Climate change Archives - Observatoire de la prévention

Will cultured meat soon be on our plates?

Dr Martin Juneau, M.D., FRCPCardiologue et Directeur de la prévention, Institut de Cardiologie de Montréal. Professeur titulaire de clinique, Faculté de médecine de l'Université de Montréal. / Cardiologist and Director of Prevention, Montreal Heart Institute. Clinical Professor, Faculty of Medicine, University of Montreal.22 September 2021

OVERVIEW

To preserve the planet’s environment and produce enough food to meet growing global demand, experts believe that in the future there will be a need to reduce livestock farming and conventional meat consumption.
Cultured meat is presented as a sustainable alternative to farmed meat for those who want to protect the environment but do not want to become vegetarians.
For cultured meat to be consumed on a large scale, production techniques and social acceptability will have to make significant progress.

Today there are 7.3 billion human beings on our planet, and it is expected that there will be 9 billion by 2050. The Food and Agriculture Organization (FAO) estimates that in 2050, 70% more food will be required to meet the demand of the growing population. This poses a great challenge because of limited resources and arable land. Meat production (especially beef and pork) is the most resource-intensive, and experts believe it would not be responsible, or even possible, to continue to produce more and more of these foods. Even though meat consumption is declining in developed countries, it is increasing globally because consumers in developing countries are getting richer and meat is seen by the new middle class in these countries as a desirable luxury food.

Among the solutions proposed to get out of this impasse is cultured meat (or lab-grown meat), which is presented as a sustainable alternative to farmed meat for those who want to protect the environment, but who do not wish to become vegetarians. It should be noted that some experts consider that cultured meat poses certain problems and that it would not be a viable alternative to conventional meat (see here and here). We will come back to this a little later in the text.

How is meat grown?
To grow meat, you must first obtain a muscle sample from a live adult animal (by biopsy, under anesthesia) and isolate a subpopulation of cells called “stem” or “satellite” cells. These stem cells participate in muscle regeneration and have the ability to differentiate into muscle cells themselves. The muscle stem cells are then cultured in bioreactors in the presence of a nutrient medium containing growth factors that induce rapid proliferation. The cells are then transformed into muscle cells that form structures called “myotubes” no larger than 0.3 mm in length and mechanically assembled into muscle tissue and ultimately into ground meat or artificial “steak”.

Problematic use of fetal calf serum and growth promoters
The best culture medium for growing cells contains fetal calf serum, obtained from fetal blood after slaughtering a pregnant cow. The procedure usually used (cardiac puncture of the still alive calf fetus) is considered cruel and inhumane by many. This is a problem since large numbers of calves would have to be produced to meet the demand for large-scale meat cultivation, and this use is unacceptable to vegetarians and those who follow a vegan diet or lifestyle. Fortunately, it is now possible, on a laboratory scale, to grow muscle cells without the use of fetal calf serum. However, the serum-free culture will need to be adopted on an industrial scale. To replace fetal calf serum, the industry will need to use growth factors and hormones that will need to be produced on an industrial scale. The use of growth promoters is prohibited in the European Union for conventional meat production; however, you cannot grow meat without using these growth factors and hormones. Overexposure to certain growth promoters can have harmful effects on human health, but this is a subject of debate and several countries approve the supervised use of stimulators in animal production.

From cell to steak
Real muscle (meat) is made up of muscle fibres organized into bundles, blood vessels, nerves, connective tissues, and adipocytes (fat cells). Simply producing animal muscle cells is therefore not enough to recreate meat. This is why in 2013 the first dish prepared from cultivated meat was a simple burger-type patty. Industries that develop cultured meat must now attempt to recreate a 3D structure that will resemble real meat as much as possible, a task that is proving difficult. It’s about recreating the taste experience associated with eating a steak, chicken thigh or shrimp.

Researchers have recently made progress and successfully created small samples of cultured meat that mimic real meat. Using a new approach, a Japanese research group succeeded in growing beef muscle cells in long filaments aligned in a single direction, a structure that closely resembles muscle fibres. When these cultured cells were stimulated by an electric current, the filaments contracted, similar to muscle fibres. Researchers at the University of Tokyo have so far managed to produce pieces of cultured meat weighing a few grams at most. The next challenge will be to successfully produce larger pieces of cultured meat, up to 100 g, and introduce other tissues (blood vessels, fat cells) to mimic meat more convincingly. It should be noted that the culture medium used in this study contained fetal calf serum, an ingredient that cannot be used industrially for ethical and economic reasons, as mentioned above.

Cultured chicken meat
Singapore’s food regulatory agency approved the sale of meat grown by the US company Eat Just in 2020. It was the first time that the sale of cultured meat had been permitted by a state. Eat Just grows chicken meat using a process that does not require antibiotics. This cultured meat is safe because it contains very low levels of bacteria, much less than conventional chicken meat. Cultured chicken meat contains a little more protein, has a more varied amino acid composition, and contains more monounsaturated fat than conventional meat. The muscle cells are grown in 1200-litre bioreactors and then combined with plant ingredients to make chicken nuggets. The Singapore-approved process uses fetal calf serum, but Eat Just plans to use a serum-free culture medium in their future productions.

Estimation of the environmental cost of cultured meat
Cultivated meat production offers many environmental advantages compared to conventional meat, according to a study published in 2011. It would reduce greenhouse gas (GHG) emissions by 78 to 96%, use 7 to 45% less energy and 82 to 96% less water, depending on the type of product. In contrast, a more recent and rigorous study suggests that in the long term, the impact of cultured meat on the environment may be greater than that associated with livestock farming. Cultivated meat production will certainly reduce global warming in the short term since less GHGs will be emitted compared to cattle farming. In the very long term however (i.e., several hundred years), models predict that this would not necessarily be the case, because the main GHG generated by livestock, methane (CH₄), does not accumulate in the atmosphere, unlike CO₂ which is practically the only GHG generated by cultivated meat. Another study based on data from 15 companies involved in the production of cultured meat concludes that it is less harmful to the environment than the production of beef, but that it has a greater impact on the environment than the production of chicken, pork and plant-based “meat”. In order for the environmental score of cultivated meat to be better than that of conventional products, the industry would have to use only sustainable energy.

