5.4.1 Human health

Exposure to air pollution outdoors and indoors, temperature extremes, airborne pathogens and allergens, and ultraviolet radiation directly affect human health. The following focuses on air pollution effects due to anthropogenic emissions.

Air Pollution

Exposure to indoor and outdoor air pollution was responsible for 6 million (Global Burden of Disease [GBD] Risk Factor Collaborators 2017) to 7 million (WHO 2018) premature deaths in 2016. The GBD Study estimated that long-term exposure to ambient PM was responsible for between 3.6 and 4.6 millions of those premature deaths and between 95 and 118 million years of healthy life lost from heart disease, stroke, lung cancer, chronic lung disease and respiratory infections (Cohen et al. 2017; GBD Risk Factor Collaborators 2017; HEI 2018). Consequently, exposure to ambient PM2.5 is the highest environmental risk factor for the global burden of disease and sixth among all risk factors in terms of disability-adjusted life years lost, behind high blood pressure, smoking, low birth weight, high levels of blood sugar and high body mass index (GBD Cancer Collaboration 2017). The estimates of premature deaths underestimate the total number of individuals affected, because air pollution has potential effects on everyone who breathes the air, rather than being the sole reason for early death in a small subset of the population (Committee on the Medical Effects of Air Pollutants [COMEAP] 2010).

Even brief periods (minutes to hours) of exposure to high concentrations of pollutants can have significant health impacts (WHO 2006), and episodes of unusually high air pollution attract public concern (e.g. Vidal 2016; Safi 2017). However, the greatest damage to public health is associated with long-term exposure – living in areas of high annual average exposure (HEI 2017). Importantly, there is no known safe level of annual average PM2.5 exposure (WHO 2013).

About 43 per cent of the world’s population, primarily in lowincome countries, uses biomass for heating and cooking. The resulting indoor and outdoor air pollution contributes to acute lower respiratory infections (ALRTI) and pneumonia among children, and chronic obstructive pulmonary disease (COPD) and lung cancer among adults (WHO 2007; Sumpter and Chandramohan 2013; WHO 2018). The GBD Study attributed between 66 and 88 million disability-adjusted life years (DALYs) lost, and between 2.2 and 3.0 million premature deaths in 2016 to household air pollution (GBD Risk Factor Collaborators 2017), whereas WHO estimated the burden to be approximately 3.8 million premature deaths (WHO 2018).

An additional 0.09 to 0.38 million deaths in 2016 from chronic lung disease were attributed to ambient ground-level O3 exposure (GBD Risk Factor Collaborators 2017). Associations of mortality with other gases are well established, notably NO2 (a marker of traffic pollution) and SO2 (a marker of industrial pollution) (WHO 2013). Because these are markers of mixtures, it is unclear to what extent effects associated with them are caused by the gases themselves or by correlated pollutants (WHO 2013; COMEAP 2018).

The number of deaths attributable to air pollution varies widely among countries, reflecting different pollution levels as well as differences in population size, demographics, underlying rates of disease and other socioeconomic characteristics (Figure 5.14)

Figure 5.14: Deaths per 100,000 people in 2016 attributable to ambient PM2.5 air pollution; age-standardized data
Age standardization allows the estimates to be compared for countries with different age distributions. Note that these estimates do not include deaths attributable to exposure to household air pollution. Source: Adapted from HEI (2018).

Between 2010 and 2016, deaths attributable to ambient PM2.5 exposure increased by 11% per cent globally, due to increased air pollution, as well as growth and ageing of the population. In 2016, 95 per cent of the world’s population lived in areas with levels of PM2.5 exceeding the WHO air quality guideline (HEI 2018). While mortality attributable to PM2.5 has declined in Western Europe and North America, many other regions have seen sharp increases. Deaths attributable to ground-level O3, though much fewer, have increased nearly 60 per cent globally between 1990 and 2015, with increases in some countries as high as 250-400 per cent (HEI 2017).

In addition to premature mortality, air pollution contributes to a wide range of chronic and acute diseases, especially cardiovascular (Brook et al. 2010; McCracken et al. 2012) and respiratory disease (American Thoracic Society 2000). Studies suggest associations between air pollution and other diseases such as diabetes (Eze et al. 2015); adverse birth outcomes (Stieb et al. 2012; Li et al. 2017) including premature births, low birth weight (Fleischer et al. 2014) and birth defects (Farhi et al. 2014); and neurological ailments, including dementia (Calderon-Garciduenas and Villarreal-Rios 2017). Emerging research highlights the potential interactions between air pollution and airborne pathogens and allergens (Hussey et al. 2017; Liu et al. 2018).

People who are elderly, very young, with pre-existing cardiorespiratory diseases or of low socioeconomic status are most susceptible to air pollution (Sacks et al. 2011). Women and children have higher exposures to air pollution indoors, where cooking and heating with solid fuels is the major source (Smith et al. 2014). There is increasing evidence that indoor smoke contributes to cataracts, the leading cause of blindness worldwide (Clougherty 2010; Sacks et al. 2011; Global Alliance for Clean Cookstoves 2014; Villeneuve et al. 2015; WHO 2016b).

