Record Heat in London

Heat Wave in a London Context

Today the UK experienced its hottest day on record, with temperature reaching 104.3^oF (40.2^oC). Considering that British temperature records go back to the 1600s, that's a pretty long record to beat. But how does this week's furnace-like weather compare to a normal summer day in London?

To compare, I looked at daily high and low temperatures from July and August, 1990-2015, from the Hampstead weather station (GHCND: UKE00105915) in London. I plotted what percentage of the days had highs in different three-degree wide temperature bins (59-61 F, 62-64 F, etc.), shown in figure at right. The red bars show that the most common temperatures weraround 70^oF.

This week's temperatures are over 30^o hotter than a "typical" day. If Londoners were prone to freak out, this would be a good time to do so.

Even aside from breaking a 300+ year record, any temperature above the 80s is extremely rare in London. The percentage of days which get that hot are so small they are hard to see in the graph, so I added light pink bars in the background that are magnified by a factor of ten. Only 1.5% of summer days are in the 86-88^o range, .4% in the 89-91^o range, and less than .3% in the 92-94^o range.

This week London is over ten degrees hotter than these extreme temperatures.

Daily low temperatures show a similar, if less extreme, pattern. Typical minimum temperatures are in the mid 50's, with vanishingly small number of days with minima above 68^oF (2nd figure at right). I didn't see any specific figures for London, but parts of Britain did not go below 77^oF (25^oC) , over 20^oF warmer than typical.

Capital Comparisons

While this week's heat wave brough nearly unheard-of temperatures to Great Britain's capital city, the United State's capital and Northern Virginia are more used to scorching days. A typical daily high in the DC area is around 90^o, with temperatures of 104 or higher about 1% of the time (top panel at left). Similarly, daily lows in the mid 70s are comparable to London's extreme night time temperature this week (bottom panel at left).

If global heating increases the temperature by another few degrees F, London's generally pleasant summer weather will be punctuated by more hot days reminiscent of Washington's summer. This will create the need for massive efforts to adapt, such as installing air conditioning and hardening infrastructure for hot days. On the other hand, Washington DC already has many days where it is barely tolerable to work outside; the same temperature rise that would make London summers less pleasant would add a week or more per summer of temperatures around 100^o or higher.