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How Much Is The CET Affected By UHI?

June 11, 2017

By Paul Homewood

Reposted from WUWT, originally published in January.

It’s old, but still relevant:



The answer is blindingly obvious, from above: they are all subject to considerable modern local urbanisation immediately to the North, including heated greenhouses designed to replicate a Mediterranean climate.

The Met Office relies upon just three weather stations to record the Central England Temperature: Stonyhurst (Lancashire), Pershore (Worcestershire) and Rothamsted (Hertfordshire).

The Met Office averages these three temperatures and makes a 0.2 degrees C negative adjustment to compensate for the UHI effect.

The Met Office has made this adjustment since 1974. Bizarrely, they don’t seem to know exactly why 1974 was chosen other than being able to speculate that “It was probably around then that the effects of urbanisation began to be noticed, although this date as chosen may be slightly arbitrary”[1].

But is this 0.2 degrees negative adjustment adequate for the three CET weather stations? I suggest it may not be:

All three weather stations have material modern urbanisation starting within 100 to 200 metres in their Northern quadrant, this development being associated with the rapidly expanding research and educational institutions which control the land on which they are sited. These institutions are often built around old country houses with formal gardens sited to their South in the UK, so their commonality of orientation is unsurprising.

Rothamsted Research (f/k/a Rothamsted Experimental Station) now shelters its weather station from the North winds and warms it up by modern buildings rapidly thrown up to the NNE:


Stoneyhurst College has expanded in the NNW, and now hugely shelters its weather station from the North winds and warms it up with new building and nearby tarmacadam ball sport courts:


Pershore College has gone a step further and covered the land immediately to the NNW with heated greenhouses , car parks and new building, having a similar effect on the Pershore weather station as its two sister sites. Surely a greenhouse designed to enable “plants to flourish in a semi-Mediterranean climate” sited up wind of a weather station may have some effect?


It is not beyond the wit of man to postulate that these localised, specific effects might artificially inflate the recorded temperature. Increasing the data to a temperature not properly compensated for by the small 0.2 degrees C adjustment applied by the Met Office, thereby inflating the CET to a number more amenable to the Met Office and the IPCC.

This would particularly warm data recorded in colder temperatures, where winds are more likely to be from the North.

The Met Office plans to

“overhaul” its CET datasets during mid-2017. Included in this “overhaul” is a review as “to what adjustments have been made (e.g. urbanisation adjustments, and changes to allow for differing climatological characteristics between the different sites used over the years so as to avoid introducing any inhomogeneities)”.[2]

Not before time. The CET problem, from a birds eye view, is staring the Met Office in the face.

  1. June 11, 2017 1:17 pm

    This may be relevant to this discussion

    • Jack Broughton permalink
      June 11, 2017 9:27 pm

      Have started to read the very interesting analysis of the CET trends in the paper. The use of rates of change does help rather than just temperature / time.

      Global warming appears to be as often said somewhere between 0.4 and 0.8 deg K / Century, varying more with months than one might expect. In the conclusions it is said that the temperatures are indicative of AGW, while, if they are linear, are they not just indicative of global warming in recovery from the LIA, rather than AGW?

    • Jack Broughton permalink
      June 11, 2017 9:31 pm

      Fascinating paper using temperature change rates. However, the conclusion that the positive change rate is consistent with AGW is dubious: surely it is consistent with global warming but is not the Anthropogenic part purely a guess at causation?

  2. Broadlands permalink
    June 11, 2017 1:18 pm

    NOAA/NCDC corrects their older US 48 state temperatures (1920s 30s), by lowering all of them, monthly and seasonally. Their mean lowering is about 0.7- 0.8°F. These older adjustments seem contradictory if UHI correction is the goal? These corrections are with respect to the official US Weather Bureau, NOAAs predecessor.

    • richard verney permalink
      June 12, 2017 8:10 am

      I think the argument is that the corrections are mainly made because there is a need to adjust for TOB (time of observation), not the need to adjust for UHI.

      There is conflicting evidence as to whether TOB is a material factor in data trends which trends are based upon min/max figures recorded.

  3. June 11, 2017 6:27 pm

    Would not common sense and common decency suggest that you just move the sites, it would cost far less than most of the Idiocy wasted on trying to to guess how to adjust for location. What is accuracy worth?

    • A C Osborn permalink
      June 12, 2017 11:01 am

      You lose “continuity” when you do that, so historic comparison is difficult.

      • June 14, 2017 4:01 am

        What are you gaining if the existing sites aren’t reliable? How far would the sites have to move to be accurate? I understand not wanting to lose “continuity” but would it be an issue if they were still accurate, sounds as though “continuity” may already be in question if there is a bias in the adjustment. Just curious.

  4. Terbreugghen permalink
    June 11, 2017 7:02 pm

    It would not make sense to “just move the site” as any change would interrupt the validity of the record from old site to new. All manner of explanations for variations in temp. would be offered.

    The better choice would seem to be to find a site that had a continuous record of measurement but was not developed since before 1970. I imagine it is next to impossible to find such a site?

