High Summer 2022: Second Hottest since at least 1659

It puzzles me slightly that there is so much focus on the “meteorological summer” – June, July and August. June is usually cooler than the two later months and September can be hotter. So, if we’re going to compare how generally hot summers have been, a more logical period of whole months is June through September.

We might also look at other periods. I compared various periods for all years over the Central England Temperature record in 2018 and reported that that year was the hottest on record for the periods April through July and May through July, although as can be seem from yesterday’s post the meteorological summer in 2018 wasn’t freakishly hot. As I explained at the time, summer 2018 didn’t “break all records” because temperatures dropped significantly around 8th August.

If we want an alternative to the meteorological summer, though, the most useful periods might be the “whole summer”, June through September, or, for sheer sustained heat, “high summer”, July and August.

Strictly speaking the hottest period of the year is typically late June to late August (Fig 1), but I’m dealing in whole months here.

Fig 1 Daily mean temperature ranges in the CET record, Met Office.

I’ll look at the “whole summer” once the data is available for 2022, but here’s my chart for “high summer”:

Fig 2 CET mean “high summer” temperatures, graph by Tim Joslin from Met Office data (legacy data used except for May-Aug 2022, which is thus provisional data)

What stands out for me is that the high summers from 2018 through 2022 have been on average a full 0.25C hotter than those in any other 5 year period (1995-9) and over 1.5C hotter than those from 2007-11, which seems quite a turnabout over such a short period, though not unprecedented. For example, Tambora and another unidentified(!) eruption cooled the global climate in the 181os, producing the “year without a summer” in 1816.

Despite several heatwaves, one of them the all-time hottest by some margin, high summer 2022 was “only” the second-hottest on record, after 1995. Of course, there were some hot days in 1995, notably 31st July and 1st, 2nd, 11th and 21st August:

Fig 3, To 30 highest UK average maximum temperatures from Met Office

I love that chart from the Met Office. If it looks familiar that’s because I used it in a previous post.

I’ve previously speculated on what daily high temperature could feasibly be reached in the UK. In the same spirit it seems to make sense to compare summers with the years around them. Was summer 2022 freakish in a globally warmed world? If not, then it could presumably get even hotter.

Fig 4 High summer mean CET (top) and deviation (lower) of mean CET from 21 year mean centred on the year, 1859-2022, graph by Tim Joslin from Met Office data (legacy data used except for May-Aug 2022, which is thus provisional)

It turns out that, although high summer 2022 was notable, on average it was “only” (provisionally) 1.79C hotter than the mean for the most recent 21 years, whereas 1911 was 2.73C hotter than the mean for the years 1901 through 1921. Several other high summers were more “freakish” than 2022, though none more than 1995 at 2.37C hotter than contemporary summers.

It seems reasonable to suppose that another high summer could be as freakish as 1911. In a globally warmed world such a summer would be nearly 1C hotter, on average than 2022. That is, we could have an extra 60 degree days of heat over July and August.

This extra heat might not be distributed evenly. Instead of every day and night being nearly 1C hotter, perhaps 20 days (and nights) would be 3C hotter or 12 days (and nights) 5C hotter. 5C hotter would mean peak temperatures of, for example, 35C rather than 30C or 40C rather than 35C.

Or to put it another way, an extra 5C on the mean daily temperature would move a day from not even being amongst the 30 hottest (Fig 3), to the very hottest.

A longer period of extreme temperature than in 2022 would be more serious, because some of the effects are no doubt cumulative, such as exhaustion caused by “tropical nights”.