Category Archives: Heatwaves

Phew! What a scorcher…

I’ve seen this phrase uttered more than once over the past couple of days thanks to high temperatures and humidity. But ask anyone to define a hot day and you’ll get a different answer every time.

Growing up in the 1970s / 80s redtop newspapers would use the phrase once the mercury was nudging 80F (26.7C). But to ‘scorch’ you need sunshine, preferably at least 10 hours of it. Considering statistics from the Heathrow airport climate station in west London there have been 463 scorchers since 1959, the most recent happening on July 5th with 29.5C recorded and 13.9 hours of sunshine. There have now been 9 scorchers this year, already matching the number that were recorded in 2014 and only 3 short of last year.

But even with last month’s heatwave this year has some way to go, however, to match the amount measured in 1976 and 1995: 31 days!



Hot spell is minnow among historic heatwaves

Heatwave hype has been building over the past few days and, for once, the media has been justified in its coverage of the current spell.

Temperatures over the past few days have been enough for the Met Office to trigger its Heath-Health Watch whereby the mean temperature (an average of the maximum and minimum) for two consecutive days reaches 23.5C.

A couple of years ago I compiled a list of heatwaves for this area back to 1852 where the mean temperature reaches at least 23.5C three days running. This spell, the only other June heatwave (the other being 1976!), only just scrapes into the list.

Although it felt hot this spell, in terms of Premier League quality, was more Middlesbrough than Chelsea.heatwave table

june heatForecasters say today is likely to be the hottest June day for 40 years though I’d be surprised if we exceed the 34.2C recorded on June 27th 2011. It would be the fifth day running that 30C has been reached in this area, enough to fulfil the World Meteorological Organisation’s (WMO) definition of a heatwave.

Whatever happens today the fact that the heat has been produced by a tropical maritime airmass is remarkable. With France and Spain recording some very high temperatures of late the same pattern in July and August could put more records at risk of being broken.

This week marks the 41st anniversary of the start of probably the finest British summer in history, but anyone hoping that yet another parallel with the 1970s is about to come true should take a look at the latest model runs.

june low
The latest GFS operational run suggests a much cooler, more unsettled end to June – a polar opposite of 1976…



Is London heading for a hot summer?

Before I’m accused of going all Daily Express the following is based on winter statistics for the London area and other variables rather than the latest expert hopecast.

Even before looking at the data in depth the chart below shows that a warmer than average summer is more likely after a mild winter. The winter just gone was the third mildest in a record going back to 1797.


There are some real corkers in that list, including 1995 when this area recorded the driest August on record. Other notable summers included 1990 – England in the semi-finals of the World Cup and another notably fine August: the then hottest UK temperature was set that year when a maximum of 37.1C was recorded at Cheltenham – a record that lasted until 2003. The year 1989 also stands out with a notably sunny summer.

So far, so good. But what about rainfall? Some 145mm of rain fell this winter – pretty much on the nose average for this region. Combining warm winters with similarly average rainfall gives the following list.

with similar rain

Though some years have disappeared there are still some decent summers, and notably sunny too. The year 1975 stands out as does the sunniest summer on record, 1911! Both were also very dry summers.

Altough the teleconnection with El Nino is tentative in our part of the world the winter seemed to follow the pattern of most positive ENSO episodes, so it is worth having a look to see where the data goes. The latest forecast by NOAA suggests:

A transition to ENSO-neutral is likely during late Northern Hemisphere spring or early summer 2016, with a possible transition to La Niña conditions during the fall.*

If the forecast goes to plan the second ‘rainfall list’ would narrow further:

Screen Shot 2016-03-08 at 02.44.05

Viewed by graph reveals that ENSO values of all the years decreased over the course of the year. Series 1 is 1998, series 2 is 1983 etc.

Screen Shot 2016-03-08 at 02.48.01

In conclusion, the results would suggest that there is a 66% chance of a decent summer with below average rainfall and above average sunshine. In terms of details June 1st is still a very long off in meteorological terms – so whether it includes any heatwaves that would put it my premier league of hot spells is anyone’s guess at this range.

If it’s anything like 1959, 1975, 1983 or 1998, however, I think most folk will be happy.

*The above contradicts some forecasts which suggest a continuation of the general pattern that persisted during the winter: warm SSTs in the Atlantic / warm water south of the Grand Banks were largely responsible for the cyclonic westerly type of weather that caused the mild weather. In summer this would cause changeable weather rather than long spells of settled weather.


