Are Heatwaves Getting Worse? – Watts Up With That?

From NOT A LOT OF PEOPLE KNOW THAT

By Paul Homewood

As promised, I am returning to the Met Office’s State of the UK Climate Report:

https://www.metoffice.gov.uk/about-us/news-and-media/media-centre/weather-and-climate-news/2024/temperature-extremes-and-records-most-affected-by-uks-changing-climate

The press release made this claim:

Climate change is causing a dramatic increase in the frequency of temperature extremes and number of temperature records the UK experiences.

New analysis of observations shows that extremes of temperature in the UK are most affected by human induced climate change. This means the UK is seeing, on average, more frequent periods of hot weather, bringing challenges for infrastructure, health and wellbeing.

Using an example of 28°C, the frequency of days reaching this threshold has increased nearly everywhere across the UK. Where in the 1961-1990 averaging period only London and Hampshire recorded six or more days over 28°C, by the latest decade (2014-2023) this has spread across much of England and Wales, with frequencies in the south east increasing to over 12 days each year in many counties.

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Their methodology of counting days when a temperature of 28C has been recorded somewhere has no statistical significance whatsoever, because the sites are changing all the time. We know that they have introduced dozens of poorly sited weather stations in recent years, which regularly feature as daily record highs, and are often two or three degrees higher than nearby sites. We also know how UHI has boosted temperature readings in recent years.

For the methodology to be reliable, it needs to be based on a fixed set of stations. I have therefore analysed temperatures at Radcliffe Observatory in Oxford. The chart below counts the number of days when temperatures were over 28C:

https://climexp.knmi.nl/data/xgdcnUK000056225.dat

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On the face of it, I see little of concern.

The summer of 2018 sticks out with 23 days, the same number as in 1911 and 1995. There were 21 days in 1976 as well.

In most summers we may get about five days or so of hot weather; why should this be a cause of alarm?

Moreover Oxford is a hotter place than it was a century ago because of UHI. I can’t claim any scientific basis for what follows, but if we count the number of days >27C for the years up to 1970, and then add on the number of days >28C since 1970, we get this:

This assumes, of course, that Oxford’s temperatures since 1970 have been increased by 1C because of UHI. This is an extremely simplistic assumption!! But I don’t think it is an unreasonable one in principle. My guess would be that the UHI effect since 1911 is probably a lot more than 1C.

The graph shows that there is no trend in hot days, certainly not since the mid 19thC.

1911 appears at the top of the list, bearing out the news reports at the time which graphically described the severity of the summer long heatwave, not only in Britain, but also in France.

But other years in years past also stand out, such as 1826 and 1868.

But even if there is no UHI in Oxford, which would be a ridiculous claim, the worst that is happening is that we now get days of 28C, which 150 years ago might have been 27C instead.

And it is certainly not bringing challenges for infrastructure, health and wellbeing.