Half of the world’s population experienced an extra month of extreme heat in 2024. Climate change is causing heatwaves to last longer and occur more frequently. But scientists see that the deadly problem is still too often underestimated.
Between May 2024 and May 2025, four billion people – half the world’s population – were exposed to more “extreme heat”. These are temperatures higher than the 90 percent highest local temperatures of the past thirty years. The effects were greatest in island states, such as Aruba and Indonesia.
A group of international scientists mapped how climate change doubled the number of extremely hot days in 195 countries, compared to a world without warming. A total of thirty days were added. They also saw that 67 record heatwaves of the past year were influenced by climate change.
The heatwave that plagued Mediterranean countries in July 2024 was studied extensively. In that month, temperatures in Greece, France, Spain, Portugal and Morocco rose so high that more than twenty people died. There were also several forest fires that month.
These are the results of research by World Weather Attribution, Climate Central and the climate center of the Red Cross. With the research, the scientists want to increase awareness of extreme heat.
They call heat and its consequences an “under-illuminated” problem. We often read about floods and hurricanes when it comes to weather extremes, they say, while heat is by far the deadliest form of extreme weather.
Tens of thousands of people die from heat in Europe
The health effects of heat have not yet been studied equally well everywhere. This is because deaths are often linked to other causes, such as heart or kidney disease. It is known that the elderly, pregnant women and people from low-income classes are particularly vulnerable. The effect is greatest in cities.
In recent years, several studies have been published that estimate the number of heat-related deaths in Europe. The figures do not always match, but they do indicate tens of thousands of victims per year. Nature even attributes 63,000 deaths to the summer heat of 2022. Climate change is increasing these deaths, writes The Lancet Public Health.
That only concerns European countries, especially around the Mediterranean. In poorer parts of the world, the health effects of heat have been little studied. This makes it difficult to sketch a global picture.
The scientists from this research offer solutions at multiple levels. Take rest during the hottest hours, drink enough water and limit physical activities. Adjustments to homes also help, such as better ventilation and shade. Heat plans from cities make a difference, just like warning systems.
But ultimately, reducing the burning of fossil fuels is most important. The greenhouse gases released in the process warm the atmosphere. Without climate policy, the heat will only increase, the scientists warn.
Weather is not the same as climate
Weather conditions and climate are not the same. Climate is the weather measured over a long period.
That is why scientists are often reluctant to make direct links between (extreme) weather and climate change. But here they agree: the warming of the climate causes weather extremes to increase.
Explaining extreme weather, such as storm, rain and drought, on the basis of climate change is called climate attribution. For this, scientists use climate models, statistics and meteorological data.