Original article republished from Carbon Brief under a CC license. 

Children born in 2020 will face “unprecedented exposure” to extreme weather events, including heatwaves, droughts and wildfires, even if warming is limited to 1.5C above pre-industrial temperatures.

That is according to a new study, published in Nature, which calculates the number of unprecedented extreme events that people born in different decades and countries might live through.

Using a case study focused on Brussels, the researchers find that people born in 2020 will experience an “unprecedented” 11 heatwaves in their lifetime – even if global warming is limited to 1.5C by the end of the century.

In contrast, in a pre-industrial climate, a person living in the Belgian capital would likely experience just three such heatwaves, according to the study.

More than half of children born in 2020 – around 62 million people – will experience “unprecedented lifetime exposure” to heatwaves, even if warming is limited to 1.5C, the study finds. 

However, this number nearly doubles to 111 million under a scenario where warming hits 3.5C.

The study also analyses crop failures, river floods, tropical cyclones, wildfires and droughts. 

The research “helps the climate community build new narratives that better clarify the impacts [of climate change] on younger generations and vulnerable populations”, one expert who was not involved in the study tells Carbon Brief.

Intergenerational justice

As the planet warms, extreme weather events such as heatwaves, floods and droughts are becoming more intense, more frequent and lasting longer.

A popular 2021 study found that children born in the 21st century will be exposed to more extreme weather events in their lifetimes than their parents and grandparents.

The paper found that in a scenario of 3C of warming above pre-industrial levels, a child who turns six 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 heatwaves over their lifetime than a six-year-old living in a pre-industrial climate.

The authors also found a “particularly strong increase” in children’s future exposure to extremes in the Middle East and North Africa.

The lead author of the study – Prof Wim Thiery from Vrije Universiteit Brussel – told Carbon Brief at the time that today’s youth will live “an unprecedented life”, in which they will “face conditions which older generations have never experienced”.

Four years later, Dr Luke Grant – a researcher in Thiery’s team – has led a new study building on the ideas of the 2021 paper.

Grant tells Carbon Brief that rather than counting the number of extreme events that an individual might experience, his new study counts the number of people that reach an “unprecedented state” of exposure to extremes.

Prof Kaveh Madani is the director of the UN University Institute for Water, Environment and Health and was not involved in the study. He tells Carbon Brief that the paper “helps the climate community build new narratives that better clarify the impacts [of climate change] on younger generations and vulnerable populations”.

The authors define “exposure” as the number of extreme events that a person experiences in their lifetime, relative to the number they would have experienced in a pre-industrial climate.

“Unprecedented lifetime exposure” is defined as exposure so high that it has only a one-in-10,000 chance of happening in a world without any greenhouse gas emissions.

‘Unprecedented lifetime exposure’

The authors present a case study of extreme heat in Brussels, Belgium, to explain their method.

They define a heatwave as a three-day extreme heat event, which reaches average temperatures that would be expected once per century in a pre-industrial climate.

Using models from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP), the authors calculate heatwave frequency in a world without climate change. They also assess scenarios in which warming is limited to 1.5C, 2.5C and 3.5C by the end of the century.

They combine this data with demographic information, including how many people are born in the country each year and their average life expectancy, using data from sources including the ISIMIP database and UN population estimates and projections.

In a world without climate change, the study finds that a person born in 1960 in Brussels would have a one-in-10,000 chance of experiencing six of the pre-defined heatwaves in their lifetime. Any member of this “birth cohort” who experiences more than six heatwaves in their lifetime has therefore faced “unprecedented lifetime exposure” to extreme heat, according to the study.

The authors find that a person born in Brussels in 1960 is likely to experience three heatwaves on average during their lives under all of the three future warming pathways– meaning that they are unlikely to face “unprecedented lifetime exposure” to heat.

By contrast, the researchers find that many younger age cohorts will experience unprecedented heatwave exposure. For many younger age cohorts, lifetime exposure to heatwaves is greater for higher warming pathways. 

For example, people born in Brussels in 2020 will experience 11 heatwaves in their lifetime if global warming is limited to 1.5C by the end of the century. If warming rises to 2.5C or 3.5C, they could experience 18 or 26 heatwaves, respectively. 

