This article was written by Kate Allen and was published in the Toronto Star on December 3, 2025.
As Toronto continues to grapple with extreme weather, a slate of proposals meant to address what the city calls its “most urgent climate threat” — extreme heat — delays longanticipated measures by years and leaves vulnerable residents at risk, critics say.
After a severe heat wave last June exposed what Mayor Olivia Chow called “serious gaps” in the city’s heat relief strategy, council directed staff to report back with improvements. That request came amid ongoing efforts, endorsed by council, to create a maximum indoor temperature bylaw that would enforce safe living conditions for renters.
On Tuesday, city staff released a package of updates to those plans that critics called “disappointing.” While the reports touch on everything from drinkingwater trailers to airconditioning grants to proactive public pool repairs, critics said they don’t protect residents who need it the most, and that a “very significant delay” in implementing the most impactful measure — the maximum temperature bylaw — will leave many Torontonians exposed to harm. The proposals will be considered by the mayor’s executive committee next week.
“My patients can’t wait,” said Dr. Samantha Green, a family physician and president of the Canadian Association of Physicians for the Environment. “I have patients who are suffering from heatrelated illness when we are experiencing extreme heat in Toronto. And we experienced a lot this summer,” Green said.
Last summer’s heat was extreme, the reports make clear: Toronto suffered through six separate heatwaves with a combined 29 heat warning days. Another report released Tuesday found that of all the climate threats facing Toronto, “heat will intensify most rapidly, redefining how summers are experienced with every passing year.”
Last June, when Pearson broke a Humidex record, the city struggled. Residents were frustrated to find pools closed after the city touted them as places to cool off, and advocates warned that unhoused people had nowhere safe to go.
In one of Tuesday’s reports, staff admitted that the city “did not sufficiently prepare pools to operate,” leading 21 of them to temporarily suspend operations on one day. Those challenges were related to the city’s policies to keep its own employees safe, an obligation under Ontario law — and one the Star previously reported had been flagged by the Ministry of Labour four years earlier.
The city says it boosted pool staffing levels by 30 per cent this summer to ensure lifeguards and other aquatics staff could take necessary breaks to prevent heat illness, as well as added fans and other cooling and safety measures. Those extra staff and resources cost an additional $2.9 million, a figure that staff anticipates requiring again next year, assuming summer’s heat is similarly severe.
The reports called the reliable operation of pools “critical to an effective heat response.” Experts said this focus is misguided.
“Pools are nice to have, but they are not a solution to protect the most vulnerable,” said Green.
The people most at risk of harm from heat include infants and very young children, the elderly, people with limited mobility or chronic illnesses, unhoused people, and workers exposed to heat on the job. Pools are of limited or no use to these groups: Construction workers, babies, and elderly people who need help walking can’t just pop over to Sunnyside and jump in.
The most important strategy, experts say, and one backed up by public health evidence, is to maintain safe temperatures in indoor living spaces. After the western heat dome in 2021, the B.C. coroner found that nearly all of the 619 people who died were found in homes, most without access to airconditioning.
Last year, council endorsed a plan to create a maximum temperature bylaw that would require landlords to keep residences below 26 C, and asked staff to come back with a plan to implement the new rules. Instead of an implementation plan, Tuesday’s report recommends carrying out a “compliance analysis” in 2026 and reporting back to council in 2027 with the results of that study.
This article was written by Daniel Opasinis and was published in the Toronto Star on August 13, 2025.
Some relief from the latest blistering heat wave is expected as Environment Canada forecasts the arrival of a cooler air mass.
The weather agency anticipated the slightly cooler air to arrive Tuesday night, but also warned the GTA and eastern Ontario may continue to sizzle in hot and humid conditions into Wednesday.
Environment Canada announced the multiday heat alert on Saturday, warning that temperatures could feel like up to 42 C with humidity.
A 70 per cent chance of precipitation is expected for Wednesday, with a risk of thunderstorms in late morning and afternoon. A high of 28 C will feel like 37 C with the humidex. Wednesday night could see more showers and a possible thunderstorms before skies are expected to clear through the evening. The nighttime temperature is forecast to drop to 21 C.
On Thursday, temperatures are expected to climb back up to 28 C under sunny skies. That will be followed by a clear night with a low of 19 C.
More sun is expected Friday with a high of 27 C and a low of 21 C.
Saturday’s forecast calls for more sunshine and a high of 29 C. There’s a 20 per cent chance of showers at night as some clouds roll back in. The evening will also bring a low of 23 C.
