The Urban Heat Island Effect On British Summers
As I wrote a couple of days ago, there is a big discrepancy between the Met Office’s HadUK dataset, which shows this summer as being 0.4C hotter than 1976, and its own Central England Temperature series, which shows the two summers as tied
One of the major differences between the two datasets is that CET is based on rural stations, unlike HadUK.
It is therefore worth looking at the Min and Max temperatures:
Source: https://www.metoffice.gov.uk/hadobs/hadcet/data/meantemp_ranked_seasonal.txt
(Look at some of the older dates. For instance, winter 1796 was warmer than winter 2020. Winter 1686 was warmer than winter 1975. Spring 1893 was warmer than spring 2014. Summer 1826 was warmer than summer 2018. Summer 1846 was warmer than summer 1983 – Ed)
Both datasets show 1976 as being hotter in terms of daily max temperatures, though the gap is smaller on HadUK.
But the biggest difference between the two sets is on minimum temperatures, which accounts for about two-thirds of the difference in mean temperatures.
This begs the question of how much UHI has contributed to HadUK temperatures this summer. We know that many of the sites used by the Met Office are urban, that the UHI effect has increased in recent decades and that the Met Office do not adjust for it.
(Actually the Met Office claim they do adjust for the UHIE, by removing 0.2C from readings in urban areas. This is ridiculous for two reasons. First, they chose virtually the smallest amount they could get away with, and second, most of their weather stations are located in places where there are uncertainties of up to 5C, which makes their reduction of 0.2C virtually meaningless – Ed)
While we all have our theories, it is plainly not our job to prove or disprove anything. The massive discrepancy between CET and HadUK must now be explained by the Met Office themselves.
It is, of course, a much wider issue than a single comparison with 1976. The whole HadUK dataset is contaminated with spurious UHI warming, which cannot simply be waved away.
Finally, have a look at this little puzzler, which compares CET with Heathrow:
What I want to draw your attention to is the relative figures for Minimum temperatures. The comparison with 1976 is virtually identical between CET and Heathrow, both about 0.7C lower in 1976.
Heathrow is 0.74C warmer this summer, which is much less than the 1.49C listed for HadUK.
We regularly rightly call out the heat spikes during the day at Heathrow, but at night the heat there quickly dissipates, unlike in urban areas.
This is strong evidence that HadUK minimum temperatures are inflated by UHI effect.
See more here notalotofpeopleknowthat
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