Temperature-attributable mortality projections under scenarios of climate change for Oslo, Norway.

Background & Aim Climate change and evolving of population dynamics, including ageing and changes in
population size, are reshaping temperature-attributable mortality patterns. However, there is limited evidence on
the prospective trajectory of heat- and cold-attributable mortality in Oslo, particularly under combined scenarios of
global warming and population development. This study aims to project heat- and cold-attributable mortality in Oslo
and assess the distinct contributions of each of these drivers, utilising high-resolution data.

Methods We conducted a two-step approach with time series analysis with distributed lag non-linear models to
estimate heat- and cold-attributable mortality relationship based on mean daily ambient temperature. Then, we
performed a health impact assessment to compute the attributable mortality to heat and cold in the baseline period
(2010–2019) and by the end of the century using regional population projections, mortality rates and projected daily
temperature under two climate scenarios: RCP4.5 and RCP8.5.

Results For the RCP4.5/Medium Road scenario, the attributable mortality fractions for heat and cold are projected
to increase over time, with values ranging from 9.05% (95%CI: 1.55–15.90) in 2010–2019 to 9.78% (95% CI: 2.96–15.86)
in 2090–2099. Cold mortality consistently dominates the total, while heat mortality remains relatively low, starting at
1.80% (95%CI: 0.10–3.68) at baseline and increasing slightly to 3.12% (95%CI: 0.34–5.94) by the end of the century. In
contrast, the RCP8.5/Strong Ageing scenario shows a more pronounced rise, with temperature-attributable mortality
increasing from 9.07% (95%CI: 1.53–15.89) in 2010–2019 to 11.86% (95%CI: 4.29–18.53) in 2090–2099. In this scenario,
heat mortality contributes significantly more, rising from 1.83% (95%CI: 0.12–3.85) in 2010–2019 to 5.99% (95%CI:
1.23–10.35) by 2090–2099, reflecting the greater climate and population impact under RCP8.5 and the Strong Ageing
pathway.

Conclusions Our findings highlight the need for climate and population dynamics to be considered in public health
policies. Tailored interventions are crucial to mitigate heat and cold-attributable mortality, particularly for vulnerable
populations. Future research should integrate socio-economic factors and explore adaptation strategies to refine
mortality projections and inform policy.