With the summer season in the UK now over, it is instructive to place the hot, dry summer we have experienced into the longest possible historical perspective. How hot was the summer of 2022 as a whole? How dry was it? And how intense was the heat at different times over the summer?
To answer these questions, I make use of two of the longest high quality multi-century climatic time series from anywhere in the world: the monthly Central England Temperature (CET) series dating back to 1659 and the monthly England and Wales Precipitation (EWP) series dating back to 1766. (I also use the daily max and min CET series dating back to 1878).
The CET series was originally compiled in 1953 (and then updated in 1974) by the late Professor Gordon Manley. Manley’s data were checked for homogeneity and then updated to 1991 by David Parker, Tim Legg and Chris Folland in 1992.
The EWP series has been worked on over the years by different climatologists, but the work of J Glasspole and F J Nicholas in the 1920s and 1930s should particularly be recognized, as too the rigorous statistical work in 1984 of Tom Wigley, Phil Jones and Janice Lough of the Climatic Research Unit at the University of East Anglia.
Both series are now routinely updated and maintained by the National Climate Information Centre, hosted by the Met Office Hadley Centre for Climate Change in Exeter and can be accessed accordingly: the EWP series and the CET series.
I use these series for my analysis because they allow for the longest historical comparison, 364 years in the case of temperature and 257 years in the case of rainfall. There are of course larger areas (e.g. the whole of the UK) or smaller ones (e.g. southeast England) which could be used for comparative analysis, but they do not provide anything like the historical length offered by CET and EWP. For climate change studies it is instructive to work with the longest records.
The region of the UK for which the CET series is representative is a roughly triangular area centred in the west midlands and enclosed by Lancashire, London and Bristol. The long-term temperature variations of this region have been shown to be highly correlated over the historical period with the temperature of the whole of England and Wales (see for example ‘The Climates of the British Isles’, which I edited in 1997 with Elaine Barrow). The EWP series, as the name implies, describes aggregate rainfall across the whole of England and Wales.
How Hot Was It?
First of all, let’s look at the summer season as a whole, namely the months June, July, August (or JJA for short). Table 1 shows that for the region representative of Central England, summer 2022 was the 7th hottest in 364 years of measurements with a mean temperature of 17.2°C. In recent years, 2018 summer was marginally hotter, but the standout summer remains 1976 at 17.8°C. 1995 was the 3rd hottest in the CET series at 17.4°C.
Table 1: The 10 hottest summers (JJA) in the CET series – 1659-2022 – by monthly mean temperature. Daily maximum temperatures only available since 1878.
|Temp (°C)||Year||Days above 25°C||Days above 30°C||Maximum Daily Temp||Max spell length above 25°C (days)||Max spell length above 30°C (days)|
If we look at specific months (Table 2) then, again, no records were broken in 2022. With a mean temperature of 18.7°C, August 2022 was the 7th equal warmest month, but a full degree C behind the record heat of July 2006 (19.7°C) and half a degree behind the record August of 1995 (19.2°C).
Why then was there so much attention paid in the media to the record temperatures of summer 2022? This reason is clear if we look at the individual daily maximum temperatures. (Note: daily max and min temperature in the CET series only commence in 1878, so we have just 145 years of context to work with). We see that the CET daily maximum of 37.3°C on 19th July 2022 broke the CET daily record of 34.8°C, set in fact the day before. Both these days exceeded the previous daily record of 34.1°C on 25th July 2019. During the very hot summer of 1976, the hottest individual day reached only 33.2°C in the daily CET series.
Table 2: The 10 hottest individual months in the CET series – 1659-2022 – by monthly mean temperature. Daily maximum temperatures only available since 1878.
|Temp (°C)||Month||Year||Days above 25°C||Days above 30°C||Maximum Daily Temp||Max Spell Length Above 25°C (days)||Max Spell Length Above 30°C (days)|
So, in summary …. Since the days of Oliver Cromwell in the middle of the 17th century, Central England has experienced several summers hotter than 2022. During this long period, it has also experienced several hotter months than either July or August 2022. But in the 145 years for which we have comparable daily data, since 1878 when Gilbert and Sullivan’s comic opera HMS Pinafore debuted in London, Central England has not experienced any individual days hotter than those of the 18th and 19th July 2022.
