Towards a more robust and flexible approach to assess intergenerational inequity in exposure to climate extremes and impacts

Across the globe, today’s young generations will be more frequently exposed to climate extremes over their lifetime than older generations. Previous work has established this finding by combining simulations of historical and projected trends in climate extremes together with data on past and future demographic changes (Thiery et al. 2021, Grant et al. 2025). This kind of research can be relevant for child and youth-focused climate litigation, helping assess to what extent different global warming or emission scenarios imply intergenerational inequity in exposure to local climate hazards. However, research has so far focused on a limited set of climate extreme indicators, and did not fully assess uncertainty across the climate impact modelling chain from emissions to impacts.

 

We now build on this existing lifetime exposure framework and combine it with a chain of climate model emulators constituted of a Simple Climate Model (SCM) and the Rapid Impact Model Emulator Extended (RIME-X, Schwind et al., submitted). A Simple Climate Model can quickly reproduce the evolution of Global Mean Temperature (GMT) in response to emissions from more complex climate models. RIME-X can then translate those into resulting local changes in climate or climate impact indicators, and produce a full assessment of associated uncertainty encompassing the GMT response to emissions, the local climate response to global warming, and interannual variability. It has already been used to produce projections for 40+ indicators, and this list can be extended to further indicators whose evolution predominantly depends on the level of global warming and for which historical and future simulations are available. 

 

We also update the lifetime exposure framework to consider more recent demographic data, and package it into a GitHub repository called dem4cli (short for ‘demographics for climate’) that will be made publicly available. We use spatially explicit population reconstructions and projections from the COMPASS project, and national-level life expectancy and cohort size estimates and projections from UNWPP2024.

 

This work delivers more robust calculations of lifetime exposure to changes in extremes or climate impacts, by leveraging the ability of the SCM-RIME-X emulator chain to represent both their forced response to emissions as well as the combined uncertainty arising from the GMT response to emissions, the local climate response to global warming, and interannual variability, in combination with updated demographic data. This new framework is designed to generate such policy-relevant information in a more flexible and systematic manner, as it can in theory be applied to any available emission or GMT trajectories, and extended to a broad range of climate hazards. We argue that this framework can provide meaningful science-based contributions to the evidentiary base of child and youth-focused climate lawsuits. 

 

Thiery, W. et al. Intergenerational inequities in exposure to climate extremes. Science 374, 158–160 (2021)

Grant, L. et al. Global emergence of unprecedented lifetime exposure to climate extremes. Nature 641, 374–379 (2025)

Schwind et al. RIME-X v1.0: Combining Simple Climate Models, Earth System Models, and Climate Impact Models into a Unified Statistical Emulator for Regional Climate Indicators. Geoscientific Model Development (submitted)