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Miloud Belhachemi, right, a construction worker who is building a tramway, pours a bottle of water on his head as temperatures soar to 36C (96.8F), in Marseille southern France, Thursday, July 27, 2006.CLAUDE PARIS/The Associated Press

This is part of a series examining the health repercussions for Canadians of a changing climate. Today's subject: Extreme heat.

The latest report from the Intergovernmental Panel on Climate Change predicts substantial increases in occurrences of extremely hot seasons throughout North America in early, middle and late 21st century.

Julien Weber didn't realize it was a "life or death" situation for his grandmother during the summer of 2003, when a severe, weeks-long heat wave swept through Europe. The 81-year-old lived alone in a small house in the Alsace region of France, where temperatures are not generally hot enough to warrant having air conditioning. Despite their invitations that she stay with them that summer, his grandmother chose to remain on her own. Had the family known that more than 35,000 people across Europe would perish from the heat, they might have insisted.

Before the heat wave, Weber's grandmother was a "quick thinker," he explained, but by the end of the summer, she was noticeably slower, sometimes taking 10 to 15 seconds to answer a question. She never regained her sharpness or her health.

In Toronto alone, an estimated 120 people a year die from extreme heat, which is known as a "silent" killer because it's not a visible threat like fires and floods. Peter Berry, a senior policy analyst with Health Canada, says extreme heat is a "significant risk" to Canadians and especially to seniors, young children and people with chronic illness. Even healthy people can suffer from heat stroke, heat exhaustion, cramps and edema (swelling).

Heath Canada describes extreme heat as the potential for hot weather conditions to result in an unacceptable level of health effects, including increased mortality. Clean Air Partnership, a non-profit that addresses climate-change issues, says maximum temperatures in Toronto are expected to rise 7 C over the next 30 to 40 years and a fivefold increase in extreme heat events is predicted over the same time period.

"This is major," said CAP deputy director Kevin Behan, adding that by 2040, Toronto may jump from having one heat wave every other year, on average, to two or three heat waves each year.

"Looking forward, everywhere is going to get hotter in Canada," said Ewa Jackson, director of ICLEI – Local Governments for Sustainability, an organization that works with about 250 Canadian municipalities. "It's just a matter of how much of that will be in the form of extreme heat – more intense heat for longer periods of time versus just average increases."

In 2009, Health Canada worked with four pilot communities to develop heat-alert and response programs. Windsor, Ont., is expected to be particularly hard hit. Its program includes information about heat alerts and where people can access pools and public cooling centres. Karina Richters, the city's environmental co-ordinator, said developing consistent heat-alert messaging with their Michigan neighbours was essential "because a lot of our population gets their weather information from the city of Detroit."

A key aspect of extreme-heat planning is identifying vulnerable populations – older people, people in lower income groups who may not have the means to cool themselves and immigrant populations who may not understand English heat-alert messaging. Another critical component is vulnerability mapping – identifying areas that are most susceptible to the urban heat-island effect, the increase in temperature caused by concrete, building materials and a lack of vegetation. That information is then used to develop response plans and determine the locations of cooling centres.

But Jackson said adapting to extreme heat isn't as simple as installing air conditioning in homes and public spaces. Too often, the way we respond to extreme heat actually increases our emissions, she says. "People turn on their air conditioners more and then you have brownouts. It's a true Pandora's box: It's hot, but then all these other things could happen because it is hot."

Of particular concern are people with mobility issues living in high-rises – what happens if the elevator stops working?

"If you're living on the 20th floor and you're an 80-year-old person … it's a real difficulty," she says. "You can't pump water past the sixth floor of a high-rise if there's an electrical failure. So people are stuck without water [and] it's the middle of a heat wave."

(During Toronto's 2013 ice storm, thousands of homes and residential buildings lost power and some people were unable to leave their apartments due to mobility or other issues.)

Long-term care facilities have to take special precautions to protect their aging residents. Although many provinces have temperature-range guidelines for these facilities, with 22 C the most common cutoff point at which some kind of cooling protocol is required, there doesn't appear to be a standardized, nationwide regulation on when air conditioning is required.

Donna Rubin of the Ontario Association of Non-Profit Homes and Services for Seniors said most of their facilities have air conditioning, but there's still a "chunk of homes" that do not, though they all have to have protocols for dealing with extreme heat.

While air conditioning, which increases greenhouse-gas emissions, may be a necessary short-term solution, long-term measures include increasing urban green spaces. Planting trees lessens the effects of climate warming and is also a way of dealing with extreme heat when it happens, Jackson explained. "I much prefer to stand in a park under a tree than in a parking lot if it's really hot."

Richters says the city of Windsor has identified urban "hot spots" and will prioritize tree planting in these areas. It is also looking at retrofitting buildings with white roofs that help reflect heat. Green roofs, though more expensive, are also being considered.

Peter Berry said Health Canada's pilot program in Fredericton was completed and its project in Winnipeg and the Assiniboine region of Manitoba was adopted by the entire province. And, as Health Canada continues its work with provincial and local groups across the country, more municipalities are developing plans.

Vancouver moved to adopt extreme-heat measures in 2010 following the death of a homeless person from heat exhaustion, and Montreal developed its plan more than a decade ago. Toronto has completed vulnerability mapping but is still in the process of developing its response plan, due out in June.

Though ICLEI is working with Calgary on climate-change adaptation, Jackson says the city is still reeling from last June's flood and planning for extreme heat isn't a priority.

"The public is really reactive," Jackson says. "Then a major weather event happens and suddenly everyone wants to know what the city is doing."