The number 120 flashes to mind as I rush to another patient with difficulty breathing on a sweltering July night. It’s the number of heat-related deaths in Toronto each year, but with Canada heating twice as fast as the world average, that number is likely rising. In Montréal, last summer, 66 people died during a single heat wave.

Thankfully, my patient was luckier. Maureen (not her real name) was very sick, but pulling through. She was elderly and lived in an apartment without air conditioning. For a few days, she felt her chest getting heavier, until it seemed like she was drowning. With enough oxygen and medicines, her breathing eased, but in her struggle for breath she’d suffered a minor heart attack.

Maureen’s story is familiar: the heat and smog of summer are linked to higher risks of death from heart and lung diseases. Air pollution can trigger heart attacks in adults and set off asthma in children. People affected by wildfires know this from experience.

When it’s hot out, your body adjusts by expanding blood vessels close to the skin, bringing heat to the surface. You sweat more, which cools your body as it evaporates. Your heart pumps faster to push blood through this cooling cycle. However, as temperatures rise, it gets harder to keep up, especially in high humidity. If your body’s cooling system gets overwhelmed, your organs start shutting down.

Older and lower-income adults like Maureen are at a disadvantage. They’re often on medications or have chronic illnesses that lowers their ability to sweat, circulate blood, stay well-hydrated, or even physically leave stuffy apartments. Social isolation makes it harder to call for help. Maureen wanted to see her family doctor, but getting there with her walker, by herself, had proved to be too challenging.

Even if we’re in different circumstances, we can learn from her story. How hot we feel depends on many factors, including air flow, humidity, contact surfaces, and clothing. To cool down more efficiently, we can use fans, cover windows in daytime, and drink plenty of liquids to replenish lost sweat. Thirst signals that we're already dehydrated.

If you have AC, dressing for the weather can still improve comfort, save on energy bills, and give others a break from overly chilled spaces. Reducing reliance on AC also avoids blasting hot exhaust outdoors, burdening the electrical grid during peak hours, and contributing to climate change. We want to keep enjoying our summers and prevent them from being intolerable and dangerous for our kids.

Having studied the health risks of climate change and seen them first hand, I can assure you that we’re in an emergency. We can do lots as individuals, and accomplish even more through effective policies, from smart urban design, to public health investments, to carbon pollution pricing. While Maureen recovers, we can push policy-makers to take rapid and ambitious action.

Let’s act like our lives depend on it. Because they do.

Edward Xie is an emergency physician and assistant professor at the University of Toronto.

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