Premier league of heatwaves (1850-2020)

The media are always keen to say ‘a heatwave is on the way’ when it is more likely to just be a short spell of fine weather with temperatures a few degrees above average.

The Daily Express has flagged up ridiculous weather stories so often that it is now beyond parody
The Daily Express, which usually goes over-the-top when there is any sign of heat on the horizon, has been relatively quiet of late

Forecasts of 30C and above see editors up and down the land reaching for their stock pics of office workers and kids enjoying ice creams in parks.

‘Hotter than the Costas’ and other hackeneyed headlines are wheeled out as photos of scantily-clad women frolicking in the sea at Brighton illustrate this amazing fact – the more ubiquitous shirtless lorry drivers on the capital’s roads never seem to make the final editions.

So how do you quantify a heatwave? Even in an average year the UK normally sees at least one spell of very warm weather that can often feel much warmer than it actually is.

Looking at data for the London area stretching back to the early 1800s there has been plenty of hot spells, including the summer of 1808 where birds reportedly ‘dropped out of the sky’ from heat exhaustion.

The term ‘heatwave’ does not appear in any publication in the British Newspaper Archive until 1867. The Manchester Courier and Lancashire General Advertiser on May 11th 1867 features a letter from Mr R.H. Allnatt. Writing from the British Hotel, Jersey, he states that “…the atmosphere became most oppressive. A heat-wave seems to have passed over the island, and from noon till sunset the thermometer stood in shade at 90 deg.”

The World Meteorological Organization’s description of a heatwave is “when the daily maximum temperature on more than five consecutive days exceeds the average maximum temperature by 5°C, the normal period being 1961-1990″. Though it has no official definition the UK Met Office, working with the Department of Health, provides a ‘Heat-Health Watch System’ for England which is triggered when a threshold temperature in the South East is  31°C by day and 16°C overnight for at least two consecutive days.

A mean daily temperature of 23.5°C or higher has been achieved in this area on 199 days since 1852. To qualify for the Met Office’s Heat-Health Watch System the list, which goes back 163 years, narrows. However, to make my job easier, I have narrowed the list further to 3 consecutive days where the mean has been 23.5°C or higher. Though I loathe really hot weather in my experience I can put up with it for a couple of days. It is only when it gets to the third day of hot, sleepless nights that it starts becoming unbearable.

The 500mb renanalysis chart of the heatwave of August 1876
The 500mb renanalysis chart of the heatwave of August 1876

The first heatwave that fits my parameters, and ranks 7th in the heatwave premier league, began on August 13th 1876. Obviously in those days news would have taken a while to filter through. On the front page but tucked away at the bottom of the far right column of Reynolds’s Newspaper on August 20th a report talked on “excessive heat in Norfolk”:

“The weather has been intensely hot in Norfolk, and two fatal cases of sunstroke are reported from Blofield. A similar casualty occurred at Thorndon. A spark from a Great Eastern Railway engine has fired a barley field near Wherstead, Suffolk, in consequence of the extreme drought. The damage done is estimated at £300.”

A report on the “Glorious Twelfth” in the London Daily News on Monday 14th says:

“Not a cloud obscured the burning rays of the sun, and in the middle hours of the day moving about on the moor was not unattended with danger.” The weather was the complete opposite of the previous two years where “rain fell so continuously that only the keenest of the keen ventured abroad”.

500mb reanalysis of the 1893 heatwave
500mb reanalysis of the 1893 heatwave

It would be another 26 years before Greenwich would see another heatwave of the same magnitude. Tucked away on page 16 of Lloyd’s Weekly Newspaper on Sunday 20th August 1893 a national round-up column spoke of ‘The Excessive Heat’ of the past week of that heatwave which ranks 11th in the league of heatwaves.

“A farmer, named Calvert, of Barlow, died of sunstroke on Tuesday whilst engaged in harvest work. A man named George Wight fell down in the street at Birmingham on Tuesday, and was taken to the hospital, where it was stated that he was suffering from sunstroke. The intense heat had a remarkable effect on the temperature of the sea in the Channel. A Sandwich correspondent said the water was the warmest it had been for 25 years.”

Several cases of sunstroke were recorded among soldiers from Plymouth Garrison. A regiment from West Riding were ordered off parade while some regiments took the unprecedented step of parading in shirtsleeves. An engine-driver, when running the express into Stoke station, became seriously ill and died directly after his admission to hospital. His death is attributed to the intense heat. Harvesters in Ashford, Kent, also downed tools after a fatality and several cases of sunstroke.

National newspapers of the day took a broader view of proceedings. The Daily Telegraph‘s assumption on the cause of the heatwave and prognosis of conditions was actually better than it is today.

“Not more than twice or thrice in the present century probably has heat as intense and persistent as that now registered been experienced in England. Since Saturday, when announced the formation of an anticyclone over the British islands, there has been a nearly constant and slowly progressive increase of temperature, until yesterday the maximum thermometric reading of the year so far was attained, 90 degrees in the shade being recorded at the Meteorological Office, Westminster.”

The Times on the same day remarked on how people were dealing with the intense heat:

“Such is the force of habit that the social mechanism still keeps working, though nobody really cares for anything except the heat. In the shops, in the Stock Exchange, even in Parliament, people meet and go through the form of doing business, but their langour tells its own story — that the sun has been too much for them.”

The paper describes a “great thunderstorm that had kept everyone in the south of England awake a week earlier” that was assumed to have been the end of a hot summer. But the heat built again.

“Sunday was one of the most exhausting days in human memory; and Tuesday and yesterday, at all events in London, were days to be remembered and quoted. Nothing more like a Italian scirocco has ever been felt here than the west wind which blew at midday yesterday. Very scientific thermometers, indeed, pretend that the heat was nothing exceptional, but the skin, the brain, and the temper of the average man told a different story.”

It would appear that the return of the heatwave took forecasters by surprise and the paper continues on with a familiar ‘why weren’t we warned’ tone:

“And the worst was that the forecast, to which our excellent Meteorological Office has taught us to look with so much confidence, promised quite other things. It spoke of weather unsettled, thundery, and showery later,” and in the north it promised ” westerly and varying breezes; changeable, showery, thundery, cooler. “What tricks were the barometers playing ? Was Ben Nevis having its little joke, or was the office itself suffering from sunstroke?”

On its front page on Saturday, August 19th, The Yorkshire Evening Post featured a prominent sketch of a City gent Picture courtesy of the British Newspaper Archive
On its front page on Saturday, August 19th, The Yorkshire Evening Post featured a prominent sketch of a City gent
Picture courtesy of the British Newspaper Archive

The Daily Chronicle turned its editorial attentions to the “alarming” effects the heat was having on peoples’ attire

“The social effects began to operate at an early stage at Westminster, on temper as well on habiliments. They have now penetrated that last refuge of conventional respectability, the City, where the chimney-pot de rigueur has been dethroned by the straw of comfort, and the waistcoat has actually disappeared before the coloured silk scarf.”

The paper reports of people falling ill with fever in the heat, possibly caused by water supply. While the Thames, thanks to reforms by the County Council, was not smelling Glaswegians close to the Clyde were not so fortunate, the river being “overpoweringly odorous all the summer”.

“We must grin and bear it, as may. We shall grumble when the temperature falls, pretty much as we are doing now. For, Macanlay somewhere says, man is never satisfied with what he has, but is always straining after what he has not. And this is particularly true of Britons and their weather.”

Little is written of the 17th ranked 1906 heatwave that ran from August 31st to September 2nd though a diary note on page 3 of the Portsmouth Evening News on Thursday 6th September said the effect of the heat proved decidedly detrimental to education in Portsmouth. It reports:

“Not that the attendance has fallen off to any appreciable extent as result of the very trying weather, but its effect has been very marked, nevertheless, as the youngsters have proved very heavy and slack, with the result that the lot has been decidedly trying.”

The glorious summer of 1911, surprisingly, did not produce a spell that would satisfy my heatwave criteria.

August 9th, 1911, saw the first incident of 100F (37.8C) being recorded in London. The record beat the previous high on 97F. The report also makes mention that many areas recorded at least 97F
August 9th, 1911, saw the first incident of 100F (37.8C) being recorded in London. The record beat the previous high on 97F. The report also makes mention that many areas recorded at least 97F

The season, which produced hot weather throughout July and August, is worthy of mention, however, because August 9th saw the first occasion 100°F was recorded in London. Considering the magnitude of this milestone the media of the day seemed reluctant to go overboard with the coverage, simply reporting the facts. The day after the hottest day ever the Dundee Evening Post had some advice on attire for hot weather, including a reported sighting of Keir Hardie in a “duck suit”.

By 1923, a heatwave that placed 14th, reports were going beyond records of temperature and heat-related deaths. On July 16th a reader of the Gloucester Citizen was bemoaning the fact that visitors to London were being subjected to “heatwave profiteering”.

Ice was in short supply and only available in restaurants and cafes and the price of fruit and salad had risen “beyond reason”. The author writes:

“A Fleet Street shop, for example, lemons have suddenly risen from a modest penny to a more formidable threepence, and the explanation is: “There has been an eruption at Etna, you know”. “To point out that the present stock of lemons was received long before Etna began to make its dangerous influences felt is merely to invite a shrug of the shoulders and gesture indicating “take it or leave it.”

The London Letter column in the Hull Daily Mail on Friday 13th July mentions MP’s braving the stifling heat to hear Prime Minister Stanley Baldwin’s statement on European policy, and also “London The Boil”.

1923 heatwave“The heat wave continues to keep in its fiery grip. It absolutely dominates the daily lives of our seven million population, whose habits are rapidly approximating to those much nearer the equator. Hyde Park ladies fashionably attired may be seen sitting under sunshades beneath the shadiest trees in their stockinged feet. Their shoes rest beside them on the parched grass.”

“In Fleet Street there has been a long queue, as nondescript as an old-time butter queue during the war ration period, outside a shop where ice cream wafers are sold at the rate of about two hundred a minute. Men are wearing white suits, waistcoats have vanished, straw hats are at a premium. Most of the licensed bars are doing little more than pussyfoot trade in long iced teetotal drinks. An actor appearing in So This is London, says that he gets home half-an-hour earlier nowadays. Though the theatre is quite well filled, the audience is too hot to applaud. So the show goes slick through.”

The column, written decades before the advent of air conditioned comfort became the norm, also gives advice on where to keep cool in the capital. Previous favourites had included the cold-storage warehouses along the riverside at Blackfriars Bridge, the Monument and Westminster’s “Byzantine” tower.

“I am quite certain the coolest place in London is in a boat under the stone bridge that spans the Serpentine. Scores of overheated Londoners seek these cool arches. There, if you can crush in, you may smoke a cigarette, in almost too chilly comfort, while London boils just outside.”

The Yorkshire Evening Post on Friday, August 29th 1930 Image courtesy of British Newspaper Library
The Yorkshire Evening Post on Friday, August 29th 1930
Image courtesy of British Newspaper Library

The heatwave of August 27th – 29th 1930, which ranks 15th, produced another interesting ‘London Letter’ column in the Portsmouth Evening News about too-hot cabs and heatwave profiteering: a greengrocer raising the price of lemons from 1d to 13d, despite there being crates available in storerooms!

This 'Sainsbury & Son' advert appeared on p7 of The Bucks Herald on Friday, August 19th, 1932
This ‘Sainsbury & Son’ advert appeared on p7 of The Bucks Herald on Friday, August 19th, 1932

Two years later and newspapers were reporting the ‘hottest day for a generation’. The heatwave of August 18th – 20th August 1932 saw the temperature reach 99°F (37.2°C). This heatwave ranks 9th.

“Tragedies attributable to the heatwave were reported from all parts the kingdom yesterday. From the provinces 14 heat deaths were notified. Three cases of suicide which the Paddington coroner said were attributable to the effects of the intense heat and ill health were subjects of inquests Paddington yesterday afternoon.”

The Leicester Chronicle reported cases of heat exhaustion and the curious sight of people carrying home butter in jugs while the 7.25pm and 7.30pm express trains from King’s Cross to the Western Highlands had shower baths installed in sleeping cars to help passengers cope with the heat.

The heatwave of August 6th – August 8th 1947, which ranks 18th, was sparsely reported save for the usual heat stroke casualty stories and the fact that Cheltenham recorded 11 hours of sunshine on one sweltering day.

By 1948 signs of a move away from straight reporting of heatwaves were beginning to appear. An Hour in the Heatwave, a report taken during the hot spell of July 28th – 30th, ranked 12th, was published in the Essex Newsman.

The reporter, Gilbert Saunders, gave a simple but highly readable account of people going about their daily life in the heat.

