Heat waves are increasing across Canada — and hotter nights are also dangerous

When it comes to climate change, there is one fairly well-understood extreme that will affect humans in the decades to come: heat.  

Scientists know that climate change will see events like hurricanes, droughts, floods and heat waves increase in frequency or intensity. But when it comes to heat waves in particular, it's already being seen across the world with deadly consequences. According to a recent study published in the journal The Lancet, more than five million deaths annually between 2000 and 2019 were associated with "non-optimal temperatures," with roughly 500,000 of these deaths related to heat. 

While many of these deaths occur in tropical countries, heat waves are beginning to affect more northerly climes.

During the heat wave that suffocated British Columbia at the end of June into the first week of July, more than 800 people (as of this writing) died in the province. For comparison, in the same period last year, there were 232 deaths, according to B.C. Coroners Service's chief medical officer, Dr. Jatinder Baidwan. The coroner's office is continuing to investigate all of the deaths in order to nail down exactly how many were heat-related.

While we know that daytime temperatures are rising, in some regions — specifically in parts of Ontario and Quebec — nighttime temperatures are warming faster. 

Those warmer nights mean our bodies don't have any time to cool off. For people with health issues like heart disease or asthma, for example, this can be extremely problematic and potentially deadly.

"Our bodies were not designed to put up with environmental heats that exceed the high 30s," Baidwan said. "If you think about it, what happens to an air conditioning unit? When you stress it, it builds up with lots of ice on the outside and then it stops working. And in some ways that's a great analogy for what happens to our bodies. With extreme heat, we just find it really hard to do the usual homeostatic sort of mechanisms and protocols that happen in our body."

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The heat wave that affected the Pacific Northwest was highly unusual — a one in 1,000-year occurrence, according to a recent analysis by the group World Weather Attribution, a collection of scientists who analyze severe weather events. However, parts of eastern Canada, including Ontario and Quebec, are seeing more frequent heat waves and tropical nights, defined as nighttime temperatures 20 C or higher. 

For example, according to the Climate Atlas of Canada, the number of tropical nights in Toronto averaged roughly 6.9 annually from 1976 to 2005. With climate change, under a scenario where carbon emissions decline substantially, that is expected to climb to 17.6 annually from 2021 to 2050.

If current rates of carbon emissions continue, the average number of tropical nights in Toronto is expected to hit 20.6 annually from 2021 to 2050. From 2051 to 2080, under the two different scenarios for emissions, the average number would rise to 26.4 and 42.8 respectively.

In 2018, a heat wave blanketed Montreal from June 29 to July 5; temperatures averaged roughly 34 C during the day. Nighttime temperatures didn't fall below 20 C. In all, 66 people died.

"We're seeing an increase in hot extremes in Canada that's larger than the global mean warming," said Nathan Gillett, a research scientist with Environment and Climate Change Canada. "The average warming in Canada is about twice the global mean warming. And the heat extremes are also increasing at a similar rate. And it's not just the hottest, maximum temperatures, but the minimum temperatures, the nighttime minimums that are also increasing."

Widespread effects on nature

Average temperatures in Canada have already warmed by 1.7 C and the country is warming at more than twice the rate of the planet. 

Increasing heat waves with higher-than-average temperatures during days and nights are also taking a toll on animals and delicate ecosystems, as well as crops.

A study published in the journal Global Change Biology last October found that nighttime temperatures are rising across most of the world. In those areas that saw more nighttime temperature warming than daytime, there was more cloud cover, higher precipitation and more humidity. This can affect nocturnal animals, but also animals that are active during the day who use the cooler nighttime temperatures to recover from heat stress.

"[The changes] increase the boundaries at which nocturnal species can operate. So you may get shifts in ranges, which then messes up ecosystems from changing competition and changing predation/prey relationships, and things like that," said Daniel Cox, lead author of the study and a research associate in the U.K. at the University of Exeter's Environment and Sustainability Institute.

A new set of metrics

With the changing climate, governments are finding they need a new set of metrics for severe heat events. 

In 2013, Australia added new colours to their heat maps, as temperatures soared beyond anything they'd experienced in the past.

More recently, on Tuesday, the U.K. Met Office issued its first Amber Extreme Heat Warning as temperatures were forecast to rise to the 30s in parts of the country. Daytime temperatures in the 30s may not seem high compared to some parts of Canada but it's all about what people are accustomed to. 

In another example of how governments are attempting to adapt to a warming climate, a team from the Institut national de la recherche scientifique (INRS) in Quebec, together with the Institut national de santé publique du Québec (INSPQ) announced on Wednesday that a new heat wave warning threshold for the province should be introduced. Quebec's warm seasons, researchers said, are starting earlier and ending later. 

As Earth continues to warm, air conditioning may seem like a possible solution. The problem is that energy is needed to operate them, and this also produces heat. And cities create "heat islands" where heating is further amplified by  concrete structures, adding more stress to people who are living in a hotter climate. Some cities like Toronto and Montreal are trying to introduce greener building codes and designs to address this. 

"[Heat waves aren't] something we think about as a big hazard in Canada, but as the climate warms, we're going to see this more and more," said Environment and Climate Change Canada's Gillett. "Heat waves cause deaths and and are dangerous. And yeah, it is something … that we're going to see more and more here in Canada."