Sunday is forecast to be partly overcast with a 40 per cent chance of showers and a high of 28 C, followed by a cloudy night with a low of 18 C.
Environment Canada offers tips to avoid heatrelated health risks in the city, and warns about deteriorating air quality amid the humidity.
“Check on older adults, those living alone and other atrisk people inperson or on the phone multiple times a day,” the heat warning reads.
The weather agency shared that symptoms of heat stroke and heat exhaustion — headache, nausea, dizziness, thirst, dark urine and intense fatigue — should be closely monitored.
Tips to protect yourself in the intense heat include drinking water before you feel thirsty; limit direct exposure to the sun and try to schedule outdoor activities during the cooler parts of the day; and never leave people — especially young children — and pets inside a parked vehicle.
Prescriptions let lowincome tenants apply for subsidies to lessen heat risk
This article was written by Ben Spurr and was published in the Toronto Star on August 4, 2025.
In a small room off the lobby of a St. James Town highrise on Friday, Dr. Samantha Green was busy handing out lifechanging prescriptions.
Throughout the morning, a steady stream of tenants in the Toronto Community Housing building came to sit at a foldout table across from Green, another doctor and a medical student, who asked them questions about their health and income status. After a short consultation, two dozen residents walked away with a prescription — not for medicine, but for something that could be just as vital to their wellbeing amid Toronto’s increasingly stifling summer heat: a new air conditioner.
According to the City of Toronto, residents on Ontario Works or the Ontario Disability Support Program can apply for financial aid to buy a cooling unit, if they get a doctor’s note saying it’s medically necessary.
Green, a family physician with the Unity Health Network, said despite the fact that heat can pose a serious health risk, particularly to lowincome groups, many social assistance recipients and healthcare workers don’t know about the subsidy. She’s been trying for years to raise awareness about it, but said it’s been “slow going,” so she decided to start hosting popup AC clinics.
“It just occurred to me that a faster way to do this would be to actually partner with local community organizations and go to communities and provide prescriptions, where appropriate, for air conditioners,” she explained.
Green held the first popup last month at another building in St. James Town, an apartment community near Bloor Street East and Sherbourne Street, where many residents are lowincome.
That day she prescribed 18 air conditioners. Over two hours at 375 Bleecker St. on Friday, she and her colleagues issued about 24 prescriptions.
The atmosphere at the popup was more community gathering than medical appointments. A group of women in head scarves chatted in the middle of the small room, while a boy played on a tablet in the corner, and volunteers set out plates of candy.
The consultations Green held with each tenant didn’t involve a physical exam — instead, she collected information about access to cooling devices and any medical conditions that might put them at increased risk from high heat. She told the Star level of care is no less than what patients would receive before getting a prescription at a walkin clinic.
Rahul Kamtam was among those who got an AC prescription. He has been diagnosed with schizophrenia and said during heat waves the temperature in his fifthfloor apartment soars, making it hard to read or concentrate.
Being able to cool down the heat would be a boost for his mental health.
Kamtam said he didn’t see anything unusual about a physician issuing prescriptions for air conditioners.
“This is also kind of a medication, right? When your temperature is going up, you take fever medication to bring your temperature down, and AC is almost doing the same thing,” he said.
According to information posted by the city, which administers provincial assistance programs, to get the cost of a cooling unit covered, OW and ODSP clients need a prescription that includes a diagnosis indicating the device is part of a treatment plan, and that without it the person could be hospitalized or “face severe risk to life.”
One AC unit or portable fan per family will be covered up to a maximum cost, every four years. Although the coverage limit isn’t listed, numbers gathered by Health Providers Against Poverty, which partnered with Green on the popup, suggest it’s about $400. Medical conditions that require a cooling device include cancer, chronic heart or lung conditions, HIV, dialysis and severe asthma, according to the city website. The cooling applications fall under discretionary benefits, and are approved on a casebycase basis.
The province covers the cost of OW and ODSP discretionary benefits. Lowincome residents who aren’t on provincial social assistance can also apply to the city for cooling device coverage through its Hardship Fund. Toronto says that in 2024 it issued about 650 subsidies. It has also launched a pilot project to give air conditioners to lowincome seniors.
This summer, Toronto has experienced a succession of heat warnings with temperatures that feel in the high 30s or low 40s.
Green said giving people a chance to keep cool under those conditions is essential. High temperatures can cause heat exhaustion and heat stroke, which can be deadly, and can also exacerbate underlying chronic conditions like heart disease, chronic kidney disease and respiratory disease, she said.
