Even moderate temperature changes can lead to death


3 Feb 2016

Extreme hot and cold temperatures result in fatalities, but according to new research from Public Health Ontario (PHO) and the Institute for Clinical Evaluative Sciences (ICES), even moderate daily temperature changes are associated with increased deaths.

The study, Assessment of the effect of cold and hot temperatures on mortality in Ontario, Canada: a population-based study, is published in this week’s Canadian Medical Association Journal Open. Led by PHO environmental and occupational health scientists Dr. Hong Chen and Dr. Ray Copes, it found that even 5°C changes to daily temperatures in winter and summer were associated with more deaths in Ontario.

“The risk of extreme heat and extreme cold on health is well known,” says Chen, who is also an adjunct scientist at ICES. “However, we were surprised to find that even moderate changes in temperature had an impact on death rates in Ontario, with cold weather having a greater impact.”

These health impacts were seen even on winter days when average temperatures were 0°C and on summer days when temperatures were 23°C.

“This may be particularly important for homeless people and those who live in marginal housing,” notes Copes, PHO’s chief of environmental and occupational health. “We need to change our thinking about how temperature impacts health. There may be impacts even on days when temperatures are not considered extreme and no heat or cold alerts have been called."

Key findings:

  • In Ontario, each 5°C change in daily temperature was associated with approximately seven more non-accidental deaths per day in winter and about four more non-accidental deaths per day in summer.
  • Cold-related effects are more strongly linked to cardiovascular-related deaths, especially in people under 65 years of age; heat increased respiratory-related deaths.
  • Effects from cold lasted longer – over several days – compared to effects from heat, which were undetectable the day after exposure.
  • Using data provided by ICES, the researchers analyzed records of 352,818 Ontario residents who died from non-accidental causes from 1996-2010. The study was funded by Heath Canada.


Public Health Ontario is a Crown corporation dedicated to protecting and promoting the health of all Ontarians and reducing inequities in health. Public Health Ontario links public health practitioners, front-line health workers and researchers to the best scientific intelligence and knowledge from around the world. For the latest PHO news, follow us on Twitter: @publichealthON.

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Janet Wong


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Updated 3 Feb 2016