149: Portugal, Spain and France - a comparison

In Post 138 I compared the temperature trends of the Scandinavian countries to see it there were any similarities. There were. In fact there was almost perfect agreement between the 5-year average trends of Norway, Sweden and Finland as far back as 1900 (see Fig. 138.3). As both Norway and Sweden had about twenty sets of station data that went back to 1900 and Finland had about ten, this demonstrated that averaging over a large number of independent data sets eliminates most measurements errors: a consequence of regression towards the mean.

In Post 144 I repeated this procedure for trends from Ireland, Scotland and England and obtained a similar result (see Fig. 144.3), although the trend for England differed slightly from the other two due to its greater urbanization. This demonstrates that neighbouring regions should have similar climates, or at least they should experience similar changes to their climates. So is this also the case for Portugal, Spain and France? I ask this because the results from Post 146 suggest that before 1980 the climate of Spain was cooling while Post 145 suggests that that of Portugal was warming. Well, the results in Fig. 149.1 below show that in fact the temperature trends of Spain and Portugal are very well correlated as far back as 1940, then they diverge. France, on the other hand, is only very weakly correlated to both Spain and Portugal.

Fig. 149.1: A comparison of the 5-year average temperature trends since 1800 for Portugal (green), Spain (red) and France (blue). The two upper trends are offset by +2°C for clarity and the bottom two trends are offset by -2°C.

This discrepancy can be explained in part by the number of stations contributing to the mean temperature anomaly (MTA) of each country per month (see Fig. 149.2 below). Before 1940 there are only two stations contributing to the Portugal MTA, which is probably why it diverges from the Spain MTA which consistently has over ten contributing stations. However, this cannot fully explain the poor correlation of the French data to that of either Spain or Portugal, even though France also has a low number of stations before 1940. The issue here is that the France MTA has a high number of contributing stations after 1960, as do Spain and Portugal, and yet its correlation to both of their MTAs is still poor after 1960. That said, its overall trend since 1860 does follow that of Portugal quite closely.

Fig. 149.2: The number of station records included each month in the averaging for the mean temperature trends of each country in Fig. 149.1.

It should be remembered, though, that the MTAs of both Portugal and France before 1940 are strongly dependent on only two or three sets of station data, and in both cases most of these stations are located in the biggest cities: Paris, Marseille, Lisbon and Porto. These four stations also all appear to exhibit severe continuous warming since 1900 consistent with the effect of urban heat islands. In which case the similarity between the MTA trends of Portugal and France before 1940 may simply be a consequence of parallel economic development in their largest cities.

Instead these comparisons suggest that France may actually have a completely different climate to the Iberian Peninsula even though it is its closest neighbour. The reason for this may be down to geography and the influence of the Pyrenees mountain range at the border that effectively insulates one region from the other.

148: Italy - temperature trends STABLE before 1980

Whereas France only has four long stations with over 1200 months of data, Italy has at least twelve long stations, most with data stretching back over two hundred years. This means it is possible to determine  with a high degree of certainty the extent of climate change in Italy as far back as 1820. What this climate data shows is that the climate of Italy was stable for almost two hundred years up until 1980. Then over the last forty years it has warmed by about 1°C.

In addition to its twelve long stations, Italy also has 81 medium stations with over 480 months of data (for a full list see here). The locations of these 93 stations are shown on the map in Fig. 148.1 below. While the stations are generally spread evenly, there is a higher concentration of long stations in the north of the country compared to the south, and some clustering around Milan, Venice and Rome.

Fig. 148.1: The (approximate) locations of the 93 longest weather station records in Italy. 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 Italy 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 each station in Italy were calculated using the same 30-year period, namely from 1961 to 1990. 

The resulting MTA is shown as a time series in Fig. 148.2 below and clearly shows that temperatures were stable for over two hundred years up until 1980. Then they appear to increase rapidly by about 1.0°C over thirty years. That said, the change is comparable in size and speed to natural variations seen in earlier parts of the trend such as in 1940. On the other hand the MTA after 1980 is based on data from many more stations (up to ninety) and so is likely to be more accurate.

Fig. 148.2: The mean temperature change for Italy since 1740 relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1881 to 1980 and has a slight positive gradient of +0.03 ± 0.12 °C per century.

