41. Netherlands - temperature trends - VARIABLE

The Netherlands has one of the longest instrumental temperature records in the world, and probably the most complete record covering the last 300 years. The record from De Bilt (Berkeley Earth ID: 175554) had nearly 3700 months of data in 2013 that stretched back to 1706 (see Fig. 41.1 below). Only Berlin Tempelhof (Berkeley Earth ID: 155194) has earlier data that extends to 1701, but it has fewer months overall and significant gaps in its record before 1756.

Fig. 41.1: The temperature trend for De Bilt since 1706. The best fit is applied to the interval 1731-2005 and has a positive gradient of +0.29 ± 0.04 °C per century. The monthly temperature changes are defined relative to the 1976-2005 monthly averages.

As I showed in the last post, Belgium also has one long record that stretches back to the 18th century, but it has virtually no other data before 1973. The Netherlands is much better in this respect. There is one other dataset with some sporadic 19th century data, and overall there are five long station records with more than 1200 months of data. In addition, there are another 25 medium records with more than 480 months of data. Details of all these 30 stations (and other shorter records) are listed here, while their geographical locations are shown on the map in Fig. 41.2 below.

 

Fig. 41.2: The locations of long stations (large squares) and medium stations (small diamonds) in the Netherlands. Those stations with a high warming trend are marked in red.

It can be seen from the map above that the stations in the Netherlands are fairly randomly distributed across the country, but that their number appears to be significantly less than the 30 stations stated previously. This is because in nearly a dozen cases two or more stations are located within 10 km of each other. I intend to look at this is more detail in a later post, where I will look at what this says about data reliability. 

The other impact of this clustering is the effect it could have on the station weightings in the regional average. Normally if a cluster of records is found the weighting of each record should probably be reduced as they will tend to repeat each other's data and geographical coverage. However, as most of the station records appear in effect to be paired up, they will almost all have the same reduced weighting, so the weighting reduction should largely cancel. This is largely confirmed by the results I will show later in this post. The other point to note, is that the clustering really only impacts the medium stations, most of which have data after 1970 only. So the weighting problem will only have a slight effect on the overall trends after 1970.

Fig. 41.3: The temperature trend for the Netherlands since 1706. The best fit is applied to the interval 1731-2005 and has a positive gradient of +0.31 ± 0.04 °C per century. The monthly temperature changes are defined relative to the 1976-2005 monthly averages.

If we average the anomaly data for all the long and medium stations we get the trends shown above in Fig. 41.3. The overall trend indicates that the region has warmed by about 0.31 °C per century since 1700. This equates to an overall warming of about 0.97 °C. But as I explained in Post 14, the current human industrial and domestic energy consumption in the country suggests that the region should have warmed by at least 1.0 °C over the same period simply as a consequence of all the heat that is produced each year by human activity. So, just as for Belgium, we see little need to call on the effects of carbon dioxide emissions and the Greenhouse Effect to explain the observed temperature rise.

The other interesting feature of the data in Fig. 41.3 is the shape of the temperature trend between 1800 and 1950. There is clearly a peak around 1860 that is seen not just in the De Bilt record in Fig. 41.1, but also in the Zuid-Limburg station data. This suggests that temperatures in the mid-19th century in the Netherlands were actually higher than they are today. This is a phenomenon that I have identified and highlighted previously in other countries and regions such as New Zealand (see Post 8), Australia (see Post 26) and South America (see Post 35). In fact it appears to occur over most of the Southern Hemisphere, or at least in those parts that have sufficient data before 1900.

The anomaly data used to construct the trend in Fig. 41.3 was derived by first calculating the monthly reference temperatures (MRT) for the period 1976-2005 for each record, and then subtracting these from the raw data. These were then averaged. Temperature records were only included in the trend in Fig. 41.3 if they had at least 480 months of data, and at least 320 months of this data was within the MRT interval of 1976-2005. This was to ensure that all temperature anomaly records were measured relative to identical reference points. The result was that three medium stations were excluded because they had insufficient data after 1975. These were the stations at Den Helder, Maastricht and Groningen. 

