The risk of dangerous heat for people over 60 has been severely underestimated, according to a new modeling study published in the journal "The Lancet Planetary Health". The authors use data on actual heat tolerance in older adults, rather than just results from experiments with young and healthy volunteers.
The main conclusion is that warming of 1.5°C above pre-industrial levels would expose 22% of the population over 60 to a dangerous combination of heat and humidity for at least one month per year. This equates to approximately 290 million people.
Why age changes the assessment
The human body cools itself by sweating and by increasing blood flow to the skin. As we age, these mechanisms can weaken. The risk also increases due to the higher prevalence of cardiovascular, pulmonary, and other chronic diseases, as well as medications that can affect thermoregulation.
The study uses "wet-bulb temperature" experiments with people over 60 in the United States. This indicator combines air temperature and humidity and is important because at high humidity, sweat evaporates more difficultly, and the body's cooling becomes ineffective.
Previous models often used thresholds defined for young and healthy participants. According to the authors, this created an overly optimistic view of the conditions under which the human body can no longer compensate for heat stress.
What the scenarios mean
With global warming of 1.5°C, older people would face a level of dangerous heat that for young adults is only expected at warming close to 4°C. The difference shows how strongly age changes physiological vulnerability to extreme temperatures.
Every additional degree of global warming would mean about 1 billion more people experiencing approximately one more month per year of heat and humidity exceeding the body's ability to cool down.
"Unbearable heat will cover significantly larger territories and last longer, affecting many more people than previously thought," the authors note in their conclusions.
The highest-risk regions
In a 3°C warming scenario, older residents of South Asia and the Persian Gulf region could be exposed to dangerous heat day and night for three months a year. Among the most vulnerable are areas in India, Pakistan, Bangladesh, Myanmar, and Niger, where extreme weather is combined with poverty and limited access to cooling.
The researchers warn that heat can increase pressure for migration. "The results obtained show that unbearable heat will increasingly force people to leave their homes – both within their own countries and abroad, creating new humanitarian and political challenges," they note.
What measures are needed
The authors call for rapid reduction of greenhouse gas emissions and for heat protection plans that explicitly prioritize older people from risk groups.
They emphasize that many heat-related deaths occur indoors. Therefore, access to air conditioning, cooling centers, good home insulation, early warnings, and active care for lonely and chronically ill older people is key to reducing the risk.
Data from "Lancet Countdown" already show that heat-related mortality for people over 65 has increased by 167% compared to the 1990s. This does not mean that all these cases can be explained by temperature alone, but it underscores the growing health pressure from climate change on the most vulnerable groups.