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Tropical Nights On The Rise? Not According to CET!

August 11, 2020

By Paul Homewood



Tropical nights were once so uncommon in Britain that just eight were recorded in the 30 years between 1961 and 1995.

Now, thanks to the heatwave, we have seen 16 such uncomfortably hot evenings this summer, with more forecast for this week.

These hot nights, when the mercury does not drop below 20 degrees, were once so uncommon in Britain that they were not logged, but now a large proportion of our summer nights are spent tossing and turning, and this year looks likely to set a record.

Climate change means that tropical nights are likely to continue to increase year on year, and become a regular part of our summers, meteorologists have warned.

Data shows that the average number of tropical nights per year only became statistically significant after 1995. Now, there has been an unbroken run of at least 10 tropical nights per summer from 2011 to 2020.

Grahame Madge, a Met Office spokesperson, told The Telegraph: “Minimum daily temperatures of 20.0 C or above are still extremely rare events in the UK, but with a changing climate we can expect to see more incidents. Mostly it is weather stations in the south east of England which record these high temperatures, and there have only been three in Scotland since 1961 and none in Northern Ireland over the same period. However, as well as in increasing frequency of events we can also expect to see more occurrences outsides of the south east of England.

“There is a huge interest from the public about daytime high temperatures. While this is important, tropical night temperatures can be extremely challenging for those with underlying health conditions as it means that when overnight temperatures remain high, it is very difficult to get any respite and rest before the next day’s heat begins to build.” 


But is there any real evidence for any of this?

We know how the Met Office cheated by excluding older, inconvenient data records, when they declared a record daily record rainfall for June this year at Honister. Can we be confident that they have not also ignored old data showing equally warm nights in this instance? I am hugely suspicious when we are told tropical nights “ were once so uncommon in Britain that they were not logged

We also need to question the effect of UHI, which undoubtedly will have affected their results.


Accepting that warmer nights are more likely to occur in the south east, if what is claimed is true we should see similar trends in CET:



In fact, we don’t. There was one standout night in July 2016, when temperatures hit 19.4C, the highest on record. And there are clusters of warm nights in 1995, 2003 and 2006.

But only three nights since 2006 have been above 17C. It is notable that seven such nights occurred in the 1940s.

Moreover, no night so far this summer has hit the 17C mark, and apart from one instance in June temperatures have been well below daily records:

In short, CET does not support the Met Office’s claims. If it did, we would see the frequency of warmer nights increasing.

There is no evidence that global warming trends have affected the south east, but not the rest of the country in this way.

If their claims are true, they seem to be the result of UHI and ignoring older data.

  1. Brian Smith permalink
    August 11, 2020 7:02 pm

    Please spell out abbreviations in full the first time they are used. I don’t know what CET or UHI mean. Thank you.

    • August 11, 2020 10:14 pm

      Central England Temperature Series

      Urban Heat Island effect

      • Chaswarnertoo permalink
        August 12, 2020 8:51 am

        Kinder than I would have been, Paul. Some background reading is required, Brian.

      • August 12, 2020 9:19 am

        I agree with Chaswarnertoo – you don’t have the time to spoon-feed pedants, Paul. Keep up the brilliant work!

  2. LeedsChris permalink
    August 11, 2020 7:25 pm

    I’m not sure where they get their data from. I’m a bit of a weather buff and looking at the this summer – June, July and August until last night I can only see 6 nights where the minimum was 20c or above for at least one UK weather station.

  3. Phillip Bratby permalink
    August 11, 2020 7:36 pm

    But, but, but Shukman has just told us on the news that in the 3 decades to 1990 there were 44 tropical nights and in the latest 3 decades there were 84 tropical nights. We all know Shukman is always right. at 18.20

    • Harry Passfield permalink
      August 11, 2020 7:43 pm

      And there was me thinking he was always Left.

    • August 11, 2020 7:43 pm

      But they now claim ‘a large proportion of our summer nights are spent tossing and turning’.

      So 44-84 nights in 30 years is a large proportion? A large portion of baloney more likely.

  4. Broadlands permalink
    August 11, 2020 7:54 pm

    Why does it even matter when there is nothing meaningful that can be done to prevent it? Lowering carbon emissions to zero by 2050? Even if done that just leaves atmospheric CO2 where it is.

    • Chaswarnertoo permalink
      August 12, 2020 8:49 am

      And has no effect on climate.

    • August 12, 2020 10:48 am

      And that can of worms relies on a contradiction both of physics and
      geological history but hey, who these days lets statistically significant empirical data get in the way of thinly veiled marxism! The Enlightenment is dead, right?

  5. Tonyb permalink
    August 11, 2020 9:02 pm

    Does just one location in the entire UK need to be above 20c in order for this to be a record.?

    Certainly in our neck of the wood in the south west coast no nights have reached that criteria.

