Rising temperatures are already a leading climate health threat, straining nearly every major system in the human body
Climate change is causing more frequent, longer, and more intense heatwaves around the world, affecting not only the environment but also nearly every major system in the human body. As temperatures rise, the body must work harder to regulate its internal temperature, increasing the risk of heat exhaustion, heatstroke, dehydration, and death. Extreme heat places significant strain on the cardiovascular, respiratory, and nervous systems, leading to higher illness and mortality rates, reduced ability to work safely, and greater health risks for vulnerable populations.
In addition, climate change is expanding the spread of climate-sensitive diseases by creating warmer conditions that allow mosquitoes and other disease-carrying insects to survive in new regions for longer periods. According to the IPCC, warming from 1.5°C to 2°C is expected to increase the transmission of vector-borne diseases such as dengue, malaria, and West Nile virus. Europe has already experienced a nearly 297% increase in climatic suitability for dengue transmission; rising temperatures are reshaping disease risks and posing growing threats to public health.
Heat-related deaths per million people, annually
Increase in heat warnings issued
In the summer of 2025, Europe experienced another season of record-breaking heat. A prolonged August heatwave pushed temperatures above 45°C in parts of Portugal and Spain and above 42°C in southwestern France, exposing millions of people to dangerous levels of heat stress. Similar extremes were recorded across Asia, the Middle East, and North America; these realities are impossible to ignore; extreme heat is a global public health challenge.
Heat does not affect everyone equally. Some populations are far more vulnerable because of age, health conditions, occupation, or socioeconomic circumstances. This includes older adults, children, outdoor workers, and low-income communities. The Lancet Countdown on Health and Climate Change (2025) found that average annual heat-related deaths have increased by 52 deaths per million people, while heat warnings have risen by 318%. Nearly every region in Europe experienced an increase in heat-related mortality during 2015–2024 compared with 1991–2000.
Extreme heat also fuels environmental hazards that further threaten health. Hot, dry conditions increase the likelihood of wildfires, releasing smoke, and fine particulate pollution that can travel hundreds of kilometers. These pollutants worsen respiratory and cardiovascular disease, reduce air quality, damage ecosystems, and place additional pressure on healthcare systems.
Increase in Europe's climatic suitability for dengue transmission
Peak temperatures recorded in Portugal and Spain, August 2025
As climate change accelerates and the 1.5°C Paris Agreement emissions target is at stake, governments must strengthen heat action plans, improve early warning systems, protect workers, and reduce greenhouse gas emissions to protect people and combat growing health risks posed by extreme heat.
