• Jacob Bourne

Dangerous Urban Heat Exposure Increased Nearly 200% Globally

Climate change is a global problem, but the impacts are not evenly distributed, and some regions like the Arctic and many populated areas are warming faster than others.

urban greening
Tramway track in Czech Republic covered in grass to reduce urban heat island effect. Credit: Shutterstock/Yuri Hoyda

Given the complexity of planetary systems, it’s difficult to predict how these disparate trends will evolve, but new research has highlighted the particular vulnerability of the world’s cities. A study recently published in the Proceedings of the National Academy of Sciences found that climate change and the urban heat island effect together are posing grave heat danger to human settlements.

Astonishingly, the study revealed that between 1983 and 2016, extreme heat exposure in 13,115 cities around the world increased by almost 200%, affecting 1.7 billion people, suggesting prior studies underestimated extreme heat exposure. Moreover, with global average temperatures continuing to rise, the resilience of urban areas is severely stretched. According to the United Nations, this is a problem as 55% of the world’s population dwells in urban areas, a proportion projected to increase to 68% by 2050.

In addition to causing illness and fatalities, extreme heat can reduce labor productivity, economic output, damage infrastructure, spark conflict and strain healthcare and other services. Furthermore, the urban poor is especially vulnerable to these risks due to lack of access to air conditioning and even shade in some communities.

The study also exposed a lack of understanding of the intersection between population growth centers and the places with the most significant risk of further extreme temperature rise. However, in regions experiencing rapid urbanization, such as Southern India, total urban warming exceeded urban population growth as the driver of exposure.

“This geographic pattern parallels recent global analysis of station observations of extreme humid heat that suggest areas of the planet may soon exceed human biophysical capacity, regardless of local acclimatization,” the authors stated.

Better understanding how the warming will intersect with pockets of population growth could help bolster early warning systems in advance of heatwaves and guide urban planning efforts to help mitigate the warming. It’s also critical because the increased incidence of heat exposure can be mainly attributed to temperature rise in some areas, while in other areas, it’s largely caused by the population growth itself.

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“Reducing the impacts of extreme heat exposure to urban populations requires globally consistent, accurate, and high-resolution measurement of both climate and demographic conditions that drive exposure,” the authors stated. “Such analysis provides decision-makers with information to develop locally tailored interventions and is also sufficiently broad in spatial coverage to transfer knowledge across urban geographies and climates.”

While much of the extreme heat exposure has occurred in places where one might expect, such as cities located in low latitudes or the Sun Belt of the U.S., the unexpected heatwave in the Pacific Northwest in June of this year causing hundreds of deaths, is an example of why a warming climate behooves a greater focus on heat mitigation planning for just about everywhere. Although the human body can acclimate to warmer temperatures to a certain degree, there’s a limit to how much it can take. When the core body temperature rises to 42 to 43 degrees Celsius, death generally occurs; however, when the humidity is 100%, the heat tolerance threshold drops to 37 to 38 degrees Celsius.

In addition to working to halt or reverse climate change, urban planners can tackle the issue by implementing building designs that reduce the urban heat island effect. This includes measures such as planting trees and vegetation and using cool roof technologies. Reflecting the sun’s rays away from buildings and infrastructure may increasingly be used as a way to offset urban warming. Scientists at Purdue University recently gained Guinness Book of World Records recognition for creating the “world’s whitest paint.” The paint is so white that it can reflect 98.1% of incoming solar radiation, compared to only 80% to 90% for conventional white paint. Such reflective coatings can help cool buildings and reduce reliance on air conditioning.


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