Fig. 41.4: The number of sets of station data included each month in the temperature trend for the Netherlands.

The actual number of stations used to construct each monthly point in the trend in Fig. 41.3 is illustrated above in Fig. 41.4. This shows that the trend before 1900 is almost entirely due to the data from De Bilt in Fig. 41.1, while the data from 1900 to 1950 comes from the five long stations. After 1950 as many as 27 station records were used for each monthly average.

Fig. 41.5: Temperature trends for all long and medium stations in the Netherlands since 1750 derived by aggregating and averaging the Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1801-1980 and has a gradient of +0.29 ± 0.03 °C/century.

So the question is, how significant are these results? And also how reliable are they?

Well, one way to test this is to compare these results against those produced by climate science groups like Berkeley Earth. The first thing to remember, though, is that the Berkeley Earth anomaly data for each station record is different from that which I have calculated here because it uses homogenization and breakpoint alignment to adjust the data, techniques that I have profound misgivings about because they could introduce warming to the overall trend that is not actually there. That is why I restrict my analysis to the raw data with all its imperfections.

However, if we apply the same averaging process to the Berkeley Earth adjusted data as I have employed to the raw data, we see that the trends we get (as illustrated in Fig. 41.5 above) agree very well with those published by Berkeley Earth and shown in Fig. 41.6 below. In fact the size and positions of most of the peaks in the two figures are virtually identical. This suggests that the two processes (mine and Berkeley Earth's) are broadly consistent, even if the anomaly data for each station that is used in the averaging is different. What it also shows, though, is that the Berkeley Earth trend that incorporates homogenization and breakpoint adjustments is somewhat different from the trend I have presented in Fig. 41.3 that avoids using such controversial techniques. For example, according to Berkeley Earth, the warming in the Netherlands since 1900 is at least 1.5 °C, and there was no warm period in the mid-19th century. It is these disagreements over data and methodology, and the effects they have on the resulting temperature trends, that partly fuels the climate scepticism debate.

Fig. 41.6: The temperature trend for the Netherlands since 1750 according to Berkeley Earth.

If we try to quantify the difference between the Berkeley Earth temperature trend and the raw trend I have constructed in Fig. 41.3 we find that the adjustments made by Berkeley Earth  have two main effects. The first is to flatten the trend before 1900. The second is to exaggerate the temperature rise after 1900 by about 0.3 °C. These adjustments are illustrated in Fig. 41.7 below.

Fig. 41.7: The contribution of Berkeley Earth (BE) adjustments to the anomaly data after smoothing with a 12-month moving average. The linear best fit to the data is for the period 1901-2010 (red line) and the gradient is 0.266 ± 0.009 °C per century. The orange curve represents the contribution made to the BE adjustment curve by breakpoint adjustments only.

Conclusions

It is clear from Fig. 41.3 that there has been a large degree of warming in the Netherlands over the last 300 years, but that this is probably less than than the 1.5 °C we are being led to expect for anthropogenic global warming (AGW) in the Northern Hemisphere as claimed by the IPCC and the HadCRUT4 data. 

The magnitude of this warming is probably only about 1 °C. However, this temperature rise is only what one would expect from the growth of industrial energy use over this period (for the Netherlands I have previously calculated that it should be about 1.0 °C) as I explained in Post 14. 

However, there is also evidence of significant natural variation in the temperature record (such as the warming in the mid-19th century) that is inconsistent with current IPCC claims.

Consequently, the data presented here does not really add support to the theory that carbon dioxide is the primary driver of warming, otherwise the warming seen in the Netherlands should be much larger, and there would be no anomalous fluctuations in temperature before 1900.

Finally, there is the issue of historical perspective. If temperatures in the recent past were both higher than now and at times lower than now, why are we worried about current temperatures when they appear to be fluctuating between normal bounds?

