Black curve

Long-term average (1756−2005) daily mean temperature for each calendar date.

Red/blue curve

Daily mean temperature for each date in a selected year.

Grey band

Range between highest and lowest recorded daily mean temperature for each date, within the first 250 years of data.

All temperatures shown in the graph represent conditions approximately valid for Stockholm as in the middle of the 19th century. Artificial effects on the temperature data, from the growing city and due to insufficient protection from radiation of old thermometers, have been removed.

Datasets

Background

Early meteorology in Sweden

In the eighteenth century, during the Enlightenment, it was common that astronomers carried out weather observations as the science topic today known as meteorology was not yet born. In Sweden, the earliest instrumental weather observations were made in Uppsala in 1722. Anders Celsius (1701–1744), now most famous for his thermometer scale presented in 1742, was involved in making these first measurements already when he was a young student at the university and he continued with making weather observations in Uppsala for many years. Thanks to Celsius’ work, temperatures in Sweden have been measured in the Celsius scale already since the 1740s.

Pehr Wargentin ⁠ — ⁠ father of the weather observations in Stockholm

In 1735 another young person, Pehr Wilhelm Wargentin (1717–1783), registered as a student at the university in Uppsala to study mathematics and astronomy. Wargentin assisted Celsius in the making of both weather and astronomical observations. In 1746 Wargentin presented a thesis based on his studies of planet Jupiter’s moons.

After Wargentin had been elected as the secretary of the Royal Swedish Academy of Sciences in 1749, he became engaged in planning for the construction of an astronomical observatory in Stockholm. The building was inaugurated in 1753. Wargentin became the director and immediately moved into apartments in the middle storey, where he lived for the rest of his life.

The duties of the academy’s secretary were plentiful, ranging from being the responsible editor of the academy’s transactions to finding financial support for buying and manufacturing instruments at the observatory and to laying out plans for various scientific investigations. Wargentin discussed with his colleagues about the best way of conducting weather observations and he argued for the introduction of standardized routines. On January 1, 1754, Wargentin started to keep a diary of weather observations made at the astronomical observatory in Stockholm and he continued to make these observations himself almost every day until he died on December 13, 1783.

Wargentin’s scientific work as a climatologist

Wargentin wrote seven articles with topics related to meteorological instruments, weather and climate, which were published in the academy’s transactions between 1749 and 1778. This set of articles provides a good view of how well, or little, scientists of those days understood climate and weather phenomena. In the first of these papers he discussed different thermometer types that were in common use at the time. He judged the Swedish type, made by Celsius and other colleagues, to be the most reliable. This probably explains why the Celsius type rapidly became the standard in Sweden.

In the last of the seven articles, Wargentin analysed his own temperature observations made in Stockholm during 1758–1777 together with observations in Uppsala from 1739–1757. He was able to demonstrate that a common belief of those days that climate repeated itself every nineteenth year was a false idea. Hence, he demonstrated the efficiency of scientific methods for testing a hypothesis. He also stressed the importance of undertaking more observations to help scientists to better understand nature’s rules.

From Wargentin to SMHI

After Wargentin had died, another astronomer, Henric Nicander (1744–1815), took over the role as the academy’s secretary and also the task of doing weather observations. Later, observing the weather became regarded as a simple routine work and the job was left to other staff such as attendants and caretakers. Scientists at the academy became more engaged in planning for the establishment of a national network of weather observing stations.

Largely as a result of the academy’s efforts, the first successful Swedish national network of weather stations on land, with about 25 stations, was established in 1859. About a decade earlier, another network with weather observations being made at about 15 lighthouse stations had been established by marine authorities. Together, they were the start of the modern network of several hundred weather stations managed by the Swedish Meteorological and Hydrological Institute (SMHI).

Stockholm observatory ⁠ — ⁠ a unique long-term weather observing station

The old astronomical observatory in Stockholm is one of the stations in the SMHI network and measurements there have always been made at the same geographical location. The World Meteorological Organization (WMO) acknowledged in 2017 this site as a long-term observing station, implying that it is considered as highly important for climate science due to its long-term sustainable observational standards and high-quality time series data. Stockholm has the longest record among all the WMO long-term stations.

Long weather record⁠  —  ⁠challenge for climate scientists

Much, however, has happened during the more than 260 years that have passed. Not just has climate changed and become warmer, but also observation routines, instruments and their exact positions have changed (since 1961 at 59°20'30.1"N, 18°03'17.6"E, 44 m a.s.l.). The local environment has also changed as Stockholm has grown from being a rather small city having a few hundred thousand citizens to a large urban area with more than a million people. This has led to a local warming since the middle of the 19th century due to the so-called urban heat island effect. Thus, it is a challenge for scientists to use the hundreds of thousands of individual observations to obtain so-called homogeneous data series; i.e. data that only show how weather and climate has varied.

Scientists at Stockholm University have studied how to derive homogeneous daily air temperature and air pressure data for Stockholm back to 1756. This work started with a doctoral thesis in Physical Geography (Moberg, 1996) and continued in projects done together with scientists in other European countries having similar long-term daily instrumental weather records and with colleagues at Uppsala University and the SMHI (Moberg et al., 2002; Moberg et al., 2003). The dataset presented here is based on the outcome from that work and has been updated to the present by merging with recent data from the SMHI resource Öppna Data.

Citation

Anders Moberg (2020) Stockholm Historical Weather Observations. Dataset version 3. Bolin Centre Database. https://doi.org/10.17043/stockholm-3

References

Moberg A. 1996: Temperature variations in Sweden since the 18th century. Avhandlingsserie / Naturgeografiska institutionen, Stockholms universitet, 1104-7208 (5)

Moberg A, Bergström H, Ruiz Krigsman J, Svanered O. 2002: Daily air temperature and pressure series for Stockholm (1756–1998). Climatic Change 53: 171–212. https://doi.org/10.1023/A:1014966724670

Moberg A, Alexandersson H, Bergström H, Jones PD. 2003: Were Southern Swedish summer temperatures before 1860 as warm as measured? Int. J. Climatol. 23: 1495–1521. https://doi.org/10.1002/joc.945