Is it hotter than normal?

MaxTemp_Average_1981-2010_June

This map shows how the average of the maximum daily temperature in June varies across the UK.

It was hot last night. And hot today. But is this hotter than normal? Is this global warming?

Human beings have a remarkably poor perspective on such questions for two reasons.

  • Firstly we only experience the weather in a single place which may not be representative of a country or region. And certainly not the entire Earth!
  • And secondly, our memory of previous weather is poor. Can you remember whether last winter was warmer or colder than average?

Personally I thought last winter was cold. But it was not.

Another reason to love the Met Office.

The Met Office have created carefully written digests of past weather, with month-by-month summaries.

You can see their summaries here and use links from that page to chase historical month-by-month data for the UK as a whole, or for regions of the country.

Below I have extracted the last 12 months of temperature summaries. Was this what you remembered?

  • May 2017: UK mean temperature was 12.1 °C, which is 1.7 °C above the 1981-2010 long-term average, making it the second warmest May in a series from 1910 (behind 2008).
  • April 2017: UK mean temperature was 8.0 °C, which is 0.6 °C above the 1981-2010 long-term average.
  • March 2017 :UK mean temperature was 7.3 °C, which is 1.8 °C above the 1981-2010 long-term average, making it the joint fifth warmest March in a series since 1910.
  • February 2017: UK mean temperature was 5.3 °C, which is 1.6 °C above the 1981-2010 long-term average, making it the ninth warmest February in a series since 1910.
  • January 2017: UK mean temperature was 3.9 °C, which is 0.2 °C above the 1981-2010 long-term average. It was a cold month in the south-east but generally milder than average elsewhere.
  • December 2016: UK mean temperature was 5.9 °C, which is 2.0 °C above the 1981-2010 long-term average, and the eighth warmest December in a series from 1910.
  • November 2016: The UK mean temperature was 4.9 °C, which is 1.3 °C below the 1981-2010 long-term average.
  • October 2016: The UK mean temperature was 9.8 °C, which is 0.3 °C above the 1981-2010 long-term average.
  • September 2016: The UK mean temperature was 14.6 °C, which is 2.0 °C above the 1981-2010 long-term average, making it the equal second warmest September in a series from 1910.
  • August 2016: The UK mean temperature was 15.5 °C, which is 0.6 °C above the 1981-2010 long-term average.
  • July 2016: The UK mean temperature was 15.3 °C, which is 0.2 °C above the 1981-2010 long-term average.
  • June 2016: The UK mean temperature was 13.9 °C, which is 0.9 °C above the 1981-2010 long-term average.

So all but one month in the last year has been warmer than the 1981 to 2010 long term average. It is almost as if the whole country were warming up.

But UK mean temperature is not we feel. Often we remember single hot or cold days.

So I looked up the maximum June temperature recorded in England or Wales for every year of my life.

Each point on the graph below may have occurred for just a day, or for several days, and may have occurred in a different place. But it is broadly indicative of whether there were some ‘very hot days’ in June.

June Maximum Temperatures

The exceptional year of 1976 stands out in the data and in my memory: I was 16. And 2017 is the first June to come close to that year.

But something else stands out too.

  • From 1960 to 1993 – the years up until I was 34 – the maximum June temperature in England and Wales exceeded 30 °C just 6 times i.e. 18% of the years had a ‘very hot day in June’.
  • Since 2001 – the years from age 41 to my present 57 – there were 10 years in which the maximum June temperature in the England and Wales exceeded 30 °C i.e. 63% of the years had a ‘very hot day in June’.

Similarly,

  • From 1960 to 1993 there were 6 years when the maximum June temperature fell below 26 °C  i.e. 18% of the years didn’t have any very hot days.
  • Since 2001 the maximum June temperature in the England and Wales has always exceeded 26 °C.

Together these data tell us something about our climate – our average weather.

They tell us that weather such as we are experiencing now is normal. But it didn’t used to be: our climate – our average weather – has changed.

Is this global warming?

Broadly speaking, yes. In our new warming world, weather like we are experiencing now is likely to be become more common.

More technically, global warming is – obviously – global and requires the measurement of temperatures all around the world. It also refers to climate – the average weather – and not individual weather events. So…

  • The fact that this year we have had exceptionally hot days this June is not global warming: indeed 1976 was hotter!
  • But the fact that exceptionally hot days in June have become more common is a manifestation of global warming.

P.S. This Met Office page shows all the weather ‘records’ so you can check for when new ‘records’ are likely to be set.

5 Responses to “Is it hotter than normal?”

  1. Victor Venema (@VariabilityBlog) Says:

    What is the reason for the gap? If this were a graph of a single station, I would have guessed that the gap indicated some change in the measurements, rather than a climatic change.

    Could still be, also for an average over a larger region. There is likely a transition to automatic weather stations in this period. This often influences the extremes even more than the mean and the data in the UK is not homogenised.

    • protonsforbreakfast Says:

      I have written to John Kennedy at the Met Office to ask about the gap: I will keep you posted. The gap is unfortunate, but as you know better than most, we have to work with the data we have.

      I should have added caveats. This could be an instrumental cause. I think this is unlikely because the Met Office are very careful and use – by world standards – well-managed and maintained networks. They also parallel test new equipment before deploying across their networks. Equipment which read significantly differently would not be deployed. The possibility that new equipment might capture peaks more reliably is plausible, but the difference is very large.

      Also I ‘cherry-picked’. I saw the data in two parts and it seemed to tell a story, so I told it. I could have been more rigorous.

      Nonetheless, I feel that the article is correct in stating that (a) warmer weather has become more likely in the UK and that (b) it is this change in likelihood that is significant, rather than any single occurrence of any particular event.

  2. edhui Says:

    The gap does rather spoil the graph since the two parts look fairly horizontal if shifted. It’s like a broken hockey stick. Yesterday was certainly hotter than any NPL water rocket challenge I can remember. If the contestants had painted their rockets black, they would have had greater thrust as the water turned to steam in flight.
    The top of my car steering wheel was too hot to touch let alone hold- something I’d only previously experienced in the tropics, and the car thermometer read 39C, stabilizing at 38C when I was driving.

    • protonsforbreakfast Says:

      The gap is irritating and I have written to a colleague at the Met Office to ask why it is there!

      Steam?!! Mmmm. I think the rockets could have gone faster for a couple of reasons, but also I can think of reasons why they would have slowed down. Overall, I think temperature is marginal. 38 °C is very hot, but quite plausible over a black road surface.

      All the best. Michael

  3. telescoper Says:

    Reblogged this on In the Dark and commented:
    I remember the summer of 1976 very well indeed, both for the heat and for the fact that the West Indies’s victory over England in the test series that summer, including bowling England out for 71 at Old Trafford.

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