Expert Commentary

Integrated assessment of black carbon and tropospheric ozone

Report by the U.N. Environment Program and World Meteorological Organization on the impact of black carbon and other substances on the climate and health.

Efforts to limit climate change generally focus on reducing carbon dioxide emissions caused by burning fossil fuels. However, another byproduct of fossil fuel combustion is black carbon, a major component of soot. Sources include diesel truck and car engines as well as wood fires, kilns, and stoves. Particles of black carbon in the atmosphere absorb sunlight and can have significant effects on the temperature, as do ozone, methane and other chemicals.

A report jointly authored by the United Nations Environment Program and World Meteorological Organization, “Integrated Assessment of Black Carbon and Tropospheric Ozone,” analyzed the impact of black carbon and other substances on the atmosphere and modeled predictions for the difference that emissions reduction would have on climate and population health.

The report’s findings include:

  • Reducing black carbon and tropospheric ozone will slow the rate of climate change within the first half of this century. Emissions standards for black carbon alone could trim 0.5°C off global temperatures.
  • Measures targeting “short-lived climate forcers” such as methane, black carbon and ozone could immediately reduce impacts on public health, water and food security. Black carbon particles contribute to the loss of 50 million tons of crops annually and may lead to as many as 2.5 million premature human deaths a year.
  • Even small-scale projects can help significantly reduce black carbon emissions. For example, modifying the design of brick kilns used in Mexico can increase their efficiency by 50% while reducing black carbon emissions by 80%.

While reducing black carbon emissions must be part of the effort to reduce climate change, the authors state that “this assessment does not in any way suggest postponing immediate and aggressive global action on anthropogenic greenhouse gases.” In addition, they note that “the costs and benefits of the identified measures are region specific, and implementation often faces financial, regulatory and institutional barriers.”

Keywords: carbon, global warming, greenhouse gases, fossil fuels, coal, pollution, medicine