What´s the weather got to do with it? - Infant mortality in Northern Sweden during the demographic transition
Climate vulnerability (the risk of humans being affected negatively by weather) is mediated by individual, environmental and societal factors. Little is known about climatic determinants of infant mortality in pre-industrial societies in a subarctic environment. Our project will investigate how seasonality and weather influenced infant mortality among different population groups in northern Sweden between 1800 and 1950. We will study:
•the association of seasonality and weather with infant mortality and stillbirths,
•modification of climate vulnerability by ethnicity and socio-demographic factors,
•long-term trends in climate vulnerability.
Parish register data and recordings of monthly temperature and precipitation (rain, snow) will be used. The association of month of birth and weather at birth with infant mortality will be quantified statistically. Stratified analyses will assess differences in climate vulnerability by ethnicity (Sami vs. non-Sami), by sex and by parental occupation. Long-term trends in climate vulnerability due to socio-economic development and the demographic transition will be studied.
Our study will highlight interactions of the natural and social environment affecting infant mortality and stillbirths in rural societies living under harsh conditions, and identify the most vulnerable groups. Given the unique historical data available, this project will fill an international knowledge gap in the field of environmental health.
Final report
Purpose and development
The aim of the project has been to investigate the significance of weather and climate for infant mortality in northern Sweden between 1800–1950. The project has targeted three key research issues 1) the relationship between season and weather for infant mortality and stillbirth, 2) how ethnicity and socio-demographic factors modified vulnerability to the climate and 3) changes over time in terms of vulnerability to the climate. The project has resulted in 7 published articles.
The project has followed the original plan in terms of purpose, research issues and implementation. The discrepancy that has occurred is that more studies focused on mortality during the first month of life (neonatal mortality) in relation to mortality during the entire first year of life. The reason for this discrepancy is that early in the analyzes we found that newborns constituted a particularly vulnerable group to the climate.
The development of the project has followed a step-by-step process where the initial analyzes of the relationship between season and temperature at birth have been extended to also treat temperature before birth (7 days before) and temperature throughout the first month of life. Over time, the project has included several parishes in northern Sweden and expanded the statistical methods for better adaptation of, for example, seasonal effects and trends. The theoretical framework has been expanded by adding to a greater extent the importance of social and cultural mechanisms for children and women's health.
Implementation
The project group consisted of four participants belonging to different subject areas: sociology, epidemiology, statistics, and history. All project participants are linked to the interdisciplinary research environment, CEDAR (Center for Demographic and Aging Research), Umeå University.
During the first year of the project, significant time was spent on data preparation, which mainly consisted of: 1) extraction from historical population databases including all born / dead in northern Sweden 1800–1950, which was provided by the Demographic Database, Umeå University and 2) historical weather data (daily local temperature measurements) provided by Statistics Sweden.
Initially, descriptive analyzes were performed of the relationship between temperature and mortality for individual congregations to then include larger geographical areas and add more factors that were expected to be able to modify the effect of temperature.
The project has been carried out according to the project plan and the ongoing work has taken place in project form where all participants have been involved in each study; from planning, implementation / analysis to the final product in the form of writing articles.
Results
The changing significance of temperature: from cold to heat
The project has been able to demonstrate the changing effect of temperature on infant mortality between 1800–1950. Until the end of the 19th century, low temperatures had the most significant effect on neonatal mortality and the risk of stillbirth. During the first three decades of the 20th century, temperature had no proven effect on the risk of infant mortality, and during the latter period of the study, 1930–1950, showed a significant effect of high temperature. The risk of both neonatal mortality and stillbirth increased at temperatures just above 20°C .The analyzes have shown that the temperature that is most favorable for newborns (lowest mortality) is around 15 °C, which is in line with international research.
Gender differences in vulnerability
In studies of gender differences in infant mortality, we have found that boys generally have higher mortality risks than girls. Regarding the importance of temperature, boys are more vulnerable to temperatures than girls, where the risk of neonatal mortality and stillbirth for boys increases at high temperatures. In combination with the fact that boys have a higher risk of being born prematurely and thus have a low birth weight, the heat / high temperature thus constitutes an additional risk factor for newborn boys. These gender differences could be demonstrated for the entire period examined 1800–1950.
The importance of social class and ethnicity
The project has shown differences in temperature-related vulnerability between different social classes and between Sami and non-Sami. With regard to social class, it emerged that the differences in temperature-related vulnerability changed over time and where the effect of heat was greatest among workers during the later period (1930–1950). Some studies examined differences in infant mortality between Sami and non-Sami 1800–1899, where the results showed an increased vulnerability of low temperatures for the Sami population. The non-Sami population benefited from warm temperatures, mainly during the summer.
The conclusions that can be drawn from the climate's impact on the risk of infant mortality are that deviating temperatures (extreme heat and extreme cold) have a negative impact on pregnant women and newborns' health where factors such as gender, social class, and ethnicity modify vulnerability. Temporal differences in the effect of temperature on infant mortality have been related to societal changes in living conditions, the development of maternal and childbirth care and trends in breastfeeding patterns.
New research questions
The new research questions generated by the project are the significance of temperature and climate for other types of negative birth outcomes than those studied within the framework of the project, for example regarding low birth weight and premature birth (premature birth). Another research question is the significance of temperature and climate for children born in 1950 and up to the present day. We know that the risk of mortality related to extreme cold has decreased in line with improvements in living standards and the development of maternity and childbirth care since 1940 and onwards. In the studies we conducted, the effect of heat does not diminish to the same extent and in combination with the current elevated average temperature, this opens up for further studies of the relationship between temperature and negative birth outcomes in a Swedish context.
Dissemination of results
The results of the studies conducted within the project have been disseminated in the form of 1) international conference participation and presentations, 2) seminars and lectures, at Umeå University, Tampere University and Kent State University, 3) workshops with both national and international participants 4) social media and personal websites etc. and 5) peer-reviewed open-access publications
List of publications
Peer-reviewed articles in open-access journals:
Karlsson, L, Junkka, J, Lundevaller, E and Schumann, B (2021). Ambient temperature and stillbirth risks in northern Sweden, 1880-1950. Environmental Epidemiology. Vol: 5, Issue: 6, https://doi.org/10.1097/EE9.0000000000000176
Karlsson, L, Junkka, J, Schumann, B, Häggström Lundevaller, E (2021). Socioeconomic disparities in climate vulnerability: neonatal mortality in northern Sweden, 1880–1950. Population and Environment. https://doi.org/10.1007/s11111-021-00383-9
Junkka, J, Karlsson, L, Lundevaller, E, Schumann, B (2021). Climate vulnerability of Swedish newborns: gender differences and time trends of temperature-related neonatal mortality, 1880 - 1950. Environmental Research. https://doi.org/10.1016/j.envres.2020.110400.
Karlsson L, Lundevaller E and Schumann B. (2020) Neonatal Mortality and Temperature in Two Northern Swedish Rural Parishes, 1860–1899 — The Significance of Ethnicity and Gender. International Journal of Environmental Research and Public Health 17. https://doi.org/10.3390/ijerph17041216.
Schumann B, Häggström Lundevaller E and Karlsson L. (2019) Weather extremes and perinatal mortality - Seasonal and ethnic differences in northern Sweden, 1800-1895. Plos One 14: e0223538. https://doi.org/10.1371/journal.pone.0223538
Karlsson L, Lundevaller EH and Schumann B. (2019) Season of birth, stillbirths, and neonatal mortality in Sweden: the Sami and non-Sami population, 1800–1899. International Journal of Circumpolar Health 78: 1629784. https://doi.org/10.1080/22423982.2019.1629784
Karlsson L, Lundevaller E and Schumann B. (2019) The association between cold extremes and neonatal mortality in Swedish Sápmi from 1800 to 1895. Global Health Action 12: 1623609. https://doi.org/10.1080/16549716.2019.1623609
Conference presentations:
Indigenous infant mortality by age and season of birth, 1800-1899. Does season of birth affect children's survival chances? European Social Science History Association Conference, Belfast, April 4-7, 2018.
The association of extreme temperature and neonatal mortality: Swedish Sápmi 1800-1895. 21st Nordic Demographic Symposium in Reykjavik June 15, 2019.
Perinatal mortality and weather extremes in pre-industrial societies: the role of season and ethnicity, northern Sweden 1800-1895, 21st Nordic Demographic Symposium in Reykjavik 15 June 2019.
The association of extreme temperature and neonatal mortality: Swedish Sápmi 1800-1895, The 3rd European Society of Historical Demography Conference, 26-29 June 2019, Pécs, Hungary.
