‘Will a newborn experience more climate extremes than a 60-year-old?’ The answer to this question is rather intuitive: ‘Yes, of course’. When it comes to the question ‘But how much more?’ then, interestingly, climate scientists didn’t have the answer – until recently.
Bridging climate science and demography
The question how many extreme events a person will face across their lifetime, and how this compares across generations and regions, is an important question. First, it is a question of very high societal relevance. Since late 2018, young people from around the world have been leading climate protests: youth climate advocates have been organizing protest demonstrations, school strikes, and more recently even hunger strikes to demand more climate ambition from policy makers. Their actions continue to receive both ample support and fierce criticism, in some cases also originating from older generations. Meanwhile, government actions are falling short of achieving the emission reductions required to halt global warming at the safe levels agreed upon under the Paris Agreement (Rogelj et al. 2016). The absence of sufficiently ambitious climate policies entails the risk that the climate crisis turns into a generational conflict, sometimes paraphrased by the catchphrase “ok, boomer”. Simply put, many young people feel that they will face the impacts of climate change but today lack the political and economic power to make a change, while older people may themselves not experience the long-term effects of their (lack of) decision-making.
Besides the societal relevance, it is also an important legal question. Recent years have seen a surge in climate litigation: lawsuits filed by citizens or NGOs against countries, companies, or international entities like the European Union. In the famous Urgenda case, the Dutch government has been convicted and is now forced to ramp up its climate ambition. Many similar lawsuits are now ongoing in an increasingly large number of countries. Interestingly, in a growing number of cases young people are the claimants. For instance, 16 young people including Greta Thunberg are now suing several G20 countries for violating the UN children rights treaty which they signed themselves. From this perspective, it is a highly relevant legal question whether a 15-year-old will face more impacts from climate change than, say, a 60-year-old; if so, she or he is also more entitled to start a climate lawsuit against an inactive government.
For me, hearing this legal question being asked by someone in the audience during one of my public lectures on climate change sparked the idea of this research. The remark struck me because I realized that while we have all the data to answer this question, our current research paradigm impedes such a human-centered approach. In climate science, we typically study aspects of climate change by comparing two time windows. For instance, we compare end-of-21th-century heatwave characteristics to those under present-day climate conditions. Such a perspective, called the period perspective in demography, impedes quantification of what climate change will imply for a specific person born in a specific location in a specific year. For this, a cohort perspective is required, which considers characteristics of a particular generation (a birth cohort) along the course of its lifetime. Like the well-known distinction between the Eulerian and Lagrangian perspective in atmospheric science, where a Eulerian observer is located at a fixed point in space while a Lagrangian observer moves along the flow, embracing the cohort perspective in climate science may lead to interesting new research insights. That gives us a third reason why this is a good question to ask.
How asking this question translates in climate impact modeling
What is special about our study is that we integrate the exposure of an ‘average’ person in a birth cohort to extreme events across their lifetime. While bridging between climate science and demography, we can for the first time quantify, for example, lifetime exposure to extreme heat waves (the kind that would only occur once every 100 years under pre-industrial climate conditions).
The selected person is compared to someone 60 years old in 2020.
FIG 1 / Adapted from Thiery et al. (2021)
In figure 1, you can see the outcome of our approach. We calculated the lifetime exposure for every generation born between 1960 and 2020, and this for every country in the world under a 1.5°C-compatible scenario, a 2°C-compatible scenario and a scenario leading to 2.4°C of global warming based on the pre-Glasgow pledges. Please be aware of the restrictions when using numbers on a national scale.
For updated warming levels based on new NDC submissions and announcements the Climate Action Tracker is a reliable source of information.
In our study the average exposure (number of heat waves experienced over lifetime) of these cohorts under the different warming scenarios is compared to the average lifetime exposure of a 60-year-old person assuming historical warming and the same warming scenarios for the future (see figure 1) or of a 60-year-old person assuming pre-industrial climate conditions (see figure 2).
In addition to heat waves, our study also addresses lifetime exposure to other extreme events, including droughts, crop failures, river floods, tropical cyclones, and wildfires (see Figure 2). To this end, we generated a very large collection of extreme event projections based on ISIMIP global-scale impact simulations (Lange et al. 2020) and combined these with future global temperature trajectories and demographic information on life expectancy from the UN WPP, population density from (Jones and O’Neill 2016), and cohort size from the Wittgenstein Center. The Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) gathers an international group of climate and impact scientists that comprehensively quantify the biophysical and socioeconomic impacts of climate change; as part of this effort me and my colleagues run global-scale models and make the data publicly available.
Our results show that children are to face disproportionate increases in lifetime extreme event exposure – especially in low-income countries. Under pre-Glasgow climate pledges, newborns across the globe will on average face seven times more scorching heat waves during their lives than a person born in 1960 – which could very well be their grandparent. In addition, children born in 2020 will on average live through 2.6 times more droughts, 2.8 times as many river floods, 1.5 times as many tropical cyclones, almost three times as many crop failures, and twice the number of wildfires as people born 60 years ago.
FIG 2 / Adapted from Thiery et al. (2021).
Why we also compare to a no-climate change reference person
While comparing generations against each other is intuitive, it disregards the fact that people born in 1960 are already facing increasing weather extremes (just have a look at the recent news to understand this). For this reason, we decided to also compare exposure of different birth cohorts and under different warming scenarios to the exposure of a reference person living under pre-industrial climate. As it is not at all certain that current climate pledges are really met - in fact, current policies are largely insufficient (see Climate Action Tracker) - we have also extended the range of global warming scenarios to 3.5°C of global warming by 2100.