“In the stadium The other side of the river, where Chelmsford have their stadium, Ted Boxall, private builder, was getting on with a job that he started on Wednesday and hopes to finish by today. He is making a surround and small archway for the counter over which cups of tea are passed to directors and guests in the board room under the grandstand. Ted (who asked : “You’re not mistaking me for Mr. Rowe, are you?”) was surrounded with litter of Essex boarding and sawdust. He paused to wipe a hot brow, explained that he does “lots of odd jobs” for the club. Ted gets a hand from the players when its needed. Earlier this week he finished off two sets of concrete steps, one each side of the grandstand, so that fans will be able to get on the raised ground without having to scramble up the sides of a small mountain of ash and clinkers.”

An hour in the heatwave, published in the  Essex Newsman - Friday 30th July 1948
An hour in the heatwave, published in the Essex Newsman – Friday 30th July 1948

“On the Corner At London Road corner, his face red from the heat but bearing the everpresent grin, Special Constable Thorn clicked and swivelled his 6ft 3in and kept the traffic moving, all unaware that the next day’s Essex Chronicle was already printing a letter suggesting that his courtesy, service, and goodwill should be rewarded with the Freedom of Chelmsford.”

“In the Newspaper Office And inside the building of the Essex Chronicle, Norman White, bespectacled family man, sat down at the side of the roaring press and took a bite at some sandwiches. The first of seven editions was streaming out. “Ought to be pretty early tonight,” he shouted above the din. “With luck we should all be away between half-past nine and ten …… “

The Aberdeen Journal, in its edition published on Friday 30th July, reported on conditions in London and how the population was coping (or not!) with the heat:

“The metropolis last night was like a large restless household—with all the lights ablaze, doors and windows thrown open, the family fretful, and endless pots of tea brewing far into this morning.

aspro heatwave ad Yorkshire Post and Leeds Intelligencer - Wednesday 13 August 1947“Perhaps one in ten among the 8,000,000 of us slept after midnight. For the rest, we tossed and turned and saw out this heatwave night, when temperatures were never below 71 degrees, a variety of ways. About midnight I walked past the gaunt old Edwardian mansions in Kensington. With the exception the lights that burned from every window, the scene was reminiscent of the early days of the Blitz.

“Families trekked across the roadway in varying stages of undress to their little bits of ornamental gardens. With them went camp beds, bed linen, umbrellas, “in case,” the children, and the household pets, choose a cool open-air camping spot and feel wonderfully adventurous and spartan in the process.”

Yorkshire Evening Post - Thursday 14 August 1947
Yorkshire Evening Post – Thursday 14 August 1947

“At regular intervals the adolescent members of the squatting colonies were dispatched to the tea and coffee stalls on the corner, and perhaps for the first time in years these traders ran out of stocks. On the Kensington-Chelsea boundary, where life becomes noticeably less inhibited and on occasions less swish, a mixed group of young artists was sleeping on the pavement off Fulham Road.

“Round the next corner, where many theatrical and film stars live, several had slung hammocks on their meagre front lawns – one actually suspended between the bathroom windows of two adjacent houses. Midnight street wear for both sexes was cool if unconventional —silk pyjamas, bath robes, tennis shorts, and one in kilt and bathing costume top who could have gone straight into the arena at Lonach.”

The column goes on to describe the situation in the House of Commons where the heat had reached “almost Turkish bath intensity”.

“Some members were in natty tussore silk suitings, but this helped little, and it was many of their number who appealed to the Speaker to have more windows opened. The Speaker, panting like the rest of us, said they were all open. If they wanted more cool breezes from the Thames, members would have to smash the windows.”

More evidence of reportage became evident during the June 1952 heatwave which ranks 8th.

A report on life in the heatwave published on July 5th 1952 Image courtesy of the British Newspaper Archive
A report on life in the heatwave published on July 5th 1952
Image courtesy of the British Newspaper Archive

Peter Chambers, of the Evening Express, wrote:

“London is hot. It is going to get hotter. That merry mercury column is poking up into the eighties already. That’s what faces us at the height of a heatwave.

“Bus tyres sizzle on the melted tarmac in the streets. At office windows, the girls are pattering away at their typrewriters with damp, discouraged fingers.

“It’s a scorcher. Even the sparrows are panting.”

The reporter describes the scene at London Bridge at 9.30am: “Well, as I came over London Bridge with the 9.30 surge of sweltering suburbia, a bus conductor hopped off his traffic-jammed vehicle and grabbed a couple of ice chips off a Billingsgate lorry. One for him, one for the driver. “What I want, mate,” said the driver ungratefully, “is a ‘ole block of the freezin’ stuff – to sit on.” That is the male reaction to the heatwave.

