The relationship between climate change and human health

Experts speak to climate activism within medicine

For many experts

Eight years ago, Dr. Anna Gunz, a pediatric intensivist in London, saw her first patient who was impacted by climate change.

A baby from a remote Indigenous community in the northwest had been brought in with a severe lung infection. After two difficult weeks in the ICU, Dr. Gunz tried to offer the mother some words of comfort by recognizing how far they were from home, only for them to tell her that it didn’t matter where they were.

The words surprised Dr. Gunz. The mother explained that a few years ago, their community’s landing strip had been flooded, and a teenager had died of sepsis because medical personnel weren’t able to perform an evacuation in time. Since then, the community was prophylactically evacuated and scattered across the north every winter. Her husband was in a hospital up north, while her son was being treated in Toronto. For this family, going home was an impossibility.

In an interview with The Journal, Dr. Gunz said this story “sen[t] chills down” her spine. She said the mother’s situation was a consequence of climate change: their landing strip had been flooded at an unusual and unprecedented time of year.

Their story wouldn’t be the last. A few years later, Dr. Gunz met another family from the north who couldn’t return home because an ice jam flooded their community. The town’s residents had to be flown out one or two at a time while their homes and sanitation systems filled with water, unsure if their communities would ever be the same.

A patient of hers with mild asthma passed away one unusually hot and humid day from a cardiac arrest. A child told her they were terrified of tornadoes because they wouldn’t be able to take shelter in her basement, which wasn’t wheelchair accessible. And this summer, Dr. Gunz saw an unprecedented surge in viral infections during the July heatwaves—viruses she’d never seen in the summer until now.

For Dr. Gunz, who has a background in geography and environmental science, these connections between human health and the climate were immediately apparent, although she says it took longer for the medical community to warm up to the issue.

This November, world leaders are gathering in Egypt at COP27 to determine how they can tackle climate change—an issue the Lancet calls the “greatest global health threat facing the world in the 21st century.” Canada ranks last amongst all G7 nations in terms of climate action progress and has warmed at double the global average rate of warming since 1948.


It was a hot summer day in 2021 when Dr. Kim-Chi Tran stepped outside to meet an orange sky. Dr. Tran, who lives in Scarborough, was initially caught off guard by the sight. The haze in the air, she later realized, was coming from smoke blown from wildfires raging in northwestern Ontario.

Though people were still masking at the time, which reduced some of the possible health consequences of smoke inhalation, Dr. Tran recalls the experience as “a very eerie feeling that we had never experienced before in Toronto.” To her, it was an uncomfortable reminder of the toll climate change was already taking on communities across Canada and the world.

The summer of 2021 was one of the worst wildfire seasons Ontario had ever experienced. That year, 1,200 fires burned nearly 800,000 hectares of land in northwestern Ontario. Environment Canada issued air quality and visibility warnings for Kingston as smoke and particulate matter clouded the skies.

“Just a one degree increase in temperature brings about 10 to 15 per cent more lightning, and lightning causes up to 30 to 50 per cent of wildfires in the country. We’re going to see more fire,” Ed Struzik, a fellow at the Queen’s Institute for Energy and Environmental Policy who’s written extensively about the impact of wildfires, told The Journal.

Research shows wildfire smoke can contribute to and exacerbate a number of heart and lung diseases, resulting in a spike in hospitalizations that will increase the burden on our already-strained healthcare system. According to Struzik, inhaling wildfire smoke can be about as noxious and carcinogenic as smoking cigarettes.

Heat is another climate change-related stressor that poses risks to human health, according to Dr. Gunz. Here in Kingston, cooling centers have gone from being non-existent just a few years ago to a regular summer feature many rely on to stave off the extreme summer heat. A 2022 report from the University of Waterloo named Kingston as one of the most at-risk cities for extreme heat events in the nation—above Toronto, Montreal, and Ottawa.

Health agencies in Canada and the United States have only recently begun to ask physicians to track heat-related illnesses, according to Dr. Gunz, but she doesn’t think that data will address the full scope of the issue just yet.

According to her, the health consequences of a hotter environment aren’t only limited to heatstroke and dehydration. Hot temperatures will increase the prevalence of everything from heart attacks and stroke to kidney stones to infectious diseases to respiratory illnesses. What’s more, even a small increase in temperature can raise the likelihood of aggression, violence, and suicide.

