Contributor to Global Warming - Black Carbon

Author:  Liu Amy

Date:  April 2008

Researchers have found that black carbon pollution is now thought to surpass all greenhouse gases except carbon dioxide in its warming effect in the atmosphere. Scripps Institution of Oceanography at UC San Diego atmospheric scientist V. Ramanathan and University of Iowa chemical engineer Greg Carmichael have recently found that black carbon, or soot, which originates largely from biomass burning and diesel exhaust, contributes to global warming three to four times more than previously estimated.

In 2007, the UN-sponsored Intergovernmental Panel on Climate Change (IPCC) reported that black carbon pollution contributed 0.2 to 0.4 watts per squared meter to radiative forcing, or the atmospheric warming effect on the earth's surface. However, Ramanathan and Carmichael's study found that black carbon's actual radiative forcing contribution is 0.9 watts per squared meter, more than doubling previous estimates. Black carbon's contribution to radiative forcing was found to be more than that of any other greenhouse gas.

Ramanathan and Carmichael used data from satellites, aircraft, and surface instruments to study black carbon's effect on global warming. Unlike previous studies, they took into account black carbon's interactions with other aerosols, or fine solid or liquid droplets suspended in air. Aerosols come from sources such as sulfates, which are compounds released into the atmosphere through coal and oil burning. The interaction of black carbon with sulfates and other aerosols amplifies its warming effect, according to Ramanathan and Carmichael.

The problem of black carbon pollution is relatively easy to reverse, say Ramanathan and Carmichael. Black carbon stays in the atmosphere only for a few weeks, unlike greenhouse gases such as carbon dioxide, so reducing black carbon would diminish its warming effect on the atmosphere relatively quickly. Also, readily-available commercial products, such as smokeless cookers, contain technology capable of reducing black carbon emissions. A quarter or more of total black carbon in the atmosphere comes from China and India, where households often burn animal dung for cooking and coal for heating. Researchers like Ramanathan therefore support efforts such as Project Surya, a program which would provide smoke-free cookers to about 20,000 rural Indian households and allow researchers to study the cookers' effects on black carbon pollution reduction in the region.

According to Carmichael, emphasizing the relative ease of reversing black carbon pollution through available technologies would help increase public and political interest in black carbon emissions-reducing programs and therefore would help tackle global warming problems. "It offers a chance to get better traction for implementing strategies for reducing black carbon," he said.

Written by Amy Liu

Reviewed by Jess Kloss

Published by Pooja Ghatalia