Cutting soot emissions: Fastest, most economical way to slow global warming

Aug 31, 2011

A new study of dust-like particles of soot in the air — now emerging as the second most important -- but previously overlooked -- factor in global warming provides fresh evidence that reducing soot emissions from diesel engines and other sources could slow melting of sea ice in the Arctic faster and more economically than any other quick fix, a scientist reported here today.

In a presentation at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), Mark Z. Jacobson, Ph.D., cited concerns that continued melting of sea ice above the Arctic Circle will be a tipping point for the Earth's climate, a point of no return. That's because the ice, which reflects sunlight and heat back into space, would give way to darker water that absorbs heat and exacerbates warming. And there is no known way to make the sea refreeze in the short term.

Jacobson's calculations indicate that controlling could reduce warming above parts of the Arctic Circle by almost 3 degrees Fahrenheit within 15 years. That would virtually erase all of the warming that has occurred in the Arctic during the last 100 years.

"No other measure could have such an immediate effect," said Jacobson, who is with Stanford University. "Soot emissions are second only to carbon dioxide (CO2) in promoting global warming, but its effects have been underestimated in previous climate models. Consequently, soot's effect on climate change has not been adequately addressed in national and international global warming legislation. Soot emissions account for about 17 percent of , more than greenhouse gases like methane. Soot's contribution, however, could be reduced by 90 percent in 5-10 years with aggressive national and international policies."

Soot or "" consists of particles, nearly invisible on an individual basis, released in smoke from combustion of fossil fuels and biofuels. Major sources include exhaust from diesel cars, buses, trucks, ships, aircraft, agricultural machines, construction equipment and the wood/animal dung fires that hundreds of millions of people in developing countries use for used for cooking and heating. Black carbon particles become suspended in the atmosphere and absorb sunlight, just like a black t-shirt on a sunny day. The particles then radiate that heat back into the air around it. Black carbon also can absorb light reflected from Earth's surface, which helps make it such a potent warming agent.

The good news is that decreasing soot could have a rapid effect, Jacobson said. Unlike carbon dioxide, which remains in the atmosphere for years, soot disappears within a few weeks, so that there is no long-term reservoir with a continuing warming effect. And the technology for controlling black carbon, unlike that for controlling CO2, already is available at relatively modest cost. Diesel particulate filters, for instance, can remove soot from car and truck exhaust. Government and other agencies also are trying to introduce low-soot cookstoves in developing countries. "Converting gasoline- and diesel-burning cars and trucks to electric or hydrogen vehicles and reducing emissions from diesel generators could have an immediate effect on warming," according to Jacobson.

Jacobson, who developed the first detailed climate model to include the global effects of soot, reported on use of the model to gain new insights into the effects of soot trapped inside and between the water droplets that make up clouds. Previous research on black carbon and climate overlooked that topic. Jacobson said the information is important because black carbon within clouds makes the clouds "burn off" and disappear over heavily polluted urban and other areas. Climate models that ignore this "cloud absorption" phenomenon underestimate the effects of black carbon on climate.

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Callippo
1 / 5 (1) Aug 31, 2011
The soot and dust emissions are actually even more harmful, because they do cause the condensation of water wapor in small droplets, which are too small for being able to fall down in the form in rain. I don't think, the cutting of smog pollution could stop the global warming (in my theory the main source of global warming is geothermal) - but it could prohibit the worst consequence of global warming: the droughts and the lack of drinkable water sources.
sstritt
4 / 5 (4) Aug 31, 2011
Wasn't it just a few weeks ago that we were being told that were it not for the sooty emissions for most of the 20th century, global warming would have been worse?
Callippo
1 / 5 (1) Aug 31, 2011
Wasn't it just a few weeks ago that we were being told that were it not for the sooty emissions for most of the 20th century, global warming would have been worse?

You're completely right. The role of seeds to global temperature is much more complex, which is why I don't overestimate it too much. The particles can make more seeds for rains, which would cause, the atmosphere will get actually drier and less cloudy above the continents. In accordance with it it seems, the global warming correlates positively with droughts and with the absence of rains too. The droughts correspond the clean sky rather than cloudy sky.

On the other hand, the clouds can actually absorb more light, than they reflecting, thus contributing to the global warming instead. And for infrared portion of light the clouds aren't very reflective at all, because their droplets are smaller than the wavelength of infrared light.
emsquared
1 / 5 (1) Aug 31, 2011
Wasn't it just a few weeks ago that we were being told that were it not for the sooty emissions for most of the 20th century, global warming would have been worse?

No, I believe it was probably aerosols that you're thinking of. Most aerosols actually increase the albedo of the earth.

They're singling out black body carbon in this article as a contributor to warming.
hush1
5 / 5 (1) Sep 01, 2011
http://fabiusmaxi...erosols/

The title is astonishing:
"Aerosols (pollutants, like soot) as a driver of climate change"

The article's content is more astonishing - a premonition to Jacobson's paper.
GSwift7
3 / 5 (2) Sep 01, 2011
Don't get carried away. It's just one paper amongst many others and they don't all agree. This is one of the greatest areas of uncertainty.

to emsquared:

soot is one kind or aerosol. look it up. there are many kinds or aerosols. Some are dark and some are light in color. The size and composition are also important as well as what they are made of. It's complex. Soot from wood burning isn't a problem we can do much about, so kinda moot.
sstritt
1 / 5 (1) Sep 01, 2011
@hush1
Great link! Everyone should read this.

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