Access to respite, however, won’t come equally to everyone. According to Dr. Gunz, children, those without access to air conditioning or adequate shelter, and those who have limited mobility, such as the elderly or people with disabilities, will struggle to protect themselves from rising temperatures, even though they’re often the least to blame for global warming.

“You’re going to have these people in apartment buildings, without water, without power, without refrigeration, and some of them won’t actually even be able to get outside or into cooling centers,” Dr. Gunz said.

The health consequences of high temperatures are a labour issue as well, according to Jeremy Milloy, a historian of public health and the Integrity of Creation and Climate Change lead at the Providence Centre for Justice, Peace, and Integrity of Creation in Kingston.

Those who work outside or in hot, enclosed environments, like farm labourers, service workers, and delivery drivers, are at greater risk of heat-related injury and illness, Milloy told The Journal. The lack of legislation regarding extreme heat in the workplace means those who are most at risk are also the least likely to be protected.

“We could use better regulation around unsafe work and extreme heat,” Milloy said. “We need to be aggressively retrofitting our buildings for energy efficiency, so that it’s easier to keep cool to protect [people] from climate change. We need to have better public transit so that people can get around in extreme heat events without walking long distances.”

When the environment is reshaped by climate change, so is our health. Milloy points to the loss of greenspace around Kingston as an issue that intersects with multiple dimensions of human health.

Trees provide shade and cooling, prevent floodwaters from rising, and improve mental health, but Milloy claims these benefits aren’t prioritized by our government the way greater urban development is. Developers in Kingston recently attempted to turn the Davis Tannery, a local wetland home to several crucial species of flora and fauna, into a new residential area.

Bryan Collins is a PhD candidate at Queen’s University in the department of environmental studies. His research focuses on how climate change is affecting our food systems and agriculture here in Kingston. Over the course of his investigation, Collins has spoken to several farmers in the area who say they’re already struggling to adjust to the effects of climate change.

“[The farmers] tell me stories about how climate change has affected them, such as having to switch to different crops that are more adapted to hotter climates,” Collins said in an interview with The Journal.

“They’ll tell me stories of how extreme weather events are becoming more common, such as severe wind events that are destroying their infrastructure like greenhouses, or how hail is destroying their crops, which is happening more often nowadays than it has in the past.”

These repercussions are forcing some farmers to adapt or give up on the business entirely. With the loss of locally grown produce, Collins said, Kingstonians will have to rely on imported and processed foods grown on large-scale farms that are less healthy and more expensive.

Those farming projects also can’t provide economic benefits to the local community and will contribute to greenhouse gas emissions as a result of the shipping and transport costs, Collins said.

Dr. Tran sees climate change as an issue that poses an existential threat to human and planetary health. Though healthcare professionals aren’t used to seeing environmental health as something bound up in human health, when the healthcare industry itself is responsible for 4.6 per cent of Canada’s emissions—more than the flight industry—Dr. Tran believes physicians have a responsibility to act.

Although Queen’s has yet to make a pledge to divest its holdings from fossil fuel companies, Dr. Tran and the Canadian Association of Physicians for the Environment (CAPE) have convinced the Ontario Medical Association to consider such a move.

The health impacts of climate change are already here, Dr. Tran said, pointing to the rise of allergies, insect-borne diseases, respiratory issues, and climate-related despair and anxiety as just a few of these examples. Today, global leaders stress the importance of limiting warming to a maximum increase of 1.5°C if we want to avoid a climate catastrophe—but our hospitals need to adapt to issues that are affecting us now.

“Our healthcare systems [need to ask], are we located in an area prone to flooding, prone to tornadoes, or hurricanes, or wildfires? […] What is the response in the hospital? Are we equipped to deal with like a mass casualty event? Do we have the right equipment? Does our infrastructure have the energy resources?” she asked.

Dr. Tran was reluctant to call herself a climate activist at first, but after seeing friends and colleagues make dramatic changes to reduce their carbon footprint, she realized that unless she took action, she would only continue to feel anxious about the future of our planet.

In 2018, she cold emailed the CEO of her hospital, convinced them to form a green team, and enrolled them in a program to track and reduce the waste and emissions they were producing.

“It’s not that we have to create these like wonderful, magnificent solutions, like carbon capture technology and all that,” she said. “We just need to be aware that we can’t continue doing the bad stuff. We can’t continue extracting fossil fuels, burning fossil fuels, when we can help it.”


