144: Evidence against temperature adjustments #4 (British Isles)

In the previous four posts I examined the temperature changes for Ireland (see Post 140), Scotland (see Post 142), England (see Post 143) and Great Britain (see Post 141). While all four sets of temperature data appeared similar from 1900 onwards, there were some differences, and these differences were most apparent in a comparison of the earlier data for Ireland and Great Britain. When the Great Britain data was separated into different trends for Scotland and England a similar degree of difference was observed with the Scotland data appearing to correlate more closely with Ireland, and England with Great Britain. In this post I will look to show this pictorially by comparing the various trends directly.

First, if we compare the data for Ireland, Scotland and England with Great Britain we see that England shows the closest agreement after 1900 but Scotland shows the better agreement before 1840 (see Fig. 144.1 below). The data depicted here are the 5-year moving averages of the mean temperature anomalies (MTAs) for each country as shown by the yellow curves in Fig. 140.2, Fig. 141.2, Fig. 142.2 and Fig. 143.2 in previous posts.

Fig. 144.1: The 5-year average temperature trends since 1760 for Ireland, Scotland and England each compared to that of Great Britain. For clarity the trends for Ireland and England are offset by +2°C and -1.5°C respectively.

What is striking about the trends in Fig. 144.1 is how similar they all are after 1860, while the greatest disparities occur before 1860. The reason for this is evident from Fig. 144.2 below which shows that the number of stations used to calculate each of the MTA for Ireland, Scotland and England drops below five before 1870. From this we can conclude two things. First, this suggests that if there are too few stations used in determining the MTA the accuracy decreases. Secondly we see that when there are sufficient stations used to determine the MTA the accuracy is so good that there is little difference between the MTA for different neighbouring countries. 

This is not the first time such conclusions have been drawn. The same effects were seen in Post 138 (Evidence against temperature adjustments #3) comparing trends in the different Scandinavian countries and Post 57 (The case against temperature data adjustments #1) comparing them in various central European countries. In all cases the conclusion is the same. If trends for neighbouring countries agree, then they are likely to all be correct, not all equally incorrect. Therefore no adjustments to the temperature data are needed or justified. A similar result is also encountered when comparing random samples of stations from the same region as was shown for the USA in Post 67 (More evidence against temperature data adjustments #2). The reason for this is that averaging a sufficiently large number of independent data sets results in a reduction in the size of the errors imported from each. This is known as regression towards the mean.

Fig. 144.2: The number of station records included each month in the averaging for the mean temperature trends in Fig. 144.1.

The second comparison I have performed is to compare data for Ireland, Scotland and England with each other. This is shown in Fig. 144.3 below. Now we see that the two countries that agree most closely are Scotland and Ireland while the data for England appears to exhibit more warming after 1980 and before 1900. This additional warming could be in excess of 0.5°C since 1840.

Fig. 144.3: Comparisons of the 5-year average temperature trends since 1760 for England and Scotland (two top curves, both offset by +2°C), Scotland and Ireland (two middle curves), and Ireland and England (two bottom curves, both offset by -2°C).

Conclusions

Once again a comparison of temperature data for neighbouring countries indicates that most adjustments to the data are unnecessary as the averaging process will correct for most errors via regression towards the mean.

The data for Scotland and Ireland are in closest agreement, probably because both have similar population densities and are more rural.

The data for England is in closest agreement with that of Great Britain, probably because England is the largest country in Great Britain and so its stations will always make the dominant contribution compared to other countries such as Scotland or Wales. 

The greater warming seen in England (of over 0.5°C) is further evidence that warming within countries is driven not just by carbon dioxide levels in the atmosphere and the greenhouse effect, but by local energy consumption as well. So net-zero will not be a panacea.

142: Scotland - temperature trends STABLE before 1980

In my previous post I looked at the temperature trends for Great Britain, i.e. the United Kingdom (UK) minus Northern Ireland. These exhibited a large amount of warming (over 1°C), most of which has occurred after 1980. This is not surprising as it is in agreement with other temperature trends that I have analysed, most of which also appear to exhibit some warming after 1980. However, in Great Britain there was still significant warming before 1980, albeit at a much slower rate compared to the post-1980 period. This is more unusual and is also slightly different to the situation found in Ireland (see Post 140) where any warming before 1980 was negligible. So why the difference? Is Ireland the outlier, or is it Great Britain? 

