Article – The first intense heatwave of summer swept across southern Ontario last week, transforming Toronto’s concrete jungle into a shimmering mirage of heat rippling off pavement. At Trinity Bellwoods Park, I watched as families sought refuge under maple trees, their children’s laughter occasionally punctuated by the distant wail of an ambulance.
“We’ve already seen a 30% increase in heat-related emergency calls compared to this time last year,” Dr. Eileen de Villa, Toronto’s Medical Officer of Health, told me during our interview at her downtown office. The fan in the corner did little to cut through the humid air as she reviewed the city’s heat response protocols. “Climate change isn’t some distant threat anymore—it’s affecting Ontarians’ health right now.”
As summer settles in across the province, a complex web of health risks emerges with the rising temperatures. From Windsor to Thunder Bay, Ontarians face interconnected challenges that health experts are increasingly viewing through a holistic lens.
The most immediate threat comes from extreme heat itself. According to Public Health Ontario’s most recent climate change assessment, heat-related emergency department visits have increased by 22% over the past decade. For elderly residents living in older apartment buildings without air conditioning, these statistics represent a daily struggle.
“My apartment was 34 degrees inside yesterday,” 78-year-old Margaret Chen told me at a Toronto cooling center. “I couldn’t sleep, couldn’t eat. My heart was racing.” Chen lives alone in a mid-century high-rise in North York, one of the urban heat islands where temperatures can be up to 7 degrees higher than surrounding areas.
But beyond the direct impact of heat, Ontario’s summer brings cascading health risks that often affect the most vulnerable first.
Last summer, air quality in eastern Ontario deteriorated dramatically when wildfire smoke from Quebec blanketed communities with a thick, acrid haze. Health Canada data showed a 42% spike in asthma-related hospital visits during this period, with children and those with pre-existing conditions suffering most severely.
Dr. Samantha Green, a family physician with Unity Health Toronto, has witnessed these effects firsthand. “What’s particularly concerning is how these environmental factors compound existing health inequities,” she explained as we walked through her clinic. “My patients who work outdoors, who can’t afford air conditioning, who already have chronic conditions—they’re the ones bearing the brunt of these changes.”
Water quality presents another seasonal concern. While Ontario’s larger lakes and rivers are regularly monitored, smaller bodies of water can develop harmful algal blooms during hot weather. These blue-green algae can produce toxins that cause skin irritation, gastrointestinal illness, and in severe cases, liver damage.
Last August, Lake Erie’s western basin experienced one of its largest algal blooms in recent years, prompting public health advisories in several shoreline communities. According to the Ontario Ministry of Environment, Conservation and Parks, warming water temperatures combined with agricultural runoff create ideal conditions for these dangerous blooms.
Meanwhile, the changing climate has expanded the range of disease-carrying insects across the province. The Public Health Agency of Canada has documented a northward expansion of blacklegged ticks, which can transmit Lyme disease, into areas of Ontario where they were previously rare.
“Twenty years ago, we barely saw any Lyme disease cases,” said Dr. Curtis Russell, an entomologist with Public Health Ontario. “Now we’re identifying hundreds of cases annually.” During our field research near Peterborough, Russell demonstrated the careful “tick dragging” technique used to monitor populations, pulling a white cloth through the underbrush that quickly collected several of the tiny arachnids.
For residents like Rebecca Mayhew, a teacher from Belleville who contracted Lyme disease in 2021, the expansion of these vectors represents a life-altering reality. “I used to take my students on nature walks without a second thought,” she said, sitting in her garden with long sleeves despite the heat. “Now I’ve had to completely rethink how I interact with the outdoors.”
What makes these summer health risks particularly challenging is their interconnected nature. Heat waves exacerbate air pollution, which worsens respiratory conditions. Drought followed by sudden heavy rainfall—increasingly common in Ontario’s changing climate—can contaminate water sources and increase infection risks.
Public health units across the province are adapting to this complex landscape. Ottawa Public Health recently launched an integrated summer health risk monitoring system that tracks heat, air quality, vector-borne disease risk, and water quality in a single dashboard.
“We’ve moved beyond siloed approaches,” explained Dr. Vera Etches, Ottawa’s Medical Officer of Health. “When we issue a heat warning now, it comes with specific guidance for people with respiratory conditions if air quality is also compromised.”
Community-based approaches are also emerging. In Hamilton, the Neighborhood Cooling Network has organized a system where air-conditioned businesses, libraries, and community centers open their doors during extreme heat events. Volunteers check on vulnerable residents and help transport them to these cooling spaces.
“The solutions need to be as interconnected as the problems,” said Maria Duarte, the network’s coordinator, as we toured one of their cooling centers in a former retail space. “We can’t just tell people to stay cool or avoid ticks—we need to create the conditions where everyone can actually follow that advice.”
For individual Ontarians navigating these summer health risks, experts recommend a layered approach: stay informed about local conditions, create emergency plans, check on vulnerable neighbors, and advocate for community-wide adaptations.
As I left Dr. de Villa’s office, she offered a final thought that has stayed with me: “The health impacts of our changing climate aren’t evenly distributed. Our response shouldn’t be either.”
The summer sun beat down on the sidewalk outside, another ambulance siren wailed in the distance, and the reality of Ontario’s new normal felt impossible to ignore.