For a 3°C global warming pathway, a 6-year-old in 2020 will experience twice as many wildfires and tropical cyclones, 3 times more river floods, 4 times more crop failures, 5 times more droughts, and 36 times more heatwaves relative to a reference person living under pre-industrial climate conditions.
Under a 3.5°C warming scenario, children born in 2020 will even experience 44 times more heatwaves.
At and above 1.5°C of end-of-century warming, the expected lifetime exposure to heatwaves, crop failures, droughts, and river floods for people born after 1980 would have been virtually impossible – <0.01% chance – in a world without global warming. This basically means that people younger than 40 today will live an unprecedented life in terms of heatwave, crop failure, drought, and river flood exposure even under the most stringent climate change mitigation scenarios. For heatwaves and crop failures this even applies to all generations born after 1960.
It’s not just a difference between generations, region and income also matter
It is important to note that these global numbers hide important regional variations. Young generations under 25 years old in the Middle East and North Africa will face at least seven times more extreme events under pre-Glasgow pledges compared to a no-climate change reference, and for newborns this even rises to more than 9 times - strongly above the global average increase of five times. For children, the second most hard-hit region is sub-Saharan Africa. Grouping countries by income instead of geographic regions shows that low-income countries are hit particularly hard: young generations in low-income countries will face by far the strongest increases with a more than fivefold increase for newborns in overall lifetime extreme event exposure (figure 3).
FIG 3 / Adapted from Thiery et al. (2021)
This is problematic for several reasons. First, young generations in these regions contributed the least to the climate crisis via greenhouse gas emissions. Second, children in low and lower-middle income countries are often more vulnerable and therefore risk higher impacts from these extreme events. This is clearly explained in the Save the Children report that is based on our analysis. Third, today there are very large numbers of children living in these hard-hit regions. For instance, while 64 million children born in Europe and Central Asia since 2015 will experience 3.8-4.0 times more extreme events under pre-Glasgow pledges, 205 million children of the same age in sub-Saharan Africa face a factor 5.4-5.9 increase in lifetime extreme event exposure, and even 49-54 times more heatwaves. The combined rapid growth in population and lifetime extreme event exposure highlights a disproportionate climate change burden for young generations in the Global South.
The income groups are defined based on present-day conditions. The region definitions are taken from the World Bank
FIG 4 / Adapted from Thiery et al. (2021)
And we even have strong reasons to think that our calculations underestimate the actual increases that young people will face: we only consider changes in frequency (not duration and intensity), we count multiple extreme events occurring within a year as one, and disregards potential co-occurrence (which we know is the case in reality).
Facing the findings scientifically and personally
Looking at these results as a scientist, we find them to be in line of our knowledge of climate change:
The higher the warming level, the stronger the escalation in extreme event frequency
Heatwaves show the strongest increases in frequency, while tropical cyclones change the least (they instead intensify)
The strongest increases typically occur in the tropics
The results of our paper are based on state-of-the-art data sets and analytic frameworks. The study was scrutinized by 6 excellent anonymous reviewers and the 99 pages of written correspondence between authors and reviewers, which is exceptionally long, made sure of all issues being uncovered and dealt with. While we understand these results perfectly as scientists, many people told me that seeing the actual numbers was a punch in the stomach as a person, as a parent. By no means it is surprising that young generations will be so much more exposed to extremes – and especially heatwaves, but seeing the actual figures framed in their context is very sobering (figure 5).
FIG 5 / Based on data from (Thiery et al. 2021)
Disclaimer concerning national numbers
It is important to note that these numbers presented in this article are quite robust on global level and across large regions. The smaller the scale gets, the more the results may be affected by natural fluctuations of the occurrence of extreme events as represented in the underlying climate model realisations. In addition, the exposure under the given warming scenarios has to be approximated by exposure estimates derived from a given set of standard scenarios that have been simulated by global climate models (see method explained in the supplementary information of our paper). This introduces additional uncertainties that can affect results in particular on a national scale. We nevertheless decided to provide the global maps of national numbers as they allow to get an impression of the regional distribution of the exposure changes with robust large scale patterns across countries.
What immediate policy action could change for young people around the world
Young children have most to lose when global warming reaches high levels, but they also have most to win if ambition to lower warming levels is ramped. As the global maps in figure 1 show, the lifetime exposure of newborns to extreme heatwaves will be larger than that of the 1960 birth cohort in any country of the world under 1.5°C warming, but the increase is even larger under pre-Glasgow pledges. This highlights an immediate gain of increased climate ambition in terms of lifetime exposure to these extreme events for young people.
Our results overall highlight the strong benefit of aligning policies with the Paris Agreement for safeguarding the future of current young generations. Limiting global warming to 1.5°C instead of following the pre-Glasgow pledges written down in national climate plans substantially reduces the intergenerational burden for extreme heatwaves, wildfires, crop failures, droughts, tropical cyclones, and river floods (figure 2. At the global scale, these reductions range from -11% (wildfires) to -40% (heatwaves). The results of the study published in Science (Thiery et al. 2021) and the accompanying report curated by the NGO Save The Children therefore highlight the utmost need to ramp up ambitions and embark on immediate action.
Further exploration of the dataset presented in this study is possible on the website myclimatefuture.info.
Edited by Julia Reimann, Martin Park, Katja Frieler. Interactive figures by Mahé Perrette.
Please contact the ISIpedia Editorial Team (email@example.com) for more information or questions about this report.
Cover image: Annie Spratt
1 Vrije Universiteit Brussel, Department of Hydrology and Hydraulic Engineering, Brussels, Belgium
2 ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland
3 Potsdam Institute for Climate Impact Research, Member of the Leibniz Association, Potsdam, Germany