Arbeitsbereich

Bevölkerungsdynamik und Nachhaltiges Wohlbefinden

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Projekt

Future Population Dynamics under Climate Change Feedback (Dissertation)

Jakob Gregor Zellmann, Raya Muttarak (University of Bologna , Italien), Emilio Zagheni, Asli Ebru Sanlitürk; in Zusammenarbeit mit Mikhail Maksimenko (University of Bologna, Italien), Itza Akari Olguín Zúñiga (Vienna Institute of Demography, Österreich), Rosanna Gualdi (Bocconi University, Milan, Italien), Sirinya Kaikeaw (University of Bologna, Italien)

Ausführliche Beschreibung

Climate change has significantly affected various meteorological phenomena, in particular by increasing the frequency, intensity, and duration of heat waves. The acceleration of global warming has resulted in 19 of the 20 hottest years on record occurring after 2000, and projections indicate that heat waves will become even more frequent, intense, and prolonged than those that were historically observed. This trend underscores the urgency of understanding how these changes affect human health and behavior.

There is growing evidence that climate change influences demographic processes. For example, heat-related mortality is projected to rise globally, with only a modest decline in cold-related deaths despite rapid warming (Gasparrini et al., 2017). Regarding fertility, studies across diverse regions have shown that days with high average temperatures or positive temperature anomalies are associated with declines in birth rates 8-10 months later. (Barreca et al., 2018; Cho, 2019; Conte Keivabu et al., 2024; Marteleto et al., 2023). The effect size is consistently significantly negative, and the results of Conte Keivabu et al. (2024) suggest that in Spain, each hot day (>25°C) in a month decreases the total fertility rate by 0.27%. Similarly, a growing body of evidence suggests that both sudden-onset and slow-onset climate events influence internal and international migration patterns worldwide (Berlemann and Steinhardt, 2017; Hoffmann et al., 2020). In a meta-analysis, Hoffmann et al. (2020) find that, on average, a one standard deviation shift in environmental conditions is associated with a 0.021 standard deviation rise in migration. Extrapolating these trends across different SSP–RCP scenarios highlights the importance of incorporating the effects of a changing climate into population projections. For example, Masselot et al. (2025) estimate that the net death burden due to climate change, meaning the overall balance of increased and decreased deaths due to temperature changes, could rise by 49.9% under SSP3-7.0 in European countries.

This motivates a two-step approach. First, the relationships between key demographic variables and climatic conditions are estimated both globally at the national level, and for Mexican states. Second, these relationships are extrapolated in a manner consistent with existing projections of climatic conditions. In this dissertation, the variables of interest include total fertility rates, migration rates (both internal and international), and mortality rates, which together enable population projections using a cohort-component model.

The methodological contribution is twofold. First, a framework is developed to estimate the relationship between climatic factors and demographic variables. Second, a novel approach is proposed to integrate these estimates, and their future projections, into existing population projections. Applying this framework to Mexican states yields subnational population projections that explicitly account for climatic feedback. This constitutes the first track of the dissertation.

The second track extends the statistical methodology underlying the current UN population projections to explicitly incorporate climatic feedback, and it re-estimates the model accordingly. This approach generates global migration projections at the national level that are consistent with projected climatic changes.