Extreme Heat Exposure in Cities Has Tripled in Just a Few Decades, Scientists Warn

The extreme urban heat exposure has risen dramatically since the 1980s. In fact, the total exposure has tripled in the past 35 years.
Today, almost one-quarter of the world's population lives in urban areas where heat has increased. This is according to a new study, which was released on Oct. 4, 2021.

Urban heat exposure reports are often based on large estimates that ignore millions of residents at risk. We looked closer. We looked closer.

It is clear that heat exposure is increasing rapidly, with marginalized and poor people especially at risk.

Sub-Saharan Africa was and is responsible for nearly two-thirds the increase in urban heat exposure worldwide. This is partly due to climate change. The urban heat island effect temperature in urban areas is higher because of the building materials.

It is also due to the rapid increase in urban density.

Urban populations have increased dramatically, with 2 billion people now living in cities and towns. This compares to 4.4 billion in 2015.

Although the trends may vary from one city to the next, urban population growth is fastest in African cities where infrastructure was not built or planned to accommodate new residents.

(Tuholske et al, 2021)

Above: Urban heat exposure and the impact of urban warming and increased population. Extreme heat refers to at least one day of wet-bulb planet temperature exceeding 30 C. This temperature is calculated taking into consideration temperature, humidity, wind, and radiation.

The heat risk is increasing due to climate change

It is evident that the dangerous combination of rising temperatures and rapid urban growth in countries already very hot is creating a dangerous environment.

What will happen to the most vulnerable and how much will it get worse? Chris Funk examines heat exposure projections in 2030 and 2050 for his new Cambridge University Press book Drought Flood Fire.

The urban population is expected to grow, and if greenhouse gasses continue their rapid growth, we will see huge increases in heat exposure among urban dwellers.

Since pre-industrial times the planet has warmed by just over 1 degree Celsius (1.8 F). Research shows that warming is causing more extreme weather and climate conditions.

It is almost certain that we will experience additional warming by 2050 and possibly more.

Combining urban population growth and warming could result in a 400% increase in extreme heat exposure between 2050-2050. Most of those affected will be found in South Asia and Africa along with river valleys such as the Ganges and Indus. Heat risk is increasing in hot, humid, poor, and populated cradles for civilization.

Research shows that the most vulnerable people, including the poor and women, may not have access to the resources they need to stay safe in extreme heat. This includes air conditioning, health care, and rest during the hottest hours of the day.

Counting the people at greatest risk

We used data and models that combine advances in physical and social sciences to count the urban dwellers who are exposed to extreme heat.

There are more than 3 billion urban dwellers living 25 km (15.5 miles) from a weather station that has a strong reporting record. Climate simulations that simulate past weather are not intended to assess a single person's vulnerability; they were designed to gauge large-scale trends.

It is impossible to document the impact of extreme heat on hundreds of millions of urban poor people around the world.

According to the official record, only two extreme heat events had any significant impact on sub-Saharan Africa in the 1900s. Our data proves that this is not the case.

Cities are more exposed to extreme heat from 1983 to 2016. (Tuholske et al, 2021)

There are reasons to act

Urban population growth is not the problem. The convergence of extreme heat changes with large urban populations raises questions about the assumption that urbanization reduces poverty.

Urbanization has historically been associated with a shift of the workforce from agriculture to manufacturing and services. This was in conjunction with increased efficiency through industrialization. In sub-Saharan Africa there has been urbanization but no economic growth.

This could be due to technological advances that have been made post-colonially. Medical advances have led to people living longer lives and children surviving beyond infancy. However, post-colonial governments are often unable to mobilize the resources necessary to support large numbers of people who move to cities.

We are concerned that urban extreme heat exposure is largely ignored in development policy. This will make it more difficult for poor urban residents to escape poverty.

Many studies have shown that extreme heat can reduce labor productivity and economic output. Workers with low incomes are less likely to be covered by worker protections. They also have to pay high food and shelter costs and lack air conditioning.

Steps cities are possible

Both the coronavirus pandemic as well as Black Lives Matter have increased demands for scientific and political attention to injustice and inequality. A key component of integrated climate-health science that is socially relevant and more inclusive is better data.

Collaborations between scientific disciplines such as ours can be a great help to governments and businesses in accommodating new urban residents and reducing heat-related harm.

If early warning systems are implemented, they can help reduce the risk of heat stroke. To reduce heat exposure for those who are most vulnerable, the government can establish occupational heat standards. These interventions must reach those most in need.

Our research provides a roadmap for technologies and policies, not only to reduce urban extreme heat exposure in future but also today.

Cascade Tuholske is a Postdoctoral Research Scientist at the Center for International Earth Science Information Network, Columbia Climate School, Columbia University. Chris Funk, Director of Climate Hazards Center University of California Santa Barbara and Kathryn Grace Associate Professor of Geography Environment and Society University of Minnesota.

This article was republished by The Conversation under Creative Commons. You can read the original article.