Climate Change and Health Impacts.

de Schrijver, Evan (2023). Climate Change and Health Impacts. (Unpublished). (Dissertation, University of Bern, Faculty of Medicine and Faculty of Human Sciences)

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There is a well-established relationship between exposure to non-optimal temperatures and a wide range of adverse
health outcomes. At present, non-optimal temperatures contribute to 9.4% of total mortality, the equivalent
of 74 deaths per 100,000 people annually, with the majority of these deaths being a result from cold exposure
(8.5%) compared to heat (0.9%), which is larger than the global mortality burden related to air pollution (7.6%).
Evidence suggests that under various climate scenarios heat-related mortality is projected to further increase and
is likely to overtake cold-related mortality in some places. Even with full implementation of the Paris agreement
and reaching net-zero carbon emissions by 2050, the inherent inertia the climate system will continue to increase
temperatures for several more decades after, yielding a substantial additional health burden. Moreover, the projected
future heat- and cold-related mortality does not solely depend on the specific climate trajectory that is
being followed, also adaptation by populations and changes in population dynamics have the potential to vastly
modify the future mortality burden related, which have shown to be highly heterogeneous across regions. As
current mitigation policies show a large degree of misalignment with the Paris agreement that aims to keep global
warming well below 2.0°C, besides mitigation strategies, accelerated adaptation to non-optimal temperature is
essential to reduce the future heat-related mortality burden.

Prior to this Ph.D. little was known regarding changes in the heat- and cold-related mortality over long temporal
periods, the role of changes in population dynamics, vulnerability and adaptation factors and lastly the possible
mortality impacts under various climate change and population scenarios in Switzerland. Therefore, the primary
objective is to explore the impacts of heat- and cold in Switzerland, identify adaptation factors, to project future
mortality under various climate and population scenarios and to quantify the additional contribution of human
induced climate change on the overall heat-related mortality burden, to ultimately help equip policy makers with
the tools necessary to create resilient populations against a changing climate.

The main body of the thesis consists of eleven publications, of which four studies that are first-author contributions
(three published, one submitted), four second-author studies (two published, two submitted) and finally
three co-authored studies (two published, one submitted).

First, to date, most studies aiming to explore the temperature-mortality association have used weather stations
to approximate the exposure of populations to temperature, although this is known to come with substantial
limitations. Therefore we aimed to explore whether spatially resolved climate data was at least an equally good
predictor for mortality in Switzerland and 39 other countries. In this thesis, we observed that despite a small biases
in the absolute temperature observations, newly developed reanalysis data generally compare well to weather
stations, as these yielded very similar temperature-mortality association and impacts. Moreover, these findings
imply that spatially resolved weather data can now be used to explore the effect of temperature-mortality at very
high resolution, in rural regions, on a global scale and in regions with no temperature monitor stations available.
However, the analyses provide some indication of lower performance in tropical regions, therefore some caution
is required.

As we have shown that reanalysis data can be used to study the temperature-mortality association and impacts
across the world at high resolution, we aimed on leverage on this exposure data to analyse 49 years of temperaturemortality
trends in Switzerland, while also exploring the role of population ageing. This is particularly relevant
as older adults are considered particularly vulnerable to non-optimal temperature and as it is expected that progressive
ageing will amplify the total non-optimal related mortality. We observed that although the vulnerability
remained largely similar over time in Switzerland, the annual number of deaths attributable to heat has more than
tripled over the past 50 years. Similarly, the overall cold-related vulnerability substantially decreased, while the
attributable number of deaths for cold-mortality has remained constant. This implies that although vulnerability
has decreased over time, the increase in overall societal impacts can be attributed to a larger pool of susceptible
people, which is driven by population ageing and population development. Thus population ageing was found to
attenuate the decrease in cold-related mortality, while it amplified the heat-related mortality impacts, which has
significant implications for modelling the projected temperature-mortality burden under different scenarios of
climate change. Then, besides temperature being associated with substantial mortality in Switzerland, also tropical
nights have shown additive effect on mortality across various in Switzerland. Finally, mental health hospital
admissions and suicides have been associated with increases in temperature despite recent public health efforts.
Additionally, besides exploring temporal changes in the temperature-mortality impacts, we also aimed to spatially
study temperature-vulnerability, which is particularly relevant as studies have hypothesised that large differences
in vulnerability exists between urban and rural regions. Moreover, being able to identify the most vulnerable
regions at risk for temperature-related mortality in Switzerland, we have the potential to better understand
drivers of vulnerability to foster resilient population for the future impacts of a changing climate. Our findings
suggest larger temperature vulnerability in urban clusters, particularly for heat compared to rural regions, while cold related vulnerability was similar across typologies. More importantly, this thesis has shown that drivers of
temperature-vulnerability can considerably vary by urban-rural typology in Switzerland. In urban regions mainly
environmental factors modified the temperature-mortality relationship, while in peri-urban and rural regions,
also social factors could explain vulnerability.

