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

Heat stress is lasting longer

A new climate study says heat-stress seasons are stretching by as much as one to two months in parts of Mexico, Italy and other regions compared with the 1970s.

The research was published June 22 in Nature Climate Change and was first reported by the Associated Press the same day. It looks at heat as people actually feel it, not just air temperature alone, using the Universal Thermal Climate Index, or UTCI.

That matters because UTCI takes humidity, wind speed and other conditions into account. In humid weather, sweat evaporates less efficiently, which can make the body struggle to cool itself even when temperatures are not at their absolute highest.

According to AP's report on the paper, the strongest increases are appearing in parts of Southern Africa, Eastern Africa, Mexico, Central America and Southern Europe.

In some places, the study found about 50 more days a year of at least strong heat stress than in the 1970s.

Where the changes are showing up

The clearest regional examples include parts of Southern Spain, Italy, Greece and Turkey, where the study says there could be up to 40 additional days of strong heat stress.

Southern U.S. states including Texas and Florida are also seeing close to 25 or more days with very strong heat stress, according to AP's reporting on the study.

Lead author Rebecca Emerton, a senior scientist at the European Centre for Medium-Range Weather Forecasts, said the research shows heat stress is spreading into places where it has historically been rare or absent.

The findings suggest the shift is not limited to the hottest places on the map. Instead, heat stress is extending into a wider geographic band, affecting regions that have long seen more moderate seasonal patterns.

For countries such as Mexico and Italy, that means the period when heat becomes dangerous is lasting much longer than it did half a century ago.

Why tropical nights matter

The study also points to a second change that can make hot periods more dangerous: tropical nights.

AP reports that tropical nights, defined as nights when temperatures do not fall below 20C, are increasing faster than daytime highs.

That is important because overnight cooling gives the body time to recover from daytime heat. When nights stay warm, the strain can carry over from one day to the next.

Longer stretches without relief are especially concerning during heat waves, when repeated exposure can build up and make conditions more dangerous for older adults, outdoor workers and people without reliable cooling.

The rising number of tropical nights also helps explain why heat stress is increasingly being measured as a season rather than a single event.

Public-health stakes

The paper's broader message is that longer and more severe heat exposure is not only a climate metric. It is a public-health issue.

AP reported that one billion more people now face at least one day of extreme heat stress each year than they did in the 1970s.

That increase raises the pressure on heat-health plans, warning systems and local adaptation measures. It also means governments and health agencies have less room to rely on short emergency responses when dangerous heat persists deeper into the year.

The study's framing is especially relevant for places where heat has historically been treated as a seasonal nuisance rather than a longer-term health threat.

As heat stress spreads into new regions, more communities may need to prepare for earlier seasonal onset, later seasonal end points and less overnight recovery between hot days.

What comes next

The study was published on June 22, 2026, and AP's report was the first major news coverage identified in the research packet.

The open questions now are whether the journal article or the authors' institutions release more country-by-country detail, and whether national meteorological or health agencies respond with new warnings or adaptation measures.

Further reporting may also clarify how the UTCI-based findings compare with local heat thresholds used by governments and health systems.

For now, the central finding is clear: in Mexico, Italy and other regions, heat stress is arriving earlier, lasting longer and leaving less time for recovery than it did in the 1970s.