  6. Nancy & John Hultquist permalink
    August 11, 2020 10:03 pm

    We are not in the UK, but we do live at 670 m. elevation (2,200 feet) on the lee side of the Cascade Range in Washington State. Most nights the atmosphere above us is clear and a bit short of both H2O and CO2. Radiative cooling is rapid. A “tropical night” is not in our lexicon.

  7. dennisambler permalink
    August 11, 2020 11:11 pm

    It could always be down to wind farms…

    ” Wind power reduces emissions while causing climatic impacts such as warmer temperatures

    Warming effect strongest at night when temperatures increase with height

    Nighttime warming effect observed at 28 operational US wind farms

    Wind’s warming can exceed avoided warming from reduced emissions for a century”

    In the meantime, the Guardian intends to interfere in the US election:

    “85 days to save the Earth …

    … we’re all in. Are you? On November 4, a day after the presidential election, the US will formally withdraw from the Paris agreement on constraining global heating. It’s urgent that we tell the world what this means, and the Guardian is pulling out all the stops to do so. Will you help us by supporting our journalism?”

  8. Graeme No.3 permalink
    August 11, 2020 11:13 pm

    If these ‘tropical nights’ are only happening in the south-east then it surely must have something to do with population & UHI not natural warming.

    And since when have minimum summer night temperatures of near 20℃ been tropical?
    I lived for 25 years in Sydney with those, and Sydney is nowhere near the tropics, but last night was 9℃ (not cold for winter) and easier.

    • Phillip Bratby permalink
      August 12, 2020 6:42 am

      I lived for a while in Pittsburgh, where summer night-time temperatures regularly didn’t get below 20℃. Nobody would ever describe Pittsburgh as being tropical.

      Who decided that 20℃ is the definition of a tropical night-time temperature? I have seen 25℃ used with 30℃ being a ‘super’ tropical night-time temperature.

      The BBC is using the term ‘tropical night’ and 20℃ in all its current propaganda messages, with never a mention of the UHI effect or that Heathrow is hardly a tyipcal location in the S-E.

      • Ben Vorlich permalink
        August 12, 2020 9:31 am

        Must be an EU edict, Tropical Nights seems to be Europe wide now.

  9. August 11, 2020 11:42 pm

    In Sussex in the late 1950s there were many nights in summer, July/ August when it was too hot to sleep. Daytime temperatures in the 90s, dry thunderstorms with spectacular lightening, gorse fires across the South Downs and peat fires on the Weald. Apart from 1976, I don’t remember many summers that got even close. How convenient to start the comparison clock in 1961….. The UHI effect has increased dramatically since the 1950s, over most of Britain but particularily in the South East, due to the huge numbers of ‘city slickers’ now domiciled in that area. So we might expect a rise in average temperature, due to all that concrete, hot air and overheated supercomputers….

    • Graeme No.3 permalink
      August 12, 2020 12:59 am

      You reminded me of a discussion with my barber, originally from Yorkshire (and a fanatic Leeds supporter) who told me that he had trouble sleeping there in 1976.

      The answer to sleepless night in SE England is air-conditioning, which the British in India adopted in the late 1930’s. Unfortunately your government is determined to make electricity both expensive and unreliable.

  10. John Cooknell permalink
    August 12, 2020 4:09 am

    I have lived in the tropics, and not one UK night anywhere would I describe as tropical!

    My advice is get your heating checked out.

    • August 12, 2020 3:31 pm

      John, I lived in Singapore for 2 1/2 years and 20degC would have been counted as a cold snap! We did not have aircon, just fans on the ceiling and and sleeping was perfectly comfortable. Living in aircon was not recommended unless you worked in an aircon environment and those people who did seemed to have permanent colds.

  11. Colin MacDonald permalink
    August 12, 2020 8:01 am

    I think the CET refers to an area of England just beyond the M25 bubble and therefore has no relevance to the Beeb, or climate science in general. Incidentally, here in Aberdeen temperatures have barely touched 20°C this past week, so I have a good laugh about Harribin et al, bloviating about tossing and turning in their bedrooms, thinking this points to a planetary phenomenon.

  12. 2hmp permalink
    August 12, 2020 8:46 am

    The really exciting claim is when they say the highest temperature recorded was at Heathrow ! Well i never.

  13. MrGrimNasty permalink
    August 12, 2020 9:10 am

    ‘so uncommon that they were not logged’ is climate alarmist double speak for we just came up with another idea to push the warming agenda/climate alarm reinforcement.

    It’s like the weather system naming gimmick to make the public think of the normal weather as a sequence of significant unusual storms like a hurricane.

    November 2018: “The Met Office is to start tracking the number of ‘tropical nights’ in Britain where the temperature never falls below 68F (20C) in an acknowledgement that the climate is becoming more extreme. In a new report on the State of the UK Climate 2017, the forecaster has included the measure for the first time, admitting they are ‘expecting it to become more prevalent in the future.’”

    ‘Tropical nights’ is another arbitrary threshold given a catchy name to spread concern. During the current heatwave even Heathrow has dropped to 20C in every 24hour period (to the nearest dp). If they had defined it as 70F (21.1C) as would seem far more logical, there would be none.

