Living Under a Heat Dome
July 21, 2020
A heat dome occurs when the atmosphere traps hot air like a cap. Essentially, the hot air gets compressed as it nears the ground, resulting in a perpetuating atmospheric cap across the landscape. The effects of it are even more intense in urban settings that lack adequate green cover. This is because asphalt and shingles tend to absorb, retain, and radiate solar energy, even at night, while greenery and vegetation (which is more prevalent in rural and suburban areas) tends to deflect it. This is called the urban heat island effect.
As a result of the urban heat island effect, paved surfaces can be significantly hotter than the air—up to 27-50°C hotter, in fact. Even at night, when the atmospheric temperature dips, large cities can be as much as 12°C warmer than surrounding non-urban areas as pavements and buildings release heat captured during the day. This means that when it is 25°C outside the city, it can be as hot as 37°C in the city. With climate change, many Canadian cities are in for an increased number of extremely hot days. Climate models project that between 2051-2080, urban centres will see at least four times as many days above 30°C than they have in the past. For example, Winnipeg currently experiences around 11 extreme heat days per year, and this is projected to increase to 47; Vancouver experiences only about one extreme heat day per year, and this is expected to jump to 13! These projections do not even take into account the urban heat island effect, which means the actual temperatures are likely to be even higher.
Economic marginalization, institutional racism, and uneven power structures result in low-income groups and communities of color being disproportionately located in urban heat islands. We know that low-income populations are predisposed to some health conditions, like asthma and cardiovascular disease, as a result of air pollution in their neighbourhoods. This makes them more vulnerable to the public health impacts of the heat dome. We also know that chronically ill people and seniors are more vulnerable to heat, and that Canada has an aging population, making this a key concern for a large demographic of Canadians.
Community and individual risk factors that can impact vulnerability to heat-related illnesses
Canadian provinces have already felt the public health impacts of extreme heat. In Montreal in 2019, public-health officials recorded around 6,000 ambulance calls and 66 heat-related deaths. Thanks to a good heat monitoring system, public health workers in Montreal were able to track heat deaths in real-time and manage the issue more efficiently than in other cities, such as Ottawa, where no heat-related deaths were even recorded. This is because heat stroke, which would be logged as a heat-related death, does not necessarily account for all heat-related deaths. Extreme heat heightens the risk of individuals dying from underlying medical conditions, such as heart disease. With most provinces not having proper protocols and systems in place, there is an undercounting of heat-related deaths. Most Canadians, especially vulnerable populations, aren’t aware of extreme humidity as a public health concern. Without proper protocols in place, heat-related deaths will only increase, as climate change leads to extended and more intense periods of extreme heat.
The impacts of the heat dome are further compounded by the COVID pandemic, for reasons such as:
- Increased homelessness and more people exposed to heat
- A larger population of low-income Canadians, such as those who are recently unemployed, may not be able to afford their utility bills
- Some public cooling stations, swimming pools, and some indoor air-conditioned spaces are closed, and people are encouraged to stay indoors
- The healthcare system is already stressed, and there are fewer protocols in place to monitor heat impacts
While many Canadians try to seek relief from the urban heat island effect with the use of air conditioning (AC), the overuse of AC in cities is actually exacerbating the problem of extreme heat in the long run. The waste heat from running AC actually increases outside temperatures, intensifying the heat island effect. It is estimated that air conditioner heat waste increases nighttime temperatures by as much as 1.5°C.
In addition, all this cooling requires a lot of electricity. A report by the International Energy Agency (IEA) shows that the use of AC and electric fans accounts for about 10% of all global electricity consumption today. Furthermore, as incomes and standards of living continue to improve in developing countries, the growth in AC demand in the hottest parts of the world is expected to soar. In fact, AC use is expected to be the second-largest source of global electricity demand growth after the industry sector and the strongest driver for demand growth in buildings by 2050. Without clean electricity, this growth will lead to an increase in emissions from electricity generation.
Lower-income populations and marginalized communities already have a higher energy burden – they spend a larger fraction of their income on energy bills than their wealthier neighbours do. They also tend to live in urban areas with little to no tree cover or green space, further raising temperatures. People experiencing low incomes are at an even higher risk of extreme heat due to poorer quality housing, limited access to AC, and the increased likelihood that they suffer from pre-existing health issues.
To mitigate the public health impacts of the heat dome, especially for the most vulnerable populations, we need active health surveillance, improved public awareness, and outreach to vulnerable areas to prevent heat-related deaths. We also need to invest in energy-efficient AC systems and nature-based solutions.
As the Montreal experience shows, healthcare surveillance and protocols for monitoring and dealing with heat-impacts are lacking in many cities. Health Canada advocates real-time surveillance of heat-health impacts, in-service training for public health staff, and offering education and training to heat-vulnerable groups. Toronto also has strategies in place to protect vulnerable populations from extreme heat, such as the Climate Change and Health Strategy for Toronto (2015), Toronto’s Hot Weather Response Plan, the Heat Relief Network, and work on heat vulnerability mapping. Employing these sorts of practices nationwide will lead to a more coordinated and harmonized approach to dealing with extreme heat.
Furthermore, nature-based solutions, like green roofs and tree planting, increase green cover and vegetation in urban areas to prevent the formation of urban heat islands. Public health professionals can also work to reduce urban heat islands by working with urban design professionals to make better land-use planning decisions, such as those that incorporate more green cover and include green spaces.
