Prepared by Kim Perrotta, CHASE, April 2024
When working to influence policies and investments in local communities, it is useful to recognize the intersection between population health, health equity, and sustainability. Communication surveys indicate that people are more likely to support climate-related policies when they understand that those policies can produce immediate health benefits. In addition, when investments are being made in local communities to transition away from fossil fuels that are driving climate change, it is essential that consideration be given to how those investments can improve population health and reduce social inequities.
Greenspace Increases Climate Resiliency
Urban greenspace plays several important roles in our communities. Trees, plants, and grass can act as a sink for carbon dioxide, one of the greenhouse gases (GHGs) that is causing climate change. They can also reduce the risk of flooding by reducing storm water, improve air quality by absorbing or filtering certain air pollutants, and cool the air. [i]
Urban heat islands (UHIs) are communities or zones within communities that experience higher air temperatures than surrounding areas because they have more concrete and pavement and lower levels of vegetation. Many studies have demonstrated that a wide variety of urban greenspaces can cool and clean air at a site, neighbourhood, or city level. Trees, in particular, are strongly associated with reduced air temperatures and relief from heat stress at a street and neighbourhood scale. Studies have also found that dense, low-income neighbourhoods are more likely to be less green while also being home to populations that are more likely to suffer harm from extreme heat.[ii]
Extreme Heat Presents Significant Health Risks
Extreme heat presents significant health risks for people in Canada and those risks are increasing as a result of human-induced global warming. Extreme heat can produce relatively mild health impacts such as skin rashes and heat stress, but it can also aggravate cardiovascular and respiratory conditions, and increase emergency room visits and hospital admissions, and result in premature deaths. The heat dome that hit British Columbia in 2021 contributed to over 600 premature deaths.[iii] Extreme heat has also been associated with adverse reproductive outcomes such as miscarriages and congenital defects and increases in aggressive behaviour and violent and non-violent crimes.[iv]/[v]
The scale of heat-related impacts depends on the temperature, duration, and timing of the heat-related event, the degree to which the population is acclimatized to the temperature, and the resilience of the community. Even small differences in temperature from seasonal averages can be associated with an increase in adverse health impacts and death.[vi]
Extreme Health Presents Greater Risks for Some
When the humidex reaches or exceeds 30, everyone is at increased risk for heat-related illnesses and deaths. Some populations, such as very young children, older adults, and people with pre-existing health conditions, are more sensitive to heat. Other populations, such as outdoor workers, athletes who train outdoors, and those who do not have homes, are at greater risk from extreme heat because they have greater exposure to it or are more active in it.[vii]
People who experience social or economic disadvantages can be at increased risk as well because the stresses in their lives can make them more sensitive to heat and because they can experience greater exposures to it. During the BC heat dome, for example, deaths in the community were more than four time greater than normal with much higher death rates among people who live on low incomes, in homes without air conditioners, and in neighbourhoods with lower levels of greenness.[viii]
Greenspace Improves Health and Health Equity
A 2015 systematic review of studies on the impact of greenspace on health, found that greenspace was associated with decreased stress, healthier births, and a decrease in premature deaths from all causes. It suggested that children who live near parks and playgrounds have healthier weights, improved cognitive function, fewer symptoms of attention-deficit and hyperactivity disorder (ADHD), and reduced levels of stress. That review concluded that, while all members of a community benefit from exposure to greenspace, children and people who live on low incomes appear to benefit the most.[ix]
Greenspace Fosters Physical activity and Metabolic Health
A 2021 review of studies that examined greenspace’s impact on physical activity and metabolic disorders concluded that greenspace increases physical activity and decreases rates of obesity, diabetes, and other chronic health conditions.[x] For example, a 2022 study conducted in Metro Vancouver and Fraser Valley found that park availability was associated with lower rates of diabetes and obesity, higher rates of leisure walking, and increased levels of moderate to vigorous physical activity.[xi]
Greenness Improves Birth Outcomes
A 2022 study adds weight to the suggestion that residential greenness contributes to healthier pregnancies in all women. Using data from 2.2 million livebirths from Canadian cities, this study found that mothers who live in greener areas have a reduced risk of giving birth to small babies or babies with low birth weight regardless of the social or economic circumstances of their neighbourhoods. These associations held when corrected for air pollution.[xii]
Greenness Improves Mental Health and Health Equity