Heat kills more people worldwide than any other form of extreme weather, and the threat is growing “exponentially” because of climate change, according to the World Health Organization. Young and older people, as well as those on low incomes or suffering from chronic disease, are at higher risk.
So are people living in decadesold apartment buildings. Many of Toronto’s highrises were built in the 1960s or ’70s and were designed to keep heat in during cold winters, said Lidia Ferreira, a community engagement specialist with Community Resilience to Extreme Weather, which worked with Green on Friday’s popup.
“But right now, we have a totally different environment. So every summer, it’s getting hotter and hotter,” she said.
High temperatures, humidity expected to last to Tuesday
This article was written by Elissa Mendes and was published in the Toronto Star on July 28, 2025.
Things are sizzling once again in Toronto, as the city is back under an Environment Canada heat warning.
The heat warning is expected to last through Tuesday, Environment Canada said, adding there’s “some uncertainty” about how long it’ll last in other parts of the province.
Central Ontario could emerge from the heat warning Monday night, the agency said, while it could last into Wednesday in other areas.
What’s the Environment Canada forecast for Toronto?
Monday will be sunny as fog patches disappear in the morning, with a high of 33 C feeling like 40 with humidity. The UV index will rise to 9 again. At night, expect a 30 per cent chance of showers with a low of 22 C.
Tuesday — expected to be the tail end of the heat warning — will be partially overcast with a 40 per cent chance of showers and a high of 31 C. Tuesday night will see a 40 per cent chance of showers as temperatures dip to 21 C.
With the heat warning expected to be over by Wednesday, Toronto will see a high of 30 C, a 30 per cent chance of showers and some clouds overhead. Wednesday night will be cool and clear with a low of 17 C.
Thursday will see sunshine and a high of 26 C, cooling to 15 C at night.
Friday will be more of the same with a sunny daytime high of 25 C and nighttime low of 15 C.
Heading into the weekend, Saturday will see blue skies and a high of 26 C.
What are the symptoms to watch out for?
Watch out for early signs of heat exhaustion, Environment Canada urged, which include headache, nausea, dizziness, thirst, dark urine and intense fatigue. If you suspect heat exhaustion, stop your activity and drink water, the agency said.
Heat stroke, however, is a medical emergency, the agency said. Signs of heat stroke include red and hot skin, dizziness, nausea, confusion and a change in consciousness. If a person might have heat stroke, call for emergency medical attention and try to cool them down.
Extreme heat events mean you should check on older adults, people who live alone and other atrisk people inperson or over the phone multiple times per day, Environment Canada said.
How can I keep cool and stay safe?
Environment Canada urged people to drink water often — and before you feel thirsty. You should also close your blinds or shades and open your windows if it’s cooler outside than it is inside.
You should also turn on air conditioning, use a fan or move to a cooler area of your home, Environment Canada added.
If you want to take part in activities, schedule them for the coolest part of the day, Environment Canada said, encouraging people to limit direct sun exposure and to wear light, loosefitting clothing with a widebrimmed hat.
Anyone looking for free ways to cool down can also use the city’s interactive map of community centres, pools, libraries and other heat relief spaces.
This article was written by Anastasia Blosser and Elissa Mendes, and was published in the Toronto Star on July 24, 2025.
It was nice while it lasted.
After nearly a week of temperatures in the low to high 20s, more hot and humid weather is on Toronto’s horizon, according to Environment Canada, which has issued another heat warning for the city.
The weather agency said temperatures will be the hottest Thursday, when the heat event is expected to kick off.
“While daytime high temperatures will not be as extreme on Friday and into the weekend, night time lows are expected to remain warm throughout,” Environment Canada added in its warning.
Temperatures are expected to hover around the high 20s to low 30s but the humidity could make it feel as hot as 44, according to the heat warning. There will also be onandoff rain throughout the next week, the local forecast says.
It has already been shaping up to be a hot summer for the city with there already being multiple stretches of heat warnings over the past month.
The sun will stick around on Thursday with a high of 34 C, which could feel like 42 because of the humidity. At night, clouds will roll in, bringing a 40 per cent chance of showers with them. The low will be 24 C.
Friday will also be cloudy with a 60 per cent chance of showers and high of 29 C. Skies will remain cloudy at night and temperatures will drop to a low of 20 C.
Kicking off the weekend, skies will begin to clear on Saturday with a high of 28 C and low of 18 C.
Sunday will bring a mix of sun and cloud with 30 per cent chance of showers and cloudy periods in the evening. There will be a high of 28 C and a low of 19 C.