Cold impacts on neonatal mortality in an extreme climate - the role of ethnicity in pre-industrial Sweden, The 31st annual conference of the International Society for Environmental Epidemiology (ISEE 2019), 25-28 August 2019, Utrecht, the Netherlands.
Presentation of research projects and research results:
https://www.umu.se/nyheter/pojkar-extra-drabbade-av-temperaturrelaterad-spadbarnsdodlighet_11468073/
https://www.umu.se/forskning/projekt/vad-har-vadret-med-dodligheten-att-gora-spadbarnsdodlighet-i-norra-sverige-under-den-demografiska-transitionen/
The aim of the project has been to investigate the significance of weather and climate for infant mortality in northern Sweden between 1800–1950. The project has targeted three key research issues 1) the relationship between season and weather for infant mortality and stillbirth, 2) how ethnicity and socio-demographic factors modified vulnerability to the climate and 3) changes over time in terms of vulnerability to the climate. The project has resulted in 7 published articles.
The project has followed the original plan in terms of purpose, research issues and implementation. The discrepancy that has occurred is that more studies focused on mortality during the first month of life (neonatal mortality) in relation to mortality during the entire first year of life. The reason for this discrepancy is that early in the analyzes we found that newborns constituted a particularly vulnerable group to the climate.
The development of the project has followed a step-by-step process where the initial analyzes of the relationship between season and temperature at birth have been extended to also treat temperature before birth (7 days before) and temperature throughout the first month of life. Over time, the project has included several parishes in northern Sweden and expanded the statistical methods for better adaptation of, for example, seasonal effects and trends. The theoretical framework has been expanded by adding to a greater extent the importance of social and cultural mechanisms for children and women's health.
Implementation
The project group consisted of four participants belonging to different subject areas: sociology, epidemiology, statistics, and history. All project participants are linked to the interdisciplinary research environment, CEDAR (Center for Demographic and Aging Research), Umeå University.
During the first year of the project, significant time was spent on data preparation, which mainly consisted of: 1) extraction from historical population databases including all born / dead in northern Sweden 1800–1950, which was provided by the Demographic Database, Umeå University and 2) historical weather data (daily local temperature measurements) provided by Statistics Sweden.
Initially, descriptive analyzes were performed of the relationship between temperature and mortality for individual congregations to then include larger geographical areas and add more factors that were expected to be able to modify the effect of temperature.
The project has been carried out according to the project plan and the ongoing work has taken place in project form where all participants have been involved in each study; from planning, implementation / analysis to the final product in the form of writing articles.
Results
The changing significance of temperature: from cold to heat
The project has been able to demonstrate the changing effect of temperature on infant mortality between 1800–1950. Until the end of the 19th century, low temperatures had the most significant effect on neonatal mortality and the risk of stillbirth. During the first three decades of the 20th century, temperature had no proven effect on the risk of infant mortality, and during the latter period of the study, 1930–1950, showed a significant effect of high temperature. The risk of both neonatal mortality and stillbirth increased at temperatures just above 20°C .The analyzes have shown that the temperature that is most favorable for newborns (lowest mortality) is around 15 °C, which is in line with international research.
Gender differences in vulnerability
In studies of gender differences in infant mortality, we have found that boys generally have higher mortality risks than girls. Regarding the importance of temperature, boys are more vulnerable to temperatures than girls, where the risk of neonatal mortality and stillbirth for boys increases at high temperatures. In combination with the fact that boys have a higher risk of being born prematurely and thus have a low birth weight, the heat / high temperature thus constitutes an additional risk factor for newborn boys. These gender differences could be demonstrated for the entire period examined 1800–1950.
The importance of social class and ethnicity
The project has shown differences in temperature-related vulnerability between different social classes and between Sami and non-Sami. With regard to social class, it emerged that the differences in temperature-related vulnerability changed over time and where the effect of heat was greatest among workers during the later period (1930–1950). Some studies examined differences in infant mortality between Sami and non-Sami 1800–1899, where the results showed an increased vulnerability of low temperatures for the Sami population. The non-Sami population benefited from warm temperatures, mainly during the summer.
The conclusions that can be drawn from the climate's impact on the risk of infant mortality are that deviating temperatures (extreme heat and extreme cold) have a negative impact on pregnant women and newborns' health where factors such as gender, social class, and ethnicity modify vulnerability. Temporal differences in the effect of temperature on infant mortality have been related to societal changes in living conditions, the development of maternal and childbirth care and trends in breastfeeding patterns.
