Stockholm Historical Weather Observations — Monthly mean air temperatures since 1756

Anders Moberg

Weather observations of several meteorological variables have been made continuously at the old astronomical observatory in Stockholm since 1756. As a part of a collection of data for selected variables, the dataset provided here contains monthly mean air temperatures for the period 1756–2018. Three variants are available: (i) non-homogenized monthly mean temperatures, as estimated from the local temperature observations, (ii) homogenized monthly mean temperatures, adjusted after 1870 to exclude the urban warming trend in the city, and (iii) homogenized monthly mean temperatures having an additional adjustment applied to data for May–August in the period before 1859, to correct for a supposed warm bias of the observed temperatures due to likely poor protection of thermometers against radiation.

Citation

Anders Moberg (2019) Stockholm Historical Weather Observations — Monthly mean air temperatures since 1756. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/stockholm-historical-monthly-temperature-1

References

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

Moberg A, Tuomenvirta H, Nordli Ø. 2005: Recent climatic trends. In: Physical Geography of Fennoscandia. (Ed: Seppälä M). Oxford Regional Environments Series, Oxford University Press, Oxford: 113–133

Data description

Data are provided in three separate files having 14 columns, available in two file formats:

1. plain text files (.txt)

2. tab-separated value files (.tsv)

File content:

Column 1: Year

Column 2–13: Monthly mean temperature for January through December (unit: °C)

Column 14: Annual mean temperature (unit: °C)

The dataset also includes plots of time series of annual and seasonal mean temperatures in png format.

Further information about the data file content is found in a README text file.

Comments

The observation site is included in the national station network managed by the Swedish Meteorological and Hydrological Institute (SMHI), with station number 98210 (manual station) and 98230 (automatic station), but data in the current dataset can differ from those in the SMHI database.

The three variants of monthly mean air temperatures presented here are derived from the associated dataset with daily mean temperatures.

The first variant (non-homogenized data, see Moberg et al. 2002) accounts for changes in observation times and also includes the following adjustments:

1. Adjustments in 1819–1825 for an incorrectly calibrated thermometer probably being used.
2. Adjustments in 1756 and 1763 for missing or poor daily observations.

Note: In the corresponding dataset with daily mean temperatures, these two particular adjustments are not applied to the non-homogenized data, but they are applied there to the homogenized data.

The second variant (homogenized data, see Moberg et al. 2002) additionally includes an adjustment after 1870 to eliminate an urban warming trend and the effect of other inhomogeneities detected in homogeneity tests against surrounding reference station data. The main purpose of applying this adjustment is to obtain a homogenized record that, throughout its entire length, is approximately respresentative of the rural conditions that prevailed before the mid–19th century. The size of the adjustment changes with time and varies over the year. It causes homogenized temperature data after 1967 being on average 0.8°C colder than non-homogenized temperatures.

The third variant (with additional adjustment to data for May–August in the period 1756–1858), has been derived as in Moberg et al. (2005) based on conclusions in Moberg et al. (2003). It includes the following additional adjustments, relative to the second variant:

May and August: −0.3°C.
June and July: −0.7°C.

The motivation for this additional adjustment is based on the available knowledge about the position of the old thermometer in combination with results from homogeneity testing and other statistical modelling. However, it should be seen as an ad hoc judgement rather than a result from a strict statistical analysis. Nevertheless, this variant of monthly mean temperatures is judged to be the one that currently best represents the true temperature history for the May–August season. Further research would be needed to better assess the need for adjustments in the early period and to determine their size and how they should be applied. Actually, there is a need also to undertake further analysis of how to better adjust the temperature data for the modern urban heat island effect.

Data from before 2013 are based on manual observations. Data from 2013 onward are derived on the automatic weather station (SMHI station 98230). Monthly mean temperatures presented here may differ from those that can be obtained directly from the SMHI due to differences in calculation procedures.

Further information about instrument positions and original data sources is available in the comments to the associated dataset with thermometer observations.