2012-2016

Climate, social and demographic change and disease in Sweden during three hundred years

PROJECT PURPOSE AND CHANGES
Aim of this project was to analyse the association between climate variability and mortality in Sweden between the 18th and the 20th century.
Studies in modern societies have shown that both heat and cold can have negative health impacts, especially on cardiovascular disease events and respiratory health problems. Often it is the elderly and chronically ill who are most vulnerable. Little evidence, however, exists on the role of weather on mortality in a pre-industrial society, and how this role might have changed in the course of industrial development and the epidemiological transition.
Therefore we wanted to investigate the impact of temperature and precipitation on total and cause-specific mortality in Skellefteå, northern Sweden, between ca. 1750 and 1950. We used vital data of the databases Tabellverket (1749-1859) and Poplink (1800-1950) of the Demographic Database at Umeå University, and monthly temperature and precipitation data from Umeå, Uppsala and Tornedalen.
No major changes of research aims occurred. In the course of the project, the inquiry was extended to assess the mediating role of harvest outcomes in climate-mortality impacts.

THE THREE MOST IMPORTANT RESULTS OF THE PROJECT AND THEIR IMPLICATIONS
Building upon previous analyses for Uppsala, we first used parish data from the Skellefteå region for the period of 1749 to 1859 to assess the impact of seasonal climate variability on annual death counts.
We found in both locations similar, remarkable impacts of precipitation in springtime and in autumn - death counts increased with higher rainfall levels in autumn, while they decreased with more rainfall during springtime. In Skellefteå, it was children aged 3 to 9 who appeared most vulnerable to adverse weather conditions.
Using the Poplink dataset, we then analysed weather impacts in three different periods: 1800-1859, 1860-1909, 1910-1950, roughly reflecting different stages of industrialization in the Skellefteå region. Unlike in the previous studies, we now could assess impacts on total and cause-specific mortality at the monthly, rather than on the annual level. Cause-specific mortality was analysed according to two main categories: Infectious diseases, and cardiovascular diseases.
We also involved a climatologist (Dr. David Hondula, Arizona State University) to improve estimates of local precipitation for the period prior to 1860 when no measurements were yet done in Umeå. Dr. Hondula developed a model to estimate monthly precipitation in Umeå/Skellefteå for this time, based on recordings from Uppsala and Tornedalen.
The 19th to mid-20th century was characterized in Skellefteå by growing population numbers and decreasing mortality, although industrialization did not really start before the 1900s. Even in the latest period, deaths from infectious diseases still outnumbered cardiovascular deaths. The last period was the warmest, and the second the coldest.
Our statistical analyses showed that higher temperature was associated with lower total mortality with a delay of up to a few months. This pattern was not as strong for longer lags (six to twelve months after exposure). The protective effect of higher temperatures on total and cause-specific mortality was largest in the first period and less pronounced from 1860 onwards. Higher precipitation was also associated with lower total mortality at lag 0-2 months during all periods.
In general, patterns for weather-related mortality from infectious and cardiovascular diseases were similar to those of total mortality. The estimates were however less precise because of lower counts - there were many missing data for cause of death, particularly before 1860.
As a side-project, we looked into agricultural outcomes as a potential mediating factor between climate and mortality. Using contemporary assessments of harvest quality from Västerbotten, we found that the most important weather factor for harvest failure was summer temperature. Harvest failure increased mortality the next year, the effect being larger for children than for adults. Its role in linking weather and mortality, however, seems more complex than expected.
Our first studies assessed seasonal climate variability on the total number of annual deaths, confirming that the timing of rainfall and temperature during the year plays a role. The Poplink analyses, however, took another perspective, looking into weather impacts on monthly deaths.
In a next step, we will combine the two approaches, by stratifying these analyses on a monthly level by season. This way, we hope to show how heat, cold, rain and snow affect mortality on a finer scale at different times of the year.

NEW RESEARCH QUESTIONS GENERATED FROM THE PROJECT
As a future spin-off project, we plan to investigate specific health outcomes of weather more closely, namely mortality from measles, dysentery and tuberculosis.
Another new research idea is to look into climate-mortality associations in Sami communities in the late 18th and the 19th century. The necessary population data are available at the Demographic Database in Umeå.
A collaboration is planned with Prof. Scott Sheridan, a meteorologist from Kent State University, USA, to develop a weather typology based on historical measurements on temperature and precipitation. This holistical approach of defining weather conditions shall then be applied to analyse weather-mortality impacts in Skellefteå between 1800 and 1950.

