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.