A 2022 Canadian study strengthens the suggestion that urban greenness produces mental health benefits and reduces health inequities. This study included data for nearly 27,000 residents, 45 to 86 years of age, who live in urban areas, with measures of greenness within 500 metres of their homes, and three self-reported measures of mental health. It found that: residents’ perceptions of their mental health were more favourable for those who lived in greener areas; perceptions of depression decreased as neighbourhood greenness increased; the positive response to greenness was consistent across all age-groups, races, and sexes; and the strongest association between the beneficial impacts of greenness on mental health were among those living on lower incomes.[xiii]
Greenness Reduces Premature Deaths
A long-term study conducted in Canada affirmed the view that greenspace can reduce premature deaths. The study followed 1.3 million healthy, non-immigrant adults from 30 large urban centres across Canada from 2001 to 2011. This study found a significant decrease in the risk of premature deaths with increased greenness around the homes of participants in the study. The risk of premature death from six common causes each decreased by 8 to 12%. This reduced risk was found with greenness within both 250 and 500 metres of peoples’ homes.[xiv]
Greenspace Not Equitably Distributed
A 2020 study that examined the relationship between neighbourhood walkability, air pollution, and greenness across different socio-economic conditions in Vancouver, Toronto and Montreal, found that less deprived neighbourhoods were more likely to be highly walkable, have lower levels of air pollution, and have higher levels of greenness, while highly deprived areas were more likely to be less walkable, have higher levels of air pollution, and lower levels of greenness. The researchers concluded that inequitable access to greenness increases the risks to health from extreme heat events and discourages physical activity among materially deprived populations.[xv]
Urban Trees Not Equitably Distributed
A 2020 scoping review that focused on the health outcomes associated specifically with urban trees found that urban trees are positively associated with physical activity, weight management, mental health, reduced stress, healthy birth outcomes, and reduced indicators for chronic diseases. It affirmed that there are disparities in the distribution of trees with greater tree coverage in higher-income neighbourhoods.[xvi]
Quantifying the Health Benefits of Trees
One study conducted in Toronto focused on identifying and quantifying the health benefits specific to trees alone. It found that people who live in neighbourhoods with a higher density of trees on their streets are significantly more likely to report better health and to have fewer cardio-metabolic conditions such as cardiovascular disease or diabetes. The study team estimated that having 11 more street trees on a city block is equivalent to have a $20,000 increase in income in terms of the impact on cardio-metabolic health.[xvii]
Policies to Promote
- Greater investments in parks, greenspace, and trees in urban centres
- Prioritize low-income neighbourhoods and urban heat islands for de-paving, tree planting, and investments in parks and greening
To learn more, see the report and blog produced by CHASE with the CPHA and OPHA:
- Report: Climate Change, Population Health and Health Equity: Public Health Strategies and Five Local Climate Solutions that Produce Health and Health Equity Benefits
- Blog: Bringing Health and Health Equity into Natural Heritage in Peel Region.
[i] Zupancic et al. 2015. The impact of green space on heat and air pollution in urban communities: A meta-narrative systematic review. David Suzuki Foundation.
[ii] Zupancic et al. 2015. The impact of green space on heat and air pollution in urban communities: A meta-narrative systematic review. David Suzuki Foundation.
[iii] Chief Coroner of British Columbia. 2022. Extreme Heat and Human Mortality: A Review of Heat-Related Deaths in B.C. in Summer 2021
[iv] Auger et al., 2014; Auger et al., 2017d; Auger et al., 2017b; Auger et al., 2017c as cited by Health Canada. 2022. Health of Canadians in a Changing Climate – Advancing our Knowledge for Action.
[v]Health Canada. 2022. Health of Canadians in a Changing Climate – Advancing our Knowledge for Action. (Mares, 2013; Ranson, 2014)
[vi] World Health Organization. 2018. Heat and Health.
[vii] https://climatedata.ca/resource/heat-waves-and-climate-change/
[viii] Henderson SB et al. 2022. Analysis of community deaths during the catastrophic 2021 heat dome, EnvironmentalEpidemiology: Vol 6, No1
[ix] Zupancic T et al. 2015. Green City: Why Nature Matters to Health: An Evidence Review. Toronto Public Health.
[x] De la Fuente F et al. 2021. Green Space Exposure Association with Type 2 Diabetes Mellitus, Physical Activity, and Obesity: A Systematic Review. Int. J. Environ. Res. Public Health. Vol 18
[xi] Frank Lawrence et al. 2022. Chronic disease and where you live: Built and natural environment relationships with physical activity, obesity, and diabetes. Environment International. 158
[xii] Villeneuve Paul et al. 2022. Residential proximity to greenness and adverse birth outcomesin urban areas: Findings from a national Canadian population-based study. Environmental Research. Vol 204. March.
[xiii] Cottagiri SA Villeneuve P et al. 2022. Increased urban greenness associated with improved mental health among middle-aged and older adults of the Canadian Longitudinal Study on Aging (CLSA). Environmental Research. Volume 206.
[xiv] Crouse DL et al. 2017. Urban greenness and mortality in Canada’s largest cities: a national cohort study. The Lancet Planetary Health, Volume 1, Issue 7.