Monday will be similar, with a mix of sun and cloud and a high of 30 C. Later in the day, there will be cloudy periods and a low of 20 C.
Tuesday will be cloudy with a 30 per cent chance of showers and high of 28 C.
As temperatures climb, Environment Canada is urging people to drink water often — and before you feel thirsty.
As well, you should plan outdoor activities for the coolest parts of the day, limit direct sun and heat exposure and wear light and loose clothing with a widebrimmed hate.
Open your windows if it’s cooler outside than indoors, but otherwise, keep your blinds and shades closed, the agency said. You should also turn on air conditioning or a fan, or move to a cooler part of your home.
Also, watch out for signs of heat exhaustion, which might include a headache, nausea, dizziness, thirst, dark urine and intense fatigue. People who suspect heat exhaustion should stop activities and drink water, the agency said.
On the other hand, heat stroke is a medical emergency, with signs including red and hot skin, dizziness, nausea, confusion and a change in consciousness. If you see signs of heat stroke, call for emergency medical attention and try to cool the person down.
Torontonians can also use the city’s interactive cool spaces map to find public pools, community centres and other free spots to beat the July heat.
This article was written by Allie Moustakis and was published in the Toronto Star on July 5, 2025.
Toronto is moving back into the heat (and humidity) this weekend.
The second heat warning of the summer was issued Friday for the Greater Toronto Area and much of the province as humidex values are expected to exceed 40 later this weekend.
Temperatures are expected to climb up to the low 30s on Saturday and Sunday, feeling hotter with the humidity.
Environment Canada said the heat warning will be in effect for much of Saturday and last until Sunday night.
Don’t let the clouds fool you. Saturday will be sticky, hitting a daytime high of 31 C, which will feel closer to 41 with the humidity. Winds will gust to 20 km/h and there’s a 30 per cent chance of showers plus a risk of thunderstorm heading into the afternoon. The UV index is expected to be high, reaching past nine, before temperatures drop to a low of 23 C at night.
Sunday will be similar with a mix of sun and cloud, a 30 per cent chance of showers and a high of 33 C. Chances of rain will jump to 40 per cent at night with a low of 20 C.
The beginning of next week is expected to see slightly cooler temperatures — with a 28 C daytime high on Monday and 27 C high on Tuesday.
Humidity can make temperatures feel warmer, trapping moisture on your body and making it difficult to dry off after sweating, according to Environment Canada, who urge people to avoid exerting themselves and head for cooler temperatures when they overheat.
Toronto offers an interactive cool spaces map, but people can also protect themselves by taking a cool shower, using a fan, drinking extra water and avoiding alcoholic, caffeinated and sugary beverages, an expert previously told the Star.
This article was written by Dean Flannery and was published in the Toronto Star on June 25, 2025.
It’s been hot in Ontario, and dangerously so. For the past few days, my phone has been blasting out regular health warnings about the extreme temperatures.
Not that I’ve needed the reminder. Opening my front door this week has been like opening the oven door when the broiler is running. On Monday, temperatures hovered between 33 and 36 C. With the humidex, it felt as hot as 46 C at times, the kind of heat that can make you feel ill fast if you don’t take steps to cool yourself — assuming you have the means to do so.
But what about those who depend on others to keep their environment healthy?
That’s the situation for students across Ontario, where heat waves can occur even in spring and fall and most public schools lack air conditioning. This week, thousands of kids are spending their last week of school in spaces that are uncomfortably hot and offer limited opportunities for cooling.
In Toronto, only 30 per cent of public schools have central air conditioning. In Hamilton, it’s 50 per cent — and the more than $50 million it would take to fix that state of affairs is beyond the school board’s budget.
Yet instead of investing in cooling infrastructure, Premier Doug Ford’s government has taken to blaming school boards for excessive classroom heat. Meanwhile, kids are left with a patchwork of protocols to help them cope, which can include being kept indoors and cycled in and out of designated cooling spaces such as libraries and gyms.
So just how hot is too hot for classrooms? Some school boards give administrators the option to cut the day short if outdoor temperatures reach the high 40s — but even the Toronto District School Board acknowledged this week that it was unlikely to do so, because of the burden on parents.
As kids can’t simply leave class and call it a day, they have to endure real harms to their wellbeing, not to mention their ability to learn and write exams. You may be inclined to shrug off these harms, given the limited duration of heat waves. But you’d also be shrugging off the province’s obligation to provide students with fundamentally safe learning spaces all year long, not just when the cost of doing so is convenient.
