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.
No comments:
Post a Comment