Cost of cultured meat
The first cultivated beef burger was produced in 2013 by a Dutch laboratory at an estimated cost of US $416,000. In 2015, the cost of production (on an industrial scale) was reduced to around $12, and it is expected that the price could be the same as conventional meat within ten years. The cultured chicken nuggets produced by Just Eat each cost $63 to produce in 2019, so industries still have some way to go for cultured meat to become affordable enough for consumers to consume on a regular basis.

Cultured meat: an alternative for Canadians?
According to a 2018 Dalhousie University survey of 1,027 Canadians, 32.2% of respondents planned to reduce their meat consumption in the next 6 months. However, cultured meat is not very popular with Canadians as only 18.3% of those consulted said that this new type of “meat” represented an alternative to real meat for them. There is hope, however, as younger consumers (40 and under) seem more likely (34%) to view cultured meat as an alternative.

Will cultured meat one day replace conventional meat on our plates? Although there is still progress to be made before this is possible, both in terms of production and social acceptability, we can hope that the important efforts made will lead to results within a decade. Ideally, for our health and that of the planet, we should reduce our consumption of meat (of all kinds) and eat mainly plants, as is the case with the Mediterranean diet and other traditional diets.

Environmental impacts associated with food production

OVERVIEW

Food production is responsible for about 25% of the greenhouse gases emitted annually, with half of these GHGs coming from animal farming, mainly in the form of methane.
The agricultural sector is also an important source of fine particles responsible for air pollution, with the majority of these pollutants coming from ammonia generated by livestock farming.
Overall, a reduction in the consumption of animal products, particularly those from cattle farming, is therefore absolutely essential to limit global warming and improve air quality.

The latest report from the Intergovernmental Panel on Climate Change (IPCC) confirms that, if nothing is done, the constant build-up of greenhouse gases (GHG) in the atmosphere will cause temperatures to increase by more than 1.5ºC above pre-industrial levels over the next century, namely the target set by the Paris Agreement to minimize the negative effects of global warming. There is therefore an urgent need to drastically reduce the emission of these gases if we want to prevent the consequences of this warming, already visible today, from becoming out of control and causing an increase in the incidence of extreme climatic events (droughts, heat waves, hurricanes, forest fires), disrupting life on Earth (extinction of species, fall in agricultural yields, increase in infectious diseases, armed conflicts) and increasing the incidence of several diseases linked to excessive heat.

Carbon dioxide and other greenhouse gases
The main greenhouse gas is carbon dioxide (CO₂), which now has a concentration of 417 ppm, about twice as much as in pre-industrial times. However, it should be noted that other gases, even if they are present in smaller quantities, also contribute to global warming. These gases, such as methane or certain molecules used for industrial purposes, capture heat in a much greater way than CO₂ and therefore have a higher global warming potential (GWP) than CO₂. For example, a tonne of methane has a GWP 28 times greater than a tonne of CO₂ over a 100-year period, while the GWP of some industrial gases such as sulfur hexafluoride can reach almost 25,000 times that of CO₂ (Table 1). In other words, even if many of these gases are present in minute quantities, on the order of a few parts per billion (10^-9) or even per trillion (10^–12), their emission is several times that of CO₂ and therefore significantly contributes to warming.

Table 1. Global warming potential of various greenhouse gases.¹Values are for the year 2018, except for CO₂ which is for 2020. Derived from the United States Environmental Protection Agency (EPA).² Calculated for a 100-year period. From Greenhouse Gas Protocol. *ppm (part per million or 10^-6); **ppb (part per billion or 10^-9); ***ppt (part per trillion or 10^–12).

To calculate this contribution to global greenhouse gas emissions, the method generally used is to convert these emissions into CO₂equivalents (CO₂eq) by multiplying their quantity in the atmosphere by their respective GWP. For example, 1 kg of SF₆ is equivalent to 23,500 kg (23.5 tonnes) of CO₂ (1 kg × 23,500 = 23,500 CO₂eq), while it takes 1000 kg of methane to reach an equivalent amount of CO₂ (1000 kg × 28 = 28,000 CO₂eq). When this method is applied to all gases, it is estimated that 75% of greenhouse gas emissions are in the form of CO₂, the remainder coming from methane (17%), nitrous oxide (6%), and various fluorinated gases (2%) (Figure 1).

Figure 1. Distribution of greenhouse gas emissions. Adapted from Ritchie and Roser (2020).

Emissions sources
The use of fossil fuels to support human activities (transport, electricity production, heating, various industrial processes) is the main source of greenhouse gases, accounting for around three quarters of total emissions (Figure 2). This enormous “carbon footprint” implies that the fight against global warming necessarily requires a transition to “cleaner” sources of energy, in particular with regard to transport and electricity production. This is especially true in a country like Canada, where we emit an average of 20 tonnes of CO₂eq per person per year, which ranks us, along with the United States and Australia, among the worst producers of GHGs in the world (Quebec, for its part, does better, with about 10 tonnes of CO₂eq per person per year).

Figure 2. Contribution of the food sector to the annual production of greenhouse gases. Adapted from Ritchie and Roser (2020).

Another industry that contributes significantly to greenhouse gas emissions, but that we hear much less about, is food production. It is estimated that around 25% of all these gases come from the production and distribution of food, a proportion that rises to 33% when food waste is taken into account. The food sector involved in animal protein production alone is responsible for half of these food-related GHG emissions, mainly due to methane produced by livestock and aquaculture (31%) (see box). Livestock farming also requires large spaces, created in some cases by massive deforestation (in the Amazon, for example), which eliminates huge areas of plants that can sequester CO_s. Livestock farming also requires large quantities of forage plants and therefore the use of nitrogen fertilizers to accelerate the growth of these plants. The CO₂ and nitrous oxide released into the atmosphere during the production of these fertilizers therefore contribute to the GHG generated by livestock.

