Mexico, Italy and others see up to two more months of heat stress than in the 1970s, study says

A new study in Nature Climate Change says human heat stress has expanded sharply since the 1970s, with some countries now seeing one to two extra months of uncomfortable or dangerous-feeling conditions each year.

The research, reported by the Associated Press on Monday, points to especially large increases in Mexico, Kenya, Italy and other warm regions. In parts of Southern Africa, Eastern Africa, Mexico, Central America and Southern Europe, the number of days with at least strong heat stress has risen by as many as 50 days a year compared with the 1970s.

The study measures heat stress by looking at how weather feels to the human body, not just air temperature alone. It uses the Universal Thermal Climate Index, which factors in humidity, wind speed and related conditions that affect the body’s ability to cool itself.

How the heat pattern has changed

The paper says parts of Southern Spain, Italy, Greece and Turkey can now see up to 40 additional days of strong heat stress. AP also reported that the ten warmest nights each year have warmed faster than the ten warmest days, leaving less overnight relief after hot spells.

That matters because the body depends on cooler nights to recover from daytime heat. The study defines tropical nights as nights when the minimum temperature stays at or above 20C.

Rebecca Emerton, the study’s lead author and a senior scientist at the European Centre for Medium-Range Weather Forecasts, said heat stress is expanding into regions where it has historically been rare or nonexistent, according to AP.

Jennifer Francis, a climate scientist quoted by AP, said the paper adds stark detail about the growing danger. Her comments pointed to the role humidity plays in making high temperatures more harmful to people.

Why the findings matter

The study says one billion more people now face at least one day of extreme heat stress each year than they did in the 1970s. That finding adds to evidence that climate change is affecting the human body through longer, wetter and harder-to-recover-from heat, not only through higher daytime readings.

The public-health concern is broader than a single hot afternoon. When heat lingers into the evening and overnight, people can lose the chance to cool down, which raises risks for older adults, people with health conditions and anyone without reliable access to air conditioning or other cooling.

The researchers’ focus on feels-like heat also helps explain why some places can face dangerous conditions even when the thermometer does not show record-breaking air temperature. Humidity and wind can make the same temperature feel far worse, and can slow the body’s ability to shed heat.

What the study adds

AP said the paper was published Monday in Nature Climate Change. The study adds another layer to the climate record by comparing present-day heat stress with conditions in the 1970s, rather than only measuring recent year-to-year variation.

It also points to a widening gap between daytime heat and nighttime recovery. The faster warming of the ten hottest nights, compared with the ten hottest days, suggests that some of the most dangerous changes are showing up when people are supposed to be resting.

The paper’s regional findings show that the impact is not limited to one continent or climate zone. The biggest changes cited by AP include Southern Africa, Eastern Africa, Mexico, Central America and Southern Europe, with Mexico and Italy among the countries singled out in the reporting.

What comes next

The findings support practical adaptation measures, including heat-health action plans, early warning systems and climate risk assessments. Those tools matter most where longer heat seasons and hotter nights make it harder for communities to recover between events.

The study also strengthens the case for treating heat stress as a core climate risk, not just a seasonal inconvenience. For policymakers, the key question is no longer whether dangerous heat will arrive, but how long it will last and whether people can safely cool off when it does.

AP identified Rebecca Emerton as the study’s lead author, and the report said the work comes from the European Centre for Medium-Range Weather Forecasts. The article also quoted climate scientist Jennifer Francis on the growing health threat from heat and humidity.