Stockholm Historical Weather Observations — Daily mean air temperatures since 1756

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.

Citation

Anders Moberg (2020) Stockholm Historical Weather Observations — Daily mean air temperatures since 1756. Dataset version 2. Bolin Centre Database. https://doi.org/10.17043/stockholm-historical-daily-temperature-2

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 a comma-separated values (csv) text file. The data file has five columns with the following headers: date, raw, homo, adjust, site.

Column 1: Date (yyyy-mm-dd).

Column 2: Non-homogenized daily mean temperature according to the observations.

Column 3: Homogenized daily mean temperature, adjusted after 1870 to account for the urban heat island effect and with some early values infilled in using data extrapolated from Uppsala.

Column 4: Homogenized daily mean temperature, as in column 3, but with additional adjustment of May⁠ – August temperatures before 1859 to correct for a supposed warm bias in summer months.

Column 5: Data source ID code, identifying data from: (1) Stockholm, manual observations, (2) Uppsala, adjusted to represent Stockholm, (3) Stockholm, SMHI automatic weather station (used from 2013 onwards). Data from Uppsala are used for a few short periods in 1756 and 1763 and only in the homogenized data in column 3 and 4.

Temperature unit: °C rounded to one decimal.

Code for missing values in column 2: −999.0.

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). Data in the current dataset can differ from those in the SMHI database before 2013.

Data until 2012–12–31 are the same as in an earlier version of this dataset. Data after 2013–01–01 are obtained by automated daily download of daily mean temperatures for station 98230 in the SMHI resource Öppna Data. These data from the SMHI are used for column 2 in the data file here. Data in columns 3 and 4 have been adjusted as described below.

The first two variants of daily mean temperatures (columns 2 and 3 in the data file) have been calculated as described by Moberg et al. (2002).

The first variant (non-homogenized data) consists of daily mean temperatures calculated to account for changes in the observation times and the number of observations per day. Thus, they are estimates of daily mean temperatures obtained directly from the observations without any further corrections.

The second variant (homogenized data) includes the following adjustments, relative to the first variant:

1756–04–03⁠– 1756–10–31: The observed temperatures in Stockholm during this period are judged to be too high, and of poor quality. Therefore, daily means for this period have been replaced with temperatures estimated from contemporaneous observations in Uppsala through a linear regression model.
1763–02–25 – 1763–02–28: No observations were made. Daily temperatures have been extrapolated from Uppsala.
1819–08–01 – 1825–01–13: Correction by −0.7 °C because an incorrect thermometer was probably used.
1870–01–11⁠– present: Adjustment for urban heat island trend and other inhomogeneities.

The adjustment for the urban warming trend, and the effect of other inhomogeneities detected in homogeneity tests against surrounding reference station data, is applied such that the most recent homogenized temperatures are made somewhat colder than the non-homogenized temperatures in order to make the entire series being respresentative of rural conditions that prevailed before the mid-19th century. The size of the adjustment changes with time from 1870 until 1967 and is thereafter held at a constant level until the present, although the adjustment has an annual cycle and therefore varies between the dates in each year. This adjustment causes homogenized temperature data after 1967 to be 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: day 1⁠– 4: 0.0 °C, day 5⁠– 9: −0.1 °C, day 10⁠– 13: −0.2 °C, day 14⁠– 18: −0.3 °C, day 19⁠– 22: −0.4 °C, day 23⁠– 27: −0.5 °C, day 28⁠– 31: −0.6 °C.
June: day 1–30: −0.7 °C.
July: day 1–31: −0.7 °C.
August: day 1⁠– 4: −0.6 °C, day 5⁠– 9: −0.5 °C, day 10⁠– 13: −0.4 °C, day 14⁠– 18: −0.3 °C, day 19⁠– 22: −0.2 °C, day 23⁠– 27: −0.1 °C, day 28⁠– 31: 0.0 °C.

This gives an average adjustment by −0.3 °C for May and August and −0.7 °C for June and July. 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 daily mean temperatures is judged to be the one that currently best represents the true temperature climatology 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. There is a need also to undertake further analysis of how to better adjust the temperature data for the modern urban heat island effect, because the current adjustment is based on results from a study made in the late 1990s.

The number of daily observations used to calculate the daily means has varied with time, as described in the comments to an earlier version of this dataset. Information about instrument positions and original data sources is available in the comments to an associated dataset with thermometer observations.

Version history

Version 2

Data in version 2 is updated daily to the present, whereas data in version 1 ended in 2018-12-31. Data in version 2 are the same as in version 1 until 2012-12-31. From 2013-01-01 onward daily mean temperatures for SMHI station 98230 are downloaded automatically from the SMHI resource Öppna Data and used without any changes in the data column labeled ‘raw’. Data in the columns labeled ‘homo’ and ‘adjust’ are corrected in the same way as in version 1 but one or two daily mean temperatures each year may differ by 0.1 °C compared to version 1 because of differences in rounding to one decimal.

Version 1

Initial release.