The climate change seen in Finland over the last 200 years closely resembles that seen in Sweden. Between 1830 and 1920 the mean temperature rose by just over 0.5°C. Unfortunately the trend before 1890 is based on the average of less than three datasets so its reliability is open to question. Then from 1920 to 1980 the temperature appears broadly stable before rising again by about 1°C in the 1980s.
Like Norway and Sweden, Finland has an impressive number of weather stations, but only about twenty of them predate 1960. Overall the country has eleven long stations with over 1200 months of data before 2014 but only two have a significant amount of data before 1890. The country also has an additional 106 medium stations with over 480 months of data. These 117 long and medium stations are distributed across the country with a higher concentration in the southwest than elsewhere, and only eighteen are within the Arctic Circle (see Fig. 137.1 below). For a full list of stations see here.
Fig. 137.1: The (approximate) locations of the 117 longest weather station records in Finland. 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 Finland 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. 137.2 and clearly shows that temperatures were fairly stable up until 1980. However at some point in the 1980s (probably in 1988) the mean temperature appears to increase abruptly by about 1°C. A similar temperature jump is seen in many regions across Europe, but in this case it is merely comparable to other fluctuations seen in the 5-year average such as those seen in the 1930s. It is therefore hard to ascertain if this jump is real, or exactly where in time this temperature rise is occurring and how much of it is permanent.
Fig. 137.2: The mean temperature change for Finland since 1880 relative to the 1971-2000 monthly averages. The best fit is applied to the monthly mean data from 1896 to 1980 and has a positive gradient of +0.23 ± 0.31 °C per century.
The process of determining the MTA in Fig. 137.2 involved first determining the monthly reference temperatures (MRTs) for each station using a common reference period, in this case from 1971 to 2000, 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. 137.2 each month is indicated in Fig. 137.3 below. The peak in the frequency between 1960 and 1990 suggests that the 1971-2000 interval was indeed the most appropriate interval to use for the MRTs.
Fig. 137.3: The number of station records included each month in the mean temperature anomaly (MTA) trend for Finland in Fig. 137.2.
The data in Fig. 137.3 indicates that the greatest amount of temperature data available in Finland occurs after 1960 with almost 120 long and medium stations in operation at any one time. This drops to about twenty before 1960 and to about ten for most of the first half of the 20th century. Before 1890 there are only two stations in continuous operation, Helsinki (BE ID: 13544) and Helsinki-Vantaa Airport (BE ID: 175422), neither of which have any data before 1829. All the other data before 1840 comes from fragmented data from three or four other stations.
All this means that the MTA for Finland before 1960 will be less reliable than its values after 1960 while the MTA before 1890 is based on only two stations, both of which are in Helsinki. As an MTA generally needs to be calculated using data from at least sixteen different stations in order to be accurate (see Post 57 for evidence), this suggests that any MTA before 1890 is unlikely to be representative of the country as a whole while the MTA before 1950 may also be slightly biased. Nevertheless, we can calculate an MTA for Norway back to 1740. If we do so we obtain the trends shown in Fig. 137.4 below. This appears to indicate continuous warming of about 1°C from 1840 to 1930 with a further 1°C of warming occurring since 1930. But if we discount the data before 1890 due to insufficient stations, then we are left with the data in Fig. 137.2 which paints a rather different picture.
Fig. 137.4: The mean temperature change for Finland since 1740 relative to the 1971-2000 monthly averages. The best fit is applied to the monthly mean data from 1891 to 2010 and has a slight positive gradient of +1.00 ± 0.18 °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. 137.5 below. This again was determined by averaging each adjusted monthly anomaly from the 117 longest stations and suggests that the climate has warmed continuously by nearly 2°C since 1830. In fact the 10-year average suggests a warming of nearly 2.5°C.
Fig. 137.5: Temperature trends for Finland based on Berkeley Earth adjusted data. The best fit linear trend line (in red) is for the period 1891-2010 and has a positive gradient of +1.03 ± 0.08°C/century.
Comparing the curves in Fig. 137.5 with the published Berkeley Earth (BE) version for Finland in Fig. 137.6 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. 137.5 using adjusted data is as effective and accurate as the more complex gridding method used by Berkeley Earth in Fig. 137.6. In which case simple averaging should be just as effective and accurate in generating the MTA using raw unadjusted data in Fig. 137.4 and Fig. 137.2. In other words, any discrepancy between the adjusted data in Fig. 137.5 and the unadjusted data in Fig. 137.4 cannot be due to the averaging process. And any form of weighted averaging would also not affect the results.
Fig. 137.6: The temperature trend for Finland since 1750 according to Berkeley Earth.
Most of the differences between the MTA in Fig. 137.4 and the BE versions using adjusted data in Fig. 137.6 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. 137.4 and Fig. 137.5.
The magnitudes of these adjustments are shown graphically in Fig. 137.7 below. The blue curve is the difference in MTA values between adjusted (Fig. 137.5) and unadjusted data (Fig. 137.4), while the orange curve is the contribution to those adjustments arising solely from breakpoint adjustments. The overall adjustment from 1840 to 2013 is small, less than ±0.1°C (see orange curve). The main impact is an offset in the MTA values of about 0.5°C (see blue curve). This is solely due to a use of different MRT intervals for the data in Fig. 137.4 and that in Fig. 137.5 and so can be ignored.
Fig. 137.7: The contribution of Berkeley Earth (BE) adjustments to the anomaly data in Fig. 137.5 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 1891-2010 has a positive gradient of +0.021 ± 0.005 °C per century. The orange curve shows the contribution just from breakpoint adjustments.
Summary
The temperature data for Finland illustrates the difficulty of determining the true extent of climate change when the data is partial or inadequate. Has the climate of Finland warmed by almost 2.5°C since 1840 as the Berkeley Earth adjusted data in Fig. 137.5 suggests, or has the climate been stable for most of the 20th century as the data in Fig. 137.2 appears to indicate? Is the warming seen before 1900 (when carbon dioxide levels barely increased) due to climate change, or is it due to an urban heat island (UHI) in Helsinki (which accounts for all the data)? Without more data it is hard to tell, but one way we could might be to compare Finland with its neighbours. This I will do in the next post.
Acronyms
BE = Berkeley Earth.
MRT = monthly reference temperature (see Post 47).
MTA = mean temperature anomaly.
List of all stations in Finland with links to their raw data files.
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