One way to find out is to look separately at the constituent parts of Great Britain: England, Scotland and Wales. If some of these are more similar to Ireland, then that may suggest Ireland is not the outlier but some other parts of the UK may be. Unfortunately there are only about eight stations in Wales of any note, of which only five are medium stations with over 480 months of data, and none have more than a thousand months of data. This means that it is only possible to determine an accurate temperature trend for Wales since 1970. As the most significant differences in the temperature data of Ireland and Great Britain occur well before 1970, the data from Wales is unlikely to be of much use is determining the cause. So for this analysis I will concentrate on England and first Scotland where the quality of the data is far greater.

Fig. 142.1: The (approximate) locations of the 22 longest weather station records in Scotland. Those stations with a high warming trend between 1911 and 2010 are marked in red while those with a cooling or stable trend are marked in blue. Those denoted with squares are long stations with over 1200 months of data, while diamonds denote medium stations with more than 480 months of data.

Scotland has nine long stations with over 1200 months of data before 2014 and a further thirteen medium stations with over 480 months of data. These stations are well distributed across the region as the map in Fig. 142.1 above illustrates. This means a simple average of their monthly temperature anomalies should yield a reasonably accurate temperature trend for the country as a whole. This trend is shown in Fig. 142.2 below.

Fig. 142.2: The mean temperature change for Scotland since 1760 relative to the 1956-1985 monthly averages. The best fit is applied to the monthly mean data from 1826 to 1975 and has a slight positive gradient of +0.18 ± 0.07 °C per century.

In order to quantify the changes to the climate of Scotland the temperature anomalies for all stations with over 480 months of data before 2014 were determined and averaged. This was done using the usual method as outlined in Post 47 and involved first calculating the temperature anomaly each month for each station relative to its monthly reference temperature (MRT), and then averaging those anomalies to determine the mean temperature anomaly (MTA) for the whole country for each month. The MRTs for Scotland were calculated using the same 30-year period as for the UK in Post 141, namely from 1956-1985. The resulting MTA is shown as a time series in Fig. 142.2 and clearly shows that temperatures were fairly stable for over 150 years up until 1975 with only a slight increase being detectable. However, this increase is less than the natural variation in the 5-year average (see the yellow curve in Fig142.2).

Then at some point in the 1980s (probably in 1988) the mean temperature appears to increase abruptly by about 1°C. This is a phenomenon that has been seen in many other temperature trends across Europe. There is also some evidence of additional warming before 1840 which results in an average trend of +0.28°C per century from 1781 to 1980, a 50% increase on the trend for 1826-1975 in Fig. 142.2. However, as the trend before 1850 is based on data from only two stations (see Fig. 142.3 below) it cannot be relied upon.

Fig. 142.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for Scotland in Fig. 142.2.

If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data in Fig. 142.4 below. This again was determined by averaging each month the anomalies from the 22 longest stations and suggests that the climate was fairly stable before 1880 but then warmed by over 1°C thereafter. In fact the 10-year average suggests there was no warming from 1781 to 1920 but the trend from 1901 to 2020 shows a warming of over 0.75°C. Not only that but the warming is more continuous in nature than the raw data in Fig. 142.2 indicates.

Fig. 142.4: Temperature trends for Scotland based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1826-1975 and has a positive gradient of +0.33 ± 0.03°C/century.

What is also apparent is that the trend in Fig. 142.4 for data from 1826 to 1975 is almost double the equivalent trend in Fig. 142.2. The reason for this is the adjustments made to the data by Berkeley Earth (BE). These adjustments include homogenization, gridding, Kriging and most significantly breakpoint adjustments. These lead to changes to the original temperature data, the magnitude of these adjustments being the difference in the MTA values seen in Fig. 142.4 and the raw data in Fig. 142.2. The magnitudes of these adjustments are shown graphically in Fig. 142.5 below. 

Fig. 142.5: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 142.4 after smoothing with a 12-month moving average. The blue curve represents the total BE adjustments including those from homogenization. The linear best fit (red line) to these adjustments for the period 1851-2010 has a positive gradient of +0.158 ± 0.002 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

The blue curve in Fig. 142.5 is the difference in MTA values between the adjusted data (Fig. 142.4) and the unadjusted data (Fig. 142.2), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. Overall these adjustments appear to add almost 0.3°C of warming to the trend between 1840 and 2010. Before 1840 the adjustments reduce the warming. The overall impact can be seen more clearly if we compare the 5-year averages for the raw data and the BE adjusted data as is shown in Fig. 142.6 below.

