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Soot is No. 2 global-warming culprit, study finds (+video)

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A study published last year suggested suggested that the use of kerosene lamps was also a significant source. Soot from the lamps contributes about 270 billion tons of soot a year to the atmosphere, representing about 7 percent of warming impact from all energy-related soot, according to the study published last November in the journal Environmental Science and Technology.

The new study estimates that in 2000, humans injected soot into the air at a pace of about 7.5 trillion tons a year globally.

Researchers describe the warming effect in terms of the amount of energy deposited on a patch of Earth one meter square. As of 2005, study notes, the accumulated direct and indirect effects of carbon-dioxide emissions since the dawn of the Industrial Revolution amounted to about 1.56 watts per square meter. Methane was No. 2 at 0.86 watts per square meter. The latest estimate for black-carbon soot now puts it's contribution to the energy warming the planet at 1.1 watts per square meter and perhaps as much as 2.1 watts per square meter.

The effects vary by region as well. Eastern and southern Asia, major sources for the soot, can experience a warming effect from soot 10 times higher than the global average, the researchers estimate. Soot falling on ice and snow in the Arctic has accelerated warming there by speeding the pace at which snow and ice melt during the long hours of summer sun.

Indeed, the mid to high latitudes of the northern hemisphere have seen some of the most pronounced effects of warming from soot, the study notes, because that's where most of the world's population lives.

Scientists also have linked high soot levels to shifts in the regional distribution and intensity of rainfall during Asian monsoons.

Initially, calls from some climate scientists during the past decade to focus first on reducing emissions of shorter-lived but powerful warming agents, such as methane or soot, have been met with polite nods and a resumption of heated debates over CO2 emissions. But the increasing recognition of the adverse health effects of soot, as well as the experience from efforts to control soot, are changing that, some researchers say.

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