One in Three People Worldwide Now Struggle With Dangerous Extreme Heat, New Research Reveals

Extreme Heat Is Reshaping Daily Life for Billions of People

A groundbreaking new study has revealed a stark and troubling reality: approximately one in three people on Earth now lives in areas where extreme heat dangerously restricts their ability to carry out normal daily activities. The findings, published in the journal Environmental Research: Health, paint a vivid picture of how accelerating climate breakdown is quietly eroding human livability across the globe.

Driven by decades of fossil fuel combustion, soaring temperatures are making it unsafe even for young, physically healthy adults to perform basic tasks — such as climbing stairs, doing household chores, or walking at a moderate pace — during peak daytime hours in summer months.

The Toll on Older Adults Is Especially Severe

While the heat crisis touches people of all ages, older individuals face a disproportionately heavy burden. The elderly are less capable of regulating body temperature through sweating, leaving them far more exposed to heat-related health risks.

The research, which draws on seven decades of global data covering population trends, temperature records, and human development, found that people aged 65 and older now endure roughly 900 hours per year during which extreme heat severely curtails safe outdoor activity. In 1950, that figure stood at around 600 hours. The difference represents more than a full month of lost daytime activity annually.

Poorer Regions Bear the Heaviest Burden

In a glaring example of climate injustice, the communities suffering the most from extreme heat are predominantly those in low-income nations — countries that have contributed far less to global greenhouse gas emissions than wealthier industrialized nations.

In several tropical and subtropical regions, heat restricts safe outdoor activity for older residents for between one-quarter and one-third of the entire year. The areas facing the most critical conditions include:

• South-West Asia: Bahrain, Qatar, Kuwait, the UAE, Iraq, and Oman
• South Asia: Pakistan, Bangladesh, and India
• West Africa: Mauritania, Mali, Burkina Faso, Senegal, Djibouti, and Niger

Geographic and Economic Divides Within Nations

Even within individual countries, vulnerability varies dramatically. In India, heat limitations are most acute across the Indo-Gangetic Plain and eastern lowlands, while residents of the Western Ghats and Himalayan foothills face comparatively milder restrictions. In South America, communities in the Amazon basin are significantly more exposed than those living at higher elevations in the Andes.

Wealth also plays a decisive role. In many Gulf states, affluent residents can retreat to air-conditioned homes and offices, while low-income migrant workers performing outdoor construction and manual labor face potentially lethal levels of heat and solar radiation with little protection.

How Scientists Measured 'Liveability' in the Heat

The study, led by researchers from the Nature Conservancy, introduced a rigorous framework for assessing livability under varying heat conditions. Scientists used METs — a unit representing the average energy a person expends at rest — to define safe thresholds of physical activity at different temperatures.

• A manageable temperature allows adults under 65 to sustain up to 3.3 METs of activity — such as light sweeping or moderate-paced walking — without triggering heat stress or disrupting the body's ability to maintain a stable core temperature.
• Unliveable conditions are defined as environments where activity must be reduced to just 1.5 METs, essentially limiting people to sedentary behaviors like sitting or lying down.

To assess age-related differences, researchers measured sweat production and skin moisture levels in participants exposed to controlled heat chamber environments for varying durations.

2024 Was the Most Dangerous Year on Record

Comparing climate and population data from two distinct periods — 1950 to 1979 and 1995 to 2024 — researchers documented a clear and accelerating trend: heat-related livability limitations are expanding in both intensity and geographic reach.

The single most severe year recorded in the entire dataset was 2024, underscoring that the crisis is not a distant future concern but a present-day emergency already unfolding.

Urgent Action Required on Two Fronts

The study's authors are calling for immediate responses at both the global and local levels.

On the global stage, they stress that rapidly reducing emissions from oil, gas, and coal remains the only true long-term solution to halting the expansion of dangerous heat zones.

At the community level, they urge governments and policymakers to prioritize:

• Heat early warning systems to alert vulnerable populations
• Cooling infrastructure in the most affected regions
• Targeted protections for elderly residents and outdoor laborers

Lead author Luke Parsons emphasized the urgency of the situation: "Hundreds of millions of people can no longer safely go about their daily lives outside during the hottest parts of the year — and those people are overwhelmingly in countries that have contributed least to the problem."

Parsons added that 2024 offered a chilling glimpse of what a world 1.5°C above pre-industrial temperatures could look like, reinforcing the critical importance of preventing warming from reaching 2°C or beyond.

"Local investments in cooling and early warning systems are essential," he noted, "but they are not a substitute for the fundamental imperative to limit global warming itself."