Dr. Mili Roy, an ophthalmologist in Toronto, grew up deeply connected to nature. Coming from an immigrant family, she always felt a need to protect what was precious to her. As she progressed through her medical training, she grew increasingly concerned about the way the environment around her was changing. Still, she always found herself too busy with her career to truly take action.

The birth of her first child changed her mind. While holding her newborn, Dr. Roy decided she was going to dedicate her life after retirement to climate advocacy, so it could be her legacy to her children.

Being a parent only made juggling work and life more difficult. Soon, the environment became the last thing she had time for, but Dr. Roy still found herself feeling torn between the urgency of the climate crisis and her inability to act.

While she was sitting in on conference discussion about the environment and medicine, Dr. Roy came to realize the needs of the environment and the needs of the healthcare system were one unified issue. She came to realize the environment couldn’t wait for her retirement.

“Being a physician was not an obstacle, but in fact, was going to enable me to be more impactful,” she told The Journal. “Being able to approach [climate change] as a physician and framing a lot of the risks and the benefits and the solutions through the lens of health has been a huge advantage.”

As the co-chair of the Ontario Climate Emergency Campaign, Dr. Roy is hoping to utilize the social and political leverage doctors and health professionals wield to convince policymakers to take more drastic climate action. She represents over 850,000 Ontarians concerned about the climate, where she’s trying to use the democratic process to demand greater climate action and help constituents make the connection between the climate and their personal lives.

“Physicians and health care workers, we know from communications data and research, are some of the most trusted voices in the public sphere. We are also neutral; we’re not coming out for personal gain, we’re not coming out from a political stance,” she said.

“Some people may not respond to calls for climate action based on the environment alone. Once you make that connection with their own health and the health of your loved ones, they’re more likely to engage and support climate action.”

Last year, 220 leading medical journals published a coordinated editorial calling healthcare workers around the world to start standing up for climate action. At COP26 in Glasgow, delegates from over 102 countries and 600 organizations representing 46 million healthcare professionals signed a call for climate action addressed to world leaders.

Through CAPE, physicians are beginning to come to terms with their own responsibility to tackle climate change through their everyday work.

Across the nation, Dr. Roy said, anesthesia departments are trying to find ways to do without the carbon-intensive gases normally used during surgery. Family doctors are changing the choice of inhalers they prescribe to reduce the consequences of emissions they release.

Dr. Roy’s story holds hope for the future as well. The environmental issues she worried about as a child, like acid rain and the hole in the ozone layer, have been greatly mitigated today as a result of focused climate action.


About two decades ago, a heated debate was stirring about Ontario’s coal-fired electricity plants. The facilities, which produced over a fourth of the province’s electricity in 2004, faced fierce opposition from environmentalists who disparaged the consequences of air pollution and coal transport.

By presenting data on the healthcare costs of air pollution and the carcinogenic effects of smoke, physicians helped put an end to Ontario’s coal industry by showing policymakers the impact fossil fuels had on public health.

“Doctors can see when people have been ingesting particulates, and they can trace those back and figure out where they’ve come from,” Warren Mabee, director of the Queen’s School of Policy Studies and Institute for Energy and Environmental Policy, explained to The Journal. “They were able to quantify what it would cost in terms of healthcare and develop some really credible models as to what those costs were.”

In 2014, Ontario closed down the last of its coal-fired electricity plants, improving respiratory health in the process. To Mabee, events like this prove that climate action is possible, and that healthcare workers can be vital leaders in the fight.

Dr. Gunz believes those efforts can start with students and universities, which serve as training grounds for future medical professionals and climate leaders.

When she entered medicine, she recalled, she was discouraged from exploring how the environment affected human health. At first, she felt relieved by the temporary respite from her worries about our future, but once she saw her patients, colleagues, and loved ones being impacted by the consequences of climate change, she knew she couldn’t avoid the issue any longer.

“If you’re fighting to improve clean air, you’re also going to also improve from a mitigation standpoint in terms of climate change,” she said.

“The more we talk about climate change and get people to understand how it impacts their health and their children’s health and their grandchildren, we’re hoping that that will help give people the motivation to push for change. But also, we need to do that at a systemic level in our institutions and politically.”


Climate change, doctors, Environment, global warming, Healthcare, medicine

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