Where does methane come from?
Methane (CH₄) is the end product of the decomposition of organic matter. Methanogenesis is made possible by certain anaerobic microorganisms from the archaea domain (methanogens) which reduce carbon, present in the form of CO₂ or certain simple organic acids (acetate, for example), to methane, according to the following reactions:

CO₂+ 4 H₂ → CH₄ + 2 H₂O

CH₃COOH → CH₄ + CO₂

The methane generated by livestock comes mainly from the fermentation of carbonaceous products inside the digestive system of ruminants. In these animals, the digestion of plant matter generates volatile fatty acids (acetate, propionate, butyrate), which are absorbed by the animal and used as a source of energy, and lead in parallel to the production of methane, about 500 L per day per animal, most of it being released through the mouth of the animal. Globally, livestock is estimated to emit about 3.1 Gt of CO₂-eq as methane, which represents almost half of all anthropogenic methane emissions.

Aquaculture is another rapidly expanding form of farming, now accounting for over 60% of the global supply of fish and seafood for human consumption. Although GHG emissions from this sector are still much lower than those associated with livestock, recent measurements nonetheless indicate a sharp increase in its global warming potential, mainly due to an increase in methane production. In these systems, the sediments accumulate food residues used for the growth of fish and seafood as well as the droppings generated by these animals. The transformation of this organic material leads to the production of methane, which can then be diffused into the atmosphere.

Finally, it should be noted that the majority of aquaculture systems are located in Asia, where they are often established in regions previously occupied by mangroves, ecosystems located along the coasts and deltas of tropical regions. The destruction of these mangroves (very often for shrimp farming) is very harmful to global warming, because mangrove forests collectively store around 4 billion tonnes of CO₂and their elimination therefore has a concrete impact on the climate.

A good way to visualize the impact of livestock farming on GHG production is to compare the emissions associated with different foods of animal and plant origin based on the amount of protein in these foods (Figure 3). These comparisons clearly show that products derived from livestock products, beef in particular, represent a much greater source of GHGs than plants. The production of 100 g of beef protein, for example, generates on average 100 times more GHGs than the same amount of protein from nuts or legumes. This is true even for beef produced in the traditional way, i.e., from animals that feed exclusively on grass: these animals grow more slowly and therefore emit methane for a longer period, which cancels out the benefits that could be associated with the sequestration of CO₂ by the grass that they eat.

Figure 3. Comparison of GHG levels generated during the production of different protein sources. Based on Poore and Nemecek (2018), as modified by Eikenberry (2018).

These huge differences in GHGs associated with the production of everyday food therefore clearly show that our food choices can have a significant influence on global warming. Since the majority of GHG emissions come from livestock, it is evident that a reduction in the consumption of meat, and animal products as a whole, will have the most positive impact. These benefits can be observed even with a fairly modest reduction in meat intake, as in the Mediterranean diet, or simply by replacing products from ruminants (beef and dairy products) by other sources of animal protein (poultry, pork, fish) (Figure 4). Obviously, a more drastic reduction in meat intake is even more beneficial, whether through the adoption of a flexitarian diet (high intake of plants, but little meat and animal products), vegetarian (no animal products, with the exception of eggs, dairy products and sometimes fish), and vegan (no animal products). This remains true even if the plants consumed come from abroad and sometimes travel long distances, because contrary to popular belief, transport only accounts for a small proportion (less than 10%) of the GHGs associated with a given food.

Figure 4. Potential for mitigation of GHG emissions by different types of diets. Adapted from IPCC (2019).

It is impossible to completely decarbonize food production, especially in a world where there are over 9 billion people to feed daily. On the other hand, there is no doubt that the GHG footprint of food can be significantly reduced by reducing the consumption of products derived from ruminants, such as beef and dairy products. This is extremely important, because the status quo is untenable. According to recent models, even if GHG emissions from fossil fuels ceased immediately, we would still not succeed in reaching the target of a maximum warming of 1.5ºC due to emissions produced by the current food production system.

Another aspect that is often overlooked is how fast and significant this positive impact of a reduction in cattle breeding products can be. Even though methane is a GHG almost 30 times more powerful than CO₂, its life in the atmosphere is much shorter, around 10–20 years vs. several thousand years for CO₂. Concretely, this means that an immediate drop in methane emissions, for example following a drastic reduction in the consumption of beef and dairy products, can have measurable effects on GHG levels in the following years and therefore represents the fastest and most efficient way to slow global warming.

Pollution from food
In addition to contributing to global GHG emissions, another environmental impact of food production is its contribution to air pollution. This negative impact of the food sector should not be overlooked, because while the influence of global warming caused by GHGs will be felt above all in the medium and longer term, atmospheric pollutants have an immediate effect on health: air pollution is currently the 7^th leading cause of premature death worldwide, being directly responsible for around 4 million deaths annually (Figure 5). In some countries, such as the United States, it is estimated that agriculture and livestock are responsible for about 20% of this air pollution-related mortality.

Figure 5. Leading causes of premature mortality worldwide. Note that air pollution is the only risk factor of environmental origin, not related to lifestyle. From GBD 2016 Risk Factors Collaborators (2016).

Fine particles of 2.5 µm and less (PM_2.5) are mainly responsible for these negative impacts of air pollution on health. Due to their small size, these particles easily penetrate the lungs to the pulmonary alveoli, where they pass directly to the pulmonary blood vessels and then to all arteries in the body. They then produce an inflammatory reaction and oxidative stress that damage the vascular endothelium, the thin layer of cells that covers the inner walls of the arteries and ensures their proper functioning. The arteries therefore dilate less easily and tend to contract more, which interferes with normal blood circulation. For all these reasons, it is cardiovascular diseases (coronary heart disease and stroke) that represent the main consequence of exposure to fine particles, and alone are responsible for about 80% of all deaths caused by ambient air pollution (Figure 6).

Figure 6. Distribution of premature deaths (in millions) caused by fine particles PM_2.5.
Note the predominance of cardiovascular disease as a cause of death linked to air pollution. Adapted from Lelieveld et al. (2015).