There’s also the fact that schools are workplaces, where putting teachers in the position of having to deal with naturally distressed kids and inadequate options for relief is not only an unjustifiable occupational burden but also a gendered one: 76 per cent of teachers in Ontario are women.
The need for investment is urgent, and it’s not going away. Kids today are dealing with heat events that are more frequent and more intense than what their parents or grandparents dealt with. In an April 2025 report on the need for better cooling in childcare spaces, the Canadian Environmental Law Association estimates that a 10yearold in 2024 would’ve experienced 36 times more heat waves than a 10yearold in 1970.
In recognition of this increased exposure, CELA and the Canadian Partnership for Children’s Health and Environment are calling on the federal and provincial governments to create a comprehensive plan to address the need for investment in healthier, more climateresilient schools and childcare spaces.
These calls for leadership rather than excuses come at an opportune time. Queen’s Park and Ottawa, so often engaged in stultifying jurisdictional battles, have been uncharacteristically aligned in their desire to fasttrack infrastructure projects. In an era of sweeping power moves, they’d be wise to apply some of this energy to cleaning up the lingering messes that have been exacerbated by chronic underfunding of our social infrastructure.
Building climate resilience in schools starts with establishing a legal maximum for indoor temperatures. CELA and CPCHE want Ontario to amend the Education Act or pass regulations to set the threshold at 26 C in both schools and childcare spaces, and they want it to offer dedicated infrastructure funding to make this a practical reality. Far from arbitrary, the proposed threshold is based on BC Centre for Disease Control analysis of the heat dome that struck British Columbia in 2021, killing hundreds.
Amid a rapidly warming climate, air conditioning in schools can no longer be considered a luxury. It’s an essential public health intervention — one that Ontario politicians enjoy in their workplaces and that kids deserve, too.
This article was written by Dr. Shazma Mithani and was published in the Globe & Mail on June 24, 2025.
Few people expect to end up in the emergency department because of hot weather, but heat-related illness sends many people to the hospital every year.
During the summer months, I frequently see patients suffering from heat exhaustion and dehydration. Many who come in are surprised at how quickly their symptoms develop after feeling well spending time outdoors for hours. In more serious cases, patients arrive dangerously close to heat stroke – a life-threatening condition requiring immediate medical attention.
According to data from the Canadian Hospitals Injury Reporting and Prevention Program, extreme heat events are contributing to a rise in emergency visits, particularly among vulnerable populations. And the Canadian Medical Association has said: “Illness from extreme heat waves places extra demands on a system already strained by a lack of primary care access and record ER wait times.”
As temperatures rise this summer, here are some things to know about heat-related illness and how to lower your risk.
HEAT STROKE IS MORE THAN JUST ‘OVERHEATING’
Heat-related illness happens when the body can’t regulate its temperature properly. Although mild overheating might seem like no big deal, progression of this overheating, while failing to cool down, can lead to serious health complications.
The term heat stroke is often misused to describe much milder heat-related illness. If you’ve ever overheated or felt drained after a hot day, this is almost certainly not heat stroke. True heat stroke is a medical emergency characterized by confusion, loss of consciousness and a dangerously high body temperature. It requires emergency department care and rapid treatment; failing to recognize it can be fatal.
HOW TO SPOT THE WARNING SIGNS
Heat-related illness exists on a spectrum, so recognizing early symptoms is key to avoiding progression:
Heat rash: A red, raised rash in areas of sweat production (armpits, elbow creases, knee creases and neck) that typically occurs several hours after heat exposure. The rash is usually itchy and takes a few days to resolve.
Heat cramps: Painful muscle spasms, usually in the legs or abdomen. Heat cramps can occur during exertion in hot conditions owing to a disproportionate loss of electrolytes compared with water (in sweat). They are easily treated with hydration, electrolytes and rest.
Fainting: Heat can cause the blood vessels in the body to dilate and decrease blood pressure. This drop in blood pressure can lead to fainting episodes (or heat syncope) that are managed with hydration, electrolytes and removal from heat.
Heat exhaustion: This consists of heavy sweating, dizziness, nausea/vomiting, headache and a fast heartbeat. It often occurs with prolonged or vigorous exertion in hot conditions. Without intervention, this can escalate to heat stroke. If any of these symptoms occur, it’s important to immediately get to a cool environment, and replace fluids and electrolytes. If symptoms don’t improve rapidly, this means progression to heat stroke is likely and the patient needs to go to the hospital emergency department immediately.
