Don’t think for one second that the heatwave of the last week can compare to the one that occurred in the last week of June and the first week of July 1976, because it doesn’t. Forget all the bollocks about six days with maximum temperatures of 34°C or above at St James Park, it’s true it happened, but in my opinion the statistic was manufactured more to create a headline for the global heating debate, as well as a smokescreen to deter any direct comparisons between 2020 and heatwaves in summers past.
The only way to do a fair and valid comparison between the two is to use the same UKMO heatwave definition with 2020 and 1976, and that’s what I have done. The results are a maximum of 17 days (at Waddington Lincolnshire on the 9th of July) of heatwave conditions across England compared to a maximum 8* days in 2020. The heatwave of 1976 was much more extensive than that of August 2020, and at times extended into heatwave spells in Scotland, Wales and Northern Ireland.
As regards the Met Office heatwave definition itself, I think it’s far from perfect and should be based on anomalies calculated from the same 30 year long term average rather than any fixed threshold value depending on your distance from central London.
*As the current heatwave is still ongoing I have added a day to cater for the 13th of August. It’s possible it may extend for a day more than this but I’ll update this if necessary.
Here are two thermographs for 1976 and 2020 to help illustrate my conclusion. You may notice that the 1976 extremes are all rounded to the nearest degree. This is due to the old SYNOP code not allowing tenths of degrees in temperature back then. It’s also important to realise many RAF stations in the network closed at weekends and didn’t have the benefit of 24 hour 365 day AWS to fill in missing hourly observations. Finally there were not as many stations in and around London including St James Park!
As soon as I noticed that 1976 was 44 years ago, I immediately thought about the eleven year solar cycle, which like 2020 must have been just coming out of a minimum back then. It’s probably just coincidental that the two heatwaves occurred in the year of a solar minimum but perhaps there is some kind of loose connection.