Stockholm Historical Weather Observations — Monthly mean air temperatures since 1756

Black line

Long-term average (1756−2005) temperature.

Red/blue curve

Temperature in each year, for a selected season. Last year is marked with a circle if the season is incomplete.

Grey band

Range between highest and lowest daily mean temperature in each year, for the selected season.

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 (2021) Stockholm Historical Weather Observations — Monthly mean air temperatures since 1756. Dataset version 3. Bolin Centre Database. https://doi.org/10.17043/stockholm-historical-monthly-temperature-3

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 files, one file for each variant of the data. The data are available both as comma-separated values (.csv) and tab-separated values (.tsv) files:

1. stockholm_monthly_mean_temperature_1756_2020_nonhom
2. stockholm_monthly_mean_temperature_1756_2020_homo
3. stockholm_monthly_mean_temperature_1756_2020_adjust

Each data file has 18 columns with the following headers: year, jan, feb, mar, may, jun, jul, aug, sep, nov, dec, djf, mam, jja, son, ann.

• Column 1: Year
• Column 2⁠ ⁠– ⁠13: Monthly mean temperature for January through December
• Column 14: December to February mean temperature, assigned to the year in which January falls
• Column 15: March⁠ to May mean temperature
• Column 16: June to August mean temperature
• Column 17: September to November mean temperature
• Column 18: Annual mean temperature

Temperature unit: °C rounded to one decimal.

Code for missing DJF value in year 1756: −999.0

Comments

Observation site

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).

Change from manual to automatic observations in 2013

Data from before 2013 are based on manual observations (SMHI station 98210). Data from 2013 onward are derived from 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.

Three variants of the data

The three variants of monthly, seasonal and annual mean air temperatures are derived from the associated dataset with Daily mean temperatures.

Variant 1: Non-homogenized data

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

1. Data for some periods in 1756 and 1763 have been replaced with estimated temperatures derived from contemporaneous observations in Uppsala, to adjust for missing or poor daily observations in Stockholm.
2. Adjustment in 1819 ⁠– 1825 for an incorrectly calibrated thermometer probably being used.

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 motivation for applying these corrections to the monthly, seasonal and annual non-homogenized data here is to provide a temperature record that represents the actual temperature history, including the urban warming trend, but with corrections made for the supposed unreliable data in short periods in 1756, 1763 and 1819 ⁠– 1825.

Variant 2: 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.

It should be noted that the current adjustment applied is based on results from a study made in the late 1990s. Thus, there is a need to undertake further analysis of how to better adjust the temperature data for the modern urban heat island effect all the time up to the present.

Variant 3: Homogenized data with additional adjustment 1756⁠ – 1858

The third variant (homogenized data, 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, supporting the hypothesis that the old thermometers were insufficiently protected against radiation, which could have caused observed tempertures in the summer season to be to high. However, this 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 required to better assess the need for adjustments in the early period and to determine their size and how they should be applied.

Instrument positions and original data sources

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

Version history

Version 3

Data files in version 3 are updated to 2020. Data for 1756⁠ – 2019 are the same as in version 2. Data for 2020 are obtained by calculating the arithmetic averages of the associated Daily mean air temperatures.

Version 2

Data files in version 2 are updated to 2019, whereas data in version 1 ended in 2018. Monthly, seasonal and annual mean temperature data in version 2 are calculated as arithmetic averages of the associated Daily mean air temperatures.

Some monthly and annual mean temperatures in version 2 differ by 0.1 °C compared to version 1 because of differences in rounding to one decimal or differences in calculating annual mean temperatures in leap years.

Data in version 2 include seasonal mean temperatures, whereas these were not included in version 1.

Data in version 2 are provided as csv and tsv files, whereas data in version 1 are provided as tsv and txt files.

Version 1

Initial release.