Thanks to climate change, fire seasons are stretching out and blazes are ravaging ever larger territories. The presence of smoke in our daily lives is set to increase. A public health problem that poses great challenges.

A New York bridge is lost in a yellow sky.

The intense smoke coming from the Quebec forest fires in June 2023 made New York City look like a science fiction film.


“Will the smoke from the fires in the West be transported here? At high altitude only. »

On the radio this week, in the Montreal region, the weather expert takes the time to provide a report on air quality linked to forest fires in the west of the country. She explains the risks of seeing the smoke from these fires reach Quebec and the east of the country.

With climate change, could it be that information regarding poor air quality linked to forest fires becomes part of our daily weather reports?

In any case, this is what the General Directorate of Public Health of Quebec is preparing for. In the event of air pollution from smoke from fires, it will now publish recommendations to help schools, centers for the elderly, daycares or day camps decide what activities they can hold if the air quality deteriorates.

The information will be made public in the form of color codes, depending on the concentration of fine particles in the air: blue (good quality), yellow (bad for people at risk), orange (bad), red (very bad) and purple (dangerous).

This announcement from Quebec public health authorities is a good example of necessary adaptation to climate change.

In 2023, the summer of all records, the burned territory was so vast that the fire that ravaged the country from coast to coast sent thick layers of smoke into the country’s major urban centers, from Vancouver to Montreal, to the United States and even to northern Europe.

A fog hangs over the buildings.

Smog caused by forest fires fell on Montreal in June 2023, hiding the towers of the city center.

Photo: The U.S. Press / Graham Hughes

The phenomenon of deterioration in air quality linked to forest fires is not expected to fade away.

According to a report from the United Nations Environment Program published in 2022, the frequency of uncontrolled fires is expected to increase by nearly 15% by 2030. A trend that worries public health experts. Because smoke from forest fires can be a real chemical cocktail whose effects on human health are still relatively poorly understood.

More than just air pollution

The problem with forest fires is that it’s not just wood that burns. In addition to biomass (trees, grasses or animals), other fuels can make the smoke even more toxic (buildings where different materials are stored, factories, fuel, vehicles, construction materials, etc. ).

Smoke from fires is at least composed of several gases and pollutants, such as sulfur dioxide, nitrogen dioxide, carbon monoxide, methane, volatile organic compounds (VOCs) or polycyclic aromatic hydrocarbons (PAHs).

It also contains fine particles, the famous PM2.5, whose diameter is equal to or less than 2.5 micrometers, approximately thirty times smaller than the diameter of a hair.

Why insist on their dimension? This is because due to their microscopic appearance, these particles can be deposited deep in the lungs or on the mucous membranes. And although the brain is generally better protected than other organs thanks to the famous blood-brain barrier, which acts a bit like the brain’s bodyguard, fine particles can find their way there.

But there is more. For scientists, wildfire smoke is more difficult to understand than traditional air pollution, because its content continually changes, depending on the context.

Its composition can vary depending on many factors, such as the nature of the fuel, the combustion temperature or the weather conditions surrounding the fire.explains in an interview with CBC Sarah Henderson, the director of the environmental health department at the British Columbia Center for Disease Control and Prevention.

This particularity makes research into the persistent effects of smoke on human health more complex. We don’t yet have much information about the health impact of these long-term trends.admits Sarah Henderson.

In fact, much of the existing data still comes from studies of car exhaust or smoke from wood stoves.

A science that advances slowly

Researchers know more about the consequences of routine urban air pollution, and can sometimes afford to extrapolate some of that knowledge to the effects of wildfire smoke, but there are limits.

We know, for example, that, like pollution in cities, smoke from forest fires can exacerbate diseases such as asthma or chronic respiratory failure, harm heart health, increase the risk of stroke or even cause inflammation in organs such as the lungs, kidneys or liver.

But the dynamics between the different polluting elements found in smoke from fires is complex and can operate differently than simple atmospheric pollution.

A forest fire with huge clouds of smoke.

Wildfire in 2023 in the Northwest Territories.

Photo: Reuters / Alberta Wildfire

The general impact of air pollution on people has been known for some time, but we are only beginning to understand the danger of wildfire smoke to human health.explains Anthony White (New window)neuroscientist at the University of Queensland, Australia, interviewed by the magazine National Geographic.

This problem is compounded by the fact that it can be difficult to distinguish the health effects of air pollution from those of wildfire smoke, particularly when such pollution occurs sporadically and unpredictably.

The degree of exposure of citizens to these forest fires is in fact another obstacle to overcome for researchers. Is it a question of studying the effects of a very dense smoke which envelops a village once every 20 years, or of a less dense smoke which the inhabitants breathe every summer or almost?

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Cancers and effects on the brain

In their quest to better understand the effects of wildfire smoke on human health, scientists are trying to find out whether exposure to this toxic cocktail can cause cancer and have consequences on the brain.

The most comprehensive study for this purpose was carried out by Canadian researchers, the results of which were published in the medical journal The Lancet Planetary Health (New window) in 2022.

Conducted among 2 million Canadians over a period of 20 years, the study shows that living near a burned forest can increase the chances of contracting lung cancer by 5% and by 10%. brain tumor, compared to a person living far from this kind of inferno.

This is a fairly low risk. By comparison, the probability of suffering from such cancer is 2000% higher for a smoker, compared to a non-smoker.

But for researchers, this is not enough to draw a clear conclusion. They specify that the risk is always multifactorial (genetics, lifestyle habits, man or woman, environment, etc.), and that even the stress of experiencing the fire could perhaps play a role in the results. They explain that it is therefore difficult to isolate a particular factor (smoke from forest fires).

More work is needed to develop long-term estimates of wildfire exposure that account for the complex mix of environmental pollutants released during these eventsconclude the researchers.

A fire ravages a valley near a lake.

A wildfire in British Columbia approaches a lake, summer 2023.

Photo: AFP / Darren Hull

One thing is certain: the potential worsening of wildfires – and the associated degradation of air quality – poses a significant challenge that policymakers will need to tackle head on. In an interview she gave us on the sidelines of COP28 last December, the head of the climate issue at the World Health Organization, Maria Neira, told us that air pollution is the climate effect which most threatens the health of populations.

There is not much more fundamental than the air we breathe and the air our children or our elderly parents breathe.

If we want to minimize the damage and better understand the consequences of smoke, experts agree that we will have to do several things at the same time.

First, we will need to improve forest management to minimize the fuel that fuels fires for so long. Second, we will have to adapt to this growing phenomenon by using new knowledge and new technologies that allow us to better understand the dynamics of fires. And thirdly, we will need to support research that will allow us to have more precise answers about the effects of smoke on our health in the short and long term.

Actions that will allow us to see things more clearly.

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