Primary and secondary particles
Fine particles can be emitted directly from polluting sources (primary PM_2.5) or indirectly, following the combination of several distinct particles present in the atmosphere (secondary PM_2.5) (Figure 7). Much of the primary PM_2.5is in the form of carbon soot, produced by the incomplete combustion of fossil fuels (diesel and coal, especially) or biomass (forest fires, for example). Carbon soot is also associated with various organic compounds (polycyclic aromatic hydrocarbons), acids, metals, etc., which contribute to its toxicity after inhalation. These particles can be transported aloft over very long distances and, once deposited, be resuspended in the wind. In urban areas, this resuspension also takes place under the action of road traffic. This turbulence associated with automobile traffic is also responsible for the production of another class of primary PM_2.5 called fugitive road dust.

Secondary PM_2.5, on the other hand, are formed from precursors such as sulfur dioxide (SO₂), nitrogen oxides (NO_x), various volatile organic compounds containing carbon (organic carbon) as well as ammonia (NH₃). The chemical reactions that govern the interaction between these different volatile substances to form the secondary fine particles are extraordinarily complex, but let us only mention that it is well established that the presence of the ammonium ion (NH₄⁺), derived from ammonia (NH₃), neutralizes the negative charge of certain gases and thus promotes their aggregation in the form of fine particles (Figure 7). Consequently, the presence of NH₃ in the atmosphere often represents a limiting step in the formation of these secondary fine particles and a reduction in these emissions can therefore have concrete effects on improving air quality.

Figure 7. Schematic representation of the mechanisms of formation of fine particles PM_2.5.

It is this important role of ammonia in the formation of secondary fine particles that explains the contribution of the food production sector to air pollution. Agriculture and livestock are in fact responsible for almost all anthropogenic ammonia emissions, a consequence of intensive livestock farming, the spreading of manure and slurry, and the industrial production of nitrogen fertilizers.

An American study clearly illustrates this contribution of agricultural ammonia to the negative impacts of air pollution on health. In this study, the researchers show that of the approximately 18,000 deaths caused annually by pollution derived from the agricultural sector, the vast majority (70%) of these deaths are a consequence of ammonia emissions (and therefore secondary PM_2.5), while the emission of primary PM_2.5, from plowing, the combustion of agricultural residues, and machinery, is responsible for the rest. Since the vast majority of ammonia emissions come from animal faeces and the use of natural (manure and slurry) or synthetic fertilizers to grow food for these animals, it is not surprising that the production of food from livestock is the main cause of deaths attributable to pollution from agricultural sources (Figure 8).

Figure 8. Distribution of deaths caused annually by PM_2.5 from the agricultural sector in the United States. Note that 70% of the mortality is attributable to livestock products, mainly due to the ammonia generated by the animals as well as by the spreading of manure, slurry and synthetic fertilizers for the cultivation of fodder plants (corn, soybeans). From Domingo et al. (2021).

When we compare the impact of different foods for the same quantity of product, we immediately see that the production of red meat is particularly damaging, being responsible for at least 5 times more deaths than that of poultry, 10 times more than that of nuts and seeds, and at least 50 times more than that of other plants such as fruits and vegetables (Figure 9).

Figure 9. Comparison of PM_2.5-related mortality by food types. From Domingo et al. (2021).

In short, whether in terms of reducing GHG emissions or health problems associated with atmospheric pollution, all the studies unequivocally show that a reduction in environmental damage caused by food production necessarily involves a reduction in the consumption of products of animal origin, in particular those from cattle farming. A change that is all the more profitable as the reduction in the intake of food of animal origin, combined with an increase in the consumption of plants, is beneficial for health and could prevent about 11 million premature deaths annually, a decrease of 20%.

The impact of forest fires on human health

Dr Gabrielle Denault, M.D.Médecin résident en santé publique et médecine préventive à l’Université de Montréal.31 August 2021

OVERVIEW

Wildfires will be increasingly frequent given climate change that is leading to higher temperatures and drought in many parts of the world.
Smoke from forest fires produces fine and ultrafine particles that can travel up to 1,000 kilometres and affect the health of people from afar.
In the short term, smoke from wildfires is mainly harmful to respiratory health. Some populations are more at risk of suffering the consequences.
The increase in forest fires may in turn contribute to climate disruption.

From British Columbia to the island of Evia, wildfires are increasingly part of the global landscape. The health impacts of these blazes on global health are unequivocal. Here is an overview of a natural phenomenon exacerbated by climate change.

The recent report of the IPCC, the Intergovernmental Panel on Climate Change, highlights that forest fires are likely to be more frequent and severe given the acceleration of climate change.¹ Higher temperatures favour the development of lightning, which is the main natural cause of wildfires. A climate predicted to be drier and windier will promote combustion and the spread of forest fires.² The fire season will therefore last longer. By 2039, the frequency of fires could increase over 37.8% of the planet with a rise of just 1.2 °C in global temperature. With an increase of 3.5 °C, 61.9% of the world territory will be affected by more frequent fires by 2100.³ In the most pessimistic climate scenario where greenhouse gas emissions continue to rise, this risk will affect up to 74% of the world’s land surface by the end of the century. The United States, Canada, Mediterranean countries, China and Australia will be particularly affected.⁴

In Canada, it is estimated that more than 8,000 fires occur each year. On average, more than 2.1 million hectares are destroyed annually, equivalent to the area of Victoria Island.⁵ In all the provinces, weather conditions will be increasingly conducive to wildfires. The areas burned could thus double by 2100.⁶

The smoke from wildfires is made up of carbon monoxide, carbon dioxide, nitrogen oxides, and other organic compounds. These vary according to several factors, such as the type of vegetation and the temperature of the fire.⁷ Fires also produce fine particles (diameter ≤ 2.5 μm or PM_2.5) and ultrafine particles (diameter ≤ 0.1 μm or PM_0.1) that can travel up to 1,000 km.² It is mainly these particles that are harmful to the health of populations living at a distance from fire outbreaks. Fine particles produced by wildfires may also contain more oxidative and pro-inflammatory compounds than urban air pollution caused by burning fossil fuels.⁸ One study suggests that fine particles from wildfires may be 10 times more harmful to human health than those produced by other sources.⁹

Impact on human health

Population near forest fires
Populations near fires and first responders are at risk of direct injury from burns, heat, and direct smoke inhalation. Smoke can also irritate the eyes, cause corneal abrasions, reduce visibility, and increase the risk of traffic accidents in areas near the fires.¹⁰

Respiratory health
For local or remote populations, fine and ultrafine particles enter the respiratory tract and cause inflammation to the lungs. Exposure to fine particles mainly causes respiratory symptoms, such as coughing or difficulty breathing.⁷

Many exposed individuals will not have any symptoms, but some are more likely to develop them. The extent of exposure to smoke and the presence of vulnerability factors may modulate the severity of the clinical presentation, as shown in Figure 1.

