As we continue to experience global heat waves each summer, climate change has now become an undeniable reality. The topic of heat waves and climate change began to garner attention in the early 21^st century when a 2003 heatwave caused over 20,000 deaths throughout Europe. Since then and almost every year since, news reports bear the sad news of clusters of deaths occurring during short, intense periods of heat.

Do you remember the “heat dome” that settled over much of British Columbia between June 25and July 1 of 2021? This heatwave broke 103 all-time heat records, including a 49.6 Celsius one-day high in Lytton, resulting in a wildfire that destroyed that town the next day. Within that period, 650 heat-related deaths were confirmed in B.C. (2). Back in Europe, summers regularly include death counts, like the 2023 heatwave death toll in France of 5,167 people, the majority affecting those over age 75 (3).

Climate change is the most often cited cause for the catastrophic and now almost inevitable loss of life due to extreme temperatures. About climate change itself, there are two points to consider: the first is that surface temperatures in Canada have risen 1.7 degrees Celsius in the last 75 years and are projected to rise by more than 5 degrees within the next 75 years with higher greenhouse emission scenarios (4). The second point is that we can’t ignore the first point.

Who are the most vulnerable to suffering the worst effects of excess heat? In a way, we all are. Everyone is susceptible to heat illness and exertional heat illness (EHI). EHI claims the life of young athletes, firefighters, military personnel and labourers working or performing in extreme heat. Susceptibility will vary and is influenced by factors such as dehydration, poor physical fitness and external load such as the clothing and equipment necessary for firefighters during an incendiary event. Even certain types of medications can impair sweating or reduce cardiac output, putting the patient at risk for heat-related morbidity.

Back to the question of who is most vulnerable? We already noted most of the heat-related deaths in France in 2023 were within an older age group. Given the higher prevalence of cardiovascular and respiratory disease among those aged 65 or older, this remains the highest at-risk population. In the higher greenhouse emission scenarios, this group will continue to be disproportionately affected (5). This will mean more cases of heat exhaustion, the inability to maintain adequate cardiac output due to exertion or environmental (heat) stress. As a result, the chance of more serious illness, like heat stroke, also rises. This means having a very high body core temperature leading to central nervous dysfunction. The risk of death is high, no matter at what age when heat stroke occurs.

Prevention by attention to hydration, fitness and heeding public health precautions to avoid excess heat by seeking cool air and shelter remain the stalwart guidelines. The phenomena of once in a lifetime heat wave has transformed into an annual cycle and paying attention is the first step to staying safe in the summer.