Heat stroke: This is a medical emergency that is the progression of heat exhaustion. It consists of severe confusion, loss of consciousness or even seizures. The skin is typically hot and dry (with no sweating). This is a true medical emergency: Call 911 immediately.
WHEN TO SEEK MEDICAL CARE
While mild symptoms can often be managed with cooling strategies, some situations require urgent medical care:
Dizziness, nausea or weakness that persists after rest and hydration.
Any signs of heat stroke as outlined above.
Individuals with underlying conditions such as heart disease, high blood pressure, diabetes and kidney disease who have prolonged symptoms of heat illness.
WHO IS MOST AT RISK?
Some groups are more vulnerable to heat-related illness owing to their body’s inability to regulate temperature effectively or other factors such as socio-economic conditions. These include:
Older adults: Aging affects the body’s ability to cool down efficiently.
Infants and young children: Kids lose body fluids more quickly and may not be able to express discomfort from the heat clearly.
People with chronic medical conditions: Underlying health conditions such as heart disease, diabetes or respiratory illnesses make temperature regulation more challenging.
Outdoor workers and athletes: Exposure to extreme temperatures for long periods without adequate hydration or cooling breaks leads to increased risk.
Certain medications: Medications such as diuretics, betablockers and antihistamines can impair heat tolerance.
Unstably housed: Lack of access to air-conditioned spaces and exposure to extreme heat can increase risk.
PREVENT HEAT ILLNESS BY STAYING COOL AND MONITORING FOR SYMPTOMS
The most important factors in avoiding heat illness start with awareness, preparation and recognizing symptoms early to help keep yourself and your loved ones safe.
Hydrate, hydrate, hydrate: Drink plenty of water and don’t wait until you’re thirsty. Electrolyte-rich drinks (such as Pedialyte, Skratch Labs drink mix, low-sugar Gatorade or Powerade, or equivalent drinks) can help replace lost salt in sweat during extreme heat or exertion in the heat. Avoid caffeine (including energy drinks) and alcohol as much as possible, since both can lead to dehydration.
Dress appropriately: Lightweight, light-coloured and loose clothing helps your body regulate heat better. Hats and sunglasses also provide protection.
Limit time outside during peak hours and stay cool: The hottest hours (10 a.m. to 4 p.m.) are when heat exposure is most dangerous. Limit outdoor activities, especially exertion and exercise, during this time. When you are outside, take regular breaks indoors (ideally in airconditioned spaces) or in the shade if you can’t get indoors. While outside, consider cool misting and cool compresses to help decrease body temperature.
Pay attention to symptoms: Feeling lightheaded or nauseous? Stop what you’re doing, move to a cool place and rehydrate. Ignoring the early symptoms of heat exhaustion can quickly turn dangerous.
Dr. Shazma Mithani is an emergency physician working with adult and pediatric patients in Edmonton. Mithani is actively involved with the Canadian Medical Association, Alberta Medical Association and Sexual Assault Centre of Edmonton. She is also co-host of The Doc Talk Podcast.
Ask a Doctor is a series of physician-authored columns offering insights and advice on common health topics.
Dangerously high temperatures to hit as summer officially begins
This article was written by Kate Allen and was published in the Toronto Star on June 20, 2025.
A heat wave is on its way to Toronto, the first of the summer — and the first shove into weather that is not only steamier but more dangerous.
Friday — the first day of summer — is expected to reach a high of 27 C, but will feel closer to 34 with humidity. That heat and humidity will build throughout the weekend, climbing to 34 C by Monday. There’s also little relief expected at night with lows forecast to hover in the low 20s.
A transit officer stays hydrated at the corner of Queen and Spadina as high heat and humidity is set to descend on the city.
Heat kills more people worldwide than any other form of extreme weather, according to the World Health Organization — a risk growing “exponentially” because of climate change. But despite its high death toll, experts also refer to heat as “the silent killer.”
Heat masquerades as many other health problems, making it easy to overlook. And unlike floods, wildfires and hurricanes, heat is invisible. For both of these reasons, experts say, public awareness of the risks is low.
Studies worldwide show that deaths spike during heat waves. But most of these are not caused directly by heat: they are caused by other conditions, like cardiac events, respiratory diseases, kidney disease and mood disorders.
That’s because the body’s response to heat exposure helps fight to protect core temperature, but puts stress on other organs: the heart pumps harder and faster, for example, and dehydration taxes the kidneys. It’s also because some chronic health conditions impair people’s ability to recognize they are overheating and respond to protect themselves.
