Global Heat Crisis Intensifies: One in Three People Now Face Severe Activity Restrictions
A groundbreaking study has unveiled a stark reality: extreme heat now impacts one in three people globally, severely curtailing the ability to perform basic physical tasks. This research, led by scientists from the Nature Conservancy and published in the journal Environmental Research: Health, provides a sobering preview of the escalating climate crisis, highlighting how rising temperatures are shrinking the safe window for outdoor activities worldwide.
Rising Temperatures and Physiological Limits
The study combines physiological data on heat tolerance with seven decades of global and regional information on population, temperatures, and human development. It warns that climate breakdown, driven by the continued burning of fossil fuels, is making it increasingly difficult even for young, healthy adults to engage in routine activities such as housework or climbing stairs during peak summer daylight hours. For elderly individuals, the limitations are more pronounced due to reduced sweating capacity, which impairs body temperature regulation.
On average, people over 65 now endure approximately 900 hours annually when heat severely restricts safe outdoor activity, a significant increase from 600 hours in 1950. This equates to more than a month of daytime hours lost to extreme heat conditions.
Disproportionate Impact on Vulnerable Regions
The worst-affected areas are predominantly in poorer countries or regions, despite their minimal contribution to greenhouse gas emissions compared to wealthier nations. In tropical and subtropical zones, heat restricts outdoor activity for older adults for between one-quarter and one-third of the year. The most severe challenges are concentrated in south-west Asia (including Bahrain, Qatar, Kuwait, the United Arab Emirates, Iraq, and Oman), south Asia (Pakistan, Bangladesh, and India), and parts of west Africa (such as Mauritania, Mali, Burkina Faso, Senegal, Djibouti, and Niger).
Within countries, disparities are stark based on geography, income, and occupation. For instance, in India, limitations are most acute across the Indo-Gangetic Plain and eastern lowlands, while the Western Ghats and Himalayan foothills are less affected. In South America, the Amazon basin faces greater vulnerability than the Andean highlands. In Gulf states, affluent residents can mitigate risks with air conditioning, whereas poorer migrant workers are exposed to dangerous solar radiation on construction sites and other outdoor jobs.
Measuring Liveability and Adaptation
The study advances previous research by examining social and physiological adaptation to heat, using METs (metabolic equivalents) to measure "liveability." A manageable temperature allows people under 65 to perform up to 3.3 METs of activity—like sweeping floors or moderate walking—without heat stress. In contrast, "unliveable limitations" occur when activity is restricted to 1.5 METs, primarily sedentary tasks such as lying down or sitting.
Researchers assessed vulnerability by analyzing sweat production and skin wettedness in heat chambers across different age groups. Comparing data from 1950–1979 to 1995–2024 revealed a widening global area where liveability limitations are increasing due to rising heat, with the most severe restrictions recorded in 2024.
Calls for Urgent Action
Lead author Luke Parsons emphasized the urgency of the findings: "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. Every fraction of a degree of additional warming will expand these impacts." He noted that 2024 offers a sobering glimpse of a world 1.5°C above preindustrial levels, underscoring the need to avoid 2°C or more.
The authors advocate for rapid action to reduce oil, gas, and coal consumption, alongside targeted investments in heat early warning systems, cooling infrastructure, and protections for older adults and outdoor workers in high-risk regions. However, they stress that such local measures are not substitutes for the fundamental imperative to limit global warming.