Fig. 142.6: The 5-year mean temperature change for Scotland since 1760 based on the original raw data from Fig. 142.2 (in blue) and the Berkeley Earth adjusted data from Fig. 142.4 (in red).

What the data in Fig. 142.6 shows is the amount of warming that has been added by the BE adjustments. While it is less than the natural warming it is still significant and adds over 0.2°C of warming to the period from 1876 to 2010. The result is a trend of 0.74°C per century after 1875 (as shown in Fig. 142.7 below) compared to only 0.57°C per century for the raw data in Fig. 142.2 for the same period. The main impact of the adjustments before 1900 appears to be to flatten the curve and thus eliminate any

Fig. 142.7: Temperature trends for Scotland based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1876-2010 and has a positive gradient of +0.74 ± 0.03°C/century.

Summary

What the raw data for Scotland shows is that the climate was stable for 150 years up to 1975 with warming of less than 0.18°C per century. This is similar to that seen in Ireland of 0.14°C per century (see Fig. 140.2 in Post 140) and significantly less than the value of 0.46°C per century for Great Britain (see Fig. 141.2 in Post 141). This suggests that Ireland and Scotland are not the outliers. So is England, and why?


Acronyms

BE = Berkeley Earth.

MRT = monthly reference temperature (see Post 47).

MTA = mean temperature anomaly.

Long station = a station with over 1200 months (100 years) of data before 2014.

Medium station = a station with over 480 months (40 years) of data before 2014.

141: United Kingdom - temperature trends WARMING

In this post I will consider the temperature data of the United Kingdom (UK), or more specifically Great Britain as the data for Northern Ireland was included in the analysis of the temperature change for Ireland in the last post. Overall the UK has 21 long stations with over 1200 months of data before 2014, of which two are in Northern Ireland and are thus excluded from this analysis. There are also another 73 medium stations with over 480 months of data all of which are within Great Britain or the Isle of Man (for a full list see here). The locations of these 92 long and medium stations are shown on the map in Fig. 141.1 below. What the data from these stations appear to show is that the climate of the UK has warmed gradually by about 0.6°C over the the two hundred years before 1980 but has since warmed further by a similar amount in under forty years.

Fig. 141.1: The (approximate) locations of the 92 longest weather station records in the United Kingdom (excluding Northern Ireland). Those stations with a high warming trend between 1911 and 2010 are marked in red while those with a cooling or stable trend are marked in blue. Those denoted with squares are long stations with over 1200 months of data, while diamonds denote medium stations with more than 480 months of data.

In order to quantify the changes to the climate of the UK the temperature anomalies for all stations with over 480 months of data before 2014 were determined and averaged. This was done using the usual method as outlined in Post 47 and involved first calculating the temperature anomaly each month for each station, and then averaging those anomalies to determine the mean temperature anomaly (MTA) for the country. This MTA is shown as a time series in Fig. 141.2 below and clearly shows that temperatures have increased by about 1°C since 1760.

Fig. 141.2: The mean temperature change for the United Kingdom since 1760 relative to the 1956-1985 monthly averages. The best fit is applied to the monthly mean data from 1871 to 1980 and has a positive gradient of +0.46 ± 0.10 °C per century.

The process of determining the MTA in Fig. 141.2 involved first determining the monthly reference temperatures (MRTs) for each station using a common 30-year reference period, in this case from 1956 to 1985, and then subtracting the MRTs from the raw temperature data to deliver the anomalies. If a station had at least twelve valid temperatures per month within the MRT interval then its anomalies were included in the calculation of the mean temperature anomaly (MTA). The total number of stations included in the MTA in Fig. 141.2 each month is indicated in Fig. 141.3 below. This graph shows that there was a sudden increase in stations in 1973 while some existing station were moved or discontinued at about the same time. In order to include as many of these stations as possible in the MTA the MRT interval was set as 1956-1985 so that it overlapped both periods before and after 1973.

Fig. 141.3: The number of station records included each month in the averaging for the mean temperature trends in Fig. 141.2.