Figure 1. Clinical and subclinical impact of fine particles from wildfires. From Cascio (2018).¹¹

Patients with asthma or chronic obstructive pulmonary disease may experience more exacerbations of their respiratory symptoms, use more medications to control them, and seek more health care services.¹²^,¹³^,¹⁴ People aged 65 and over, those working outdoors, and those residing in disadvantaged neighbourhoods are also more vulnerable to fine particles from fires.¹⁵ Children are also more susceptible to the harmful effects of smoke. A less well-developed immune system and a higher basal respiratory rate in children could explain this vulnerability.²

Cardiovascular health
Are the fine particles produced specifically by forest fires harmful to cardiovascular health? The answer remains to be clarified. While some studies show a significant risk of cardiovascular disease associated with exposure, others do not.¹⁴^,¹⁶

Among these, a study analyzing 2.5 million hospitalizations in areas 200 km from wildfires in the United States suggests that the risk of cardiovascular disease may be comparable to that of urban air pollution.¹⁷

Another study conducted on the 2015 California wildfires shows an association between exposure to smoke and increased emergency room visits related to cardiovascular diseases, such as myocardial infarction, ischemic heart disease, heart failure, hypertension, and arrhythmias. Adults 65 years of age and older were particularly affected. An association between smoke density and cerebrovascular events, such as stroke, has also been noted by researchers.¹⁸

Australian studies have also shown an association between exposure to fine particles from wildfires and the risk of cardiac arrest in the community.¹⁹^,²⁰

Of note, short-term exposure (less than 3 hours) to smoke produced by burning wood has the potential to increase central arterial stiffness, heart rate and decrease heart rate variability. In other words, wood smoke could have harmful hemodynamic effects on the cardiovascular system.²¹

In short, fine particles from fires are added to those generated by global air pollution, well known to worsen the incidence of cardiovascular disease.

Mortality
Exposure to smoke from forest fires is associated with an increased risk of mortality from non-specific and non-accidental causes.² In Canada, from 2013 to 2018, 620 to 2,700 premature deaths were reported to have been caused by smoke from forest fires.²² Current data do not allow us to establish a clear link between exposure to fine particles from forest fire smoke and an increase in mortality from a specific cause, such as respiratory or cardiac.

However, it should be noted that short-term exposure to fine particles caused by global air pollution is associated with an increased risk of mortality.²³ Even short-term exposure to fine particles could increase the risk of myocardial infarction mortality.²⁴ In other words, smoke from wildfires could be a risk factor for cardiovascular mortality, but this has yet to be clarified.

Other effects on physical health
Some studies suggest that pregnant women exposed to fine particles from forest fires may be at greater risk of giving birth prematurely or having a low birth weight baby. However, the data remain limited and should be interpreted with caution.²

In addition, one study found a marked increase in the number of influenza cases a few months after intense forest fires in the Montana region (USA). This could suggest a certain vulnerability to respiratory infections following exposure to smoke.²⁵ The fine particles produced by fires could alter the function of macrophages, cells of the immune system, reducing the body’s ability to effectively defend itself against respiratory tract infections.²⁶ In this sense, some researchers are currently evaluating the impact of air pollution from forest fires on the transmission and severity of COVID-19 cases.²⁷^,²⁸^,²⁹

Overall, more studies are needed to better understand the medium- and long-term impact of wildfire smoke on human health.

Mental health
Wildfires can be devastating for the communities living nearby. Emergency evacuations and the loss of one’s physical and social environment are intense stressors that can have an impact on mental health, particularly in children and adolescents.³⁰ People directly exposed to wildfires are at greater risk of major depression, post-traumatic stress disorder, and anxiety disorders.¹⁰ Access to psychological support services is therefore essential for populations strongly affected by forest fires.

Socio-economic impacts
Wildfires are also associated with greater use of medical resources. There are more medical consultations in emergency rooms, family medicine clinics and hospitalizations.³¹ In Canada, the annual health costs associated with fine particles from forest fires are estimated at between $410 million and $1.8 billion for short-term exposure. From $4.3 billion to $19 billion are attributable to chronic exposure.²² This adds to many societal costs, such as those associated with rebuilding infrastructure, contamination of drinking water by smoke ash, and loss of income.¹¹

Environmental health
Although exacerbated by human pollution, wildland fires themselves contribute to climate change. Combined with the continued emission of greenhouse gases from human activities, the loss of vegetation reduces the absorption of carbon dioxide and thus contributes to the increase in the temperature of the earth. Forest fires could also contribute to the melting of permafrost and thus promote the emission of methane,² a gas whose potential for warming the atmosphere is 25 times greater than carbon dioxide.³²

What to do about forest fires?

Learn about air quality
In Canada, the Air Quality Health Index provides information about air quality across the country³³ and the FireWork forecasting system helps predict the movement of smoke from forest fires.³⁴ The Canadian government’s WeatherCAN application is also a weather forecasting tool accessible to the population.³⁵ Local authorities are also responsible for issuing air quality warnings and health recommendations.