The graphic below shows heat exposure since birth in Brussels for three “birth cohorts” of 1960 (bottom row), 1990 (middle row) and 2020 (top row). It presents three future scenarios, in which warming is limited to 1.5C (blue), 2.5C (yellow) and 3.5C (red) by 2100. The dotted line shows the threshold for an “unprecedented” lifetime exposure to extreme heat. 

Heat exposure

The authors repeat their analysis across the Earth’s entire land surface, by dividing it into grid cells and using location-specific temperature and demographic data. 

Of the 81 million people born in 1960, they find that 13 million are likely to face unprecedented exposure to heatwaves in their lifetimes. They add that for this age cohort, lifetime exposure to unprecedented extremes does not vary depending on the warming scenario.

However, 21st century warming has a significant effect on exposure for younger generations. Under a 1.5C warming pathway, 52% of people born in 2020 will face unprecedented exposure to heatwaves. This rises to 92% under a 3.5C warming scenario.

The study adds:

“This implies that 111 million children born in 2020 will live an unprecedented life in terms of heatwave exposure in a world that warms to 3.5C versus 62 million in a 1.5C pathway.”

The charity Save the Children has published a report which unpacks the findings of the study. The graphic below, from the report, shows the percentage of people from different countries born in 2020 who will face unprecedented lifetime exposure to heatwaves under the 1.5C (top), 2.5C (middle) and 3.5C (bottom) warming scenarios.

Each circle shows a country, indicated by its three-letter countries code. The size of the circle indicates the number of people in the country. Darker circles indicate higher-income countries. 

Circles on the right hand side of the graphic indicate that more than half of the country’s 2020 cohort will be exposed to unprecedented heatwaves in their lifetime. 

“The evidence is now inescapable that heatwaves impact every community around the world,” Dr Luke Harrington, a senior lecturer in environmental science at the University of Waikato, who was not involved in the study, tells Carbon Brief. He adds: 

“This paper offers the clearest view that climate change is verifiably unfair: those who have done the least to contribute to rising global temperatures will experience the most extreme impacts.”

From floods to fires

The authors apply the same method to five other climate extremes – crop failure, wildfires, droughts, floods and tropical cyclones.

The graphic below shows the key findings. The coloured portion of the bar shows the number of people born in 2020 who will face unprecedented exposure to each extreme under a 1.5C warming pathway. The dark green and light green bars show the additional exposure under 2.7C and 3.5C warming.

The authors find that unprecedented lifetime exposure to heatwaves will affect the most people, with 62 million people born in 2020 likely to face unprecedented exposure to heat in their lifetimes if warming is limited to 1.5C.

This is followed by crop failures and river floods, which will impact 23 million and 10 million people from the 2020 birth cohort under the 1.5C warming pathway, respectively.

Lead author Grant tells Carbon Brief that he is “most confident” about his heatwave findings because temperature is a “basic” metric for climate models to “get right”.

Meanwhile, extremes such as crop failure depend on a range of factors including soil moisture, land-atmosphere interactions and rainfall, which can make it harder for the models to accurately capture changes, Grant explains.

Vulnerability

The authors also assess how “socioeconomic vulnerability” affects their findings using a global deprivation index – a tool which measures the level of disadvantage and hardship experienced by individuals or communities in a particular geographic area.

The authors use the index to identify the 20% most and least vulnerable people in each age cohort. They find that the most vulnerable groups are overwhelmingly from African countries.

The authors also conclude that “socioeconomically vulnerable people have a consistently higher chance of facing unprecedented lifetime heatwave exposure compared to the least vulnerable members of their generation”.

The graph below, taken from a news and views article about the study, shows the percentage of high vulnerability (red) and low vulnerability (pink) people in each age cohort who would be exposed to unprecedented heat, under a 2.7C warming scenario. 

Dr Marina Romanello, a research fellow at the University College London and research director of the Lancet Countdown on Health and Climate Change who was not involved in the study, tells Carbon Brief that the paper “is an important addition to the scientific literature, showing how our delays in tackling climate change are putting the future of our children at risk”. 

She adds:

“The authors have used well-established models to project future health threats, framing them around what matters the most: the wellbeing, health and survival of present and future generations.”

Grant, L. et al. (2025) Global emergence of unprecedented lifetime exposure to climate extremes, Nature, doi:10.1038/s41586-025-08907-1

Original article republished from Carbon Brief under a CC license.