The total number of stations included in the MTA in Fig. 148.2 each month is shown in Fig. 148.3 below. The peak in the frequency around 1970 suggests that the 1961-1990 interval was indeed the most appropriate to use for the MRTs. It also indicates that data from about ten stations were used to calculate the MTA for almost every month back to 1820. As fifteen stations appears to the minimum number needed to provide an accurate MTA, this suggests that the trend in Fig. 148.2 is reliable at least as far back as 1820.

Fig. 148.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for Italy in Fig. 148.2.

If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data in Fig. 148.4 below. This again was determined by averaging each month the anomalies from the 93 longest stations but here the picture is slightly different from that depicted in Fig. 148.2. Instead of a stable MTA we see a positive trend of over 0.5°C per century suggesting that the climate was warming before 1980. This clearly contradicts the raw data in Fig. 148.2.

Fig. 148.4: Temperature trends for Italy based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1881-1980 and has a positive gradient of +0.53 ± 0.04°C/century.

But if we next compare the curves in Fig. 148.4 with those from the published Berkeley Earth (BE) version for Italy shown in Fig. 148.5 below, we see that there is excellent agreement between the two sets of data at least as far back as 1770. This indicates that the simple averaging of adjusted anomalies used to generate the BE MTA in Fig. 148.4 is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 148.5. In which case simple averaging should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 148.2.

Fig. 148.5: The temperature trend for Italy since 1750 according to Berkeley Earth.

The differences between the MTA in Fig. 148.2 and the BE versions using adjusted data in Fig. 148.4  are instead mainly 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. 148.2 and Fig. 148.4. The magnitudes of these adjustments are shown graphically in Fig. 148.6 below. The blue curve is the difference in MTA values between adjusted (Fig. 148.4) and unadjusted data (Fig. 148.2), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. Between 1880 and 1980 both are considerable with the former leading to an additional warming since 1880 of over 0.5°C.

Fig. 148.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 148.4 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 1881-1980 has a positive gradient of +0.510 ± 0.009 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

The overall impact of the BE adjustments can be seen more clearly if we compare the 5-year averages for the raw data (from Fig. 148.2) and the BE adjusted data (from Fig. 148.4). This comparison is shown in Fig. 148.7 below. It clearly shows that the trend based on adjusted data (red curve) exhibits considerably more warming since 1840 but slightly less since 1990.

Fig. 148.7: The 5-year mean temperature change for Italy since 1740 based on the original raw data from Fig. 148.2 (in blue) and the Berkeley Earth adjusted data from Fig. 148.4 (in red).

Summary

The raw unadjusted temperature data for Italy clearly shows that the climate was stable from 1780 to 1980 (see Fig. 148.2).

In contrast, the BE adjusted data claims that the climate first cooled and then warmed by 0.5°C from 1880 to 1980 (see Fig. 148.4).

After 1980 the climate has clearly warmed by about 1°C but this is still only of the same magnitude as the natural variations in the climate, so it may be too early to state definitively how much of the warming is permanent and how much more is still to come.



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.

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

147: France - temperature trends STABLE before 1980

What is surprising about France is the poor quality of its temperature data. Its data is worse than for Spain, Italy, Germany, the UK, Norway, Sweden and Finland. And yet France is the de-facto home of metrology, the country that gave us SI units.

The longest temperature record in France is for Bourges in the middle of the country. It is one of only four long stations with over 1200 months of data in France. There are a further 91 medium stations in France with over 480 months of data (for a full list see here). The locations of all these 95 stations are shown on the map in Fig. 147.1 below. In this analysis I have also included two stations in the Channel Islands; a long station in Guernsey and a medium station in Jersey. The reason for this is that they are much closer to France than England and so it is more reasonable for their data to be combined with data from France than with that from the UK. It also results in another long station being included in the analysis for France thereby improving the reliability of its long-term trend.

Fig. 147.1: The (approximate) locations of the 97 longest weather station records in France and the Channel Islands. Those stations with a high warming trend 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 France 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 each station in France were calculated using the same 30-year period, namely from 1961 to 1990. The resulting MTA is shown as a time series in Fig. 147.2 below and clearly shows that temperatures were fairly stable for over 120 years up until 1980. Then they appear to increase suddenly by over 0.8°C.

Fig. 147.2: The mean temperature change for France since 1820 relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1861 to 1980 and has a slight positive gradient of +0.22 ± 0.11 °C per century.

The total number of stations included in the MTA in Fig. 147.2 each month is shown in Fig. 147.3 below. The peak in the frequency around 1990 suggests that the 1961-1990 interval was an appropriate one to use for the MRTs as it enabled all but five of the 97 datasets to be included in the MTA. All five of these medium station datasets had no data after 1900 and at least four exhibited a negative temperature trend. This suggests that in the 19th century the climate of France was cooling not warming.

Fig. 147.3 also indicates that data from less than ten stations were used to calculate the MTA for almost every month before 1945. As fifteen stations appears to the threshold number needed to provide an accurate MTA, this suggests that the trend in Fig. 146.2 is reliable only as far back as 1950. In fact most of the MTA trend before 1930 is dependent on data from only six stations. Of these, two are based in large cities (Paris and Marseille) and appear to exhibit strong linear warming trends (over 1.7°C since 1900) consistent with an urban heat island effect, and three have fragmented data (Bourges, Guernsey, and Montpellier). So only one (Chateauroux) is of any real quality and it has warmed by only about 0.3°C from 1900 to 2013.

Fig. 147.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for France in Fig. 147.2.

If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data in Fig. 147.4 below. This again was determined by averaging each month the anomalies from the 97 longest stations and suggests that the climate was slowly warming before 1980 by about 0.3°C since 1860. While this is slightly more than the 0.2°C suggested in Fig. 147.2, the difference is not that significant.

Fig. 146.4: Temperature trends for France based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1861-1980 and has a positive gradient of +0.31 ± 0.04°C/century.

Next, if we compare the curves in Fig. 147.4 with those from the published Berkeley Earth (BE) version for France shown in Fig. 147.5 below, we see that there is excellent agreement between the two sets of data at least as far back as 1825. This indicates that the simple averaging of adjusted anomalies used to generate the BE MTA in Fig. 147.4 is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 147.5. In which case simple averaging should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 147.2.

Fig. 147.5: The temperature trend for France since 1750 according to Berkeley Earth.

Any differences between the MTA in Fig. 147.2 and the BE versions using adjusted data in Fig. 147.4  are mainly 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. 147.2 and Fig. 147.4. The magnitudes of these adjustments are shown graphically in Fig. 147.6 below. The blue curve is the difference in MTA values between adjusted (Fig. 147.4) and unadjusted data (Fig. 147.2), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. Both are minimal with the former leading to an additional warming since 1860 of between 0.1°C and 0.2°C.

Fig. 147.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 147.4 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 1861-1980 has a positive gradient of +0.079 ± 0.010 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

The overall impact of the BE adjustments can be seen more clearly if we compare the 5-year averages for the raw data (from Fig. 147.2) and the BE adjusted data (from Fig. 147.4). This comparison is shown in Fig. 147.7 below. It clearly shows that the trend based on adjusted data (red curve) exhibits more warming before 1900 but very little extra afterwards.

Fig. 147.7: The 5-year mean temperature change for France since 1780 based on the original raw data from Fig. 147.2 (in blue) and the Berkeley Earth adjusted data from Fig. 147.4 (in red).

Summary

The raw unadjusted temperature data for France clearly shows that the climate warmed by less than 0.2°C from 1880 to 1980 (see Fig. 147.2)

In contrast, the BE adjusted data claims that the climate warmed by 0.3°C over the same period (see Fig. 147.4).

After 1980 the climate has clearly warmed by almost 1°C (see Fig. 147.7).

The temperature data before 1980 presented here clearly disagree with that of Spain in Post 146. However, as the MTA for Spain over the 100 years before 1950 is based on data from between twelve and fifty different stations compared to only about five for France, that would suggest that the Spain data is the more accurate.



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.

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

146: Spain - temperature trends COOLING before 1980

The analysis of temperature data for Portugal in the previous post appeared to indicate that the local climate had warmed continuously since 1870 by over 1°C in total. The caveat to this was the poor data quantity before 1940 with only two stations of significance contributing data to the regional trend, and one of them, Lisbon, clearly displayed characteristics in its data that were suggestive of the urban heat island effect. 

In this post I will look at the corresponding temperature data for Portugal's neighbour, Spain, to see if the temperature trends seen in Post 145 are repeated, as would be expected of neighbouring territories. The results will in fact show that they are not, and that the trends for Portugal before 1940 are probably wrong. In fact the data for Spain indicates that the climate cooled over the one hundred years before 1980 and has only recently begun to warm.