Reduce exposure to air pollution
Figure 2 summarizes the main measures to be taken to reduce the impact of wildfire smoke on health. In order to limit exposure to fine particles following a forest fire, recommendations may vary depending on the location. The net effectiveness of these interventions still needs to be clarified, as they are based on a limited number of small-scale studies.³⁶ It is advisable to avoid outdoor activities, including physical exercise, when the atmospheric level of fine particles is too high.¹⁵

In order to reduce the infiltration of outdoor air into buildings, it is useful to close doors and windows if the heat is not too overwhelming inside. High levels of fine particles in the atmosphere can be associated with intense heat waves. If the temperature inside is too high, the heat can be harmful to health, especially in the elderly or those with chronic diseases. Setting the heating, ventilation and air conditioning systems to recirculation mode and limiting the use of the kitchen hood are also recommended measures to reduce air intake.³⁷

Air purifiers with HEPA (high efficient particulate air) filters effectively reduce the level of fine particles and are recommended by the Government of Canada. However, these are not able to remove some polluting gases from the air. In addition, air purifiers can be expensive and therefore less accessible to everyone.²

As for wearing a mask, the surgical type is not recommended, since it does not protect against fine particles. N95 masks offer better protection, but they require an individual fit test, can give a false sense of security, and are not suitable for children. The use of these masks is recommended for workers exposed to smoke from fires.³⁸ Finally, the creation of community smoke-free spaces is also a measure that can be implemented by local authorities when the level of air pollution increases.³⁹

Figure 2. Key actions individuals can take to reduce exposure to wildfire smoke and its health risks. From Rongbin et al. (2020)²

Preventing climate change
Globally, the main goal to reduce forest fires and their health consequences would be to limit the global temperature increase to 1.5 °C instead of the 2° C targeted by the Paris Agreement. This limited increase would prevent more than 50% of the predicted forest fires if the global temperature rises by 2° C.⁴

The IPCC report highlights that even the 2° C target will be exceeded without massive and imminent interventions. Concerted government actions are therefore more than necessary to substantially reduce anthropogenic greenhouse gas emissions.

Conclusion In sum, the air pollution emitted by forest fires is associated with an increase in morbidity and mortality. Some health effects remain to be elucidated. These increasingly frequent fires reflect the impact of climate change on human health. In the short and long term, interventions and prevention measures to protect the population will be necessary in order to mitigate the social, economic and environmental consequences of these climatic upheavals.

References

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The effects of climate change on health

On May 11, the Mauna Loa Observatory in Hawaii recorded carbon dioxide (CO₂) levels of up to 415 parts per million (ppm), an atmospheric concentration almost twice as high as before the beginning of the industrial era (280 ppm). This record concentration, never reached in the last three million years, is a direct consequence of the continued growth of CO₂ emissions from the combustion of fossil fuels and land use (deforestation, change of land use). Yet, despite warnings from climate scientists over the last several years, global CO₂ emissions continue to increase, so that if the current trends continue, models predict that CO₂atmospheric concentration could reach 550 ppm in 2050 and nearly 940 ppm by the end of the century.

CO₂ is the main greenhouse gas and the increase in its concentration is correlated with an increase in the average surface temperature of the planet. Compared to the period before the start of the industrial era (before the surge of human-induced CO₂ emissions), the global average temperature of the globe has increased by about 1 °C and the majority of this increase (0.8 °C) has occurred since the 1970s (Figure 1). At present, the average global temperature is estimated to increase at a rate of 0.2 °C per decade as a result of the CO₂build-up produced by current and past pollutant emissions (up to 20% of CO₂ persists in the atmosphere for more than 1,000 years). It therefore appears that global warming could reach 3.2 °C in 2100, even if the signatories of the Paris Agreement respect their commitments to reduce pollutant emissions. The initial objective of the Paris Agreement to limit the rise in global temperature below 2 °C therefore seems unachievable.

Figure 1. Evolution of global mean surface temperatures from the pre-industrial era to the present day. The anomalies indicated represent the temperature differences in °C compared to normals calculated for the period 1951–1980.

The inability to reach this goal of “2 degrees maximum” is really worrying, as this target represented a political compromise aimed at limiting the damage caused by climate change, not at preventing it. Numerous modelling by climatologists show that each additional degree increases the risk, frequency and magnitude of the direct consequences of warming, whether in terms of extreme weather events (droughts, heat waves, hurricanes, rising of the sea level) or of its direct impact on terrestrial life (extinction of species, fall in agricultural yields, increase of infectious diseases, etc.). According to the recent work of the Intergovernmental Panel on Climate Change (IPCC), the limit of global warming should rather be around 1.5 °C to hope to avoid the main consequences of climate change. With an increase already reaching 1 °C and possibly 3 °C by the end of this century, we are on a trajectory that goes well beyond this “safety threshold” and it seems inevitable that we will be confronted, in the short and medium term, with the potentially dangerous consequences of global warming.

Health impacts
Recent analyses (here and here, for example) clearly show that the effects of climate change on health are already beginning to be felt. Figure 2 summarizes the main damage caused by global warming: diseases, injuries and deaths caused by extreme weather events (floods, heat waves, etc.), respiratory and cardiovascular diseases associated with increased air pollution, increased intoxication caused by deterioration of water quality and certain foodstuffs, malnutrition due to reduced agricultural yields, increase in insect-borne diseases, and mental health problems caused or aggravated by societal changes due to climate change (migrations, conflicts) (Figure 2). According to estimates by the World Health Organization, these phenomena caused by climate change could be responsible for about 250,000 additional deaths per year between 2030 and 2050.

Figure 2. Main consequences of climate change on health. Adapted from Haines and Ebi (2019).

Extreme weather events
Rising greenhouse gas emissions add energy to the climate, increasing the frequency, intensity and duration of extreme events such as heat waves, droughts and floods. According to the Center for Research on the Epidemiology of Disasters, the number of disasters caused by storms and floods has increased annually by 7.4% in recent decades. In 2017, a total of 712 extreme weather events were reported, generating an estimated cost of US $326 billion, nearly triple the losses recorded in 2016. Nearly half of the world’s population lives within 60 km of the sea and it is estimated that the number of people at risk of flooding could rise from 75 million currently to 200 million in 2080 if the rise in sea level of 40 cm (15 ¾ inches) predicted by the current models is realized. It should be noted, however, that this increase could be much greater and reach several metres if the Antarctic ice sheet is destabilized and/or that of Greenland disappears as a result of global warming.

