Heatwaves are a growing global threat to human health, wellbeing and livelihoods.
Across 12 major European cities during the summer of 2025, a ten-day period of extreme heat led to 2,300 deaths – 1,500 of them were attributed to climate change amplifying temperatures by 1-4°C. Heatwaves were responsible for nearly half a million global deaths every year from from 2000 to 2019.
In addition to their health risks, European heatwaves in 2025 contributed to regional glaciers melting and wildfires hitting the largest area on record, according to a new report.
And it’s not just Europe, globally 2025 was ranked as one of three hottest years on record. Heatwaves are not going away: even after emissions targets are met, heatwaves will not return to pre-industrial levels for at least 1,000 years.
Governments across at least 47 countries have implemented heat action plans, such as the United Kingdom’s adverse weather and health plan and city-level plans across India.
These plans typically include early-warning systems, coordination between health and social authorities, and public messaging urging people to stay cool. People can try to implement a variety of measures, including staying in a cool environment, avoiding strenuous activity, drinking more water and wearing lighter clothes. These are theoretically simple steps, which is why heatwave deaths are so often called needless and preventable. But the realities of everyday life make adaptation far more complicated.
How people stay cool is closely tied to existing social inequalities, making heatwaves a nuisance for some and a catastrophe for others. Older people, for instance, have reduced abilities to regulate body temperatures, are more likely to have underlying health conditions that amplify risks and may lack networks of social support during disasters. Income divides create other risk factors such as who owns air conditioning and who can afford to run it. Other factors include who can work in a cool office or work from home, versus those doing outdoor or manual labour in the heat.
Unlike hurricanes or wildfires, which force widespread evacuations, life generally does not stop when heatwaves occur. People are forced to adapt while also meeting their ongoing daily obligations. Government advice might be to stay cool during the hottest part of the day which could be in conflict with a person’s rigid workplace schedule.
There are no maximum safe working temperatures in the UK, for instance. Staying at home can be the safest option if you have air conditioning. Yet during the catastrophic 2021 Pacific Northwest heatwave in the US and Canada, the vast majority of deaths in British Columbia happened in people’s own overheated homes, where there was inadequate air conditioning or fans.
ECMWF/EU, CC BY-ND
How are people coping?
Recent research examines how people adapt their daily activities when dangerous summer heatwaves occur. Using mobile phone location data across seven countries – Brazil, China, France, India, Nigeria, Turkey and the United States – the study shows that people around the world are changing their daily lives to stay cool, ranging from leisure activities to work obligations.
These adaptations vary widely and reflect existing inequalities. People tend to withdraw into their homes during heatwaves, regardless of whether their country has widespread air conditioning or existing heat plans. In some places, people visit workplaces less (notably in France), though not everyone can afford to do so.
In others, people cut back on food shopping or going to the pharmacy as temperatures rise, essential for maintaining households and health (as the research shows has happened during heatwaves in the United States). Places for shopping and recreation – which may have air conditioning – as well as parks may serve as important refuges for those who cannot cool down at home.
Staying cool requires more than awareness and good decision-making – structural barriers, such as having to stay at work during high heat, severely limit people’s access to cooling.
Our research highlights that governments also need to pay closer attention to the space and time constraints people face, and policy efforts should grant people the flexibility to follow their advice. Research on Mexico, for example, found that those aged 18 to 35 were disproportionately likely to die from extreme heat, despite being physiologically less vulnerable than older people. This may be attributed to greater rates of outdoor work with little flexibility to use cooler spaces.
Setting maximum safe working temperatures, relative to local extremes, or allowances for flexible working hours could limit occupational health risks. Both could give workers the choice of where to spend the hottest hours of the day. There is already a precedent for climate-related leave. Spain introduced paid leave following the 2024 Valencia floods. But flexibility alone is not enough if people have nowhere to go nearby that is cool.
Governments need to focus on making accessible cool spaces available, especially in areas with low air conditioning ownership and in dense urban neighbourhoods. This means opening libraries, community centres and other public buildings as cooling centres, with extended hours and access to water. These provisions are currently absent from the UK’s heat plan, for example. Even as home air conditioning ownership rises, these investments in cool public spaces will remain essential. Air conditioning uptake will be limited by income, leaving many people in a continued state of cooling poverty.
Heatwaves are no longer a distant or occasional threat. They are a recurring feature of modern life in many places that are not used to experiencing them. Alongside early warning systems, public messaging and longer-term measures such as urban greening to reduce temperatures, governments need to do far more to help people stay cool when extreme temperatures hit.
