The link between sunshine and temperature based on UK climate records since 1933

This post shows how UK surface temperatures since 1933 are influenced by changes in net cloud cover and is co-authored with Dr Clive Best, a physicist who has formerly worked at CERN and on the Jet nuclear fusion experiment.


  • Terrestrial sunshine records provide an inverse proxy for cloud cover. Sunshine at surface means cloud free line of sight between the point on the surface and the Sun.
  • We present concordant sunshine and temperature records for 23 UK Met Office weather stations. Data is available for a handful of stations from 1908 but it is only from 1933 that there are a sufficient number of stations to provide representative cover of the UK.
  • Data from 1933 to 1956 is believed to be affected by air pollution from burning coal for home heat and power generation, therefore our main analysis focusses on the time interval 1956 to 2012.
  • Both temperature (Tmax) and sunshine hours show cyclic variation, both showing a tendency to rise in the period 1980 to 2000 in keeping with global warming that has been documented in many studies.
  • In the UK there is a high degree of covariance between sunshine and Tmax, sunny years tend to be warmer. The correlation coefficient (R2) between sunshine hours and Tmax is 0.8 whilst R2 for CO2 and Tmax is 0.66 (calculated on 5 year means). A significant portion of warming observed in the UK may be attributed to temporal variations in sunshine and cloud cover.
  • This post presents a summary of the raw data in 14 charts. Next week we will present a combined net cloud forcing and radiative forcing model with the aim of quantifying the relative contributions of dCloud and dCO2.

Figure 1 Maximum daily temperature (Tmax, red, LH scale) and minimum daily temperature (Tmin, blue, RH scale) from the Leuchars weather station. The red and blue lines are annual averages. The black lines are centred 5y moving averages. Note high degree of co-variation between Tmax and Tmin. Also note how temperatures drifted higher during the 1990s and 2000s but recently are drifting down again, in keeping with the global temperature trend.

Figure 2 Average annual hours of sunshine at Leuchars (blue columns) with a 5y centred moving average in red. Note how the 1990s and early 2000s were clearly sunnier than the preceding decades and how more recently the amount of sunshine seems once again to be in decline and this broadly mirrors the temperature evolution (Figure 1).


For more times than I care to recall I have sat down to write a book on energy and climate change. On each occasion my endeavour foundered early on through being distracted by detail. And so it was earlier this year. I had written down my lifelong recollections of climate change in Scotland – cold snowy winters in the 1970s, getting sunburned working in the fruit fields of Perthshire in the 1980s, frost free winters in the 2000s, cold snowy winters today – and I wanted to check my recollections against data – a fatal mistake. I stumbled upon the UK Met Office climate station database, a wonderful resource, and downloaded data from Leuchars, Braemar and Nairn, the three stations closest to where I grew up in Kirriemuir and where I now live in Aberdeen.

Some of this “raw data” from Leuchars is shown in Figures 1 and 2 and from looking at a few charts like these I observed cyclical changes in temperature with time that seemed to be matched by cyclical changes in the amount of sunshine. Warm years were sunnier than colder years. This led me to compile data from 23 UK stations (Figure 3) from which a clear picture of co-variance between sunshine and temperature emerged.

I wanted to be able to quantify the relationship between sunshine and temperature and contacted physicist Dr Clive Best who seemed pre-eminantly qualified to help. This has led to a 3 month collaboration and writing two papers, one on UK and the other on Global variations in cloud cover and its impact on temperature trends. The UK paper was rejected twice by Nature and by one other journal and so we have decided to hang the establishment and publish this work on our blogs. The Global paper is still out for review. This is the first of three posts on UK climate records starting with a simple description of the database. If there are any editors or academics out there who want to see this published in peer reviewed literature then please get in touch (read the Blog Rules).


All Met Office stations record maximum daily temperature (Tmax) and minimum daily temperature (Tmin), rainfall and the number of frost free days. A subset of stations also record sunshine hours and it was stations with lengthy sunshine records that formed the basis for station selection. The data are reported as monthly means. The records are not 100% complete (I’d estimate >99% complete) and where data is missing it has been patched with data from the preceding year. If there was no preceding year, the succeeding year was used.

The selected sites are shown in Figure 3 and the distribution of records in Figure 4.

Figure 3 Met Office climate stations used in this study.

Figure 4 The time distribution of records. A handful of Met Office stations have sunshine records from 1908 but this small number fails to provide statistically representative cover of the UK. It is only from 1933 that a large enough number of stations were reporting both sunshine and temperature records to provide representative geographic cover. Hence all data presentations and analysis are based on the 1933 to 2010 time interval. Since we use 5y centred means in our analysis, data from 1931 to 2012 is captured. Over this period the number of operating stations varies, with a peak in the 1980s.