Spain has many more weather stations compared to Portugal, which given the difference in size is not surprising. Despite this, the station densities of the two countries are roughly the same. Spain has fourteen long stations with over 1200 months of data before 2014 and another 69 medium stations with over 480 months of data. The locations of these stations are indicated on the map in Fig. 146.1 below. They include two stations in Gibraltar and four in the Balearic Islands. They are distributed fairly evenly across the country but there are significant clusters around Madrid and south of Seville. 

Fig. 146.1: The (approximate) locations of the 83 longest weather station records in Spain. 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 Spain 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 each station in Spain were calculated using the same 30-year period, namely from 1961 to 1990. The resulting MTA is shown as a time series in Fig. 146.2 below and clearly shows that temperatures were decreasing for over 110 years up until 1980. After which they appear to increase suddenly by about 0.8°C.

Fig. 146.2: The mean temperature change for Spain since 1780 relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1871 to 1980 and has a slight negative gradient of -0.19 ± 0.10 °C per century.

The total number of stations included in the MTA in Fig. 146.2 each month is shown in Fig. 146.3 below. The peak in the frequency around 1970 suggests that the 1961-1990 interval was indeed the most appropriate to use for the MRTs. It also indicates that data from at least ten stations were used to calculate the MTA for almost every month back to 1865. As fifteen stations appears to the minimum number needed to provide an accurate MTA, this suggests that the trend in Fig. 146.2 is reliable at least as far back as 1865.

Fig. 146.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for Spain in Fig. 146.2.

If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data in Fig. 146.4 below. This again was determined by averaging each month the anomalies from the 83 longest stations and suggests that the climate was warming before 1980. This clearly contradicts the raw data in Fig. 146.2.

Fig. 146.4: Temperature trends for Spain based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1871-1980 and has a positive gradient of +0.32 ± 0.04°C/century.

But if we next compare the curves in Fig. 146.4 with those from the published Berkeley Earth (BE) version for Spain shown in Fig. 146.5 below, we see that there is excellent agreement between the two sets of data at least as far back as 1865. This indicates that the simple averaging of adjusted anomalies used to generate the BE MTA in Fig. 146.4 is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 146.5. In which case simple averaging should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 146.2.

Fig. 146.5: The temperature trend for Spain since 1750 according to Berkeley Earth.

The differences between the MTA in Fig. 146.2 and the BE versions using adjusted data in Fig. 146.4  are instead mainly 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. 146.2 and Fig. 146.4. The magnitudes of these adjustments are shown graphically in Fig. 146.6 below. The blue curve is the difference in MTA values between adjusted (Fig. 146.4) and unadjusted data (Fig. 146.2), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. Both are considerable with the former leading to an additional warming since 1865 of over 0.5°C.

Fig. 146.6: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 146.4 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 1871-1980 has a positive gradient of +0.506 ± 0.013 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

The overall impact of the BE adjustments can be seen more clearly if we compare the 5-year averages for the raw data (from Fig. 146.2) and the BE adjusted data (from Fig. 146.4). This comparison is shown in Fig. 146.7 below. It clearly shows that the trend based on adjusted data (red curve) exhibits considerably more warming since 1870.

Fig. 146.7: The 5-year mean temperature change for Spain since 1820 based on the original raw data from Fig. 146.2 (in blue) and the Berkeley Earth adjusted data from Fig. 146.4 (in red).

Summary

The raw unadjusted temperature data for Spain clearly shows that the climate cooled by about 0.2°C from 1870 to 1980 (see Fig. 146.2)

In contrast, the BE adjusted data claims that the climate warmed by 0.3°C over the same period (see Fig. 146.4).

After 1980 the climate has clearly warmed by about 0.8°C (see Fig. 146.7).

The results presented here clearly disagree with those for Portugal in Post 145. However, as the MTA for Portugal before 1960 is based on data from less than five stations compared to two or three times as many stations for Spain, that would suggest that the Spain data is the more accurate.

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.

