It is essentially unknown how humans adapt or will adapt to heat stress caused by climate change over a long-term interval. A possible indicator of adaptation may be the minimum mortality temperature (MMT), which is defined as the mean daily temperature at which the lowest mortality occurs. Another possible indicator may be the heat sensitivity, i.e., the percentage change in mortality per 1 • C above the MMT threshold, or heat attributable fraction (AF), i.e., the percentage relative excess mortality above MMT. We estimated MMT and heat sensitivity/AF over a period of 23 years for older adults (≥65 years) in the Netherlands using three commonly used methods. These methods are segmented Poisson regression (SEG), constrained segmented distributed lag models (CSDL), and distributed lag non-linear models (DLNM). The mean ambient temperature increased by 0.03 • C/year over the 23 year period. The calculated mean MMT over the 23-year period differed considerably between methods [16.4 ± 1.2 • C (SE) (SEG), 18.9 ± 0.5 • C (CSDL), and 15.3 ± 0.4 • C DLNM]. MMT increased during the observed period according to CSDL (0.11 ± 0.05 • C/year) and DLNM (0.15 ± 0.02 • C/year), but not with SEG. The heat sensitivity, however, decreased for the latter method (0.06%/ • C/year) and did not change for CSDL. Heat AF was calculated for the DLNM method and decreased with 0.07%/year. Based on these results we conclude that the susceptibility of humans to heat decreases over time, regardless which method was used, because human adaptation is shown by either an increase in MMT (CSDL and DLNM) or a decrease in heat sensitivity for unchanged MMT (SEG). Future studies should focus on what factors (e.g., physiological, behavioral, technological, or infrastructural adaptations) influence human adaptation the most, so it can be promoted through adaptation policies. Furthermore, future studies should keep in mind that the employed method influences the calculated MMT, which hampers comparability between studies.

Purpose Over the last few decades, a global increase in both cold and heat extremes has been observed with significant impacts on human mortality. Although it is well-identified that older individuals (> 65 years) are most prone to temperature-related mortality, there is no consensus on the effect of sex. The current study investigated if sex differences in temperature-related mortality exist in the Netherlands. Methods Twenty-three-year ambient temperature data of the Netherlands were combined with daily mortality data which were subdivided into sex and three age classes (< 65 years, 65–80 years,  ≥ 80 years). Distributed lag non-linear models were used to analyze the effect of ambient temperature on mortality and determine sex differences in mortality attributable to the cold and heat, which is defined as mean daily temperatures below and above the Minimum Mortality Temperature, respectively. Results Attributable fractions in the heat were higher in females, especially in the oldest group under extreme heat (≥ 97.5th percentile), whilst no sex differences were found in the cold. Cold- and heat-related mortality was most prominent in the oldest age group (≥ 80 years) and to a smaller extent in the age group between 65–80 years. In the age group < 65 years temperature-related mortality was only significant for males in the heat. Conclusion Mortality in the Netherlands represents the typical V- or hockey-stick shaped curve with a higher daily mortality in the cold and heat than at milder temperatures in both males and females, especially in the age group ≥ 80 years. Heat-related mortality was higher in females than in males, especially in the oldest age group (≥ 80 years) under extreme heat, whilst in the cold no sex differences were found. The underlying cause may be of physiological or behavioral nature, but more research is necessary.

This study examines the impacts of climate change on future mortality in the Netherlands and the related economic costs. Our methods account for changes in both cold- and heat-related mortality for different age classes, the time dynamics associated with temperature-related mortality, demographic change and the urban heat island effect. Results show that heat and cold impacts on mortality vary considerably between age classes, with older people being more vulnerable to temperature extremes. The sensitivity of mortality to temperature is higher on hot (4.6%/°C) than cold (2.1%/°C) days for the most vulnerable group (≥ 80 years), and extreme temperatures have long time lags on mortality, especially in the cold. A main finding is that climate change is expected to first decrease total net mortality in the Netherlands due to a dominant effect of less cold-related mortality, but this reverses over time under high warming scenarios, unless additional adaptation measures are taken. The economic valuation of these total net mortality changes indicates that climate change will result in net benefits of up to €2.3 billion using the Value of a Statistical Life Year and €14.5 billion using the Value of a Statistical Life approaches in 2050, while this changes over time in net economic costs under high warming scenarios that can reach up to €17.6 billion in 2085. Implementing adaptation policies that reduce the negative impacts of warming on mortality in the heat can turn these net costs into net benefits by achieving a continued dominating effect of reduced mortality in the cold.