carbon emissions

Is black carbon a climate change quick-fix?

U. ILLINOIS (US)—One immediate way to reduce the current levels of global warming—and avert rapid climate change—researchers say, would be to focus on pollutants with short atmospheric lifetimes, like soot, also known as black carbon.

Black carbon is composed of fine particles produced from the incomplete combustion of diesel fuel, wood, crop waste, and other biomass, oil, refuse, and, in some cases, coal.

Tami Bond, a civil and environmental engineer professor at the University of Illinois, says these particles absorb light and turn it into heat, whether they are suspended in air or darkening and melting snow.

“The good news is that we can shut off black carbon’s warming today, like flipping a switch,” Bond adds. “We can’t ignore our long-term problem—greenhouse gases, which will stay around for decades. But black carbon is washed out of the atmosphere within a couple of weeks, and its snow warming lasts about a season. If we stop emitting, this warming will stop too.”

During the climate talks in Copenhagen in December 2009, the major greenhouse gas-emitting countries agreed that significant action is required to keep the global average temperature under the threshold that will trigger irreversible phenomena from large-scale glacial and permafrost melting.

An increase of the global average temperature of more than 2 degrees Celsius (3.6 degrees Fahrenheit) would trigger the widespread release of methane from these melting regions, accelerating global warming and rising sea levels.

In recognition of this opportunity, one U.S. Congressional bill has directed the Environmental Protection Agency to study black carbon’s climate effects, and the Waxman-Markey energy bill contains provisions for reducing black carbon. Bond testified at a recent U.S. House of Representatives committee hearing called “Clearing the Smoke” that explored climate impacts and potential actions.

“Research on black carbon and climate has been going on for 25 years,” she says. Research on light-absorbing particles and climate started with nuclear winter studies in the early 1980s and was first summarized in international climate assessments in 2001.

Bond’s research team has developed a history of combustion technology to estimate emission trends between 1850 and 2000. In addition, the group looks at future emission trends.

“We can model how people, economy, and technology interact. We want to understand how quickly we can make these ‘switch-off’ changes and provide emission inputs to most of the global atmospheric models. While those models estimate climate impacts, our group tells them how much black carbon there is and where it comes from.”

Recognizing black carbon as a “climate quick-fix” to help sensitive regions like the Arctic is very recent.

“Diesel engines emit about one-quarter of global black carbon. Another quarter comes from primitive household cookers used in less-developed countries. Cleaner cooking would reduce indoor air pollution, which is responsible for 1.6 million annual deaths, primarily of women and young children.”

“History shows that clean air, not economic growth, drives black carbon emissions,” Bond says. “Emissions per kilogram of coal burned have decreased by 100-1000 times in the last 100 years. This happens when societies demand cleaner environments.

Although reducing black carbon is worthwhile, it isn’t straightforward.

“Along with absorbing particles, burning also emits reflective particles, which act like little mirrors. These other particles actually cool the Earth. We measure and model particles from individual sources to understand how absorption and reflection are balanced. Our work occurs both in the laboratory, where we can control combustion, and in the field, where we learn how people really behave.”

Some black carbon sources are better targets for mitigation than others.

“Trucks and off-road vehicles are mainly responsible for black carbon in industrialized countries,” she says.

According to the Department of State’s Bureau of Oceans and International Environmental and Scientific Affairs, U.S. standards for fine particle emissions from new highway diesel vehicles are reducing black carbon emissions from these engines by 90 percent or more. Similar emissions standards have been adopted for new off-road diesel engines, including locomotives, and thousands of older diesel vehicles have been retrofitted with particle filters.

“There have been very few measurements of engines in developing countries, so we joined forces with the World Bank and Asian Institute of Technology.”

Similarly, Bond and her colleagues set up low-cost emission measurements at a non-profit group that develops improved stoves for homes. They streamlined and commercialized the prototype we provided, and now they are training groups around the world.

“Changing millions of emitters involves millions of decisions. That’s a real challenge. It requires not only technology, but marketing, delivery, and smart policy mechanisms. When we model technology change, we consider feasibility. We intend to show exactly what will be required to make changes.”

In Copenhagen, the Obama Administration committed $5 million towards international cooperation to reduce black carbon emissions in and around the Arctic. The United States anticipates these funds will be matched by other nations to develop and implement mitigation efforts, which will help reduce Arctic warming while yielding significant direct public health and ecosystem benefits.

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