“The female reaction is typified by the secretary in this office, who buzzes off to the ladies’ room every half-hour to atomise herself with eau de cologne. Ever since she read that fragrant publicity handout, which said “It’s not enough, girls, NOT to be hot and sticky, you’ve got to smell NICE-TO-BE-NEAR…”

The author takes a walk past Embankment and up to Trafalgar Square: “The girls are in topless frocks. Even the men have got their jackets off – a sight abhored further east, where the rigid convention of the City demands that you sweat it out in your dark worsted, regardless.”

At 1pm he finds foreigners feeding the pigeons by Nelson’s Columns and Londoners feeding themselves on bags of strawberries priced at 1/9. By 3pm he’d made it to the Serpentine Lido along with 3,000 other people. He describes at like “Margate on a Bank Holiday”.

The summer of 1959 was glorious but many cool nights saw the season fall short of my 23.5C threshold. It would be a long time before summers were nice again.

The top 6 of my league of heatwaves are all occupied by much more recent events, including 1976 and 1990, both of which are dealt with in the blog I wrote last year – 50 years of London heatwaves. The heatwave that topped them all, in terms of sheer intensity and produced the UK’s hottest day ever, happened in 2003.

I have vague memories of the weeks of sunshine in 1976 but the hot spells that stick in my mind the most are August 1990, when the UK temperature record was set in Cheltenham, Gloucestershire, and August 2003 when an 8-day hot spell saw the all-time UK temperature record broken when 38.5C was reached at Brogdale, near Faversham, Kent.

In terms of length, heat and sunshine, therefore, 2003 comes out on top. Though many people will argue that 1976 is the more impressive summer that year produced two spells that satisfy my criteria, coming in second and fifth. The first heatwave saw temperatures soar above 31° C for six consecutive days from June 23. The start of the second, on July 3, saw Bjorn Borg win the first of five Wimbledon mens’ titles as he prevailed over Ilie Nastase in 35°C heat. The summer of 1995, which saw my driest-ever August with just 0.7mm of rainfall all month, comes in 3rd, with six days of mean temperatures of 23.5°C or higher.

Looking back through history it is not really surprising that 2003 comes out on top. While it was hot in London the heatwave across the Channel contributed to the death of over 70,000 people throughout Europe, France being the most affected.


A complete set of 500mb reanalysis charts have been uploaded and can be watched as a GIF movie

make animated gifs like this at MakeaGif

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* There were hot spells before 1852 but I have excluded these: Luke Howard’s maxima observations from Plaistow, Stratford and Tottenham were taken under non-standard conditions and may be on the high side. I have instead focused my investigation on data recorded at the Royal Observatory, Greenwich.

** For some reason the data during a couple of years in the 1950s was incomplete – to fill in these gaps I used official data gathered at Kew. The data is completed up to the present day using my own observations taken since 1988.

*** As already mentioned prior to these dates data is unreliable as conditions for collection were not strictly controlled. However, there are many records of extreme heat. On Sunday, August 1, 1868, the Gloucester Journal published a report on the “Heat of previous years” detailing an account of hot spells going back to 1806. “Mr. G. J. Symons gives a number of interesting particulars in reference the heat of previous seasons in this country. We abstract the following

