What is an extreme heat warning and how is this different to ones we've seen before?

Extreme heat warnings are a new thing for the UK with the first being issued in 2021 by the Met Office.

It was added to the warning service last year as the UK climate is changing at an alarming rate due to man made greenhouse gas emission, such as Carbon Dioxide (CO2), being emitted into our atmosphere.

But now the first ever red warning for extreme heat has been issued by the Met Office, covering much of England.

England and Wales in particular have been experiencing high temperatures in recent days, with many areas hitting heatwave criteria and a Red Extreme Heat warning is in place from Monday, July 18.  

What is an extreme heat warning?

When the temperatures soar, hot weather places a strain on the body in particular the lungs and heart, hence the majority of serious illness and deaths caused by heat are respiratory or cardiovascular.

Statistically, heatwaves are more dangerous and produce more deaths than cold snaps, like the "Beast from the East" in 2018. Often it's not the temperature during the day, but overnight when your body can't cool down and therefore can't recover.

Those most likely at risk from extreme heat are:

  • the elderly

  • young children

  • and those with pre-existing medical conditions

However, when prolonged extremely high temperatures occur, even the fit and healthy are at risk of illness and death and not just those limited to the most vulnerable category.

Extremely high temperatures also put pressure on our infrastructure such as water and energy utilities, as well as the travel network - melting roads, buckling railways as well as increased demand on the health and fire services.

The Met Office only issue an Extreme Heat warnings when the likelihood and impacts are expected to effect a large number of the population and depending on the severity of the event.

Why has an extreme heat warning been issued?

Met Office meteorologists have issued the first ever red warning for extreme heat across much of England, with daytime temperatures expected to reach 40C in London and between 34C and 37C within the warning zone.

The emphasis is the widespread very hot weather and associated impacts likely to be seen through Sunday and at the start of next week.

Temperature Extremes expected for the UK Credit: ITV Weather

What is the highest temperature ever recorded in the UK?

The highest temperature recorded in the UK was 38.7°C, on the 25th July 2019 at Cambridge Botanic Garden. During this same event, a number of places in Europe broke national records including the Netherlands, Germany and Belgium.

Top 5 Hottest Days in the UK

1. 38.7ºC - Cambridge Botanic Garden - 25th July 20192. 38.5ºC - Faversham, Kent - 10th August 20033. 37.8ºC - London Heathrow - 31st July 20204. 37.1ºC - Cheltenham, Gloucestershire - 3rd August 19905. 36.7ºC - London Heathrow - 1st July 2015=. 36.7ºC - Raunds Northamptonshire - 9th August 1911

If we look back in time, the 6th hottest day on record occurred in 1911. The media describe the heat as unbearable, insufferable and oppressive. Roads melted, wildfires burned and many places of work were closed to avoid the heat.

The record in the UK lasted for 80 years until 1990 when the temperature was exceeded. Since then, it's been reached or exceeded four times 2003, 2015, 2019 and 2020. Further evidence that our climate is warming at an alarming rate.

What about the heatwave of 1976?

If we compare the highest temperature ever recorded in the UK with the heatwave of 1976, the temperature peaked at 35.6ºC in Southampton on the 28th June. This made it the hottest June day on record, although this doesn't appear in the UK top 5 hottest days.

What was remarkable in 1976 was the longevity of the heat. Heathrow recorded 16 consecutive days with temperatures above 30ºC from June 23 to July 8. Meanwhile five days during this time saw the temperature exceed 35ºC.

Looking at when temperatures have exceeded 35°C here in the UK since 1976 we can see two thirds have occurred since the turn of the century Credit: ITV Weather

What is different about this extreme heat warning?

In the past the UK has regularly seen warm pushes of Tropical Continental air from Europe and north Africa. This is often when we experience our highest temperatures on record. However this extreme heat is coming directly after a hot and dry spell we're already seeing across the UK.

By the time the red heat warning comes into force on Monday, July 18, temperatures in large swathes of the UK will have been in the mid to upper twenties for ten days.

And unlike other hot spells and heatwaves, there doesn't look like there will be a sudden dramatic drop in temperature as we move through next week. Yes it will become less oppressive, but as climatology goes, it will still be warm.