How Does Black Carbon Change the Climate Debate? [ PDF ]

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Local Air Pollution and Human Health

Devra Davis, Climate Institute boardmember and author, When Smoke Ran Like Water

Much of the public discussion on climate change has been focused on long-term effects such as warmer temperatures, higher sea levels, extreme weather events, alterations in the ecology of infectious diseases, and radical changes in land use. However, what is frequently left out of the conversation is the fact that some of the same actions that reduce the long-term accumulation of greenhouse gases (GHG) can also yield powerful benefits to public health in the short-term by reducing the adverse effects of local air pollution. Decreasing fossil fuel combustion will reduce GHG emissions and simultaneously reduce associated co-pollutants that affect human health: black carbon is one such co-pollutant.

Black carbon, as a component of soot, can constitute a major component of air pollution as either an aerosol or suspended particulate matter. Found in both indoor and outdoor air pollution, black carbon can have a variety of negative impacts on human health. Worldwide, three billion people rely on traditional cooking and heating methods, which comprise the main source of indoor air pollution that typically includes black carbon as a major component. The WHO estimates that as a result of indoor air pollution, 1.9 million people die each year. The great majority of deaths from this pollution, some 85%, occurs in women and children. Overall, more than half of the burden from air pollution on human health is borne by people in developing countries as a result of traditional cooking or heating methods in the home. In addition, citizens in these regions usually lack access to cleaner technologies in industry and transportation, two sectors that contribute the most black carbon to outdoor air pollution.

Scientists have long understood that the size of particles is directly linked to their potential for causing health problems: smaller particles less than 10 micrometers in diameter pose the greatest problems because they can infiltrate deep into the lungs. Those particles that are small enough to slip through the cell wall can enter the blood stream. In many cities, the average annual levels of particulate matter (PM) 10 exceed 70 micrograms per cubic meter, though guidelines say that to prevent ill health, those levels should be lower than 20 micrograms per cubic meter. The extent to which an individual is harmed by air pollution usually depends on their total exposure to other damaging chemicals and their underlying nutritional status and health conditions. Thus both the duration of exposure and the concentration of the chemicals must be taken into account, along with underlying health status. Therefore, those who spend time in the home around traditional cook stoves and those who are consistently outside in heavily polluted cities will be the most affected by air pollution. The WHO estimates that by reducing PM10 pollution from 70 to 20 micrograms per cubic meter, we can cut air quality related deaths by around 15%, thereby preventing around 300,000 deaths annually. The smallest and most dangerous particles are emitted from fires that produce soot, as well as industrial and transportation emissions from diesel exhausts.

If fossil fuel combustion and its contributions to climate change are avoided, then related air-quality shifts, such as rising ozone air pollution from higher temperatures, can also be avoided. There are hundreds of reports from developed and developing countries consistently showing that short- and long-term exposures to current air pollution levels of particulate matter and ozone negatively affect death rates, hospitalizations and medical visits, complications of asthma and bronchitis, days of work lost, restricted-activity days, and a variety of measures of lung damage in children and adults.

A total of 2.3 million people die each year from respiratory infections, lung cancer, and cardiopulmonary disease attributable to air pollution. Nearly 665,000 of those deaths alone are caused by smoke from solid fuel use, a major component of which is black carbon.
Indoor and outdoor air quality are two of the main environmental factors contributing to acute and chronic lower respiratory infections. Estimates have shown that 36% of lower respiratory infections worldwide were attributable to solid fuel use alone, and 1% of all respiratory infections to outdoor air pollution. For upper respiratory infections, 24% in developing countries were attributable to environmental risk factors including outdoor and indoor air pollution, and globally 1.5 million deaths occur annually from respiratory infections that are attributable to the environment.

Lung cancer causes the largest disease burden of all cancers globally, or about 15% of the burden of all cancers: about 5% of the disease burden of lung cancer is attributed to outdoor air pollution, and 1% to exposure to indoor smoke from solid fuels. In the U.S. the American Cancer Society found that persons living in more polluted areas of the country who are not smokers had a 30% increased risk of developing lung cancer.

One WHO estimate holds that exposure to outdoor air pollution accounted for approximately 2% of the global cardiopulmonary disease burden. Furthermore, exposures to indoor smoke from solid fuels accounted for 22% of the burden of global chronic obstructive pulmonary disease (COPD), a slowly progressing disease characterized by a gradual loss of lung function. Outdoor air pollution accounted for 3% of cardiopulmonary mortality. It is interesting to note that the attributable fractions of COPD risk factors vary greatly among countries and by gender: in countries where solid fuel is widely used in homes for cooking or heating, indoor smoke levels can be high, and mean attributable fractions often exceeded 40%, with higher values for women than for men.

The costs of air pollution in terms of human health are very high: healthcare costs, lost productivity, and human welfare impacts cost billions of dollars each year. It is therefore advisable that countries with high black carbon emissions work to reduce them to improve both indoor and outdoor air quality, and as a result improve the health of their populations. New technologies could have beneficial effects for energy efficiency, reducing the energy intensity and possibly energy use, as well as for human health and related health costs.

These largely unappreciated air pollution reduction-related health benefits could be a strong motivator for GHG mitigation action, especially in developing countries that emit much of the world’s black carbon. The challenge to the policy-making community will be to forge specific practical strategies to encourage the funding and adoption of more efficient, less polluting technologies. If the substantial public health impacts of reducing air pollution associated with GHGs become more widely recognized, their full economic and social impact can be better integrated into discussions of climate policy. Thus, active consideration of public health issues could prompt a major rethinking of the climate debate and help break the present impasse.

Autumn 2009 Climate Alert

How Does Black Carbon Change the Climate Debate? [ PDF ]

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