  • 1806: Very hot in parts of June and July. At Plaistow the temperature was 95 degrees on June 10th, and 90 degrees or upwards on three days.
  • 1808: Very hot from July 12th to 19th. On the 12th a thermometer in perfect shade in a window in St James’s Park was 81.5 degrees at 3pm, and on the 13th at the same hour, 94 degrees. On the same day four men and seven women were killed by sunstroke in various parts of the Midland counties, and numerous coach and other horses were also killed. On the 15th a very violent and destructive thunderstorm in Gloucestershire, Monmouthshire, and surrounding counties.
  • 1818:July a very hot month. At Tottenham on the 24th Luke Howard registered 93 degrees at Somerset House on the same day it was 89 degrees, and in the Strand 87 degrees at noon. The mean temperature of that day at Greenwich was 79.2 degrees, which was higher than any other day between 1814 and 1863. The following paragraph appeared in the Gentleman’s Magazine for September, 1818: “It is worthy of remark that the heat of the present summer has been universal. From the north to the south of Europe the heat has been greater and more lasting than for 40 years On July 24th the thermometer here (where!) was 98 degrees, which had never been reached except on July 16th, 1793. At Paris July 31st it was 93 degrees and at Philadelphia 100 degrees.” From 19th to 21st violent thunderstorms in the west of England.
  • 1825: July remarkable, if not unique, in its constant and excessive temperature. At Stratford Luke Howard registered 90 degrees or upwards on seven days, the highest being 97 degrees on the 18th.
  • 1826: The heat was very great. In May the thermometer reached 76 degrees, June 92, July 89, August 85. Two men were killed by sunstroke near London. The fields were as brown as the roads. After two months’ drought the rivulets were gone, and many of the wells dry. The hay crop was deficient from long drought. Country is parched, and corn in some places, though only a few inches above ground, was shooting into ear. Several hills and moors caught fire. In Worcestershire the excessive heat and drought almost wholly destroyed the pasturage, and trees were lopped to feed the cattle.
  • 1846: July 5 was very hot, 93.3 degrees being registered at Greenwich, and 94 degrees at Clapham (94 degrees has been recorded there again in the only other instance at that station.
  • 1852: July of this wet year was remarkably hot, the mean monthly temperature (66.6 degrees) having only been exceeded by July 1778 when it was 67 degrees; and July 1859 when it was 68.1 degrees. Tho extreme heat, however, was only 90.3 degrees at Greenwich.
  • 1857: On June 28, 92.7 deg. was recorded at Greenwich.
  • 1858: June was a very hot day, 94.5 degrees being reached at Greenwich.
  • 1859: Temperatures of 92, 92.5, and 93.0 degrees were recorded at Greenwich.”

Hot and bothered by London heat escalator

mean temp 23.5
Total days where the mean temp was 23.5C or higher

There are 2.5 times as many hot days during summer in London as there were 100 years ago – that’s the result I have found while looking at data for Greenwich going back to 1851.

Very hot conditions, where the mean daily temperature is 23.5°C or higher, as defined by the Met Office’s Heat-Health Watch System, have been achieved in this area on 199 days since 1852.

The Met Office, and other meteorological agencies, use 30-year averages to smooth any spikes of hot and cold years – so the result, in my view, is quite remarkable – even though it is just one dataset.

Looking at the data overall it can be seen that while average maxima has decreased by 1.6°C since 1881-1910, minima has increased by 2.1°C.

new max min 30 yr
30-year hot day max / min average since 1881

The decreased maxima is possibly explained by the fact that the sun shines, on average, just over an hour less than it did a century ago. The reason for this could be because of increased air pollution and aircraft contrails?

The increased minima, on the other hand, could be being caused by the fact that vast tracts of suburban front and back gardens are now paved over – along with the loss of the shade of many trees. This, and increased road and house building, acts as a huge radiator, keeping nights warmer than they would have been a century ago.

Experts would question the hybrid nature of my dataset, even though my observing sites are very close to those of Greenwich. It is a shame that many of the first climatological stations, such as Camden Square set up in the early 19th century by George Symons, are not still around as they would now offer an unquestionable insight into just how much London’s climate has warmed.

Sunshine hours have decreased since the 19th century
Sunshine hours have decreased since the 19th century

You could argue that there is no doubt that the warming in these data is man made though, perhaps, paved gardens keeping summer nights warmer would be a lot easier and cheaper to solve than fulfilling the carbon capture policies of many of the world’s governments. But that is an argument for another post.

For now, as the capital’s population continues to increase, it is vitally important that planners get the next generation of property developments right to keep the population cool when a heatwave strikes. Extreme heat severely affects public health, not least the suicide rate – a study has shown that above 18°C, each 1°C increase in mean temperature has associated with a 3.8 and 5.0% rise in suicide and violent suicide respectively. Planners cannot just leave it to energy-hungry air conditioning to bring relief – developments should incorporate plenty of shade and natural cooling in their designs to help counteract the health impacts of future heatwaves.

* There were hot spells before the period in this post but I have excluded these: Luke Howard’s maxima observations from Plaistow, Stratford and Tottenham were taken under non-standard conditions and may be on the high side.

** I have focused my investigation on data recorded at the Royal Observatory, Greenwich. For some reason the data during a couple of years in the 1950s was incomplete – to fill in these gaps I used official data gathered at Kew. The data is completed up to the present day using my own observations taken since 1988.