New research questions
The new research questions generated by the project are the significance of temperature and climate for other types of negative birth outcomes than those studied within the framework of the project, for example regarding low birth weight and premature birth (premature birth). Another research question is the significance of temperature and climate for children born in 1950 and up to the present day. We know that the risk of mortality related to extreme cold has decreased in line with improvements in living standards and the development of maternity and childbirth care since 1940 and onwards. In the studies we conducted, the effect of heat does not diminish to the same extent and in combination with the current elevated average temperature, this opens up for further studies of the relationship between temperature and negative birth outcomes in a Swedish context.
Dissemination of results
The results of the studies conducted within the project have been disseminated in the form of 1) international conference participation and presentations, 2) seminars and lectures, at Umeå University, Tampere University and Kent State University, 3) workshops with both national and international participants 4) social media and personal websites etc. and 5) peer-reviewed open-access publications
List of publications
Peer-reviewed articles in open-access journals:
Karlsson, L, Junkka, J, Lundevaller, E and Schumann, B (2021). Ambient temperature and stillbirth risks in northern Sweden, 1880-1950. Environmental Epidemiology. Vol: 5, Issue: 6, https://doi.org/10.1097/EE9.0000000000000176
Karlsson, L, Junkka, J, Schumann, B, Häggström Lundevaller, E (2021). Socioeconomic disparities in climate vulnerability: neonatal mortality in northern Sweden, 1880–1950. Population and Environment. https://doi.org/10.1007/s11111-021-00383-9
Junkka, J, Karlsson, L, Lundevaller, E, Schumann, B (2021). Climate vulnerability of Swedish newborns: gender differences and time trends of temperature-related neonatal mortality, 1880 - 1950. Environmental Research. https://doi.org/10.1016/j.envres.2020.110400.
Karlsson L, Lundevaller E and Schumann B. (2020) Neonatal Mortality and Temperature in Two Northern Swedish Rural Parishes, 1860–1899 — The Significance of Ethnicity and Gender. International Journal of Environmental Research and Public Health 17. https://doi.org/10.3390/ijerph17041216.
Schumann B, Häggström Lundevaller E and Karlsson L. (2019) Weather extremes and perinatal mortality - Seasonal and ethnic differences in northern Sweden, 1800-1895. Plos One 14: e0223538. https://doi.org/10.1371/journal.pone.0223538
Karlsson L, Lundevaller EH and Schumann B. (2019) Season of birth, stillbirths, and neonatal mortality in Sweden: the Sami and non-Sami population, 1800–1899. International Journal of Circumpolar Health 78: 1629784. https://doi.org/10.1080/22423982.2019.1629784
Karlsson L, Lundevaller E and Schumann B. (2019) The association between cold extremes and neonatal mortality in Swedish Sápmi from 1800 to 1895. Global Health Action 12: 1623609. https://doi.org/10.1080/16549716.2019.1623609
Conference presentations:
Indigenous infant mortality by age and season of birth, 1800-1899. Does season of birth affect children's survival chances? European Social Science History Association Conference, Belfast, April 4-7, 2018.
The association of extreme temperature and neonatal mortality: Swedish Sápmi 1800-1895. 21st Nordic Demographic Symposium in Reykjavik June 15, 2019.
Perinatal mortality and weather extremes in pre-industrial societies: the role of season and ethnicity, northern Sweden 1800-1895, 21st Nordic Demographic Symposium in Reykjavik 15 June 2019.
The association of extreme temperature and neonatal mortality: Swedish Sápmi 1800-1895, The 3rd European Society of Historical Demography Conference, 26-29 June 2019, Pécs, Hungary.
Cold impacts on neonatal mortality in an extreme climate - the role of ethnicity in pre-industrial Sweden, The 31st annual conference of the International Society for Environmental Epidemiology (ISEE 2019), 25-28 August 2019, Utrecht, the Netherlands.
Presentation of research projects and research results:
https://www.umu.se/nyheter/pojkar-extra-drabbade-av-temperaturrelaterad-spadbarnsdodlighet_11468073/
https://www.umu.se/forskning/projekt/vad-har-vadret-med-dodligheten-att-gora-spadbarnsdodlighet-i-norra-sverige-under-den-demografiska-transitionen/