Some of the most important and startling evidence of this comes from Canada. During the West Coast heat dome in 2021, British Columbia’s Coroner chose to investigate all possible heatrelated
Heat masquerades as many other health problems, making it easy to overlook deaths. That decision revealed information surprising even to doctors: of the 619 people who died, six in 10 were on registries for mood and anxiety disorders, and schizophrenia was associated with a higher risk of death than any other chronic disease.
The reasons for this are complex, but many factors likely play a role. Antipsychotic medications impact heat regulation, paranoia and social isolation make it harder to recognize risk and get help, and people with schizophrenia may be more likely to live on low incomes in substandard housing without access to air conditioning.
People with substance use disorders, epilepsy, chronic obstructive pulmonary disease, depression, asthma, mood and anxiety disorders, and diabetes were also overrepresented among those who died in the heat dome compared to deaths in the general population of people over 65.
Many people were on multiple chronic disease registries. Ontario’s coroner does not track heatrelated deaths the way B.C. does, though advocates have called for it, saying granular data like this would help understand and prevent heat deaths.
Another surprising fact emerged from the B.C. coroner’s decision to investigate all heatrelated deaths: almost all of them happened indoors, in people’s homes.
While the public may associate heat waves with a baking hot sun, the bigger risk factor is actually a roof: as the panel convened to study the B.C. heat dome deaths later wrote, “High indoor temperature was the primary cause of injury and death during the extreme heat event.”
The longer the body is exposed to extreme heat, the more stress it is under. That’s why overnight temperatures are just as important as daytime highs, if not more so. Giving the body a break to cool off and recover is critical. The majority of those who died in B.C. did not have access to air conditioning. So even as outdoor temperatures cooled off overnight, hot air remained trapped inside these homes, with temperatures consistently exceeding 26 C, the panel found.
That number is important: 26 C is considered the upper limit of safe indoor temperatures. The city of Toronto is midway through a study on whether to implement a maximum temperature bylaw that would require landlords to keep rental apartments below a certain threshold; its final report will land well after the summer months. The city has studied and debated the same idea on and off since 2014.
An infant and an octogenarian don’t have much in common. But they do share an increased vulnerability to heat, and for some of the same reasons.
Children and older adults don’t sweat as much, one of the body’s primary heatfighting tools. They also might be less aware if they are overheating, and have less ability to move to a cooler environment.
Children don’t have much control over their daily activities: they are required to be in school five days a week, for example. Most Toronto District School Board schools don’t have full air conditioning, and advocates say extreme heat in the classroom is a growing danger to kids’ health and ability to learn.
For older adults, agility challenges or cognitive impairments may impede their ability to leave home to seek cooler environments. The city’s heat relief network includes libraries, community centres and malls, but even when older adults are able to access these locations they are not typically open overnight, when cooling off is especially important.
The city announced a pilot program in May to provide air conditioning to lowincome seniors living in apartment buildings, but the $200,000 allocated to this program will cover only 300 to 400 air conditioning units, according to the city.
A Star investigation showed that serious workplace injuries in Ontario spike on the hottest days of the year. As most would expect, outdoor workers exposed to the sun are at risk — but indoor workers in hot environments are at risk too, Health Canada says.
Examples of critical injuries reported to the province on hot days, the Star’s reporting showed, included janitors in car parts factories, workers in pet food facilities and other indoor manufacturing jobs.
The Ontario government proposed a new heat stress regulation to protect workers, recognizing that heat is a rising risk to workers because of climate change. But those new rules never materialized. The minister of labour has said the current health and safety laws are “robust,” while labour leaders and opposition MPPs believe stronger protections are necessary.
There is nothing inherent about poverty itself that creates health risks from extreme heat. The risk comes from the disadvantages that attend living on a low income: poorly constructed housing and either no air conditioning or not enough money to pay to run it; neighbourhoods with fewer trees, raising temperatures from the urban heat island effect; worse access to health care and green spaces.
The city also provides $300 per household to people on social assistance through the “Hardship Fund”; last year, it issued approximately 650 subsidies for air conditioners.
Health Canada warns that people who are physically active, like runners and cyclists, should take particular precautions in extreme heat. Schedule workouts at cooler times of the day (usually early morning or late evening, rather than midday), exercise in the shade and move indoors to an airconditioned environment if possible. Also take extra water breaks, and wear loosefitting, breathable clothing.
“Try not to expect the usual performance from yourself during extreme heat,” Health Canada says.
