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Study Says Soot a Source of Global Warming

Trucks do it. Tractors do it. Fireplaces do it. Forest fires do it. They all contribute to the amount of soot in the air – and a recent study suggests that soot may be a major contributor to the global warming problem. According to the study, soot may be the second biggest contributor to global warming - just behind the infamous greenhouse gas, carbon dioxide.

“Soot - or black carbon - may be responsible for 15 to 30 percent of global warming, yet it’s not even considered in any of the discussions about controlling climate change,” says Stanford University Professor Mark Z. Jacobson, author of the study. Human beings produce most of the soot particles that pollute the atmosphere, observes Jacobson, an assistant professor of civil and environmental engineering.

“Soot consists primarily of elemental carbon,” he says, “and 90 percent of it comes from the consumption of fossil fuels - particularly diesel fuel, coal, jet fuel, natural gas and kerosene - as well as the burning of wood and other biomass when land is cleared.” A reduction in worldwide soot emissions, he maintains, could prove beneficial in slowing down the disastrous pace of global warming.

Jacobson’s findings came on the heels of a report by the United Nations Intergovernmental Panel on Climate Control (IPCC), an organization made up of hundreds of scientists from around the world. In its most dire forecast to date, the IPCC predicted that, by the end of the century, the average surface temperature of the Earth could increase by 10.4 degrees Fahrenheit, with catastrophic results - melted glaciers, flooded shorelines and long periods of drought that persist for hundreds of years.

The IPCC report pins most of the blame for global warming on human-produced greenhouse gases such as carbon dioxide and methane, which also are byproducts of fossil fuel burning. But according to IPCC scientists, atmospheric soot has relatively little effect on world climate. Jacobson disagrees.

“Only a handful of studies have considered the impact of soot on global warming,” he says, “and most of those were based on the premise that soot never mixes with other particles in the atmosphere.”

But scientists have known for many years that floating soot particles actually do combine with dust and chemicals in the air, notes Jacobson. This is a crucial point, he says, because mixtures containing black carbon absorb more sunlight and radiate twice as much heat as do particles of pure black carbon. Therefore, soot in its mixed state has the potential to make a significant contribution to global warming.

“These black carbon mixtures turn out to be one of the most important components of global warming,” says Jacobson, “perhaps second only to CO2.”

Equally surprising was the discovery in his research that soot may be responsible for more atmospheric heating than methane - another significant greenhouse gas.

“Besides its impact on global warming, soot is bad for your health,” adds Jacobson, noting that soot exposure has been linked to respiratory illnesses and cancer.

“The World Health Organization reports that about 2.7 million people die each year from air pollution - 900,000 in cities and 1.8 million in rural areas. The largest source of mortality from air pollution is indoor burning of biomass and coal. “Reduction of such burning, therefore, will not only mitigate global warming but also will save lives and improve people’s health.”