UK Heatwaves and Climate Change

The UK is experiencing a prolonged heatwave which could exceed that of the exceptional 1976 summer. It is an “Endless Summer” – like that surf movie. So is climate change to blame?

Climate Change is happening but what that really means is that whenever a heat wave occurs it will likely be 1C warmer than it would have been 100y ago. It does not imply that heatwaves will occur more often. In other words a record temperature of 35C in 1930 might now become 36C now and perhaps even  37C by 2100. Having said that, most of the observed warming occurs a night (minimum temperatures are rising faster than maximum temperatures)

Of course all this depends on exactly how you define a heatwave. This is much easier for the UK because normally we have cool summers with lots of rain. Those who can afford to escape the misery by taking a package holiday to Spain instead. Last year (2017) was a classic example with loads of rain and average temperatures just over 17C.  I would define a UK heatwave as a period of at least six weeks with hardly any rain, with daily sunshine and high ( > 26C) maximum temperatures.  There have been 3 such summer heatwaves in the last 50 years. Here they are:

June Temperature anomalies 1976

1976 was an exceptional summer. The first rain was the day I got married 28th August just as we were leaving the church, although it cleared up later! The heat was restricted to Western Europe though.

August 2003. There were extreme temperatures in France.

2003 saw record high temperatures especially in France.

June 2018

2018 is shaping up to be an exceptional summer for the UK. At the time of writing we only have data for June this year, but it seems likely that July will be warmer still. This is also why I show comparisons with 1976 also for June. August 2003 was the hottest month for Europe.

AR5 chapter 2 claims there is evidence of an increase in heatwaves in Europe, but they don’t define what a heatwave is. It seems to be the number of days temperatures exceed some threshold which I would indeed expect to increase, but that is not what I call a heatwave. It is true that Europe has been warming. This is what I calculated by using my triangulation method for Europe’s temperature anomaly (same as used for the plots above).

Global (red) and Europe (blue) temperature anomalies

Europe seems to have warmed slightly faster than the global average since 2000. Therefore you would expect the number of days above a certain threshold to increase, but these are still not heatwaves. Heatwaves are the result of a particular weather pattern with high pressure extending over the UK caused by a weak Jet stream  lying north of mainland UK. The heat which would normally migrate to the north gets trapped below it. In fact Greenland and Labrador are far cooler than normal as a result. It is actually snowing in Labrador!

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9 Responses to UK Heatwaves and Climate Change

  1. A C Osborn says:

    How much is down to UHI, badly placed Thermometers, Airport Thermometers and short term Thermometers?

    • A C Osborn says:

      The night times in Swansea have been no where near as hot as those in 2003 let alone 1976.
      When you look at the anecdotal evidence of 1976 this heat wave is no where near as severe.

      • Clive Best says:

        I agree. 1976 was hot everywhere including west country and Wales. The 2018 heat wave has mainly been in the South East and East of the country, which is where most of the media reporters live !

    • Clive Best says:

      Absolute temperatures in the centre of cities are something like 2C warmer than the countryside. However the trick is to use ‘anomalies’ so the offset supposedly gets averaged out when you subtracted the ‘monthly ‘normal’. In reality it mostly does get subtracted but you are still left with a long term urbanisation growth trend. Counter-intuitively this cools the past.

      http://clivebest.com/blog/?p=6678

      • David Walker says:

        “Absolute temperatures in the centre of cities are something like 2C warmer than the countryside.”

        Somewhat more than that, according to NASA.

        Satellites Pinpoint Drivers of Urban Heat Islands in the Northeast
        12.13.10

        Cities such as New York, Philadelphia, and Boston are prominent centers of political power. Less known: Their size, background ecology, and development patterns also combine to make them unusually warm, according to NASA scientists who presented new research recently at an American Geophysical Union (AGU) meeting in San Francisco, Calif.

        Summer land surface temperature of cities in the Northeast were an average of 7 °C to 9 °C (13°F to 16 °F) warmer than surrounding rural areas over a three year period, the new research shows. The complex phenomenon that drives up temperatures is called the urban heat island effect.

        https://www.nasa.gov/topics/earth/features/heat-island-sprawl.html

      • David Walker says:

        Even in the UK, the external temperature thermometers in cars show UHI considerably higher than 2°C – 3°C in towns, even the small town where I live in the Yorkshire Dales (pop. approx 2,500) the temperature difference at night can be 2°C and more higher than in the local countryside, and I’ve seen 5°C and more in Leeds and Manchester.

  2. Ronald Chappell says:

    CO2 GH effect is only on outgoing 15u radiation. It is not a source of additional power so no additional water can be evaporated, no additional power to energize larger or more numerous storms. Earth surface and atmosphere still pass same rate of energy flow to space except at 1 C higher temperature so that constant water vapor can radiate the heat that CO2 fails to radiate. Other than reading the thermometer it is unlikely that anyone will know the difference. Water vapor and clouds are unchanged, same evaporation rate as before since there is no source of energy to evaporate more water. Temperature lapse rate curve will just be the same as before at tropopause which will be a few meters higher but 1 C higher at the surface.

    • Clive Best says:

      Yes CO2 is involved in radiating photons in the 15u band. The more CO2 you have the higher up in the atmosphere such photons are emitted, and because this is normally cooler so less energy is emitted. As a result the lapse rate profile and surface temperature adjust very slightly to rebalance energy.

      • A C Osborn says:

        The “less energy is emitted” is balanced by the fact that there is more CO2 doing the emitting as the actual data seems to show.
        I suggest you view the video of the AGU 2013 conference here from about 13 minutes onwards.

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