Finally, it is worth noting that it was the intensity of the heatwave in July 2022, not is duration, that was exceptional (Table 2). If we use the threshold of a daily CET maximum temperature of 25°C as the definition of a ‘hot day’ and 30°C as the definition of a ‘very hot day’, and then look at spell lengths of hot and very hot weather, the summer of 1976 remains the most extreme. 1976 had a spell of 7 very hot days, compared to a spell of just 4 days in 2022 (from 11th to 14th August), and 1976 had a spell of 16 hot days compared to a spell of just 8 days in 2022 (8th to 15th August).
How Dry Was It?
Our perceptions of hot summers are also influenced by rainfall. We are likely to remember a hot dry summer more readily than a hot wet one. So, maybe if we look at the EWP rainfall series, we will find that the overall summer of 2022, or the months of July and August 2022, will stand out.
In fact, using the EWP series we see that this is not the case.
(Note: if we looked at smaller regions such as East Anglia, or southeast England we would get different results, but I am interested in the larger synoptic scales at which the climate of the British Isles operates, and the affordance these two series give us for multi-century historical comparison).
In the EWP series, the summer of 2022 yielded 110mm, the 6th driest summer in 257 years since the reign of King George III. This was quite a bit more rain than the paltry 67mm of 1995 or the 74mm of 1976.
What about the individual summer months? June 2022 had 50.3mm and, although on the dry side, this was far from exceptional. August 2022 with 37.1mm was the 16th driest August in the EWP series, so it made the driest 10 percent of years, but not the driest 5percent. 1995 saw the driest August, with just 9.1mm. July 2022 was more exceptionally dry, but even here 22.5mm meant that it was only the 6th driest in the EWP series. The two driest Julys both occurred in the nineteenth century, with just 8.2 and 9.1mm respectively.
In the context of the last few centuries, the summer of 2022 in Central England/England & Wales was undoubtedly hot and dry. But it was not exceptionally so. The summers of 1976 and 1995, for example, were both substantially hotter and drier overall than 2022 and had longer spells of hot weather. None of the individual summer months of 2022 broke either the mean temperature or accumulated rainfall records for being the hottest or the driest in over 350 years and 250 years respectively. The closest it came to beating any monthly records was July 2022 being the 6th driest month and August 2022 being the equal 7th hottest month.
So, what was exceptional about summer 2022?
It was the two individual days of 18th and 19th July. In the 145 years of CET daily maximum temperature data, since 1878, these two days were the second hottest and the hottest experienced in central England. But even then, there have been quite a number of summers in Central England with longer spells of hot or very hot weather than occurred in 2022.
None of this is to deny that British climate is getting warmer, as too of course is the average global temperature. Human perturbations to the Earth System, largely through accumulations of greenhouse gases in the atmosphere, are the primary reason for this warming. But what long climatic time series show us is that extremes of temperature and rainfall have always occurred.
A Final Word
How much warmer are central England summers today than those remembered from their childhood by the oldest Britons living today?
I compared the average summer temperature of the last 20 years (2003-2022) with that of the 20 years from 1921-1940, which people now in their 90s or 100s would still remember. Recent summers are on average just over 0.7°C warmer, 16.14°C vs 15.4°C.
If we imagine English summers from further back in history, then our own recent experience of summers is about 0.9°C warmer than our great, great, great grandparents who lived through the Napoleonic Wars (1796-1815) and a full 1°C warmer than our great grandparents who were alive in the last decades of Queen Victoria’s reign (1881-1900).
Indeed, one wonders were contemporary Britons asked to endure Late Victorian summers – with temperatures more than 1°C cooler than recent decades — how many complaints there would be about the cool English summer weather.
Mike Hulme, Cambridge, 1 September 2022