The Science article referred to in the Guardian article in my previous post is here:
Intergenerational inequities in exposure to climate extremes
For those who can't access the article directly, here is a key quote:
Our results allow for comparing lifetime exposure to climate extremes across birth cohorts globally. For example, a person born in 1960 will on average experience around 4 ± 2 (1σ) heat waves across their lifetime according to our extreme heat wave definition (see the first figure). The lifetime heat wave exposure of this cohort is largely insensitive to the three future temperature scenarios considered here. By contrast, a child born in 2020 will experience 30 ± 9 heat waves under a scenario that follows current climate pledges, which could be reduced to 22 ± 7 heat waves if warming is limited to 2°C or 18 ± 8 heat waves if it is limited to 1.5°C. In any case, that is seven, six, or four times more, respectively, compared with that of a person born in 1960. Repeating this analysis for all cohorts born between 1960 and 2020 highlights clear differences in lifetime exposure to heat waves between older and younger cohorts globally (see the first figure). The effect of alternative future temperature trajectories on the lifetime exposure multiplication factor becomes discernible only for cohorts younger than 40 years in 2020, with the largest differences for the youngest cohorts.
The previous example only uses one hazard indicator and a subset of all possible future temperature pathways. We expanded this approach and considered six extreme event categories: wildfires, crop failures, droughts, river floods, heat waves, and tropical cyclones (see table S1), which we analyzed under a wide range of temperature pathways that resulted in future warming that ranges from constant present-day levels up to 3.5°C by 2100 (see materials and methods and fig. S1). To this end, we generated a total of 273 global-scale projections with 15 impact models forced by four bias-adjusted global climate models (see table S2). Inspired by the IPCC’s Reasons for Concern Framework (7), we visualized the exposure multiplication factors, relative to a hypothetical reference person living under preindustrial climate conditions, as a function of the 2100 GMT anomaly and cohort (see the second figure and fig. S2). Life expectancy varies with the cohort, whereas the hypothetical reference person is given the same life expectancy as that of the 1960 birth cohort in our figures. Therefore, in contrast to the previous comparison of lifetime exposure across generations given historical and climate conditions (see the first figure), we assessed how projected lifetime exposure of birth cohorts is affected by climate change since the preindustrial era and by increased life expectancy since 1960.
Our results highlight that lifetime exposure to each of the considered extreme events consistently increases for higher warming levels and younger cohorts. Changes in extreme event frequencies have relatively little effect on lifetime exposure for cohorts above age 55 in 2020, but this rapidly changes for younger cohorts as they experience increasing extreme events in the coming years and decades (see the second figure and fig. S2). For a 3°C global warming pathway, a 6-year-old in 2020 will experience twice as many wildfires and tropical cyclones, three times more river floods, four times more crop failures, five times more droughts, and 36 times more heat waves relative to the reference person.
Although qualitatively consistent, quantitative exposure changes differ among categories: For wildfires and tropical cyclones, increases in exposure remain limited relative to the other categories, whereas heat wave exposure increases much more strongly, up to a factor of 44 for the 2020 birth cohort under a scenario with 3.5°C global warming. Aggregating the exposure multiplication factors across the six categories shows that people younger than 10 years in 2020 will experience about a fourfold increase in extreme events if global warming is limited to 1.5°C, an increase that older cohorts will never experience, even if a scenario toward 3.5°C warming is followed (see fig. S3A). Under a 3°C global warming pathway, children under 8 years will face an almost fivefold increase in extreme event exposure. These exposure multiplication factors scale robustly with the warming pathway and cohort across a range of aggregation methods, despite some variation in the factor values (see fig. S3).
We then calculated the probability of each person’s lifetime exposure occurring under preindustrial climate conditions. Lives with an accumulated exposure that would occur with less than 0.01% probability under preindustrial climate (that is, with less than a 1 in 10,000 chance) are classified as “unprecedented.” We found that cohorts above age 55 years in 2020 will on average live an unprecedented life only for heat waves and crop failures, whereas cohorts aged 0 to 40 years in 2020 will additionally face unprecedented exposure to droughts and flooding above 1.5°C warming (see the second figure). Aggregated across all the event categories, lifetime exposure to extremes is unprecedented at all warming levels and cohorts (see fig. S3A).
And here is a figure that gives an overview of the results of the analysis:
