As climate change accelerates, so do the hazards to human health, particularly when many extreme weather events occur simultaneously. A new scientific analysis, just published in Atmospheric and Oceanic Science Letters, warns that these "compound extreme events" are becoming more common in China, posing growing public health concerns. 

The review, headed by Dr Haosu Tang of the University of Sheffield and Professor Gang Huang of the Chinese Academy of Sciences. Dr. Haosu Tang of the University of Sheffield and Professor Gang Huang of the Chinese Academy of Sciences are leading the review, which draws on more than a decade of scientific research and raises a warning: most health systems and climate policies are currently unprepared to deal with the reality that people are increasingly confronting multiple disasters simultaneously. 

Compound events, as opposed to single heatwaves or floods, involve numerous extreme conditions that occur simultaneously or closely follow one another. For instance, dangerously high humidity and air pollution may accompany a prolonged heatwave, exacerbating the problem. 

These multi-layered hazards do more than just pile up; they magnify the risks, particularly for those who are already at risk, such as the elderly, children, those with heart or lung ailments, and those living in crowded or poorly ventilated homes. 

"Most health risk assessments have focused on one type of hazard at a time," explained lead author Dr Tang. "But in reality, people are increasingly exposed to multiple extremes at once—and these compound events interact in ways that intensify health threats." 

One example given in the paper is the combination of high temperatures and ozone pollution. According to studies, ozone levels rise with increasing temperature, particularly in urban areas. High quantities of ozone can aggravate asthma, cause respiratory episodes, and increase hospital admissions. When such an event occurs during a heatwave, the burden on the body and the healthcare system increases dramatically. 

Another concerning trend is hot day-hot night cycles that do not allow the body to rest. During a normal heatwave, colder nights provide comfort. However, with high temperatures both during the day and at night, the body is under continuous stress, raising the risk of heat stroke, dehydration, and even death. 

According to a Lancet Countdown on Health and Climate Change report from 2023, more than 62% of the world's population is already exposed to excessive heat. China, with its congested cities and elderly population, is particularly vulnerable. 

A recent assessment demonstrates how several climate dangers are converging more frequently and with greater severity. As global temperatures rise, heatwaves linger longer and become more intense. In cities, the excessive heat exacerbates air pollution from vehicles and manufacturing, resulting in hazardous health conditions. Meanwhile, shifting rainfall patterns can lead to both floods and droughts in the same area, resulting in uncertainty and damage to water systems. What is particularly concerning is that climate events, which used to occur independently, are now interacting in unanticipated and complex patterns. However, most existing climate models are unable to anticipate such overlapping catastrophes, which makes it difficult for governments to organise and safeguard people in time. 

The authors advocate for a fundamental shift in policy to successfully manage the increased health risks posed by compound climatic events, such as heatwaves followed by floods or wildfires. Instead of treating each tragedy separately, they argue for better data systems that monitor overlapping and sequential incidents throughout time. By incorporating this data into climate models, researchers can gain a deeper understanding of how one extreme event might cause another, resulting in cascade health repercussions. Regional concerns must also be addressed through targeted, localised health interventions. Simultaneously, improved air quality and emissions management are crucial to lowering the long-term burden of climate-related illnesses. The authors emphasise that tackling these difficulties requires strong collaboration across disciplines, including research, healthcare, urban planning, and governance. Above all, the report offers a compelling case: public health should no longer be an afterthought in climate debates but rather a critical component of climate resilience planning. 

This evaluation comes at a time when China and other regions of the world are dealing with multiple problems, including record-breaking heat, poor air quality, urban flooding, and overburdened healthcare systems. Ignoring how these issues are linked will only exacerbate their severity. 

As the earth heats, climate extremes will no longer occur sequentially. Health systems, urban planners, and catastrophe managers must prepare for this new reality, in which surviving one tragedy does not guarantee safety if another occurs immediately after.