Study on extreme heat in U.S. cities a warning for Canada: researcher

GUELPH, Ont. — Research that finds extreme heat risks from climate change in U.S. cities is much higher than previously thought is a warning for Canada, says one of the authors.

“A city like Vancouver isn’t going to be too dissimilar from Seattle,” said Scott Krayenhoff, a professor at the University of Guelph’s school of environmental science.

“Toronto isn’t going to be too dissimilar from Detroit or Buffalo.”

Extreme heat is becoming an increasing concern for public health officials around the world.

“Population exposure to heat is increasing due to climate change,” says the World Health Organization. It says that between 2000 and 2016, the number of people exposed to heat waves increased by about 125 million.

U.S. agencies say heat is the leading cause of weather-related deaths in that country ahead of hurricanes and floods. In 2018, about 80 deaths were blamed on a heat wave in Quebec.

Estimates of how climate change is likely to increase extremely hot days have been done before.

Krayenhoff said the new work, published this week in the Proceedings of the National Academy of Sciences, is much broader.

The paper looks at climate change estimates if there are no substantial cuts to greenhouse gases and combines them with anticipated growth in urban populations, as well as with the “heat bubble” effect of cities themselves.

“When you pave over a farmer’s field or cut down a forest and build a subdivision, that generally raises the temperature,” Krayenhoff said.

Researchers found that when the factors are combined, person-hours of heat exposure are set to skyrocket — by more than 100 times — in some southern U.S. cities by the end of the century.

Even northerly ones just across the border from their Canadian neighbours are expected to see significant impacts.

Detroit and Buffalo are forecast to have 30 times more extreme heat exposure. Seattle’s exposure is predicted to increase by a factor of 10.

“Regions of southern Ontario and southern Quebec could see fairly sizable impacts,” said Krayenhoff. “Out West, it seemed a little bit better — still cause for concern — but our results suggest the East would get hit a little more intensely.”

The paper also sets different levels for extreme heat in different cities. A scorcher in New York is business as usual in Phoenix.

“Human physiology adapts and our behaviours also adapt.”

Krayenhoff said some of the dangers of extreme heat can be mitigated by urban design.

Greenery helps — tree-lined streets or shady open spaces accessible to all — although urban cooling centres and other specific measures may become necessary.

But those won’t be enough, said Krayenhoff. Part of the research looked at what would happen if city planners did all they could to mitigate heat.

“Even under very extreme adaptation scenarios, where we added lots of trees and greenery and reflective surfaces, if we allow climate change to go on unabated, we can’t offset that amount of warming.”

Most people in North America live in cities, Krayenhoff noted, so “we really need to reduce global climate change.”

This report by The Canadian Press was first published Aug. 19, 2020

— By Bob Weber in Edmonton. Follow @row1960 on Twitter

The Canadian Press