2024 in the CET: Mild, Warm and Oh, June

Whereas 2023 was most notable for a record hot September in the Central England Temperature (CET) record and a unique Doughnut Summer when June and September were the hottest months, 2024 began with record warmth over January through May and for the meteorological Spring (March through May). We had the second warmest February and May on record. This has abruptly changed in June, with a distinct possibility of the June CET being below that for May for only the third time since the CET record began in 1659.

In 2023 June and September were the joint warmest months in the year, giving us a unique Doughnut Summer:

Fig 1 Mean CET 2023, from the Met Office

Note that every month in 2023 was warmer than the mean for the period 1961-90. I’ll be coming back to this point later.

We had the warmest September on record:

And the year as a whole was the second warmest on record, after 2022:

Fig 3 Annual mean CET temperatures, graph by the author, from Met Office data

How could 2024 possibly outdo 2023?

Well, my interest was piqued by a recent Met Office press release which began:

“The UK had its warmest May and meteorological spring on record according to provisional Met Office figures in what was also a wet and dull season for many.

May 2024’s average mean temperature of 13.1°C for the UK beat 2008’s previous record figure of 12.1°C in a series which dates back to 1884.

The month’s mean temperature has been influenced particularly by above average temperatures in the northern half of the UK, with Scotland’s May mean temperature of 12.3°C beating 2018’s previous record by 1.6°C. England and Northern Ireland also set a mean temperature record for the month of May, while Wales equalled its figure from 2008.”

That’s some beat for May, but (as I’ve asked before in similar circumstances) are we suffering from Premier League syndrome (whereby all English football records supposedly begin in 1992-3)? What if we look back further and consult the Central England Temperature (CET) record?:

Fig 4 May mean CET temperatures, graph by the author, from Met Office data

Only silver for May 2024. What the hell happened in 1833?

But what about Spring as a whole?:

Fig 5 Spring mean CET temperatures, graph by the author, from Met Office data

Now we’re getting somewhere! Whilst some freak monthly mean temperatures from the past have not been exceeded recently, the global warming signal is much more apparent over longer periods. Spring 2024 is indeed the warmest on record, with the 3 warmest (2011, 2017 and 2024) all occurring in the last 15 years. With 6 springs so far in the first quarter of this century exceeding a CET mean temperature of 10C compared to only one in the whole of each of the 19th and 20th centuries (and none before that), such an event has become approximately 24 times more likely!

We see a similar picture if we look at the first 5 months of 2024 as a whole. February, like May, was “only” the second warmest on record, not quite equalling 1779:

Fig 6 Feb mean CET temperatures, graph by the author, from Met Office data

But January through May were the warmest:

Fig 7 Jan-May mean CET temperatures, graph by the author, from Met Office data

Until I created the graph in Fig 7 I was already thinking it was time to bet on 2024 smashing the annual CET record. I was only looking only at the anomaly for the year to date:

Fig 8 Mean CET 2024, from the Met Office

The anomaly to May of 2.37C in Fig 8 far exceeds the anomaly of 1.68C for the whole of the warmest year, 2022.

But Fig 7 shows that January through May 2024 has been only a bit warmer than in 2007 and, whilst it was a warm year (every year is a warm year these days!), 2007 didn’t shatter records. Summer that year averaged only 15.3C, which is somewhat below the 21st century average – see my discussion of last year’s Doughnut Summer.

So maybe it’s just commentator’s curse that (as shown in Fig 8), June 2024 has started off so unusually cool, especially as June seems to be the month least affected by global warming, as I also discussed last year.

In fact, there’s a possibility that June this year could be cooler than May, which has only happened twice before – in 1749 when June was exceptionally cool with a mean CET of 11.9C and in 1833 when we had that freakishly warm May with a CET mean of 15.1C.

Watch this space because I’ll be keeping a close eye on the June CET.

Most months these days – all of them in 2023, as I noted in relation to Fig 1 – are warmer than the mean CET for 1961-90. Months as anomalously cool as June 2024 has been so far (-1.4C compared to the 1961-90 baseline) are rarer still, so it’ll be particularly interesting to see what happens in the rest of the month (nothing very hot is forecast for the next 10 days or so).

I wonder if erratic temperatures such as the Doughnut Summer of 2023 are telling us something about global warming. Maybe weather patterns are being disturbed by warming and, in addition, maybe warming is being spread out in time somehow. After all, with global warming, more of the heat that affects us is due to extra energy retained by the atmosphere than to incident radiation. You wouldn’t expect this to be a massive effect though, given the amount of heat already retained by the atmosphere, but maybe it’s enough to create some of these new weather records. Or maybe temperatures have just always been this erratic and there are just a lot of records to be broken! I’ll mull this over.