Variance in Sunshine and Tmax

Looking at 100 years of records from 23 stations represents a huge amount of data that presents challenges in how best to display it. Figures 5 and 6 show 5y running averages of Tmax and sunshine for all 23 stations. The most northerly station, Lerwick on the Shetland Islands, is shown in bold blue and one of the most southerly stations, Southampton is shown in bold red. The key observations:

  • There is a large variation in temperatures from N to S produced by 10˚ of latitude separation. Lerwick is, on average, about 5˚C colder than Southampton (Figure 5).
  • There is also a large N-S range in sunshine received. Note that over a year, every point on the globe should receive the same hours sunshine with a spherical horizon. That is (365.25*24)/2 = 4383 hours per year. The variance in hours sunshine therefore reflects N-S trends in cloud cover. Southampton receives about 600 more hours sunshine each year than Lerwick. Eastbourne is anomalously sunny (Figure 6).
  • There is a high degree of cyclic co-variance in Tmax across the country. Note how spikes and troughs in Lerwick match spikes and troughs in Southampton (Figure 5).
  • The N-S variance in sunshine / cloud cover is more chaotic, and lacks the strong co-variation seen in the Tmax data (Figure 6).

Figure 5 Tmax, 5y running averages for 23 UK stations.

Figure 6 Sunshine, 5y running averages for 23 UK stations.

Figure 7 The mean Tmax and sunshine from all 23 stations, 1y average

Averaging the data for all 23 stations shows a degree of co-variance between temperature and sunshine although there are instances of negative correlations where spikes down in Tmax are matched by spikes up in sunshine (Figure 7). This may reflect annual variations in sunshine distribution, for example, some years may have sunny summers while others have sunny winters. It is also evident that temperatures where higher in the 1930s and 1940s, lower in the 1950s to 1980s and higher again in the 1990s and 2000s and this decadadal structure in Tmax is also reflected in sunshine / cloud cover. If this is not obvious, then further smoothing of the data using a 5y mean shows clearly that cyclic change in Tmax is mirrored by cyclic change in sunshine hours (Figure 8).

Figure 8 The data shown in Figure 7 smoothed further by applying a 5 year running average.

The degree of correlation between sunshine and temperature is quite striking though imperfect. At the beginning of the time series it is evidently lacking altogether and this is surprising since co-variance in sunshine and temperature is intuitively expected. To explain this we call on the introduction of clean air legislation in the UK in 1956. Prior to this date, coal was burned in open hearths throughout UK cities and power stations were also located in cities, for example the iconic Battersea Power Station in central London (inset photograph). Burning all this coal produced dense and lethal smogs, and we suggest that this pre-1956 pollution has perturbed the expected correlation between sunshine and temperature. Looking at seasonal data we see that the link between temperature and sunshine holds good for the summer months, pre-1956, when burning coal was at a minimum. This will be the subject of the third post in this series.

Tmax and Tmin

The radiative and CO2 forcing models that we will present next week will consider only Tmax. That is because when considering the impact of sunshine and cloud cover on the temperature record it is daily Tmax that is most relevant. However, it transpires that there is a very high degree of co-variance between Tmax and Tmin (Figures 9 and 10), hence, conclusions drawn for Tmax may equally apply to Tmin and daily average temperatures.

Figure 9 Tmax, left hand scale and Tmin right hand scale. In the UK Tmin is typically 6.5˚C cooler than Tmax

Figure 10 Cross plot of data shown in Figure 9 showing an exceptional degree of correlation between Tmax and Tmin. By and large night time temperatures have a memory of the day before.

Figure 11 Tmax minus Tmin

Figure 11 shows the difference between Tmax and Tmin over time. The trend is perceptibly down by about 0.2˚C over a 70 year period and it seems possible this may be due to increased radiative heating at night.

Tmax – correlations with sunshine and CO2

Figure 12 Comparison of Tmax varaiance in the UK with CO2 smoothed from Moana Loa data.

Figure 12 shows the correlation between CO2 and Tmax (compare with Figure 8) and highlights a key problem with all models that seek to explain troposphere warming by CO2 alone ± other natural forcing such as volcanoes and variance in solar insolation. CO2 is periodically discordant with cooling trends, e.g 1933 to 1963 and with cyclic ups and downs in the temperature record. In contrast, cyclical change in sunshine / cloud cover can explain the cyclical variance in Tmax (Figure 8).

Figure 13 Overall, CO2 and Tmax shows reasonable correlation. But there are 5 periods of marked negative correlation where temperature is falling as CO2 is rising.

Figure 14 Data from Figure 8 cross plotting Tmax and sunshine hours has a better correlation than CO2

There is a correlation between Tmax and CO2 with R2=0.66 (Figure 13). But the correlation between Tmax and sunshine is stronger with R2=0.80 (Figure 14).

