文章全文：A rising share of people are exposed to dangerously high temperatures

The scorched Earth

A rising share of people are exposed to dangerously high temperatures

Climate change and population distribution are the cause 

As climate-change models predicted, the frequency and intensity of sweltering days has increased recently. Records were broken in Europe last week as a heatwave gripped the continent. Britain set a new maximum temperature record of 40.3°C (104.5°F), shattering the 38.7°C set in 2019. Since the 1980s temperatures have risen in the world’s cooler regions, exposing more people to stifling heat. Meanwhile, population growth has been fastest in the hottest countries, increasing the share of humanity affected. 

To measure heat exposure, we combined two large data sets. The Universal Thermal Climate Index (UTCI) produced by the EU’s Earth-observation programme, Copernicus, measures heat at hourly intervals, dividing the world into 865,000 grid squares. The UTCI combines data on air temperature and solar radiation with humidity and wind into a single composite “feels like” temperature measured in Celsius. We then fused these data with the population living in each grid square.  

UTCI above 38°C is categorised as causing “very strong” heat stress. Temperatures above 46°C cause “extreme” stress. Just 30 minutes of very strong heat stress can imperil lives, particularly among the old. Four-fifths of the world’s population have experienced at least one day of very strong heat stress—defined as at least three hours—in the past five years. 

Although large swathes of Europe’s population have endured heat above 38°C last week, it remains exceptional. Over the past five years, the average European has experienced such heat for just three days a year. But elsewhere it is the norm: people outside Europe endure similar conditions for 65 days each year.  

Extreme heat above 46°C is remarkably common, too. On average, it occurs for three days per year for each person on Earth. But the incidence is much higher in Africa and parts of Asia, particularly the Indian subcontinent. An average person living in these two continents has recently experienced such heat for 4.9 days a year, a 30% rise compared with 1980 to 1984. 

High population growth in Africa and Asia means that heat stress is now affecting more people. The hottest countries have tended to grow the fastest since 1980. So the share of time that people have felt very strong heat stress has risen by 50%. Two-thirds of those who suffer extreme heat live in countries where average annual incomes are below $2,000, meaning many cannot afford air-conditioning. Europeans should spare a thought for them as they swelter in the sun. 

■ Sources: Copernicus; European Commission; World Bank; The Economist