How nighttime heat could affect your body today

Last year was the hottest in recorded human history, and this year Canada continues to be affected by heat waves and record-breaking temperatures.

One big shift is the increase in nighttime temperatures, prompting health concerns across the country as certain nightly forecasts across Eastern Canada predict highs of 24 C, instead of the typical 14 C.

Didn’t nighttime used to be cooler?

During his 50 years studying weather in Canada, David Phillips isn’t fazed by daytime temperatures above 30 C.

What concerns him is the increase in what he calls tropical nights, when daily minimum temperatures stay above 20 C. Phillips is a senior climatologist for Environment and Climate Change Canada.

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With the recent heat domes, these nights with “jungle-like” humidity are becoming more commonplace. 

He attributes some of this to bigger cities with high density and little green space. Built-up surfaces like buildings and roads tend to absorb solar radiation and release it as heat, reducing nighttime cooling during heat waves.

Wind is also reduced at night and cloud cover keeps heat contained and prevents heat from escaping. All of this is then exacerbated by more frequent and longer-lasting heat events due to climate change.

While Phillips acknowledges that 24 C doesn’t sound bad during the daytime, the feeling is exacerbated at night, when the winds die down and humidity lingers.

“That’s when it becomes a real health issue,” Phillips said. “Most deaths from heat waves occur from exposure to heat at night.”

He added that the number of recorded deaths due to heat may be underestimated due to underlying health conditions.

Heat carries health risks

“Nighttime is when people are trying to sleep and we know that worse sleep is linked over the long term to increased risk of mental health issues and problems with cognition,” said Dr. Melissa Lem, Canadian Association of Physicians for the Environment president.

To Lem, being exposed to extreme heat is like a marathon.

“It makes your body, heart and lungs have to work extra hard to keep your body healthy,” she said. “If you’re hot overnight, you’re essentially running that marathon around the clock, and your body doesn’t get that chance to recover from the daytime stresses.”

Having lived in units without air conditioning, Lem is familiar with extreme heat exposure. “It really affected my cognition, my sharpness and my ability to focus on patient care,” she said. 

She’s known surgeons who booked air-conditioned hotels to ensure they were sharp for the next day, but recognizes it’s not an option for everyone. This is why she believes in government policy to ensure everyone has access to indoor cooling, whether they own or rent.

“When there are heat waves, we see increased rates of domestic violence and also increased rates of car crashes — not only does heat make people more volatile, but if you’re not getting that sleep overnight, it just compounds it.”

Tips for staying cool

Keeping a cool core body temperature is essential. Phillips and Lem recommend:

• Going to cooling centres, such as libraries or malls
• Staying hydrated
• Taking cool showers
• Spraying one’s face and body with water
• Wearing lighter clothing and reducing layers

They also emphasize checking on family, friends, relatives and neighbours. Often heat-related deaths occur from people living alone, especially the elderly.

“There are ways that we can adapt to this extreme heat,” said Phillips. “It’s not just giving everybody air conditioning, but looking in on people, all-night cooling centres and a buddy system.”