    3. It appears that the Stevenson Screen has direct line of sight to the SE corner of the Sainsbury lab. That structure would then radiate some of its absorbed heat directly towards the Stevenson Screen. The screen would protect the measuring apparatus from the direct radiant effect, but the dark foliage of the hedges and trees would absorb the heat and dissipate some of that as convected air heat.

    A perfect micro climate to manufacture a temperature record.

    • Jeff Todd permalink
      July 30, 2019 5:51 pm

      Years ago the BBC proved the existence and strength of the UHI, albeit accidentally and before the AGW nonsense took off. The TV program was about Victorian gardens and how the gardeners grew peach trees inside the walled garden. By growing them against one wall, they flourished; 3 thermometers placed in the garden showed that the South-facing wall had a temperature 5 degrees higher than the middle of the garden, which also had a higher temperature than the North-facing wall. A simple experiment anyone can replicate.

      • MrGrimNasty permalink
        July 30, 2019 10:31 pm

        They prove it on most forecasts – London nearly always 3C hotter than anywhere else by day, and the repetitious “minimum 8C or 9C in towns and cities, but you might get a touch of frost in the countryside”.

  13. July 30, 2019 6:24 pm

    6pm local news opens with report from Keadby power station where 4 Reclaim the Power protesters closed construction of the new gas plant for one day.
    They played their short vid taken from the tower crane
    and then interviewed a protester outside
    .. asking her if they were worried they had taken the local police time up

    The protest is rubbish … the plant exists to balance the intermittency of wind farms
    and 6 years ago the corp had built quite a large windfarm in the back garden.
    So holding up construction
    has increased CO2
    and increased particulate pollution
    cos it means one extra day supplied by dirtier gas/biofuel plants than this clean gas plant.

    By coincidence I have been through the same site 18 months ago.

  14. Athelstan. permalink
    July 30, 2019 6:27 pm

    Hmm, “The NIAB site only registered 38.1C.”

    ‘only’ 38.1 at official site, in the interests of balance then, why didn’t the beeb mention this yesterday?

    I can’t think why, can you?

    • ldr permalink
      July 31, 2019 1:36 am

      Or maybe the BBC like any other news reports only what is interesting to the general public. No one cares about who was second or whichever place in the temeperature rankings, of course 1st will take the headlines…

  15. July 30, 2019 7:21 pm

    Reblogged this on WeatherAction News and commented:
    The BBC picture of the bare ground is a doozy, but not that that matters its all about the message and the message is it’s all our fault. We can only hope these records are reevaluate by who value integrity over their quasi religious fervour to stay on message even that means obliterating history.

    Who controls the past controls the future: who controls the present controls the past.”

  16. July 30, 2019 7:24 pm

    The BBC mushed that photo yesterday, but was it taken yesterday?

  17. Pancho Plail permalink
    July 30, 2019 11:28 pm

    For those who are interested, Google Earth Pro (free to download) has a facility to show aerial and satellite photos at various times in the past. The Botanic Garden is particularly well served with a b+w wartime photo taken in 1945 and quite a few colour versions from 1999 to the present day, clearly showing the encroachment of buildings all around, and I believe also showing the Stevenson screen in a different location 20 to 30 yards north of the present location.
    Tip: when you have the locality on screen you will see a date in the bottom left corner of the map showing the date of the earliest photo. Click on this and a time line slider will appear top left.

  18. ldr permalink
    July 31, 2019 1:33 am

    Even if the UHI did have an effect here it doesn’t change that this was an unusual heatwave. Widespread 35.C+ in East Anglia is unusual and even if it is a one-off 35.C days are becoming more and more common in the South East of England in the last two decades. Plus, the majority of us live in cities and so this data is more accurate on describing our day to day experiences with the weather and how climate change will influence this.

    • July 31, 2019 9:47 am

      Undoubtedly, and I am waiting for the Met Office to send me full data for that day, so I can fully analyse, something they themselves have failed to do, preferring to highlight cherry picked records

    • July 31, 2019 10:29 am

      “are becoming more and more common” is unscientific. “Have become more common” is correct, but the ubiquitous, sloppy “are becoming more and more” requires a time machine visit to the future.

      Hopefully it will remain more common than the cold times of the early 20th century.

      • Joe Public permalink
        July 31, 2019 3:21 pm


    • July 31, 2019 2:31 pm

      Increased frequency of warmer days was a characteristic of the early 20th Century warming too..

  19. dearieme permalink
    July 31, 2019 1:49 pm

    “Given that there is no other significant differences in siting between the two”: I think you’re wrong there as I explained on an earlier thread. Howsoever that may be, I recommend you look at changes to the NIAB site over the past few years: could they explain its unaccustomedly high reading?

    Put otherwise: I’m disinclined to take either the NIAB or Botanics reading seriously yet, but do think that Botanics > NIAB is perfectly plausible.

  20. Eric permalink
    July 31, 2019 5:22 pm

    I live in Norfolk less than 30 miles from this place and I kept a digital thermometer in the shade in my back garden throughout the day. The maximum temperature shown was 34.4 degrees C – but then I’m not located in the middle of a city next to 2 large buildings. The BBC is an absolute disgrace.

  21. Bloke down the pub permalink
    July 31, 2019 7:21 pm

    The Sainsbury lab, for instance, houses 120 staff, so the heat footprint must be significant. 120 staff, all turning the AC up to 11 .

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