On November 9, 2010, the Environmental and Energy Study Institute (EESI) held a briefing on black carbon, a component of soot, a leading cause of mortality in the developing world, and a contributor to global climate change. The largest sources of black carbon emissions are diesel engines, residential heating and cooking, and open burning of agricultural lands and forests. Black carbon contributes to climate change in two basic ways: by absorbing sunlight in the atmosphere and, subsequently, by falling from the atmosphere onto snow and ice – causing these normally-reflective surfaces to absorb more heat and melt more quickly. Biomass burned in open fires and crude cooking stoves also leads to extremely high individual exposures to smoke – of which black carbon is a major component – and is a serious health threat for women and children in the developing world. This briefing provided an overview of how black carbon impacts public health and the climate (and how the effects vary regionally) as well as technologies, current initiatives, and potential policy opportunities to reduce these emissions from cookstoves, the transportation sector, and forestry and agriculture.
Black carbon is a significant contributor to climate change, and yet it remains in the atmosphere for only days at a time (compared to more than 100 years for carbon dioxide). According to the World Health Organization, indoor air pollution from burning solid fuel is responsible for 1.6 million deaths annually, and is one of the fourth worst overall health risk factors in poor countries. Many measures to reduce black carbon emissions have been called “no regrets” strategies due to their co-benefits for climate change mitigation and improved public health. In addition, some black carbon reduction strategies also reduce ozone precursors and methane, magnifying the health and climate benefits even further.
- The climate impacts of black carbon depend on the source and location of the emissions. Diesel emissions will cause warming, whereas wildfire smoke contains co-emissions (in addition to black carbon) that may contribute to a cooling effect. Any emissions sources located near the Arctic will contribute to warming because the black carbon deposits onto snow and ice, reducing the reflectivity of these surfaces.
- In all cases, reducing black carbon emissions will improve public health.
- Because black carbon stays in the atmosphere for only days or weeks, reducing these emissions has a much faster climate benefit compared to reducing greenhouse gas emissions (which can remain in the atmosphere for decades or centuries).
- In the Himalayan region, solar heating from black carbon at high elevations may be just as important as carbon dioxide in the melting of snowpacks and glaciers.
- Significant black carbon emissions from the open burning of forests or agricultural lands are reaching the Arctic. Some Arctic Council nations already ban agricultural burning, but more improvements (such as the implementation of no-burn or no-till methods) are needed.
- The Arctic Council, a consortium of eight Arctic countries, has established a task force on short-lived climate forcers that is working to develop recommendations on reducing black carbon emissions.
- Approximately six percent of global black carbon emissions come from the United States; more than half of those emissions come from diesel engines.
- Diesel exhaust (including all of its hazardous components, not just black carbon) poses seven times the lung cancer risk of all other air toxics tracked by the EPA combined.
- Diesel particulate filters can be installed in place of a tradition muffler to reduce particulate matter emissions from diesel engines by 90 percent. Every $1 spent on filters saves $12 in avoided health damages.
- Diesel particulate filters require the use of ultra-low sulfur diesel fuel, which is not available in all parts of the world.
- Retrofitting or replacing one million long haul trucks would be the equivalent of removing 21 million cars from the road, in terms of reducing the contribution to climate change.
- Indoor smoke from burning solid fuel is the fourth worst health risk factor in developing countries behind malnourishment, unsafe sex, and unsafe drinking water and sanitation. It causes 1.5 million premature deaths each year.
- There are advanced cookstoves on the market that can reduce black carbon emissions by 90-95 percent.
- The Global Alliance for Clean Cookstoves is a public-private partnership aiming to equip 100 million households with clean and efficient cookstoves by 2020.