Written by: Cassandre Clermont, biochemistry and molecular medicine student

Global warming is a recent phenomenon caused by the abnormal increase in greenhouse gases. It was the industrialization of companies that led to an overproduction of its gases. The main consequence is that this surplus accumulates in the atmosphere and causes an increase in temperature.

According to the World Meteorological Organization, global warming is increasingly felt. Indeed, between 2015 and 2019 an increase of 1.1 °C in the global average temperature was observed in comparison with the period from 1850 to 1901 [1]. This is a significant change that has been linked to an increase in the frequency, intensity and duration of heatwaves [2]. Heatwaves are harmful to the health of populations because they lead to problems of morbidity, which are the effects linked to illness and mortality [2].

The health impact of heatwaves can range from minor to fatal. The most common short-term health problems associated with the phenomenon are exhaustion, dehydration and heatstroke. However, heatstroke is the most serious effect since it can occur suddenly and cause death within a short time if the person is not treated [3]. Certain groups of people are more vulnerable such as young children and the elderly [2]. During the heatwave, the risk of mortality and morbidity increases among people aged 65 and over, even more so for those aged 75 and over [2]. According to a study published in the American Journal of Respiratory and Critical Care Medicine [4], it has been observed that during heat waves, there is an increase in hospital admissions for respiratory problems. Therefore, people with respiratory and cardiovascular problems are more at risk of being affected. This study also noted that excessive heat seems to have a greater impact on mortality than the morbidity of a population [4]. Those with chronic illnesses are also more susceptible to harmful consequences since exposure to extreme heat leads to the exacerbation of their illnesses [5]. According to an article in the International Journal of Environmental Research and Public Health, pregnant women and the fetus are also more vulnerable to unusually high temperatures. Indeed, this can have an impact on the duration of gestation, birth weight, caused an increase in neonatal stress and even an increase in the risk of stillborn children [6].

In the Clinical Journal of American Society of Nephrology, it has been observed that long-term exposure to high heat with physical activity and insufficient hydration can cause the development of nephropathy [5] which leads to kidney damage. This disease is generally observed in people with diabetes, however, nephropathy due to excessive heat could be considered as one of the first epidemics [5] caused by global warming.

Several places are more likely to be affected by heatwaves, such as the tropical and subtropical regions of the world, since their climate is already so warm that an increase in temperature can have serious impacts. Already, an increase in the heat index has been observed in some countries and it is expected that the heat index will exceed the critical threshold of human adaptability [7], which refers to the body’s ability to regulate its internal temperature in the face of higher external temperature. If this threshold is exceeded, it would cause fatal consequences. Also, developing and underdeveloped countries are more vulnerable since they have fewer or no resources to manage the problems associated with this situation. Underdeveloped regions may be at even higher risk of mortality [7], as well as regions with ageing populations.

Even Quebec feels the effects even though the average climate is cooler. During the summer of 2010 and 2018, heatwaves affected the province and led to an increase in emergency room admissions, hospitalizations and deaths [8].

In short, it is understood that global warming has a direct impact on the health of people. It would be appropriate to carry out studies to better assess the impact of long-term exposure to extreme heat on the health of individuals.