This is as far as I (EM) was able to take the empirical analysis but recognised that a physicist should be able to calculate from these data the component of Tmax variation attributable to sunshine and cloud cover and that attributable (if any) to CO2. At this point Dr Clive Best offered his assistance that led on to 3 months of fruitful collaboration. In a post next week we will present the results of combined net cloud forcing and radiative forcing models. The analysis does show that a significant portion of warming in the UK may be attributable to a decline in cloud cover and any global climate model that does not take variance in natural cloud forcing into account will overestimate the role of CO2.

A note to commenters: Please recognise this as an honest attempt to cast fresh light on the extremely complex subject of climate change. We are aware of certain weaknesses and omissions and so please raise these for discussion in a civil and scientific manner.

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18 Responses to The link between sunshine and temperature based on UK climate records since 1933

  1. Jake Haye says:

    Nice post. Just one quibble.

    AFAIK the putative temperature effect of atmospheric CO2 concentration is logarithmic, so it doesn’t seem meaningful to compare concentration with temperature directly.

    • Euan Mearns says:

      Correct. Figures 12 and 13 are really there to show that there has been an increase in temperature and an increase in CO2 but that the cyclical structure of the temperature data are not easily explained by CO2 alone. The cyclical structure requires “internal variability of the climate system” to explain it, and we will be arguing that cyclical change in cloud cover is an important part of this “internal variability”.

      In the physical models that we will present next week, the logarithmic relationship between dT and dCO2 is accounted for. At least I think it is, this is Clive’s domain.

  2. clivebest says:

    The Met Office also keep a long term archive of Central England Temperatures dating from 1650 which cover a triangular area from Lancashire, Bristol and London. The data show very similar trends to that we found for the whole of the UK. What is also interesting is that there is also an underlying linear warming trend dating right back to 1650 of about 0.03C/decade. Superimposed on this are excursions quite similar to that observed since 1950. Sometimes this linear trend is referred to as a recovery from the Little Ice Age. What I think the following graph shows is that although temperatures from 1990 to 2005 were about 0.5C above the normal this does not look exceptional compared to past excursions, and in recent years the trend has reversed.
    see graph here
    Although there is evidence of an AGW signal in the UK data natural variability in cloud cover dominates the UK climate. One might wonder at why the UK government is investing so much money and resources to reverse a global problem which will have little direct negative impact on the UK even in the long term.

    • Euan Mearns says:

      Clive, don’t know why your comment wasn’t posted automatically. There is something seriously screwed up with the commenting on this version of Word Press.

      The Central England Temperatures are interesting. I posted this comment on Climate Etc yesterday that drew an interesting comment from a poster called TonyB who also referred to the CET records about which I have to claim ignorance.

      Icelandic eruptions will be important in understanding this record, especially this one

  3. marchesarosa says:

    A few years ago I saw a post from a blogger called, unsurprisingly, “Sunshinehours” showing a steady increase decade by decade for Heathrow. I wondered why no-one had done the same sort of analysis for all the country’s weather stations and am so glad you have! It seems such an obviously important contribution to the climate debate. Well done.

    • Euan Mearns says:

      Hi Marches, I have seen a few blog comments on isolated climate records showing link between sunshine and temperature. It is actually incredibly time consuming to grab and summarise all this data: at least on a Mac using XL it is. The UK Met Office of course gets millions every year and the question needs to be asked why they have not spotted this and highlighted it to their paymasters. Too much focus on computer games me thinks.

  4. Roger Andrews says:

    FWIW, when you look at the monthly data you find that sunshine hours lead t_max and t_min by about a month. The portion of the Leuchars record shown below is a typical example.

  5. Euan Mearns says:

    Roger, this is very interesting but not too surprising. There is an instantaneous response between sun and temperature that we all feel when the sun comes out and a lagged temperature response to the warming season. Memory is evident in the Tmax and Tmin data we present here. Would you care to elaborate on your interest here, do you just happen to plot UK Met charts as a hobby, or do you have a deeper professional involvement? best Euan

    • Roger Andrews says:


      To answer your second question first, I’m a retired mining geologist/geophysicist with a lot of experience in data analysis and I guess you could say that climate change is indeed my hobby, for want of a better word. My comment arose when A.C. Osborn linked to your post over at Tallbloke’s Talkshop, and since I made it your post has been reposted at the Talkshop in its entirety.

      However, the comment was actually a veiled question. As you say, we all feel the relationship between sun and temperature, and in fact it’s a lot stronger here at lat 20N, long 103W, elevation 1,500m than it is where you are. But so far as I know the one-month lag between sunshine hours and temperature shown in the graph lacks a documented physical explanation and I was wondering whether you had looked into this.

