A short story of the struggle to get long records of air temperature in Toruń, Central Poland

by Aleksandra Pospieszyńska

Toruń, Poland
My latest paper concerns climate changes during the instrumental measurements period (18712010) in Toruń, which is located in Central Poland (Europe).
The climate is constantly changing. Some of these changes can be noticed over the course of a human life. Other changes are visible only on longer time scales.

In this post, we will look closely at the changes observed during the period of instrumental measurements.



Why do we need the longest and the best quality of measurement series in studies on climate history?

Longer series of measurements allow us to determine how the climate changes with greater accuracy, and to calibrate models, both for the reconstruction of the climate in the past and its predictions for the future.

The minimum period that can be considered in climatological research is 30 years. If we look at the last 30 years, we are dealing with a remarkably rapid increase in air temperature. Conversely, if we take another period, for example 19401970, Toruń will appear as a very cold city.
A 140-year series, however, can describe the climate in Toruń without the burden of such short-term changes. In addition, in the above-mentioned climate modelling, the longer the used measurement series are, the more reliable the modelling results of future climate change become.

Or, putting it the other way around, the GIGO (Garbage In = Garbage Out) principle applies here: bad data input will result in bad climate models. 

What are the main technical problems with a long-term series of climate data and how many of them are there?

There are many problems in the study of climate change. A short list of those I have been struggling with is shown below with a short description.

1. Data availability

Poland’s tumultuous history, with numerous wars and partitions, has caused that finding historical climate-related sources requires searching libraries and archives not only in Poland, but also in Germany, Russia, Ukraine, Lithuania and Austria. Unfortunately, numerous sets of data have been lost irrevocably. Therefore, each source found or a reconstructed long series of data is an important contribution to the climate change variability of this part of Europe.

The data from the period 18712010 are derived from hand-written sources (measurement logbooks) and printed sources (meteorological yearbooks) published first by the Prussian and then the German and the Polish meteorological services.

2. Different measurements systems and instruments

The story of meteorological measurements in Toruń, cited after my newest paper: 

In the period 1872–1890, the measurements were conducted by the Royal Prussian Meteorological Institute. Political changes in the German Empire—a change in Chancellor in 1890—led in 1891 to the meteorological service changing name from the Prussian to the German Meteorological Institute. It conducted observations almost until the end of the World War I. After the return of Toruń to Poland in 1920, in the period 1921–1939, observations in the town were conducted by the Polish National Meteorological Institute. The Second World War brought further changes in meteorological measurements—they were assumed again by the German service. After the war—from 1945, meteorological measurements and observations were conducted by Soviet army until 1947 (Zieliński, pers. comm.) and then by the National Hydrological and Meteorological Institute (PIHM). In 1971, PIHM was re-named as the Institute of Meteorology and Water Management (IMGW), and again in 2010 as the Institute of Meteorology and Water Management—National Research Institute (IMGW-PIB).

As you can imagine, each service used their own instruments and methodology of measurements, which caused interruption in data series.

3. Changing in location of measurements sites

The locations of different categories of meteorological stations in Toruń and the range of observations were changed due to political changes, two world wars, urban expansion and a change in the number of stations themselves (which are shown in the figure below). In the 1920s, for example, four stations were operated concurrently by the military meteorological services – years of stations’ operations are also shown in the figure below.


Locations and observation lengths of meteorological stations in Toruń
(Pospieszyńska and Przybylak 2018)

4. Inhomogeneity of the data

For the Toruń series, interruptions within the series are mainly seen in times when stations were moved and changes were made in measurement methods: 1878, 1889, 1921, 1939, 1945, 1970 and 1981. This inhomogeneity may lead to false conclusions during further analyses. Therefore, the data was homogenised to avoid any influence caused by e.g. changing the location of the meteorological site.

So what are the long-term changes in air temperature in Toruń?

The annual average air temperature was 7.7 °C and ranged from 4.9 °C in 1871 to 9.7 °C in 2000 and the trend in the average air temperature is upwards and statistically significant (which means this change is visible and strong) – see figure below. The trend is around 0.1 °C per decade and thus similar to that for Europe as a whole ([1], [2], [3], [4], [5]).


Air temperatures in Toruń from 1871–2010 (Pospieszyńska and Przybylak 2018)

The turn of the 20th to 21st century had the highest frequency of extremely warm years. Meanwhile, a higher frequency of extremely cool years was seen in the 1940s and before 1900.
The analysis of Toruń for the period 1871–2010 revealed a marked shortening of winter (by 29 days) and a lengthening of summer (by 19 days) in the period from the end of the 19th century to the present day. There were also significant changes in the start and the end dates of individual seasons. 

Shortening of winter and lengthening of summer as well as changes in their start and end dates confirm statistically significant warming in Europe in the last 140 years.

Details are available in my article in Theoretical and Applied Climatology.


Aleksandra Pospieszyńska, PhD
Department of Meteorology and Climatology, Faculty of Earth Sciences, Nicolaus Copernicus University

If you have questions or comments concerning Aleksandra’s post, please leave a comment below or send her an email.

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References:

Linked article: Pospieszyńska A, Przybylak R (2018) Air temperature changes in Toruń (central Poland) from 1871 to 2010. Theor Appl Climatol. https://doi.org/10.1007/s00704-018-2413-9

[1] Rebetez M, Reinhard M (2007) Monthly air temperature trends in Switzerland 1901-2000 and 1975-2004. Theor Appl Climatol 91:27–34.  https://doi.org/10.1007/s00704-007-0296-2
[2] Dobrovolný P, Brázdil R, Valášek H, Kotyza O, Macková J, Halíčková M (2009) A standard paleoclimatological approach to temperature reconstruction in historical climatology: an example from the Czech Republic, a.D. 1718 – 2007. Int J Climatol 29:1478–1492
[3] Leijonhufvud L, Wilson R, Moberg A, Söderberg J, Retsö D, Söderlind U (2010) Five centuries of Stockholm winter/spring temperatures reconstructed from documentary evidence and instrumental observations. Clim Chang 101:109–141
[4] Mikkonen S, Laine M, Mäkelä HM, Gregow H, Tuomenvirta H, Lahtinen M, Laaksonen A (2015) Trends in the average temperature in Finland, 1847-2013. Stoch Env Res Risk A 29:1521–1529
[5] Niedźwiedź T, Glaser R, Hansson D, Helama S, Klimenko V, Łupikasza E, Małarzewski Ł, Nordli Ø, Przybylak R, Riemann D, Solomina O (2015) The historical time frame (past 1000 years). In: Second Assessment of climate change for the Baltic Sea basin . Regional Climate Studies, pp 51–65

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