Does the rate of warming matter for heat-mortality?

The risk of extreme heat mortality is ever increasing with the rapidly changing climate. However, several studies that project future levels of heat mortality have been criticized to be over-pessimistic, as these studies don’t reflect on communities’ ability to adapt to heat. Adaptation to heat is highly complex and not only complicated by the changing climate but also by other mega-trends such as ageing societies or urbanization. In this work, we therefore model future levels of heat-related mortality whilst incorporating location-specific empirical adaptation as a function of mean summer temperature and time.

Concretely, we model the relationship between daily temperature and mortality by using quasi-Poisson regression time series analyses with distributed lag nonlinear models, which is a well-established approach in climate change epidemiology. The relationship expresses the change in mortality risk at specific temperature values against an optimum temperature (the so-called temperature of minimum mortality, MMT). We first model this relationship for continuous five-year intervals for several locations. Next, we express the change in MMT as a linear function of mean summer temperature and time. Adaptation is thus incorporated by shifting the MMTs according to future temperature levels and by when they are reached.

This modelling approach allows us to assess heat mortality levels for different climate scenarios at the same level of global warming but at different points in time in the future. Potential findings of this approach are relevant, as the public debate and climate policy focuses largely on warming levels (1.5, 2°C) and to a lesser extent on how fast these levels are reached.