      And to complicate the issue further I’ve since discovered that sea surface temperatures in the North Sea lag Leuchars air temperatures by a month, i.e. they lag Leuchars sunshine hours by two months. If you use sunshine as a cloud proxy these lags may need to be figured into the calculations.

  6. A C Osborn says:

    You guys may be interested in a Forum where someone has already explored this topic for Australia.
    See this

    • Euan Mearns says:

      Hi AC – thanks for link, there is an awful lot of info there to absorb quickly. Suffice to say that we have also looked at Global cloud, downloading the NASA D2 cloud from the NOAA web site – since the NASA server has been disabled. Global D2 cloud shows cyclic change that can in part explain global temperatures. The IPCC know about this and have done what they can to cast doubt on the veracity of the satellite cloud data.

      I see you’ve been posting links to our articles on various forums – thanks for your help!

  7. Roger Andrews says:


    To answer your second question first, I’m a retired geologist/geophysicist with a lot of experience in data analysis and I guess you could say that climate change is indeed my hobby, for want of a better word. My comment arrived on your blog via a link at Tallbloke’s Talkshop, and if you care to check you will find your post has now been reposted in its entirety there.

    However, the comment was actually a veiled question. As you say, we all feel the relationship between sun and temperature, and in fact it’s a lot stronger here at lat 20N, long 103W, elevation 1,500m than it is where you are. But so far as I know the one-month lag between sunshine hours and temperature shown in the graph lacks a documented physical explanation, and I was wondering whether you had checked into this.

    To complicate the issue further I’ve since found that North Sea SSTs lag Leuchars air temperatures by a month, i.e thay lag Leuchars sunshine by two months. I mention this because you may want to figure these lags in if you’re going to use sunshine as a proxy for clouds. The graphs are already posted over at the Talkshop, but if you don’t mind a couple more here they are:

    • Euan Mearns says:

      Roger, I am giving a talk on all this at the University of Aberdeen in a couple of hours and am very pressed for time. The one and two month time lags are very interesting and I guess would be classified as thermal inertia. In our analysis these get aggregated and then lost in the 1y average and lost further in the 5y average. The finest scale we have looked at the data is quarterly where we see excellent correlation between sun and temp in JJA but zero correlation in DJF – it’s a very complex picture that Clive will be posting on shortly. Our correlations were optimised on the quarterly and 5y data and were poor on the 1y data – which was a pain, but I suspect this could be due to the monthly time lags you discuss resulting in miss alignment of data at the beginning and end of the year. It could be interesting to do analysis by time shifting the Temp by 1 and 2 months.

      Its worth thinking about how temperature records are created – (Tmax+Tmin) / 2. Tmax is incredibly sensitive to whether or not the Sun comes out – at least it is in Scotland, may be different else where. There will be at least two effects here, one the instantaneous warming the other the “seasonal” memory – land and water (including lochs and rivers) warming with the aggregate increase in sunshine and insolation followed by cooling post – autumn equinox. Our winter minimum temperatures are normally Jan / Feb – one to two months after the solstice.

      Please post as many of your charts as you want to. You can also display the charts using appropriate HTML.

      • Roger Andrews says:

        Euan: Regarding your first paragraph, I guess I’d better wait to read what Clive has to say before commenting.

        Regarding the second, I get essentially the same level of correlation with sunshine hours whether I use t_max, t_min or the average of the two (R=0.84, 0.81, 0.83 for Leuchars, R=0.85, 0.82, 0.84 for Camborne). I would, however, expect this because diurnal temperature variations usually come out close to a sine wave when averaged over a month.

        Which brings up another issue. Were the readings taken by a max-min thermometer or at fixed times of day or by some combination of both? That’s something that could make a difference.

  8. The fall of (Tmax-Tmin) over time could also be due to clouds (and man-made aerosols). Clouds warm at night and cool during the day soTmin increases while Tmax decreases if clouds/pollution increases.

  9. A C Osborn says:

    Remembering Gust of Hot Air’s post, which didn’t seem to get much exposure I thought if I could get your excellent analysis a bit more it might help with Questions & Answers.
    I tried WUWT but they seem to be a bit anti the sun/cloud relationship to temperatures.

  10. Luís says:

    Hi Euan and Clive. We have discussed this privately already, but there is more here than meets the eye. In theory sunshine should yield a slightly negative correlation with temperature in Winter a strong correlation during Summer. This is mainly due to the diverse effect of polar highs during the fast and slow phases of circulation. This work is pointing not only to (the lack of) cloud cover being the culprit of the late XX century warming, but also to this warming having happened mostly during Summer. An interesting follow up work would be to analyse correlation of temperature with circulation (frequency of polar highs moving over the UK).

    Btw, the Bettersea picture is missing the pig.

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