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

145: Portugal - temperature trends WARMING

The biggest problem in quantifying the extent of climate change in mainland Portugal is the lack of data before 1960. There are only two long stations with over 1200 months of data before 2014, the most significant of which is located in the capital, Lisbon (see here). This station appears to have recorded a temperature increase of over 2°C since 1850, yet the only other station with a comparable length of data in Coimbra shows a more modest increase with significant natural variability (see here) while data from Porto appears to suggest temperatures in the 19th century were warmer than today (see here). As Lisbon is very likely subject to some degree of urban heat island effect due to its size, this makes any accurate determination of the climate changes in Portugal before 1960 problematic.

In addition to the two long stations at Lisbon and Coimbra, there are also fifteen medium stations with over 480 months of data (for a full list of stations see here). The locations of all seventeen of these stations are shown on the map in Fig. 145.1 below. This suggests that they are fairly evenly distributed across the country with no part of the country being more than 70 km from a weather station. This is consistent with the station density of seventeen in 92,212 km² (the area of Portugal), or one in every 5424 km².

Fig. 145.1: The (approximate) locations of the 17 longest weather station records in Portugal. Those stations with a high warming trend 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 Portugal 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 Portugal were calculated using the 30-year period from 1961 to 1990. The resulting MTA is shown as a time series in Fig. 145.2 below.

Fig. 145.2: The mean temperature change for Portugal since 1850 relative to the 1961-1990 monthly averages. The best fit is applied to the monthly mean data from 1871 to 1980 and has a positive gradient of +0.96 ± 0.08 °C per century.

The MTA in Fig. 145.2 clearly shows temperatures rising continuously from 1850 to 2013. However, as has already been pointed out, much of the increase before 1940 is due to the influence of the station in Lisbon. This is demonstrated by the graph below in Fig. 145.3 which shows only two or three stations contributing to the MTA before 1940. After 1960 the MTA is much more reliable as it is the result of averaging data from up to fifteen stations each month.

Fig. 145.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for Portugal in Fig. 145.2.

If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data in Fig. 145.4 below. This again was determined by averaging each month the anomalies from the seventeen longest stations and suggests that the climate warmed slowly by 0.4°C in the one hundred years prior to 1980 and then warmed by another 0.7°C in the next thirty years.

Fig. 145.4: Temperature trends for Portugal based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1871-1980 and has a positive gradient of +0.41 ± 0.04°C/century.

Comparing the curves in Fig. 145.4 with those in the published Berkeley Earth (BE) version for Portugal shown in Fig. 145.5 below indicates that there is good agreement between the two sets of data. This demonstrates that the simple averaging of anomalies used to generate the BE MTA in Fig. 145.4 is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 145.5. In which case simple averaging should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 145.2 even though the geographical distribution of stations is not completely homogeneous, as was shown in Fig. 145.1.

Fig. 145.5: The temperature trend for Portugal since 1750 according to Berkeley Earth.

While the temperature trends for the raw unadjusted data in Fig. 145.2 and the BE adjusted data in Fig. 145.4 look very similar, there are some significant differences. These can be seen more clearly by comparing the 5-year average of each dataset as shown in Fig. 145.6 below. This shows how the adjustments in Fig. 145.4 have altered the shape of the trend between 1900 and 2010 but not the overall total temperature change. The impact is to reduce the warming between 1900 and 1980 and to increase it thereafter, so making it look more like the classical 'hockey stick'.

Fig. 145.6: The 5-year mean temperature change for Portugal since 1850 based on the original raw data from Fig. 145.2 (in blue) and the Berkeley Earth adjusted data from Fig. 145.4 (in red).

The adjustments themselves can be calculated by subtracting the MTA values of the raw data in Fig. 145.2 from the adjusted values used in Fig. 145.4. The result is shown in Fig. 145.7 below.

Fig. 145.7: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 145.4 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 1871-1980 has a negative gradient of -0.238 ± 0.017 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

The blue curve in Fig. 145.7 is the difference in MTA values between the adjusted data (Fig. 145.4) and the unadjusted data (Fig. 145.2), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. Additional contributions to the blue curve come from other adjustments based on techniques such as homogenization, gridding, Kriging and also any difference in MRT interval. Overall these adjustments appear to reduce the warming between 1900 and 1980 by about 0.3°C and then increase it by a similar amount from 1980 to 2010.

Summary

Both the raw data and the BE adjusted data appear to show that the climate of Portugal has warmed by about 1°C since 1890 (see Fig. 145.6). Most of this warming has occurred since 1980.