    Since 1976 the population of Greater London has gone up 2.3 million people and it has barely more than 1% ‘green spaces’. The encyclopedia Britannica says that the UHI effect can boost night temperatures by up to 9C (with an average of 2C). The same applies to all towns and cities in the UK to a lesser but no less significant extent.

    It would be a frigging miracle if more nights didn’t stay uncomfortably warm.

    This has absolutely nothing to do with supposed global climate change caused by CO2, it is localized micro climate modification from urbanization.

    • Phoenix44 permalink
      August 12, 2020 9:21 am

      I do love how we know how uncommon something was if it was not recorded!

      More likely it was not thought relevant or interesting.

    • Mike Jackson permalink
      August 12, 2020 1:42 pm

      I can certainly vouch for UHI of 3° in Edinburgh. 10 years ago I drove once a week from Edinburgh West End into East Lothian at around 9 pm. The car thermometer — which might not have been 100% reliable but which I assume was at least consistent — regularly showed 3° degree difference. Driving into Midlothian it could be as much as 5° on occasion but that was 200 metres higher!

  14. August 12, 2020 9:24 am

    I can remember hot nights in the 60s in Hampshire. I don’t know how often or what year but in my mind it seems as if it was fairly normal to experience nights in the summer when I would throw off my blankets and just sleep under a sheet. That was the good thing about sheets and blankets…..

  15. August 12, 2020 9:25 am

    Probable reasons for increased temps in UHI areas include:

    – Grassed gardens being concreted over, heated for 16 hours during the day and then radiating the energy during the night
    – Black roofed houses
    – Increased use of air conditioning and heat pumps, exhausting extreme amounts of hot air

    And this is just a start!

  16. Phoenix44 permalink
    August 12, 2020 9:26 am

    The current hot nights in London are entirely the result of hot air from the far south being drawn northwards, not hot days as such. It is it quite, but almost Tropical air. If these conditions (standing lows I believe?) are more common, then you need to prove CO2 causes that, not “it makes things hot”.

    • Phillip Bratby permalink
      August 12, 2020 10:02 am

      The hot air is very humid. It is maintained hot by the fact that the water vapour is the only significant ‘greenhouse gas’. It is strange that this fact is not mentioned by the Met Office or the BBC.

  17. Coeur de Lion permalink
    August 12, 2020 1:01 pm

    Off thread but as I write wind is producing 0.96% of U.K. electricity. And demand is quite high at 36GW.

  18. Gerry, England permalink
    August 12, 2020 2:03 pm

    In my corner of Surrey it has been over 20C every night recently. Normally the temperature drops quite quickly after the sun sets but it has been lingering on this last week or so. Looking forward to some storms to break it all up and refresh everything.

    • MrGrimNasty permalink
      August 12, 2020 3:32 pm

      Very few places have actually had at least one TN, and most of those have only had one (including Heathrow I think).

      BBQs in the frame again – when will the authorities do the sensible thing and ban them?

      • Gerry, England permalink
        August 13, 2020 2:04 pm

        Thanks for the link which goes to show how hard it is to get temperatures that cover what people experience. There is only one station near me, Kenley, which has a totally different climate to me as it sits on top of the North Downs while I live on the lowlands. There is very little data for my area and what you do find gives you Gatwick Airport. However, the half-hourly readings do give a bit of clue in that there is only one period of 30 minutes at 20C recorded at 6.50 am. So it might be that on the records there is just a very short dip below that nobody notices as by 8.20 am it reached 23C. So bar maybe half an hour, every night for over a week has been above 20C.

      • MrGrimNasty permalink
        August 13, 2020 7:56 pm

        It’s not a 100% comprehensive list of reporting stations.

        From all reporting stations even the Met Office is only claiming 4 tropical nights as of today (any 1 or more locations exceeded on 4 nights ONLY).

        It has been close to 20C a lot of nights over wide areas and it’s understandable people would not realise it had actually dropped just below according to scientifically rigorous(ish) instruments – but pedantry matters!

        On the hottest day we had (33.2C) it was 28C at 8am, but we still have not had a true tropical night, the highest min was 19.4C. I would have sworn blind we had a week of tropical nights too.

  19. MrGrimNasty permalink
    August 12, 2020 4:39 pm

    BBC news and weather is now trotting out the line that ‘it is the first time that 6 days in a row have exceeded 34C somewhere in the country’. A few days ago they preempted the first ever run of days over 37C, but it didn’t happen so we heard no more. They lowered their expectations and came up with this meaningless ‘record’ instead.

    In ’76 Heathrow had 16 days in a row 30+C, and 15 days in a row reached 32.2C somewhere in England (odd number = 90F in old money).

    It’s a perfect example of how you can make alarm (or just interesting pub talk in the old days) out of whatever the weather happens to throw up – there’s always a record in there somewhere if you crunch it enough ways!

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