SASKATOON -- Extreme heat exposure in cities has tripled since the early 1980s, with the most vulnerable in society particularly at risk, a new study shows.

“The story that emerges is one of rapidly increasing heat exposure, with poor and marginalized people particularly at risk,” the authors said in an article in The Conversation about their findings.

The team, who published their findings in Proceedings of the National Academy of Sciences of the United States of America last week, used satellite data from 1983 to 2016 and counted the number of days per year that people in 13,000 urban areas around the globe were exposed to extreme heat.

Authors attributed the spike in extreme heat exposure in cities to a number of factors, including climate change and the “heat Island effect” – a phenomenon in which temperatures in urban areas are higher due to human activities and types of materials used in roads and buildings.

“Increased extreme heat exposure from both climate change and the urban heat island effect threatens rapidly growing urban settlements worldwide,” the authors said in their study.

Extreme heat exposure – which involves events of high temperatures and high humidity -- has been linked to a host of issues, such as: premature births; lower test scores; decreases in productivity; and, increased risk of heatstroke among children and the elderly.

Researchers behind the latest study said a huge reason for the spike of more extreme heat exposure in cities globally is the dramatic rise in number of people living in dense urban areas.

The number of people living in cities and towns has exploded since the 1980s, with two billion living in cities back then compared to 4.4 billion today. And now, nearly one in four people on Earth – about 1.7 billion -- live in urban areas where there was a spike in extreme heat exposure.

The authors said if greenhouse gas emissions and population growth in urban hubs continue to rise, “we will see massive increases in heat exposure among urban dwellers.”


About two-thirds of the global rise in urban extreme heat exposure was seen in sub-Saharan Africa and southern Asia. The authors said that governments’ lack of planning and infrastructure to deal with the explosion in urban population growth played a major role in this.

Researchers attributed this to post-colonial governments either not having or mobilizing the resources to support this influx into cities.

But they said urban extreme heat exposure in general has been largely been left out of policy conversations involving urban development. Not dealing with it will lead to people in cities having a tougher time escaping poverty, the authors warned.

“Our results suggest that previous research underestimates extreme heat exposure, highlighting the urgency for targeted adaptations and early warning systems to reduce harm from urban extreme heat exposure,” the authors added.

When it came to extreme heat’s disproportionate effect on marginalized groups, the new findings echoed previous data.

Studies in Canada found populations more at risk for heat-related illness include Indigenous people, newcomers, and lower-income people; and in an unrelated U.S. study, researchers found low-income neighbourhoods and communities with higher Black, Hispanic and Asian populations experience significantly more urban heat than wealthier and predominantly white neighborhoods.

When it came to exposure to extreme heat, the team behind the latest study urged policymakers and city planners to better address systemic inequality and injustice.

Some examples they noted included having early-warning systems during extreme heat events being paired with more opening cooling centres, the greater implementation of occupational heat standards, and fostering more collaborations across scientific disciplines to help business and governments adapt.