The economic impacts of life years lost, increased health care and lost worker productivity due to air pollution are considerable. Premature mortality due to ambient and household air pollution in 2013 was estimated to cost the world’s economy US$ 5.1 trillion in welfare losses (World Bank and Institute for Health Metrics and Evaluation 2016). This is equivalent to the 2013 gross domestic product (GDP) of Japan. WHO (2015) estimated that air pollution in Europe in 2010 cost US$ 1.575 trillion per year. In 2011, the US EPA estimated emission controls implemented as a result of the 1990 Clean Air Act Amendments avoided US$ 1.3 trillion in damages in 2010 (US EPA 2011). The impact of PM2.5 air pollution on the labour force in China in 2007 was estimated to create economic losses of 346 billion yuan (approximately 1.1 per cent of GDP) (Xia et al. 2016). A recent OECD analysis estimated the combined cost of ambient and household air pollution in Africa to be US$ 450 billion in 2013 (Roy 2016).

Asia had the highest absolute number of deaths in 2016 attributable to PM2.5 exposure, due to its large populations and high levels of industrial activity. However, PM2.5 exposures have begun to decline in China but are increasing in parts of South Asia (HEI 2018). Asian countries also bear the largest burden of air pollution caused by the production of goods consumed in other regions of the world, primarily Western Europe and North America. For example, 97 per cent of PM2.5 related deaths in East Asia were associated with emissions in East Asia, but only 80 per cent were associated with goods or services consumed in East Asia. Consumption in Europe and Russia and in North America of goods made in East Asia were estimated to contribute 7 per cent and 6 per cent, respectively, to the PM2.5 mortality burden in East Asia (Zhang et al. 2017) (Figure 5.15).

Figure 5.15: Percentage of PM2.5 related deaths in a region indicated by the column due to (a) emissions produced or (b) goods and services consumed in the region indicated by the row
China and
East Asia
India and
Rest of
Middle East
and North
Sub Saharan
Africa and
Rest of
 Where air
pollution was
China and East Asia 97% 3% 1% 1% 2% 1% 0%
India and Rest of Asia 1% 93% 1% 2% 0% 0% 2%
Europe and Russia 1% 0% 94% 18% 1% 0% 1%
Middle East and North Africa 0% 3% 2% 78% 0% 0% 5%
North America 0% 0% 1% 1% 95% 2% 0%
Latin America 0% 0% 0% 0% 1% 97% 0%
Sub Saharan Africa and Rest of World 0% 0% 0% 0% 0% 0% 93%
goods were
China and East Asia 80% 4% 3% 3% 6% 4% 2%
India and Rest of Asia 3% 84% 2% 3% 1% 1% 2%
Europe and Russia 7% 4% 86% 24% 5% 6% 4%
Middle East and North
2% 3% 4% 64% 2% 1% 4%
North America 6% 3% 3% 4% 82% 12% 2%
Latin America 1% 0% 1% 1% 4% 75% 1%
Sub Saharan Africa
and rest of World
1% 1% 1% 1% 1% 1% 84%
Source: Based on Zhang et al. (2017).

Stratospheric ozone depletion

The health risks of stratospheric O3 depletion occur as a result of increased levels of biologically damaging wavelengths of UV radiation reaching the Earth’s surface. Although some exposure to UV is necessary, too much exposure damages the skin and eyes and can cause immune suppression. Impacts include sunburn, keratinocyte (previously called non-melanoma) cancers, cutaneous malignant melanoma (CMM), Merkel cell carcinoma, photoconjunctivitis. photokeratitis (e.g. snow blindness), cataracts, pterygium and conjunctival melanoma.

In recent decades, most countries with predominantly fairskinned populations have experienced a steady increase in the incidence rates of CMM which is responsible for about 80 per cent of the deaths due to skin cancer (Lucas et al. 2015). Excessive exposure to UV radiation accounts for 60-90 per cent of the risk for CMM (Olsen, Carroll and Whiteman 2010; WHO 2004). Increasing incidence rates of CMM and other UV-related adverse health impacts are unlikely to be due to changes in UV exposure due to stratospheric O3 depletion, but rather to increases in risky sun exposure behaviour (Lucas et al. 2015). However, without the Montreal Protocol, incidence of skin cancer may have been 14 per cent greater, affecting 2 million people by 2030 (van Dijk et al. 2013).

Climate change

Over the coming decades to centuries, adverse health effects from climate change are forecast to greatly exceed any potential health benefits (Smith et al. 2014; Watts et al. 2017). The effects of climate change on human health can be classified as direct (e.g. heat waves, storms), less direct (e.g. changes in disease-vector ecology, reductions in water supply, or exacerbation of air pollution episodes) and diffuse (Butler 2014; Melillo, Richmond and Yohe 2014). The category of diffuse effects could have the largest burden of disease through means such as conflict (Kelley et al. 2015), migration (Piguet, Pecoud and de Guchteneire eds. 2011) and famine. Mental health effects arise from all three categories (e.g. posttraumatic stress disorder).

The health impacts of a changing climate will be inequitably distributed globally. Climate change and increasing climate variability “worsen existing poverty, exacerbate inequalities, and trigger both new vulnerabilities and some opportunities for individuals and communities” (IPCC 2014, p. 796).

Buildings and roads retain heat more than rural landscapes and depress humidity, creating urban heat islands. In northern mid-latitudes and subtropics, nights are up to 4°C warmer and 10-15 per cent drier in urban areas compared with surrounding rural areas. In northern Africa, the number of nights with exceptional heat stress is around ten times higher in urban areas than in rural areas (Fischer, Oleson and Lawrence 2012).