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Why air conditioners can be a problematic solution to extreme heat

As extreme heat hits many parts of the world amid a warming climate, millions of people are turning to air conditioners for relief. But researchers who study climate adaptation say air conditioning for everyone is not sustainable. Here’s why and what they recommend instead.

Passive cooling, greenery, behaviour changes are more sustainable, researchers say

A man sits on the second floor of a multi-storey building, covered in air conditioners.

As extreme heat hits many parts of the world amid a warming climate, millions of people are turning to air conditioners for relief.

Research shows that household air conditioning is one of the "most effective adaptation strategies to reduce heat-related mortality and morbidity," says a Statistics Canada report released this week. That's particularly the case for older adults and vulnerable populations such as those with mental illness.

But researchers who study climate adaptation say it can also be an unsustainable and problematic solution to extreme heat.

Anabela Bonada, manager and research associate at the Intact Centre on Climate Adaptation at the University of Waterloo, said air conditioning is "absolutely necessary" for vulnerable people who cannot leave their homes.

But, she said, it's a short-term solution and should be "the last resort — because it leads to more heat, which is what we're trying to avoid."

The problems with air conditioning

A study published in The Lancet in 2021, led by Ollie Jay, a professor of heat and health at the University of Sydney in Australia, described air conditioning as a "widespread but unsustainable cooling solution."

"It's unsustainable if we want to air condition everybody," Jennifer Vanos, associate professor in the School of Sustainability at Arizona State University and one of the study's co-authors, said in an interview with CBC News.

The study cited a number of reasons for that.

It heats up cities and the Earth in a few different ways. Firstly, air conditioners are heat pumps that move heat from the inside to the outside of a building. Bonada said that means heat from thousands of homes "is being pumped back out into the city, which is already hotter than surrounding areas."

Many air conditioners contain refrigerants called HFCs or hydrofluorocarbons, which can cause far more global warming per kilogram than carbon dioxide.

However, most of their global warming impact comes from the amount of electricity they use in places with fossil fuel-powered generation. According to the International Energy Agency (IEA), indirect emissions from space cooling have tripled between 1990 and 2021 to more than a gigatonne.

It's not very accessible to those who need it most. The cost of buying and running air conditioners tends to make them unaffordable to the most vulnerable.

The Statistics Canada study this week said that while air conditioners were in 61.1 per cent of Canadian homes in 2017, people were far less likely to have them if they had less than a high school education, lived alone or did not own their own homes.

The Lancet study found even bigger disparities in countries like China, especially among those older than 65 and living in rural areas.

Air conditioning also doesn't work outdoors, where people are often at higher risk of heat-related illness and death.

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A new report says that a disproportionate number of financially vulnerable people died in British Columbia during the punishing 2021 heat dome event. Many who died had no air conditioning.

It can strain the grid, leading to deadly blackouts during extreme heat. The lead author of a 2021 study published in the journal Environmental Science & Technology suggested that "a widespread blackout during an intense heat wave may be the deadliest climate-related event we can imagine" and an "increasingly likely" scenario.

Air conditioners can use a lot of power, and when that power demand exceeds the capacity of the grid, it has already led to deadly outages, such as in Pakistan in 2015 and 2018, the Lancet study noted.

In Canada, that's happened on a small scale — with increased air conditioning use being blamed for a hydro outage in Ottawa's west end last month.

And in British Columbia, some landlords have recently warned tenants against installing air conditioners, saying older buildings don't have the electrical capacity to handle them.

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B.C. renters are getting letters from landlords saying they cannot install air conditioners in their units, and warning they'd be responsible for any damage they might cause. One renter says he's seen the temperature in his apartment as high as 38 C — well beyond what is considered safe for long periods.

The Intact Centre's Bonada said the problem isn't just in B.C., and isn't limited to individual buildings. "Our entire infrastructure needs to be updated. Our energy grid needs to be updated in order to manage this … cooling that will be required."

It can impede other kinds of physical, behavioural and infrastructure adaptation. Blair Feltmate, head of the Intact Centre on Climate Adaptation, described an example in an email from the Mediterranean region of Europe, where he's observing adaptation to climate change impacts.

"Outdoor restaurants have 'outdoor air conditioners' running everywhere in Turkey, Greece and Italy," he said.

Bonada called that "maladaptation."

"It's not going to really lower temperatures, and it's only going to release much more greenhouse gas emissions" in those countries, which rely heavily on coal-fired electricity, she said.

A better approach, Bonada said, would be to use plants to provide shade or cooling, or just not use the patio during extreme heat.