Extreme heat
Several studies have reported an increase in mortality associated with extreme heat episodes, the best documented being those that have affected large urban areas such as Chicago in 1995 (740 deaths), Paris in 2003 (4,867 deaths), and Moscow in 2010 (10,860 deaths). Cities are particularly vulnerable to heat waves due to the “heat island” effect that generates temperatures 5 to 11 °C higher than neighbouring rural areas. If the current trend continues, it is expected that by the end of the century, extreme heat mortality could increase from 3 to 12% in the southern United States, Europe and Southeast Asia.

As mentioned in another article, extreme heat increases the risk of mortality when the temperature exceeds the thermoregulatory capacity of the human body and reaches 40 °C. Under these conditions, massive redistribution of blood to the body surface causes internal organs such as the heart to be insufficiently irrigated (ischemia) and stop functioning. Thermal shock and ischemia also promote the infiltration of pathogens into the blood and the development of a systemic inflammatory response that damages the organs (sepsis) and can also cause the disintegration of muscle fibres (rhabdomyolysis), releasing myoglobin, which is very toxic to the kidneys. Older people are particularly vulnerable to extreme heat, with a significant increase in mortality observed when the maximum temperature exceeds 5 degrees and above normal temperature (Figure 3). At the MHI EPIC Centre, a research team led by Dr. Daniel Gagnon, PhD, is studying the impact of extreme heat on the elderly and heart patients.

Figure 3. Increased risk of mortality among people aged 65 and over caused by heat exceeding normal temperatures. From WHO (2014).

Deterioration of air quality
It is estimated that the fine particles present in air pollution are currently responsible for about 9 million premature deaths worldwide, plus 1 million deaths from low altitude (tropospheric) ozone. The lungs are obviously the organs most exposed to air pollution, and people who live in polluted areas are more at risk of developing lung diseases. However, cardiovascular disease is the greatest consequence of the deterioration of air quality, accounting for about 80% of all deaths caused by ambient air pollution. Fine and ultrafine particles inhaled by the lungs reach the bloodstream where they cause an inflammatory reaction and oxidative stress that damage the lining of the vessel walls and increase the risk of cardiovascular events, especially in people who are already at risk (existing coronary heart disease, advanced atherosclerosis). It goes without saying that without a significant reduction in polluting emissions, these premature deaths will increase over the next few years, especially since certain consequences of climate change such as forest fires can further increasethe levels of air pollution by more than 10 times.

Impact on food supply
Higher temperatures, changes in precipitation cycles, and extreme weather events caused by climate change can greatly affect food production. Several countries are already experiencing declining agricultural yields, particularly in Africa and Southeast Asia, mainly because of prolonged periods of drought. Rising temperatures also have an impact on food safety: in Europe, for example, above-normal temperatures account for about 30% of salmonellosis cases and the incidence of food poisoning is strongly associated with a rise in temperatures in the previous 2 to 5 weeks.

It should also be noted that several recent studies (here, here and here, for example) have shown that the increase in atmospheric CO₂ concentrations is associated with a decrease in the nutritional quality of some important crops such as rice and wheat, lowering protein levels, several micronutrients (zinc and iron in particular) as well as B vitamins. According to a recent analysis, if, as expected, the atmospheric concentration of CO₂ exceeds 550 ppm over the next decades, 175 million people could have a zinc deficiency and 122 million people a protein deficiency (mainly in Southeast Asia, Africa and the Middle East).

Increase in vector-borne zoonotic diseases
According to the Intergovernmental Panel on Climate Change, the increased risk of transmission of infectious diseases through vectors such as mosquitoes and ticks is one of the most likely consequences of climate change. Global warming is promoting the geographical expansion of many of these vectors, including Aedes aegypti and Aedes albopictus mosquitoes, which are responsible for the transmission of arboviruses such as dengue, chikungunya, yellow fever and Zika; mosquitoes of the genus Culex, which are responsible for Nile virus transmission; and some ticks such as Ixodes scapularis, the vector for the bacterium Borrelia burgdorferi responsible for Lyme disease.

The emergence of Lyme disease in southern Canada, including southern Quebec, is a particularly worrying example of the consequences of global warming. Originating in New England (the disease was first described in the town of Lyme, Connecticut, hence its name), the tick responsible for the transmission of this disease began to be detected in southeastern Canada in the early 2000s. This expansion of I. scapularis tick territory to the north, at a rate of approximately 33 to 55 km per year, is strongly correlated with rising temperatures that now allow the tick to complete its life cycle. As a result, the annual incidence of Lyme disease in Canada has soared in recent years, from 40 cases in 2004 to nearly 1,000 cases in 2016 (Figure 4).

Figure 4. Incidence of Lyme disease in Canada between 1994 and 2016. From Ogden et al. (2014) and the Government of Canada.

Climate change is likely to have a similar impact on the risk of Nile virus infection and may even promote the emergence of diseases transmitted by arbovirus vectors (Aedes aegypti andAedes albopictus). For example, according to current models, Ae. albopictus will be present in 197 countries by 2080, including Canada, potentially exposing these populations to infectious diseases (dengue, for example) that were until now exclusively present in warmer countries.

In short, it is clear that if nothing is done, the negative effects of climate change on human health will increase, especially among populations that are vulnerable to global warming because of their geographical location (floods, drought, heat waves). But even when disasters occur elsewhere, they can nevertheless greatly influence life here, whether in economic terms (disruptions in the production of goods and services, lower agricultural yields) or social terms (massive migrations, armed conflicts). It is therefore all of humanity that is facing the climate crisis, and we can only hope that concrete actions will be quickly implemented to reduce greenhouse gas emissions.

The dangers of heat stroke during a heat wave

Heat waves are sporadic events of high temperatures, which can have serious consequences on human life. More than 70,000 people died during the heat wave that hit Europe in 2003, and another 10,860 died during a heat wave in Russia in 2010. The criteria for defining a heat wave vary from country to country. In Canada, a heat wave occurs when it is 30°C or higher for at least three consecutive days. It has been estimated that the average temperature of our planet will increase by 1°C by 2100 if we reduce greenhouse gas (GHG) emissions or 3.7°C if we do not. In 2000, about 30% of the world’s population was exposed to heat waves for at least 20 days a year. By 2100, it is expected that this proportion will increase to about 48% if we drastically reduce GHG emissions and 74% if we continue to increase GHG emissions.

