Past and future health burden: the impact of climate change and air pollution on mortality risk for Rome and Milan.

Climate change is expected to raise the threats to human health. The effects of temperatures on excess of mortality, for exposed populations, can be amplified by the simultaneous presence of air pollution.

Using Distributed Lag Nonlinear Models with delayed effects, we assess the combined short-term impact of temperature and air pollution (PM10, O₃) for Milan and Rome, the latter located at the center of the Mediterranean basin. Relative mortality risks (RRs) are estimated for the city population as a whole and the most vulnerable group of people (over the age of 85), for the historical decade 2004-2015 and for the future (2050), assuming climate and air pollution scenarios consistent with the representative concentration pathways RCP2.6 and RCP8.5. The daily mean temperature (T) and the daily apparent mean temperature (AT) exposure variables are used to proxy the effects of climate change; the MDA8 (maximum daily 8-hour average concentration) indicator for O₃ and the daily mean of PM10 characterize, instead, past and future air pollution effects. The minimum mortality temperature (T_mm), which is city specific due to human adaptability to the local climate, is defined and inferred for both cities and age groups, together with exposure-response functions for each exposure variable.

Results on past mortality show lower RRs for Rome along the whole year and a larger influence of temperature rather than air pollutant on short-term mortality. Specifically, attributable deaths are mainly associated with low temperature conditions (T<T_mm) and increase when considering the older age group. As regard of air pollutants, their combined influence sum up to those of temperature with a seasonal connotation: while PM10 affects the risk values mainly in association with low temperatures, O₃ exerts its greatest effect especially in conjunction with high temperatures.

RRs projections to 2050 confirm that Rome is the least affected city with a smaller fraction of total deaths attributable to climate change and air pollution. The effects of global warming is captured by a double-sided effect: a decrease in the cold-related mortality burden and a rise in the attributable mortality due to increasing temperatures. However, the latter effect partially offsets the relief in the health burden achieved from the former one. This substitution effect between cold- and warm-related mortality is more evident in the RCP8.5 scenario and for the 85+ age group.

Concluding, the results suggest that a more rigorous and internationally coordinated climate action, implying more stringency in related policies, can lead to significant co-benefits: in addition to reducing the future health burden, containing the air pollution implications, and achieving climate objectives, health costs and loss of life can be also reduced. Indeed, when the effects of climate change and air pollution are contained with climate policy action (RCP2.6) the number of fatalities could decrease by 8 times in Rome and 1.4 in Milan, compared to historical values.