global warming | Wanstead Meteo

It is no surprise that London’s heatwaves are getting hotter but by what rate are they increasing?

Using a list of hot spells made nine years ago I set out to find how the 30-year trends have moved through the decades since 1852.

The mean of these hot spells has increased from 24.2C in 1851-1880 to 24.9 in 1991-2020, an increase of 0.7C.

Maxima during these spells, on the other hand, has decreased from 32.6C to 31.8C. It should be noted that the spell that produced this area’s hottest ever daily maximum, 40.1C on July 19th 2022, was a 2-day affair that didn’t qualify for the list.

It is the minima that produces the most notable results with average low temperatures increasing over 2C from 15.9C to 18C! The urban heat island in full effect although the estate where a large proportion of these stats are gathered has changed little since it was built in the early 1900s.

Rainfall during these hottest heatwaves is cyclical, in keeping with daily rainfall patterns observed over the same period.

Average sunshine in these heatwaves has shown a slight decline. It is no coincidence that maxima was at its highest during 1911-1950 when there was most sun. Increased cloud cover overall would take the edge off maxima while making the nights warmer.

Since notably cold weather struck at the end of February I’ve lost count of the number of times I’ve heard this phrase uttered by the public and some sections of the press.

The ‘Beast from the East’ (versions 1.0 and 2.0) really captured the imagination in an age where everything has to have a label slapped on it; any message that these cold spells are ‘weather’ and not ‘climate’ seems to get lost.

Both spells, indeed the general pattern of our late winter weather, were driven by the stratospheric sudden warming event that lead to a split polar vortex in February – leading to a very cold end to the month and a mean temperature anomaly of -2.5C, the greatest monthly anomaly since March 2013.

To put it into perspective, however, it was nothing like some of the anomalies that occurred in the early 19th century: January 1814, for example, saw a monthly anomaly of -8.2C and coincided with the last occasion a frost fair was held on the Thames. Januaries back then were generally very cold, the 1801-1831 average monthly mean was -3C, that’s 8C colder than the most recent 1981-2010 average!

So climate now is much warmer but that is not to say that anomalously cold months can’t happen. February 1986 saw an anomaly of -5.6C, the 13th= greatest cold anomaly in my local dataset going back to 1797.

The cold December of 2010 recorded an anomaly of -4.2C, 76th= greatest cold anomaly, while anomalies of -4.1C recorded in January 1979 and March 2013 were 77th=.

With the warming climate it is no surprise that most warm months happened very recently. The balmy month of December 2015 saw a positive anomaly of 5.4C.

The ‘Beast from the East 2.0’ was caused by a narrow tongue of extremely cold air from Russia scoring a direct hit on the UK. The odds of this happening must have been low but it is an example of how, when the synoptics of the atmosphere line up perfectly, anything is possible.

And it is an example how even in a warming climate the UK can still be subject to anomalous cold and warmth at any time of the year.

As the author Mark Twain reportedly once said: “The climate is what you expect; the weather is what you get.”