Climate change and population ageing are constituting a double burden when it comes to temperature-related
mortality impacts due to increased exposure to extreme heat and vulnerability. As evidence is limited on the
projected synergistic impacts of climate change and population development, we aimed to project heat- and
cold-related mortality under various climate change scenarios and population development combined across
Switzerland and across 43 countries using over 130 million deathrecords. Our findings suggest that both heat- and
cold-related mortality will substantially increase under all scenarios of climate change and population development
under all degrees of warming. Moreover, population development will reverse the reduction in cold-related
mortality despite a warming climate, and further exacerbate heat-related mortality, leading to a substantial netincrease
of the total non-optimal temperature-mortality across the globe, with heterogeneous impacts between
regions.

Finally, with a changing climate, extremely hot summers will likely increase in frequency. However, although
most studies estimate the heat-related mortality in such summer, to date few studies have aimed to disentangle
heat-related mortality from the influence of human induced anthropogenic climate change. Therefore, in this
thesis we aimed to quantify the contribution of human-induced climate change to the observed mortality due to
heat in Switzerland during the summer of 2022. We observed that the extreme heat during the summer of 2022
amounted to more than 600 heat-related deaths in Switzerland, of which more than 60% can directly be attributed
to human induced climate change.

This PhD project is the first of it’s kind to study the temperature and health impacts in full depth and breath
in Switzerland. We have contributed on the global knowledge regarding long term temperature-mortality impacts
and understanding the dynamics of demographic changes over time in relation to temperature vulnerability.
Then, we have generated new hypotheses that vulnerability largely varies between countries, regions and
cities and that different drivers lay the foundation for adaptation, meaning that local adaptation strategies are
required. Furthermore, we have improved the epidemiological methodology regarding climate projections and
future health impacts by showing that incorporating Shared Socioeconomic Pathways and different demographic
baseline assumptions in the models, can vastly modify the measure of impact generated. Finally, we have shown
that already today a large part of the heat-related mortality burden can directly be attributed to human induced climate change. Based on the observed results and the remaining uncertainty in climate change epidemiology,
current efforts should first be aimed at expanding scientific knowledge regarding climate change and temperaturerelated
impacts to a truly global coverage as most countries still remain understudied to get a better picture of
regions that will most be affected. Then, causality of study designs applied in climate epidemiology should be
improved to have an impact also beyond the field of epidemiology, such as in climate litigation. Finally current
efforts should be targeted at understanding the complexity of adaptation and implementation of these, as the
most recent summer have been the hottest ever experienced by humankind, however will remain the coolest in
the years that are yet to come.

Item Type:	Thesis (Dissertation)
Division/Institute:	04 Faculty of Medicine > Pre-clinic Human Medicine > Institute of Social and Preventive Medicine (ISPM) 08 Faculty of Science > Physics Institute > Climate and Environmental Physics 10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
Graduate School:	Graduate School for Health Sciences (GHS)
UniBE Contributor:	de Schrijver, Evan, Vicedo Cabrera, Ana Maria, Franco Duran, Oscar Horacio, Raible, Christoph
Subjects:	500 Science > 530 Physics 500 Science > 550 Earth sciences & geology 600 Technology > 610 Medicine & health 300 Social sciences, sociology & anthropology > 360 Social problems & social services
Language:	English
Submitter:	Doris Kopp Heim
Date Deposited:	10 Jul 2023 12:09
Last Modified:	10 Jul 2023 12:09
Additional Information:	PhD in Health Sciences (Epidemiology and Biostatistics)
URI:	https://boris.unibe.ch/id/eprint/184628