Ottawa needs to adopt strategies and policies aimed at keeping residents cool, a researcher said as climate change increases temperatures.
A new University of Ottawa study on human heat tolerance suggests that it is lower than previously thought and the city needs to adopt strategies and policies aimed at cooling the population as temperatures rise.
The study, which was published on Monday, found that many regions around the world may soon experience heat and humidity levels that are unsafe for human survival.
Human thermoregulation is a scientific term used to determine the human body’s ability to maintain a safe temperature while in extreme heat.
The researchers recruited 12 volunteers and placed them in simulated heat and humidity protocols — called thermo-step protocols — to identify at what point thermoregulation becomes impossible. The participants were brought into a room where the team slowly increased the temperature and humidity to find an estimated point in the protocol where the participant can no longer thermoregulate. The participants were brought back for a subsequent three visits where the research team exposed them to humidity and temperature levels just above or below their estimated limits for up to nine hours. For example, some participants were exposed to conditions that were 42 C in temperature with 28 per cent relative humidity.
Nine out of 12 of the participants were not able to finish the full nine hours when exposed to temperatures above their threshold, while all but one were able to finish the full nine hours when exposed to conditions below their threshold.
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Robert Meade, a postdoctoral research fellow at Harvard University’s T.H. School of Public Health, said the human body can’t dissipate enough heat to maintain a thermal equilibrium in extreme conditions, which causes the body’s core temperature to keep rising until, eventually, heat stroke occurs. Meade was also a former senior postdoctoral fellow at the University of Ottawa.
Scientists have long assumed that humans can survive wet bulb temperatures up to 35 C, but Meade’s study suggests that humans cannot effectively thermoregulate at temperatures above 26 C to 31 C. Wet bulb temperatures is a measure of how much moisture is in the air and how it affects cooling of the body, and it is measured by using a thermometer with a wet wick or cloth around the bulb.
“This (protocol) existed for quite some time, but, then, recently, data from studies using this protocol have been incorporated into climate modeling. There was a paper in PNAS (Proceedings of the National Academy of Sciences of the United States of America) suggesting that, under current warming trends, some areas of the globe might exceed the limits for human thermal regulation, particularly those in the Global South,” Meade told the Ottawa Citizen in an interview on Tuesday.
“When we were looking at this research, what we basically realized is no one had actually ever gone in and looked at whether that core temperature inflection point that occurs as you’re increasing humidity actually corresponds to when a person can no longer thermoregulate. So that’s what we decided to test. If this research is getting a lot of publicity and also being incorporated into these climate models, we need to be sure that this inflection point truly reflects what we think it does.”
These findings are important for cities like Ottawa, where thermo-step protocols have been included in climate modeling and projections.
While Ottawa isn’t going to approach these limits anytime soon, according to Meade, modeling projections show that the city may reach those limits if there were an increase in average global temperatures by about 4 C.
However, Meade said many people are still at risk for heat stroke and adverse health effects when exposed to temperatures that are much lower than what was tested for the study.
“We’ve actually done studies in the lab exposing older adults, for example, to eight-hour exposures to a range of different conditions experienced during heat waves in Ottawa. What we basically found was, even at temperatures well below their limits for thermoregulation, you still experience increases in body temperature,” the research fellow added.
“There’s still cardiovascular strain, and in some cases, actually changes in blood pressure regulation. So while we might not actually be approaching limits in know, a lot of places in the world, particularly the more temperate and continental climates, heat is still becoming an increasing problem for health.”
Meade said Ottawa and other Canadian municipalities needed to adopt strategies aimed at keeping people cool. A report published by the Canadian Environmental Law Association in August 2024 urged the City of Ottawa to regulate maximum temperatures in rental or leased units to 26 C.
Meade also suggested policies that make it illegal for a power company to shut off power during a heatwave, even if the person has late bills to pay. He also suggested creating a list of older adults who city staff can call to check in to make sure they’re okay on hotter days.
This is especially important given that the city projects a “stark increase” in the number of extreme heat days in its climate emergency declaration in 2019. The city projects that it will experience 25 to 28 extreme heat days per year by 2030, with temperatures reaching above 30 C.
“However, where it becomes tricky is … both because of fossil fuels and regrades used, as well as issues around coolant use and air conditioning.” Air conditioners, he said, are “very environmentally damaging and also very costly.”
“Protecting people is relatively easy if there’s access to air conditioning, but there needs to be a lot of work done to help increase the sustainability of air conditioning.”
The postdoctoral research fellow also noted that this is a global problem. The study doesn’t take into account thermoregulation thresholds in places like India and regions like Southeast Asia, nor does it take into account thermoregulation thresholds of different age groups.
“We really don’t know how limits for thermal regulation and how the health impacts of heat actually occur on a physiological level. If we’re thinking globally, now that we know the protocols like this are valid and effective … We need to expand our estimates to those places that are getting the hottest the quickest,” Meade said.
“We simply cannot apply the estimates from areas like Pennsylvania and assume they are going to be representative of people in India or Africa, for example.”