40. Belgium and Luxembourg - temperature trends 1°C WARMING

In the next few posts I am going to take a look at the temperature trends in a few countries in western Europe, starting with Belgium. The unique feature of these countries is that they have some of the longest instrumental temperature records in the world.

Fig. 40.1: The temperature trend for Brussels since 1794. The best fit is applied to all the data and has a positive gradient of +0.67 ± 0.05 °C per century. The monthly temperature changes are defined relative to the 1976-2005 monthly averages.

 

The longest temperature record in Belgium comes, not surprisingly, from Brussels, and extends back to 1794 (see Fig. 40.1 above). That is the good news. The bad news is that there are no other temperature records with significant temperature data before 1973. Four records do have a couple of years of data in the early 1940s. But this data is probably not very reliable as there is then a thirty year gap to the rest of the data, and the early data was clearly collected under conditions of wartime occupation. The only other significant dataset comes from Luxembourg to the south of Belgium (see Fig. 40.2 below) which extends back to 1878.

The blue data in Fig. 40.1 above is the monthly temperature anomaly for Brussels, i.e. the amount by which each month's mean reading deviated from a reference value for that month for that station. Those monthly reference temperatures (MRT) were calculated by averaging all equivalent months (i.e. January or February etc.) in that dataset over the period 1976-2005. This is a later period than that used for most previous blog posts (most use 1961-1990) and is solely because of the lack of data before 1973. The monthly reference temperatures (MRT) are then subtracted from the raw monthly data to generate the monthly anomaly data. For a longer explanation of this process see Post 38 and Post 4.

It can be seen from the anomaly data in Fig. 40.1 that the range of anomaly values can be up to 12 °C, with the extreme negative values being more extreme than the extreme positive ones. These extreme negative values almost always correspond to severe winters; the winter of 1942 was particularly bad with two consecutive months (January and February) recording monthly means that were over 6 °C below normal. In the middle of a Nazi occupation I suspect that was really grim. Overall, though, this suggests that extreme winter cold spells are much deeper and longer lasting than prolonged summer heatwaves.

The other main feature of the data in Fig. 40.1 is the overall upward trend. Apart from a significant dip around 1890, this is almost continuous, and is illustrated more clearly by the 5-year moving average (yellow curve). Overall the mean temperature in Brussels rises by over 1 °C, as indicated by the red best fit line, from 1794 to 2013. However, as I pointed out in Post 14, the growth in energy usage in Belgium over the same period would be expected to raise temperatures by around 0.98 °C anyway. This would appear to indicate, that while the temperature rise is probably man-made, it is in all likelihood not entirely due to the emission of carbon dioxide and the Greenhouse Effect. 

It may be tempting to also discount this temperature record for Brussels as being an aberration or anomaly from the norm. However, if we compare it to the data for Luxembourg shown in Fig. 40.2 below, we see similar trends and features. There is a similar temperature rise after 1985, similar peaks in the 5-year moving average around 1947 and 1960, and a similar trough around 1890. The gradients of the best fit lines are similar in both cases as well, although the uncertainty for the Luxembourg best fit is much greater at almost ±0.16 °C. This, though, is partly due to the shorter time span of the Luxembourg data. 

Fig. 40.2: The temperature trend for Luxembourg since 1878. The best fit is applied to the interval 1895-2004 and has a positive gradient of +0.49 ± 0.16 °C per century. The monthly temperature changes are defined relative to the 1976-2005 monthly averages.

If we now look at the remaining data for Belgium and Luxembourg we see that there are an additional fourteen medium stations with temperature records that contain at least 480 months of data (see here for a list). Most of this data is for the period 1973-2013. The locations of the two long stations (Brussels and Luxembourg) and the fourteen medium stations are shown on the map in Fig. 40.3 below.

 

Fig. 40.3: The locations of long stations (large squares) and medium stations (small diamonds) in Belgium and Luxembourg. Those stations with a high warming trend are marked in red.

