More than half of children born in 2020 will experience unprecedented lifetime exposure to extreme heatwaves even if global warming is limited to 1.5°C above pre-industrial levels, according to new research published in Nature.

The international study, led by researchers including Luke Grant and Wim Thiery, examined how six different climate extremes will accumulate over the lifetimes of different generations under various warming scenarios. Their findings portray a stark future for today's youth.

"Our results call for deep and sustained greenhouse gas emissions reductions to lower the burden of climate change on current young generations," the authors wrote in their comprehensive analysis released on 8 May.

The research projects that under current mitigation policies, which align with a pathway reaching 2.7°C warming by 2100, the proportion of people experiencing unprecedented lifetime exposure to climate extremes will at least double from 1960 to 2020 birth cohorts.

Even more concerning, if global temperatures rise by 3.5°C by 2100, an overwhelming 92% of children born in 2020 will face unprecedented lifetime exposure to heatwaves, compared with 52% under a 1.5°C pathway. This represents a difference of 111mn children versus 62mn experiencing these extreme conditions.

"Children would reap the direct benefits of this increased ambition," the study states, noting that 613mn children born between 2003 and 2020 could avoid unprecedented lifetime exposure to heatwaves if warming is limited to 1.5°C rather than continuing on the current trajectory.

The research defines "unprecedented lifetime exposure" as experiencing a cumulative number of extreme events that exceeds the 99.99th percentile of what would be expected in a pre-industrial climate – effectively meaning a one in 10,000 chance of occurring without human-induced climate change.

While heatwaves showed the most dramatic increases, other climate extremes also presented significant concerns. For crop failures, the proportion of the 2020 birth cohort facing unprecedented exposure rises from approximately 13% under a 1.5°C scenario to 29% with 3.5°C warming. Similarly, river flood exposure increases from 5% to 14% when comparing the same warming scenarios.

"For the 2020 birth cohort, this estimate changes from 6% to 11% in a 1.5°C pathway and from 10% to 19% in a 3.5°C pathway," the researchers noted regarding tropical cyclones when limiting analysis to regions where such events can occur.

The study also revealed troubling disparities in climate impact distribution. The most socioeconomically vulnerable populations face significantly higher risks of unprecedented climate exposure, with 95% of the most deprived children born in 2020 projected to experience unprecedented heatwave exposure under current policies, compared with 78% of the least deprived.

"Socioeconomically vulnerable groups have lower adaptive capacity and face more constraints when it comes to implementing effective adaptation measures," the researchers emphasised. "Our results highlight that precisely these groups with the highest socioeconomic vulnerability and lowest adaptation potential face the highest chance for unprecedented heatwave exposure."

At the country level, the research found that under a 1.5°C pathway, equatorial regions demonstrate relatively high proportions of unprecedented heatwave exposure, with 104 out of 177 countries analysed having most of their 2020 birth cohort (≥50%) living with unprecedented exposure to heatwaves.

This pattern becomes more widespread under higher warming scenarios. In a 2.5°C pathway, 157 countries have majority populations facing unprecedented heatwave exposure. Most alarming, in a 3.5°C pathway, 167 countries have majority populations affected, with 155 countries having ≥90% of their 2020 birth cohort experiencing unprecedented heatwave exposure, and in 113 countries the entire birth cohort faces this extreme scenario.

The researchers acknowledged certain limitations in their analysis, noting that they do not account for how people might adapt to extremes and potentially reduce their exposure or vulnerability. They also do not capture non-local impacts of climate extremes, such as supply chain disruptions or market instabilities, making their estimates "conservative."

"Although we refer to heatwaves throughout the paper, our definition technically refers to a 3-day extreme heat event that is expected on average once per century under pre-industrial climate conditions," the researchers clarified, highlighting the nuanced definition of extremes used in their methodology.

Beyond the human toll, the study points to cascading effects of climate extremes through economic impacts, including "rising cost of living due to supply chain disruptions" and "taxation to recover public infrastructure."

The authors conclude with a clear message about the urgency of climate action: "This underlines the urgent need for deep and sustained greenhouse gas emission reductions to safeguard the future of current young generations."

Additional benefits of limiting warming to 1.5°C include 98mn children avoiding unprecedented exposure to crop failures, 64mn avoiding river floods, 76mn avoiding tropical cyclones, 26mn avoiding droughts, and 17mn avoiding wildfires, compared to the projected 3.5°C pathway.

As the researchers concluded: "Young generations will reap the consequences of the present-day mitigation of greenhouse gas [GHG] emissions."