The data in Fig. 141.3 indicates that the greatest coverage of the country for temperature data is after 1973 with up to 76 long and medium stations in operation at any one time. This drops to about 28 in 1930 and to less than five before 1850. This means that the MTA for the UK before 1890 will be less reliable than its values after 1950. Note that a reliable MTA generally needs data from at least sixteen stations (see Post 57 for evidence) otherwise errors in the data from individual stations become significant.

Fig. 141.4: The mean temperature change for the United Kingdom since 1760 relative to the 1956-1985 monthly averages. The best fit is applied to the monthly mean data from 1781 to 1980 and has a moderate positive gradient of +0.29 ± 0.05 °C per century.

If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data in Fig. 141.5 below. This again was determined by averaging each monthly anomaly from the 92 longest stations and also suggests that the UK climate has warmed by over 1°C. In this case, though, the warming appears to occur almost exclusively after 1875 with the climate being stable before this date and gradually warming (with some significant variation) thereafter.

Fig. 141.5: Temperature trends for the United Kingdom based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1876-2010 and has a positive gradient of +0.80 ± 0.03°C/century.

Comparing the curves in Fig. 141.5 with the published Berkeley Earth (BE) version for the UK in Fig. 141.6 below we see that there is good agreement between the two sets of data. This indicates that the simple averaging of anomalies used to generate the BE MTA in Fig. 141.5 using adjusted data is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 141.6. This is a conclusion that is not unique to this case. In fact it is true of virtually all the country and regional data I have examined for this blog so far.

This means that the simple averaging process used for the data in Fig. 141.5 should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 141.2 and Fig. 141.4. Consequently, any major discrepancy between the adjusted data in Fig. 141.5 and the unadjusted data in Fig. 141.4 cannot be due to the different averaging processes used, but must instead be the result of the Berkeley Earth adjustments.

Fig. 141.6: The temperature trend for the United Kingdom since 1750 according to Berkeley Earth.

Most of the differences between the MTA in Fig. 141.4 and the BE versions using adjusted data in Fig. 141.6 are due to the data processing procedures used by Berkeley Earth. These include homogenization, gridding, Kriging and most significantly breakpoint adjustments. These lead to changes to the original temperature data, the magnitude of these adjustments being the difference in the MTA values seen in Fig. 141.4 and Fig. 141.5.

Fig. 141.7: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 141.5 after smoothing with a 12-month moving average. The blue curve represents the total BE adjustments including those from homogenization. The linear best fit (red line) to these adjustments for the period 1921-2000 has a positive gradient of +0.097 ± 0.004 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

The magnitudes of these adjustments are shown graphically in Fig. 141.7 above. The blue curve is the difference in MTA values between adjusted (Fig. 141.5) and unadjusted data (Fig. 141.4), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. The overall adjustment from 1900 to 2013 is small, less than +0.2°C. A greater impact is seen before 1880. This appears to change the shape of the long term trend before 1900 from a gradual warming in Fig. 141.4 to a more stable climate in Fig. 141.5. This can be seen more clearly in the comparison curves in Fig. 141.8 below. These also show that the adjustments made after 1900 add slightly to the observed warming. In this case, however, both these corrections are smaller than those seen in other posts, particularly for countries in the Southern Hemisphere.

Fig. 141.8: The 5-year mean temperature change for the United Kingdom since 1760 based on the original raw data from Fig. 141.2 (in blue) and the Berkeley Earth adjusted data from Fig. 141.5 (in red).

Summary

The temperature data from UK stations appears to indicate that the climate of the UK has warmed by about 1°C since 1760, and most of this warming has occurred since 1900 (see Fig. 141.2). In fact over half the warming has occurred since 1980.

The pattern of warming is broadly the same for both the MTA calculated using raw data (See Fig. 141.2) and that based on Berkeley Earth adjusted data (see Fig. 141.5).

The MTA data of the UK before 1900 appears to show more warming than is seen in similar data for Ireland (see Post 140) even though the two territories are near neighbours and their data are more similar after 1900. One reason for this could be the greater population density and industrialization of the UK compared to Ireland. One way to test this hypothesis would be to analyse the temperature for England and Scotland separately and compare these with Ireland. If the England data is the exception then that would support the hypothesis.


Acronyms

BE = Berkeley Earth.

MRT = monthly reference temperature (see Post 47).

MTA = mean temperature anomaly.

List of all stations in the UK with links to their raw data files.