INTERNATIONAL CONNECTIONS OF THE PROJECT
- Poster presentations 2013:
"Association of seasonal climate variability and annual mortality in pre-industrial Sweden"
a) Annual conference of the ISEE (International Society of Environmental Epidemiology), August 2013, Basel, Switzerland, and
b) Annual conference of the DGEpi (German Society for Epidemiology), September 2013, Leipzig, Germany. Poster prize awarded.
- Poster presentation 2014:
"Is harvest failure the link between climate variability and mortality in a pre-industrial society? Results from northern Sweden"
Annual conference of the ISEE, August 2014, Seattle, USA.

RESEARCH COMMUNICATION MEASURES OUTSIDE THE SCIENTIFIC COMMUNITY
- Following a brief video presentation at a global health event in Stockholm, results of the first publication on climate and mortality in Uppsala (conducted prior to the Skellefteå analyses) were covered in a full-page article in the newspaper "Upsala Nya Tidning", spring 2013.
- Popular science presentation "Climate and Health in Sweden over the Centuries" at the Medical Library of Umeå University, spring 2013. Target group: staff at all levels at the hospital and university, general public.
- Popular science presentation "Climate and health in Skellefteå over 200 years" at the "Forskartorget" in Umeå, organized by Riksbankens Jubileumsfond, Dec. 2014.

THE TWO MOST IMPORTANT PUBLICATIONS
1) Rocklöv J, Edvinsson S, Arnqvist P, Sjöstedt de Luna S, Schumann B: Association of Seasonal Climate Variability and Age-Specific Mortality in Northern Sweden before the Onset of Industrialization. Int. J. Environ. Res. Public Health 2014, 11.
This publication was based on the analyses of data 1749 to 1859, and set the basis for more in-depth studies with Poplink data. This article has been accessed more than 1150 times since its publication.
2) Oudin Åström D, Edvinsson S, Hondula D, Rocklöv J, Schumann B: Impact of climate variability on total and cause-specific mortality before and during the industrialization in Sweden.
This manuscript was submitted in March 2016 to the Journal "Demographic Research" and is currently under review.

PUBLICATION STRATEGY
All publications are, or will be published in peer-reviewed open-access journals. This approach is also in line with the policy of our institution. In autumn 2016, at least one more paper is planned to be submitted for which data analyses have been finished.

PUBLICATION LIST
Published article
Rocklöv J, Edvinsson S, Arnqvist P, Sjöstedt de Luna S, Schumann B: Association of Seasonal Climate Variability and Age-Specific Mortality in Northern Sweden before the Onset of Industrialization. Int. J. Environ. Res. Public Health 2014, 11(7), 6940-6954; doi:10.3390/ijerph110706940. Accessible at: http://www.mdpi.com/1660-4601/11/7/6940
Manuscript under revision
Oudin Åström D, Edvinsson S, Hondula D, Rocklöv J, Schumann B: Impact of climate variability on total and cause-specific mortality before and during the industrialisation in Sweden (spring 2016, under review at Demographic Research)
Manuscript in preparation
Joacim Rocklöv, Sören Edvinsson, Barbara Schumann: Harvest outcomes as a potential intermediate factor between climate variability and mortality in a pre-industrial northern European community (planned submission: autumn 2016).

Publications

Rocklöv J, Edvinsson S, Arnqvist P, Sjöstedt de Luna S, Schumann B: Association of Seasonal Climate Variability and Age-Specific Mortality in Northern Sweden before the Onset of Industrialization. Int. J. Environ. Res. Public Health 2014, 11(7), 6940-6954; doi:10.3390/ijerph110706940. Accessible at: http://www.mdpi.com/1660-4601/11/7/6940
Manuscript under revision
Oudin Åström D, Edvinsson S, Hondula D, Rocklöv J, Schumann B: Impact of climate variability on total and cause-specific mortality before and during the industrialisation in Sweden (spring 2016, under review at Demographic Research)