The map in Fig. 40.3 indicates that the two long stations with over 1200 months of data and the fourteen medium stations with over 480 months of data are distributed fairly evenly across Belgium and Luxembourg. This is important because it means that we probably don't need to resort to complex weighted averages when finding the overall temperature trend. A simple mean will suffice. In which case, combining the anomalies for the sixteen stations indicated in Fig. 40.3 gives the overall trend shown in Fig. 40.4 below.

Fig. 40.4: The temperature trend for Belgium and Luxembourg since 1794. The best fit is applied to the interval 1895-2004 and has a positive gradient of +0.52 ± 0.15 °C per century. The monthly temperature changes are defined relative to the 1976-2005 monthly averages.

 

As can be clearly seen, the overall trend for the whole of Belgium is not that different from that illustrated for Brussels in Fig. 40.1, but then why would it be? Over 80% of the trend in Fig. 40.4 is entirely due to the data from two stations: Brussels and Luxembourg. This is shown graphically in Fig. 40.5 below.

 

Fig. 40.5: The number of sets of station data included each month in the temperature trend for Belgium and Luxembourg.

 

Finally, if we compare these results using the raw data with those produced by Berkeley Earth which used adjusted data, we see broad similarities but some notable differences.

 

Fig. 40.6: Temperature trends for all long and medium stations in Belgium and Luxembourg since 1794 derived by aggregating and averaging the Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1801-1980 and has a gradient of +0.28 ± 0.03 °C/century.
 

Combining the Berkeley Earth adjusted anomaly data for the same sixteen station records as in Fig. 40.4 and taking the mean value yields the two trends shown in Fig. 40.6 above: one trend for the 12-month average (in black) and a second for the 10-year average (in orange). For temperature data after 1860 the two trends are very similar to those published by Berkeley Earth and shown in Fig. 40.7 below, with the curves exhibiting similar patterns of peaks and troughs in the two figures. This does appear to validate our initial assumption that weighted averages are unnecessary when combining these temperature records due to their even geographical spacing. However, the Berkeley Earth data before 1860 looks slightly different, and quite frankly is unlikely to be very reliable, given that it is based on only one temperature record, or for the curve before 1794, on no local data at all. 

Fig. 40.7: The temperature trend for Belgium since 1760 according to Berkeley Earth.

Finally, if we look at the difference between the raw data shown in Fig. 40.4 and the Berkeley Earth adjusted data presented in Fig. 40.6 we see that while the overall net adjustments Berkeley Earth made to the data in this instance are small and result in a slightly negative contribution to the trend, there were still large corrections made to segments of the data before 1930 that in effect attempt to "flatten the curve". These do not appear to have a significant impact on the overall trend though.

Fig. 40.8: The contribution of Berkeley Earth (BE) adjustments to the anomaly data after smoothing with a 12-month moving average. The linear best fit to the data is for the period 1831-2010 (red line) and the gradient is -0.048 ± 0.009 °C per century. The orange curve represents the contribution made to the BE adjustment curve by breakpoint adjustments only.

Conclusions

It is clear from Fig. 40.4 that there has been a large degree of warming in Belgium and Luxembourg over the last 200 years. It is likely, given the agreement between the data from the two longest temperature records and their significant spatial separation, that this warming is a feature of the entire region, and is not localized to just one area (or maybe two) of the country, although given the lack of data before 1973, that is not a certainty. The magnitude of this warming is probably in excess of 1 °C. However, this temperature rise is only what one would expect from the growth of industrial energy use over this period (for Belgium it should be about 0.98 °C) as explained in Post 14. It is also less than the 1.5 °C we are told to expect for anthropogenic global warming (AGW) in the Northern Hemisphere as claimed by the IPCC and the HadCRUT4 data. Consequently, it does not really add support to the theory that carbon dioxide is the primary driver of warming, otherwise the warming should be much larger.