Extreme heat events are public health emergencies

The average number of deaths per day in British Columbia is 110, ranging from 90 to 130 most days. On 29 June 2021, 380 people died across the province [Figure]. There were 1630 deaths in the 8 days from 25 June to 2 July, about 740 more than would be expected in a normal summer.

There is often a misperception that extreme heat is most dangerous for the very frail who are already near death, a group particularly impacted by the historic European heat wave in 2003.[1] However, we found that mortality during the 2021 heat dome doubled in every age group over 50, and we observed no decrease in mortality following the end of the hot weather [Figure]. This suggests that high temperatures simply killed hundreds of people who would probably still be alive had the weather conditions been more typical.

Many of these deaths will be further investigated by the BC Coroners Service (BCCS) in the months ahead.[2] We already know from preliminary analyses of data from BC Vital Statistics that most of the excess deaths occurred in residential settings, although there were increases in deaths in hospitals and long-term care facilities as well. Many of the deaths in individual residences occurred in neighborhoods with lower socioeconomic status, where more people live alone and where there is less protection provided by surrounding greenery.

Internet-connected thermostats in some homes without air conditioning recorded indoor temperatures of nearly 40 °C.[3] People died because it was too hot inside, not because it was too hot outside. Based on prior evidence, investigations by the BCCS are likely to find that many of these people were socially isolated, which has been exacerbated during the pandemic, with physical and mental health conditions that affected their ability to take protective measures.

In total, the 2021 heat dome was associated with 740 excess deaths in British Columbia, and more in Alberta.[4] This makes it comparable with the 1936 heat wave in Ontario and Manitoba, during which at least 780 people died.[5] In more recent years, the 2010 heat wave in Quebec was associated with 280 excess deaths.[6] Together, these are three of the most deadly weather events in Canadian history. We have ample evidence that heat waves cause mass casualties in Canada and that they will become more frequent and more intense as the climate changes.[7] We must develop and resource the systems necessary to recognize and respond to extreme heat events as public health emergencies.
—Sarah B. Henderson, PhD
Scientific Director
—Kathleen E. McLean, MPH
Environmental Health Scientist
—Michael Lee, MSc
—Tom Kosatsky, MD
Medical Director
Environmental Health Services, BC Centre for Disease Control


This article is the opinion of the BC Centre for Disease Control and has not been peer reviewed by the BCMJ Editorial Board.


1.     Vandentorren S, Bretin P, Zeghnoun A, et al. August 2003 heat wave in France: Risk factors for death of elderly people living at home. Eur J Public Health 2006;16(6):583-591.

2.     BC Coroners Service. Chief coroner’s statement on public safety during high temperatures. 30 July 2021. https://www2.gov.bc.ca/assets/gov/birth-adoption-death-marriage-and-divorce/deaths/coroners-service/news/2021/chief_coroner_statement_-_heat_related_deaths.pdf.

3.     Baum KB, McClearn M. Extreme, deadly heat in Canada is going to come back, and worse. Will we be ready? The Globe and Mail. 25 September 2021. https://www.theglobeandmail.com/canada/article-extreme-deadly-heat-in-canada-is-going-to-come-back-and-worse-will-we/.

4.     Johnson L. Alberta saw spike in reported deaths during heat wave, causes still under investigation. Edmonton Journal. 7 July 2021. https://edmontonjournal.com/news/local-news/alberta-saw-spike-in-reported-deaths-during-heatwave-causes-still-under-investigation.

5.     Phillips D. Heat wave. The Canadian Encyclopedia. Topic last updated 16 December 2013. Accessed 28 September 2021. https://www.thecanadianencyclopedia.ca/en/article/heat-wave.

6.     Bustinza R, Lebel G, Gosselin P, Bélanger D, Chebana F. Health impacts of the July 2010 heat wave in Québec, Canada. BMC Public Health 2013;13(1):56.

7.     Philip SY, Kew SF, van Oldenborgh GJ, et al. Rapid attribution analysis of the extraordinary heat wave on the Pacific Coast of the US and Canada June 2021. https://www.worldweatherattribution.org/wp-content/uploads/NW-US-extreme-heat-2021-scientific-report-WWA.pdf.

Sarah B. Henderson, PhD, Kathleen E. McLean, MPH, Michael J. Lee, PhD, Tom Kosatsky, MD, MPH. Extreme heat events are public health emergencies. BCMJ, Vol. 63, No. 9, November, 2021, Page(s) 366-367 - BC Centre for Disease Control.

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