The effect of BE adjustments is to modify the shape of the trend from 1900 onwards rather than to increase or decrease the amount of overall warming (see Fig. 145.7).

While the trend since 1960 is incontrovertible as it is based on data from about fifteen different stations each month (see Fig. 145.3), the trend for earlier data is less so as it is based on only three sets of station data that profoundly contradict each other (Lisbon, Coimbra and Porto). However, data from Portugal's neighbour Spain in the next post may resolve this issue.

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.

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

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.

143: England - temperature trends WARMING

It is probably not surprising that England has more weather stations of note than Scotland. After all it has about ten times the population and almost twice the area. Yet the difference is not as great as one might imagine. For while Scotland has nine long stations with over 1200 months of data before 2014, England has only a slight advantage with ten stations. For medium stations with over 480 months of data the difference is greater with England having 55 compared to 13 in Scotland. There is, however, more clustering of stations in England as the map in Fig. 143.1 below shows.

Fig. 143.1: The (approximate) locations of the 65 longest weather station records in England. 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 England 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 England 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. 143.2 below and clearly shows that temperatures rose slightly over 150 years up until 1975 before increasing more rapidly thereafter. In this respect the MTA data for England more resembles that of Great Britain (see Fig. 141.2 in Post 141) than it does that of Scotland (see Fig. 142.2 in Post 142) or Ireland (see Fig. 140.2 in Post 140).

Fig. 143.2: The mean temperature change for England 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 positive gradient of +0.35 ± 0.08 °C per century.

The temperature trend for England was calculated 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 graph in Fig. 143.3 below indicates how many stations were available each month in order to contribute to that month's MTA.

The MRTs for England 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. 143.2 above and clearly shows that temperatures were slowly increasing for over 150 years up until 1975. 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.

Fig. 143.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for England in Fig. 143.2.

If we next consider the change in temperature based on Berkeley Earth (BE) adjusted data we get the MTA data in Fig. 143.4 below. This again was determined by averaging each month the anomalies from the 65 longest stations and also suggests that the climate was warming slowly before 1980 but then warmed more strongly by over 1°C thereafter.

Fig. 143.4: Temperature trends for England 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 +0.27 ± 0.03°C/century.

The difference between the MTA based on raw unadjusted data (from Fig. 143.2) and the MTA based on BE adjusted data (from Fig. 143.4) is shown in Fig. 143.5 below. The blue curve in Fig. 143.5 is the difference in MTA values between the adjusted data (Fig. 143.4) and the unadjusted data (Fig. 143.2) and represents the total of all the data adjustments made including those from homogenization, gridding, Kriging and most significantly breakpoint adjustments. The orange curve is the contribution to those adjustments arising solely from breakpoint adjustments.

Fig. 143.5: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 143.4 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 1871-2010 has a small positive gradient of +0.003 ± 0.003 °C per century. The orange curve shows the contribution just from breakpoint adjustments.

The overall impact of any adjustments can perhaps be seen more clearly if we compare the 5-year averages for the raw unadjusted data and the BE adjusted data as is shown in Fig. 143.6 below. This shows that the two datasets agree almost perfectly from 1870 onwards while before 1870 the adjusted data implies the climate is more stable. It should be noted though that the MTA trends before 1870 are based on data from less than five stations and this drops to less than two before 1850 (see Fig. 143.3). This is one reason why the MTA exhibits more natural variability over the earlier period before 1870.

Fig. 143.6: The 5-year mean temperature change for England since 1760 based on the original raw data from Fig. 143.2 (in blue) and the Berkeley Earth adjusted data from Fig. 143.4 (in red).

Summary

What the raw data for England shows is that the climate was warming slowly for most of the period up to 1975 (see Fig. 143.2). This is similar to the trend seen previously for Great Britain (see Fig. 141.2 in Post 141), but is different from both Scotland (see Fig. 142.2 in Post 142) and Ireland (see Fig. 140.2 in Post 140) where little warming was seen in this period. This suggests that England is the dominant country in determining the overall climate of the UK but is also the outlier. But why?

The obvious answer is that England has a much greater population density and so experiences much more urban or surface heating from human activities (see Post 14, Post 29, Post 127 and Post 134). As I pointed out in Section (iv) of Post 127, the energy consumption of Greater London is sufficient to raise the local temperature by over 4°C.


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.

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.