Still, she sympathized with the patio operators trying to attract tourists. "Really, those people shouldn't be out there. They should just be staying in that day, which is not what anybody wants to hear, right?"

Vanos, of Arizona State University, said intermittent exposure to heat is also important to help our bodies tolerate heat better and even allow us to exercise in higher temperatures. "If we don't expose ourselves to heat, then we won't acclimatize," she said.

Feeling some heat can push people to adopt behaviours that "keep us safe," she said, such as adjusting schedules to practise sports at a cooler time of day, for example.

How to keep cool without air conditioning

Both the Intact Centre on Climate Adaptation and the B.C. government offer tip sheets on protecting yourself and others from extreme heat at home, including one targeted especially at apartment dwellers.

While an air conditioner is last on the list from the Intact Centre, which put the cheapest and easiest solutions first, B.C. recommends having window air conditioner in at least one room.

Both lists include passive solutions for cooling, which the IEA says we should prioritize, such as:

  • Opening windows at night. B.C. recommends keeping them closed between 10 a.m. and 8 p.m., and then using fans to help move air, including kitchen and bathroom exhaust fans.

  • Installing thermal curtains or window coverings, and keep them closed during the day. Vanos said that in Arizona, many people also have heat-blocking window coatings that are transparent.

  • Sleeping in the coolest room in your house, such as the basement. B.C. suggests you can even sleep outside if it's feasible.

The Intact Centre recommends using plants to provide shade and reduce heat islands, including climbing plants on walls, trees outside, vegetation to replace pavement and houseplants with large leaves in front of a window or on a balcony.

Both B.C. and The Lancet recommend using water for cooling, such as cool baths, wet T-shirts and icy cold drinks.

All recommend checking on vulnerable neighbours during heat waves.

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Manitoba seniors are being warned to take precautions as most of the province continues to swelter amid an unseasonable stretch of extreme heat and humidity.

How to use air conditioning more sustainably

Both Bonada and Vanos said there are definitely some circumstances when air conditioning is needed.

Vanos spoke to CBC News on the 21st day that Phoenix had high temperatures above 43 C, and she said even nighttime lows have been staying above 33 C. "Not owning an air conditioner is quite dangerous in this climate," she said.

Following hundreds of deaths during the 2021 heat dome, the B.C. government announced last month that it's offering 8,000 free air conditioners to seniors and vulnerable people, although some critics say even that is not the most sustainable solution.

The IEA also recognizes a role for air conditioning but advocates improving its efficiency, and limiting cooling to 24 C or 25 C.

Vanos said one way to protect the grid and ensure vulnerable people have access to air conditioners is for other people to sign up for programs that let utilities remotely adjust your smart thermostat. "Temperatures will be higher in your house to protect the grid and to make sure energy is getting to other places that needs it, and then you save money by doing that."

The greenhouse gas emissions from air conditioners could be expected to diminish as the world decarbonizes its electricity grids and phases out HFCs. However, the IEA says so far, cooling demand has risen so quickly that emissions from cooling are increasing in spite of progress in greening the world's electricity grids.

The Intact Centre recommends improving draft sealing and insulation in buildings to keep heat out and cool air in as a way to improve energy efficiency in summer. Bonada said that will also help people stay comfortable in winter.

Vanos said that even if people have air conditioning, they need to adapt to extreme heat in a variety of ways, including their behaviour: "Air conditioning is not a silver bullet."

Ultimately, both Bonada and Vanos said we need to change the way we design and construct our buildings and cities.

"We can't treat extreme heat as something that will occur every once in a while," Bonada said."It needs to be incorporated into our plans or community planning or building planning."

She said that a key is more greenery, from parks to green roofs, which has been found to reduce local temperatures by up to 5 C. "So it absolutely works."

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High above Toronto’s busy city streets, green roofs are providing space and food, while helping to reduce flooding.

Many communities have already incorporated that into their future plans, but Bonada acknowledged it's a slow process.

In the meantime, she said, everyone needs to prepare themselves and their home for extreme heat.

"Out of all the perils that we deal with, it's the deadliest. So if you're not doing something for yourself right now, nobody else is going to come and save you."


Emily Chung

Science, climate, environment reporter

Emily Chung covers science, the environment and climate for CBC News. She has previously worked as a digital journalist for CBC Ottawa and as an occasional producer at CBC's Quirks & Quarks. She has a PhD in chemistry from the University of British Columbia. In 2019, she was part of the team that won a Digital Publishing Award for best newsletter for "What on Earth." You can email story ideas to Emily.Chung@cbc.ca.

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