The Forgotten Heatwave of 2020. Plus Heatwave Recap and Summary.

Well, that was unpleasant. In fact, it still is. The block I live in seems to have retained heat from the recent heatwave and I’m struggling (at midday on 16th August), even with the balcony door and most of the windows wide open, to get the temperature below 25C, compared to 20C and intermittent heavy rain (but little wind) outside. I don’t think it was below 27C in the bedroom all night, that being the highest temperature the Galileo thermometer in there is capable of recording.

We’ve just had 4 consecutive days when the maximum temperature has exceeded 34C somewhere in the south-east (and at least close to that here in London). But we’ve broken either no daily records or one, depending on the source.

Why? In large part, because two of the records were already broken in 2020.

The Met Office reported that it hit 34.2C in Wigginholt on 11th August 2022, which would have been the daily record, just beating 34.1C at Hillington in 1884. Except that on 11th August 2020 it reached 36.2C at Charlwood, according to the TORRO website. (My contemporaneous note in the margin of my trusty copy of The Wrong Kind of Snow was Heathrow at 35.7C, but that is an automatic station, so the data may have come in before the Charlwood figure and I may have missed the update).

Wigginholt hit 34.5C on 12th August this year, beating 33.9C at Epsom in 1911, but not 35.7C at Charlwood (or 35.4C at Heathrow) in 2020.

34.9C at Charlwood in 2022 comfortably beat 33.9C at Seaford in 1911, but not the suspect 35.6C at Salisbury-Wilton House that year. So what shall we say? Half a daily record?

And finally, 34.1C at Charlwood on 14th August 2022 didn’t even beat 35C in Cambridge on the same date in 1876.

Compared to this year, the 2020 heatwave from 7th-12th August was much more notable, a least in terms of peak temperatures, which exceeded 34C on each of those 6 days, breaking daily records on 7th, 8th, 11th and 12th. Wanstead Meteo suggests it was the 2nd most severe heatwave on record, after 6th-13th August 2003. One slight disclaimer: @bbcweather points out that there were more continuous days in 2022 when a temperature over 28C was recorded (somewhere in the UK*, presumably, rather than in a particular location) – 9 days, a 15-year record. [*On reflection the BBC Weather tweet must refer to continuous days with a peak above 28C somewhere in SE England, not least because 28C was exceeded somewhere in UK every day from 6th-25th July 2013. Also, the heatwave threshold is less than 28C in other parts of the UK].

Why haven’t we discussed the 2020 heatwave rather more? I guess because the Covid-19 pandemic was dominating the news at the time, even though the government was pretending it was over with its moronic Eat Out to Help Out Scheme (which I would have thought is plenty reason enough for Rishi Sunak not to become PM, or indeed continue to hold high office). The 2022 August heatwave seems to have received much more media attention.

And, as I recollect, at least the duration of the 2020 heatwave wasn’t well forecast. I remember thinking that had I known how long it would last I would have bought a standalone air-conditioning unit, which I eventually did this year, just in time to survive 40C on Hot Tuesday 2.0. The noisy machine successfully keeps the temperature down in one room, though I’m thinking of putting silver foil on the windows next time 40C is forecast!

What is this extreme weather telling us?

Heatwaves Disproportionately Hotter due to Global Warming

We’ve actually had 3 hot weather episodes this summer. During the first of these, which peaked with 32.7C on 17th June, I noted in Heatwave Horror how global warming (GW) must magnify temperatures when hot air loses less heat along the way as it moves to higher latitudes.

Forecasting Problems

Our preparedness for heatwaves might be improved by clear understanding of the risks. In Not Another Heatwave last week I noted that, to my amazement, the climate models don’t predict the observed increased intensity (due to GW) of heatwaves. This is a serious problem that merits further investigation. Watch this space.

Weather Patterns and La Nina

In UK Heatwaves: Could They Get Even Hotter? I suggested that, as well as increasing GW, recent decades have seen a reduction, especially in Europe, in global cooling caused by aerosol pollution. I see, for example, that the longest period between any of Wanstead Meteo’s top 20 heatwaves is the 24 years from 1952 to 1976. I know this proves nothing, but it amuses me to point it out!

On top of GW, we could be in a decade to decades-long period of more likelihood of hot, dry summers, as has occurred many times in the past. More on this another time.

But, as I pointed out in Not Another Heatwave! the planet is experiencing an unusually long period of La Nina conditions. It’s well established that this produces a distinctive global pattern of weather, such as flooding in Australia and drought in US and Africa. It certainly seems within the bounds of possibility that La Nina could also increase the likelihood of drought and heat (as well as dry winter weather) in Europe. A triple-dip La Nina continues to be forecast. I wonder what this portends for 2023.

Hotter Heatwaves

Obviously GW is increasing year on year (and global cooling in Europe decreasing, perhaps interrupted by recommisioning of coal-fired power stations due to the reduced gas supply from Russia), but only fairly slowly. Nevertheless, it seems even hotter temperatures could be possible in the UK in future years, as I suggested in UK Heatwaves: Could They Get Even Hotter?. In 2022 we hit 40.3C on 19th July. Similar conditions 2-3 weeks later in the year would likely be hotter, and no drought in the UK had become established by 19th July (it has now!), which would also have likely increased peak temperatures. Besides, some weather model runs predicted temperatures of up to 43C, suggesting that might at least be possible.

And if I was to guess another year in the 2020s when 40C might again be exceeded in the UK, which would I choose?

2023.

Modification history

17/8/22: Added Table 1.

18/8/22: Added note clarifying meaning of BBC Weather’s “longest heatwave in 15 years” tweet.