Extreme heat exposure in cities has tripled in decades, scientists warn

Exposure to extreme urban heat has increased dramatically since the early 1980s, with total exposure having tripled in the past 35 years.

Today, around 1.7 billion people, or nearly a quarter of the world’s population, live in urban areas where exposure to extreme heat has increased, as we show in a new study published on 4 October 2021.

Most urban heat exposure reports are based on blanket estimates that overlook millions of residents at risk. We took a closer look. Using satellite estimates of where every person on the planet lived each year from 1983 to 2016, we counted the number of days per year that people in more than 13,000 urban areas were exposed. at extreme heat.

The story that emerges is one of rapidly increasing heat exposure, with poor and marginalized people particularly at risk.

Almost two-thirds of the global increase in urban exposure to extreme heat has occurred in sub-Saharan Africa and South Asia. This is in part because of climate change and the urban heat island effect – temperatures in urban areas are higher due to the materials used to construct roads and buildings.

But it is also because the number of people living in dense urban areas has increased rapidly.

Urban populations have exploded from 2 billion people living in cities and towns in 1985 to 4.4 billion today.

Although patterns vary from city to city, urban population growth has been fastest among African cities where governments have not planned or built infrastructure to meet the needs of new urban residents. .

(Tuholske et al, 2021)

Above: Exposure of the urban population to extreme heat and the influence of urban warming and population growth. Extreme heat is defined as at least one day with a wet bulb temperature above 30 ° C. Wet bulb temperature takes into account temperature, humidity, wind, and radiation to assess the effect on humans

Climate change increases the risk of heat

It is clear that there is a dangerous interplay between rising temperatures and rapid urban population growth in already very hot countries.

How much will it get worse and who will be affected the most? Chris Funk explores these heat exposure projections for 2030 and 2050 in his new book Cambridge University Press Drought Flood Fire.

Urban population growth is expected to continue, and if greenhouse gases continue on their rapid growth path, we will see a massive increase in heat exposure among city dwellers.

The planet has warmed by just over 1 degree Celsius (1.8 F) since pre-industrial times, and research shows that warming results in more dangerous extreme weather and climate conditions.

We are almost certain to experience another degree of warming by 2050, and possibly more.

This warming, combined with the growth of the urban population, could lead to a 400% increase in exposure to extreme heat by 2050. The vast majority of those affected will live in South Asia and Africa, in the valleys. rivers such as the Ganges, Indus, Nile and Niger. The hot, humid, populated and poor cradles of civilization become epicenters of heat risk.

At the same time, research shows that marginalized people – the poor, women, children, the elderly – may not have access to resources that could help them stay safe in extreme heat, such as air conditioning, rest during the hottest parts of the day and health care.

Count who is at risk

To count the number of city dwellers exposed to extreme heat, we used data and models that incorporate advances in social and physical sciences.

Over 3 billion city dwellers live 25 kilometers (15.5 miles) or more from a weather station with a solid record of reporting. Climate model simulations that estimate time spent were not designed to measure a single person’s risk; rather, they have been used to assess large-scale trends.

This means that the effects of extreme heat on hundreds of millions of impoverished city dwellers around the world have simply not been documented.

In fact, the official record indicates that only two episodes of extreme heat have had significant effects on sub-Saharan Africa since the 1900s. Our results show that this official record is not true.

Exposure to extreme heat increased in cities from 1983 to 2016 (Tuholske et al, 2021)Exposure to extreme heat increased in cities from 1983 to 2016 (Tuholske et al, 2021)

Reasons to act

The growth of the urban population in itself is not the problem. But the convergence of extreme heat changes with large urban populations challenges the conventional wisdom that urbanization uniformly reduces poverty.

Historically, urbanization has been associated with a shift in labor from agriculture to manufacturing and services, in tandem with the industrialization of agricultural production which has increased efficiency. But in parts of sub-Saharan Africa, there has been urbanization without economic growth.

This may be due to post-colonial technological changes that improve health. People are living longer and more children are surviving infancy thanks to advances in medicine, but post-colonial governments often do not have or mobilize the resources to support large numbers of people who migrate to them. cities.

What worries us is that because urban exposure to extreme heat has been largely left off the development policy radar, the urban poor will find it more difficult to escape poverty.

Numerous studies have shown that extreme heat reduces labor productivity and economic output. Low-income workers tend to have less coverage. They are also burdened with high costs for food and shelter, and often lack air conditioning.

Actions Cities Can Take

The coronavirus pandemic and the Black Lives Matter movement have amplified demands for greater political and scientific attention to inequality and injustice. Better data that helps capture the real experiences of people is a key feature of a more integrated and socially relevant climate and health science.

Collaborations between scientific disciplines like ours can help governments and businesses welcome new urban residents and reduce heat damage.

Setting up early warning systems, for example, can reduce risks if accompanied by actions such as opening cooling centers. Governments can also implement occupational heat standards to reduce heat risks for marginalized people and enable them to avoid exposure. But these interventions must reach the people who need them most.

Our research provides a map of policies and technologies not only to reduce damage from urban exposure to extreme heat in the future, but today. The conversation

Cascade Tuholske, Postdoctoral Fellow, Center for International Earth Science Information Network (CIESIN), Columbia Climate School, Columbia University; Chris Funk, director of the Climate Hazards Center, University of California at Santa Barbara, and Kathryn Grace, associate professor of geography, environment and society, University of Minnesota.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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