When it is very hot, humid or both, the excess heat absorbed by the body must be dissipated by the skin and the respiratory system in order to maintain body temperature at 37°C: this is the thermoregulation process. The hypothalamus initiates a cardiovascular response by dilating blood vessels to redistribute blood to the body surface (the skin) where heat can be dissipated into the environment. Sweating is activated, allowing heat to dissipate by evaporation (600 kcal/hour). When it is very hot and humid, the evaporation of sweat is greatly reduced and the body struggles to maintain an adequate temperature. Heat stroke is a serious and life-threatening condition, which is defined as a body temperature above 40°C, accompanied by neurological signs such as confusion, seizures or loss of consciousness. The main risk factors for heat stroke are shown in Table 1.

Table 1. Risk factors for heat stroke. From Yeo, 2004.

Factor
Alcoholism
Cardiovascular disease
Dehydration
Extremes of age (younger than 15, older than 65)
Skin-altering conditions (psoriasis, eczema, burns)
Lack of air conditioning in home
Living in a multi-storey building
Low socioeconomic status
Obesity
Occupations with prolonged exertion and environmental exposure to temperature extremes (e.g., athletes, military workers, miners, steel workers, firefighters, factory workers, rescue workers)
Medications/drugs: · Impaired thermoregulation (diuretics, beta blockers, anticholinergics, phenothiazines, alcohol, butyrophenones) · Increased metabolic heat production (benzotropin, trifluoperazine, ephedra containing dietary supplements, diet pills, amphetamines, cocaine, ecstasy)
Previous history of heat-related illness
Prolonged sun exposure
Wearing heavy or excessive clothing

Physiological mechanisms
In a review of the literature on the causes of death during heat waves, 5 physiological mechanisms disrupting 7 vital organs have been identified (brain, heart, intestines, kidneys, liver, lungs, pancreas). The authors have identified 27 different ways in which heat-activated physiological mechanisms can lead to organ failure and ultimately death.

1- Ischemia. When the human body is exposed to heat, the hypothalamus initiates a cardiovascular response by dilating the blood vessels to redistribute blood to the body surface (the skin) where heat can be dissipated into the environment. This compensatory process can lead to an insufficient supply of blood to the internal organs (ischemia) and consequently to a lack of oxygen (hypoxia).

2- Toxicity due to thermal shock. High body temperature causes stress the body reacts to by producing stress proteins and free radicals that damage cells. This damage, combined with that caused by ischemia, affects the functioning of several organs.

3- Inflammatory response. Erosion of the intestinal mucosa allows bacteria and endotoxins to enter the bloodstream, leading to sepsis and activation of a systemic inflammatory response. If hyperthermia persists, the exaggerated inflammatory response causes damage to various organs.

4- Disseminated intravascular coagulation. Systemic inflammation and damage to the vascular endothelium caused by ischemia and heat shock can initiate this harmful mechanism. The proteins responsible for the control of coagulation become overactive and this can lead to the formation of clots that block the blood supply to vital organs. Depletion of blood clotting proteins can lead to subsequent bleeding (even in the absence of injury), which can be fatal.

5- Rhabdomyolysis. This is the rapid degradation of skeletal muscle cells caused by heat shock and ischemia. Muscle proteins such as myoglobin are released into the bloodstream and are toxic to the kidneys and can lead to kidney failure.

The heart is hit hard
In the heart, the combination of ischemia, heat shock cytotoxicity, and hypokalemia (potassium deficiency caused by excessive sweating) can lead to cardiac muscle breakdown. This myocardial injury increases the risk of cardiac arrest due to loss of myofibrils and reduced efficiency of the body in controlling heart rate and blood pressure. Stress on the heart can be exacerbated by dehydration, which thickens the blood and causes vasoconstriction, increasing the risk of coronary thrombosis and stroke. In the pancreas, erosion of the endothelial lining allows leukocytes to infiltrate the tissue, exacerbating inflammation. In the brain, the permeability of the blood-brain barrier allows toxins and pathogens to enter, increasing the risk of neuronal damage. All these physiological responses are interconnected in such a way that the failure of one organ can lead to negative effects on others, initiating a vicious cycle of deterioration that often leads to permanent damage, long-term recovery, or death.

To prevent heat stroke (according to Peiris et al., JAMA, 2014):

Schedule outdoor activities during cool times of the day.
Drink plenty of fluids. Avoid drinks with too much sugar or alcohol, which can cause dehydration.
Wear loose-fitting, light-coloured clothing.
Acclimate to new hot environments, over many days if possible.
Be aware of medication side effects. If taking medications, be aware of those that may cause fluid losses, decrease sweating, or slow the heart rate. Common medications include those used for depression, blood pressure and heart disease, and coughs and colds.
Never leave an impaired adult or a child in a car unattended.

What to do if you suspect a heat stroke
Call 911 if you notice these signs of heat stroke: body temperature over 40°C; accelerated heart rate; accelerated breathing; hot and red skin; nausea or vomiting; change of mental state (confusion, headache, difficulty in articulating words, convulsions or coma).

What to do while you wait for help:

Move the individual out of the heat.
Remove clothing to promote cooling.
Position the person on his or her side to minimize aspiration.
Immerse the individual in cold water or apply cold, wet cloths or ice packs to the skin (neck, armpits, and groin areas, where large blood vessels are located) to lower the body temperature.
Continue cooling the individual until the body temperature reaches 38.4°C to 39°C (101°F to 102°F).
Do not give any fluids to the person because it is not safe to drink during an altered level of consciousness. If the person is alert and requests water, give small sips.
Avoid aspirin and acetaminophen; they do not help with cooling.

Will cultured meat soon be on our plates?

Environmental impacts associated with food production

The impact of forest fires on human health

The effects of climate change on health

The dangers of heat stroke during a heat wave

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