Only winters in UK are warming.

The Central England Temperature (CET) is the world’s longest continuous record of temperatures dating back to 1670 and has now been updated by the Met Office to include 2015. December 2015 was the warmest ever recorded,  but overall the yearly average is nothing special, reaching just 24th warmest in the series. Ed Hawkins  has previously shown that the overall trend in warming for CET is consistent with that shown by the global data (Hadcrut4). However there are some subtle differences evident in the data as well.  For example warming started well before 1850. What is of particular interest though is that there has essentially been no warming at all during the summer months  for over  350 years!

Seasonaly-Averaged

Seasonal trends in CET defined as follows. Summer(JJA), Spring(MAM), Autumn(SON), Winter(DJF). Curves are 20y smoothed averages through the data with estimated long term temperature change.

Most warming has occurred in winter months with smaller trends during spring and autumn.  This effect can also be seen  in 3  individual monthly trends. Note also the December record set by 2015 as shown below.

3 monthsEffectively, there is no temperature trend apparent in either August or May, yet December shows  a net rise of ~2C over 356 years. Notice also how the year to year variability in December is much higher than either March or August.

Next we look at the yearly averaged CET data

Yearly

Overall CET shows about a 1C increase in the yearly average, but as we have seen most of that warming has occurred in winter months which also show the most variability. There were often severe winters between  the 17th and 19th century when the Thames regularly froze over. More recently 1963 and 2010 were particularly cold, but the overall trend has been for  warmer winters on average.  Unfortunately those of us looking forward to warmer summers look to be disappointed.  🙁

Cold winters in the UK often coincide with large meanders in the Jet Stream pulling cold polar air down from Siberia across the UK. This usually happens when there are  negative phases of the Arctic Oscillation with a less cold stratosphere. Perhaps there has been some long term  change in winter polar circulation related to a warmer arctic ?

 

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6 Responses to Only winters in UK are warming.

  1. Interesting to know; how many other people believe those inaccurate thermometers from 150y ago, temperature collected by drunk butlers? #2: how many other people believe that; ”central England is the GLOBE”?..?!

  2. xmetman says:

    How can you say in your headline that only Winters are warming, when clearly in three of the four seasons (in your first graph) the moving average shows obvious warming !

    Even summers look marginally warmer.

    When I say warming what I mean is that the smoothed 20 year mean is higher on the right hand side (2015) of the graph than it is on the left hand side (1659).

    I am also curious about the 20 year “smoothed” moving average that you are using. What kind of smoothing are you using exactly?

    I’ve done a lot of work stastically on the CET series over the years, and I can hand on heart say that a linear trend will show a rise in the mean CET of any season, be it of the calendar or the meteorological kind.

    • Clive Best says:

      The headline is intended to be provocative. However it is true that the trend in winter months is stronger than summer months. The summer is consistent with no trend. Overall CET has been rising since 1650 which can be fitted to a linear trend of ~ 0.03C/decade.

      The smoothed curve is called an FFT smooth which is based on fitting harmonics to a 20 year rolling average. It follows the trend through to the end points that way.

      Try plotting August only for CET and see if you find any warming trend.

      I also compared CET in 2012 to UK station data from Hadcrut4. They agree rather well.

  3. xmetman says:

    Clive

    Yes, I try and do that as well, but there is fine line between provocative and downright misleading!

    Have a look at a table of my seasonal results for comparison:

    https://xmetman.wordpress.com/2016/01/09/long-term-seasonal-trends-in-central-england-temperatures/

    As regards monthly trends it’s not August that’s flat lining it’s June which has a decadal trend of just +0.001°C:

    https://xmetman.wordpress.com/cet/monthly-cet/

    Bruce.

    • Clive Best says:

      Hi Bruce,

      You gave done some nice work ! The graphs are great.

      We are just niggling about trends though. In hindsight, I should have said that just summer shows no effective warming trend. Spring shows a small trend, Autumn more and Winter the most.

      The reason I say summer shows no effective trend is because the error on any single year’s measurement is at least 0.05C. If you now do a linear least square fit to the data then a slope of 0.01/decade should really be presented as 0.01±0.01C/decade. This is compatible with zero trend.

      Furthermore the annual CET trend shows a linear warming trend even before 1850, which is before rapid increase in CO2 emissions. This looks like a slow recovery from the little ice age with some AGW superimposed post 1950.

      cheers

      Clive

  4. Pingback: El cuento alarmista visto desde la mejor serie de temperatura (CET 1659 -2015) | PlazaMoyua.com

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