Pregnancy is its own type of marathon. The body is already working overtime to gestate a baby, such as pumping more blood per minute, and heat stress adds another layer of effort to these systems.
Extreme heat has been linked to higher risks of pregnancy complications including preeclampsia and gestational diabetes. But it has also been linked to worse birth outcomes, including higher risks of stillbirths and preterm birth.
A recent report from Climate Central, a nonprofit research group, analyzed “pregnancy heat-risk days”extremely hot days associated with an increased risk of preterm birth — in cities and countries worldwide.
Toronto saw an average of 15 of these days annually over the last five years, the report found: climate change had added seven of those 15 days. Worldwide, most countries at least doubled the average annual number of pregnancy heatrisk days over that period, compared to a world without climate change.
Doctors share tips to stay cool as city faces high temperatures and humidity
This article was written by Kevin Jiang and was published in the Toronto Star on June 19, 2025.
It was the height of an exceptionally humid heat wave last July when an elderly patient was rushed to the emergency room with what looked like a heart attack.
Pain coursed through their chest and they could hardly breathe, said Dr. Edward Xie, the emergency physician who treated the patient. It was the end result of several days spent mired in extreme heat and humidity.
“They needed to be admitted to the hospital for basically the equivalent of a heart attack,” Xie, who is also an associate professor at the University of Toronto, said. “It was a lot of strain on the heart. Their body was basically shutting down because it couldn’t keep up with cooling itself.”
Like many Torontonians, this elderly patient lived in an apartment without air conditioning, Xie said. With no way to escape the oppressive heat and humidity, they were left to grow “sicker and sicker” over the course of several days — made worse by their preexisting heart and lung conditions.
“I basically have the same story every year,” he continued. “On very hot days, this is the most common presentation of people who don’t have heat pumps or air conditioning.”
Like clockwork, a stream of patients present to the emergency room whenever the thermostat breaches 30 C, especially when it’s humid out, Xie said. Studies suggest an average of 120 people die of heatrelated incidents every year in Toronto — and the danger only escalates the more humid it gets, experts say.
Our bodies have two main methods of cooling down when it’s hot out.
We wet our skin with sweat, dissipating heat when the perspiration evaporates. At the same time, our hearts beat faster and our blood vessels just under the skin dilate, sending hot blood coursing toward our skin and outer extremities where it can cool off, explained Dr. Samantha Green, a family physician and expert on the health consequences of climate change.
Humidity throws both those mechanisms out of whack.
It becomes far more difficult for sweat to evaporate when the air is already filled with moisture, Green said. With its ability to cool down diminished, our bodies heat up quicker, raising our risk of heat stroke.
“As humidity increases, the effectiveness of sweating decreases. And at around 90 per cent humidity, (sweating becomes) ineffective,” Green said.
This comes with another problem. Our bodies sweat more when it’s humid out, to compensate for the reduction in efficiency, Xie said.
Excess sweating can also damage our kidneys, which require us to be properly hydrated to function properly.
Elsewhere, our hearts are straining harder than usual to pump blood toward the skin and extremities to make up for our dwindling ability to cool ourselves, Green said.
There’s a complicated method of measuring temperature while taking into account humidity — as well as wind and solar radiation — called wet bulb globe temperature.
It’s generally believed a wet bulb reading greater than 35 C is the upper limit for human survivability, said Peter Crank, an assistant professor of geography and environmental management at the University of Waterloo.
“At that point, the environment around you is essentially so warm and so humid in combination, that your body is no longer able to maintain thermal regulation,” he said.
For reference, Wednesday, when temperatures climbed above 28 C with a relative humidity above 80 per cent, had a wet bulb of around 20 C, according to weather forecasting tool Meteologix.
The people at greatest risk of high heat and humidity include the elderly; people with chronic heart, lung and kidney conditions; people who work outdoors; and people without air conditioning, the experts say.
These individuals must take extra care to cool down, Green said. If possible, she advises finding a cool space near you and visiting regularly — the City of Toronto has an interactive map of cool spaces on its website. “If that’s not possible, stay cool by taking a cool shower,” she said. If your home has no air conditioning, consider installing window covers to block out the sun during the day and keep your windows open during the night, she said.
A fan can help as well, so long as the indoor air temperature remains below 35 C.
It’s important to drink extra water when it’s hot out, Xie said. Just avoid alcoholic, caffeinated or sugary beverages, as these can dehydrate you further.
You may also consider applying an ice pack to areas of the body with more blood supply, such as the back of the neck, under the armpits or near the groin, Green added.
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