    • Ben Vorlich permalink
      June 12, 2017 9:54 am

      In my experience when you change software/hardware/systems you have a period of parallel running in order to correlate new against old. Any mismatches are investigated until a cause can be identified. Again, from personal experience, the new system would identify problems the old could not detect. If the explanation satisfied a group of experts then there would be no problem.

      This simple method seems unknown to Climate Science.

  5. June 12, 2017 5:10 am

    There are other stations around the UK and Ireland where one would expect minimal UHI effects. I am thinking of Valentia Observatory (in SW Ireland) and the Scottish stations of Tiree, Lerwick and Stornoway. To my surprise all of these four stations show an increase in annual mean temperatures of between +0.7 and +1.0 degC over the period 1975-2005. This is comparable to about +0.9 degC for CET. A difference though is that the four non-CET stations show a cyclical trend with highs around 1930-40 and lows around 1970-80. This cyclic trend does not appear in the CET data. I wonder if there are other stations closer to the CET stations than those on Scottish islands or in Ireland.

  6. June 12, 2017 7:32 am

    What anyway is the basis of the 0.2C adjustment or is it simply a wet finger in the air?

  7. June 12, 2017 8:45 am

    Good to make a comparison between the UK and Africa, one fifth of the worlds land mass-

    The Met Office has a weather station network across the whole UK, with more than 200 automatic stations.


    WMO- “Because the data with respect to in-situ surface air temperature across Africa is sparse, a one year regional assessment for Africa could not be based on any of the three standard global surface air temperature data sets from NOAANCDC, NASA-GISS or HadCRUT4. Instead, the combination of the Global Historical Climatology Network and the Climate Anomaly Monitoring System (CAMS GHCN) by NOAA’s Earth System Research Laboratory was used to estimate surface air temperature patterns”

    They flag up Africa needs 5000 automatic temps stations.

    Makes you weep.

  8. June 12, 2017 8:48 am

    MET- “Weather station sites
    Weather station sites are selected to ensure that the observations are representative of the wider area around the station and not unduly influenced by local effects- ( hmmm , not really)

    Ideal site

    Level ground.

    No trees; buildings, or steep ground nearby that might influence the measurements. ( ooops)

    Undesirable site

    Warming effect of buildings on the measurement of temperature

    Sheltering or shading effects of trees on the measurement of sunshine and wind.

    Frost hollow where overnight temperatures on still clear nights may be far lower than at neighbouring locations.

    Top of a hill or steep escarpment where winds will be unrepresentative of the wider area”

  9. Ben Vorlich permalink
    June 12, 2017 10:11 am

    I’ve often wondered why a blanket adjustment is made. In all the three cases outlined it would appear that the biggest influence of the developments is when the wind is coming from a northerly direction (NNW-NNE). Wind from the north would be most affect by any warming from the developments whilst the prevailing wind from W/SW less so.

    Having a blanket adjustment will have the effect of raising temperatures for W-SW and cooling those for NNW-NNE. I can’t find any data about wind direction for central England but have a feeling that Northerly winds are more frequent in winter. Most temperatures will be raised by more than is necessary (assuming the adjustment is approximately correct) but in a small subset the adjust will be too small. In fact it may be the case that no adjustment is required for the W/SW wind.

    Any site will have the same problem when developments happen around them, but only in a particular direction, Adjustments should also include a factor for wind direction and strength.

  10. June 12, 2017 10:18 am

    ‘Surely a greenhouse designed to enable “plants to flourish in a semi-Mediterranean climate” sited up wind of a weather station may have some effect?’

    Perhaps, but isn’t the point of a greenhouse to keep the heat inside it?

    • dave permalink
      June 12, 2017 2:26 pm

      “…isn’t the point of a greenhouse to keep the heat inside it?”

      Not all of the heat supplied. The point is to keep the STOCK of heat inside it at an artificially high level.

      It is necessary in any physical situation to distinguish between stocks and flows, and between static and dynamic analyses.

  11. June 12, 2017 10:25 am

    We live Mells, a little village in rural Somerset, about 14 miles South of Bath. Here, our Stellata Magnolia came into flower some two weeks after those in Bath; similarly, many of the plants in our garden that are harbingers of summer; roses, clematis, all two to three weeks later. However they come up with their UHI adjustment, it’s nonsense.

    • June 12, 2017 11:03 am

      MET on Microclimates.

      “If we compare the climate statistics for three locations in Devon, one upland and the other two coastal, namely Princetown, Plymouth and Teignmouth, each only 20 miles apart, you would think that the climate of these three locations would be very similar. However, looking at the statistics below, you can see that their climates are quite different. The reason for this is due, in the main, to the altitude and their proximity to the prevailing wind of these locations. Princetown, high up on Dartmoor, is at an altitude of 453 metres above mean sea-level, whereas Plymouth is 50 metres and Teignmouth is only 3 metres above mean sea-level”

      Click to access fact_sheet_no._14.pdf

      I read a WMO report a while back that suggested that microclimates had changed but not the climate at large. Will have to dig that one out.

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