Your eyes aren't deceiving you: Skies are dimmer

Reply Fri 13 Mar, 2009 04:53 am
Growing pollution leads to "global dimming"

Fri Mar 13, 2009
By Will Dunham

WASHINGTON (Reuters) - Visibility on clear days has declined in much of the world since the 1970s thanks to a rise in airborne pollutants, scientists said on Thursday.

They described a "global dimming" in particular over south and east Asia, South America, Australia and Africa, while visibility remained relatively stable over North America and improved over Europe, the researchers said.

Aerosols, tiny particles or liquid droplets belched into the air by the burning of fossil fuels and other sources, are responsible for the dimming, the researchers said.

"Aerosols are going up over a lot of the world, especially Asia," Robert Dickinson of the University of Texas, one of the researchers, said in a telephone interview.

Dickinson and two University of Maryland researchers tracked measurements of visibility -- the distance someone can see on clear days -- taken from 1973 to 2007 at 3,250 meteorological stations worldwide.

Aerosols like soot, dust and sulfur dioxide particles all harmed visibility, they said in the journal Science.

The researchers used recent satellite data to confirm that the visibility measurements from the meteorological stations were a good indicator of aerosol concentrations in the air.

The aerosols from burning coal, industrial processes and the burning of tropical forests can influence the climate and be a detriment to health, the researchers said.

Other pollutants such as carbon dioxide and other so-called greenhouse gases are transparent and do not affect visibility.

The data will help researchers understand long-term changes in air pollution and how these are associated with climate change, said Kaicun Wang of the University of Maryland.

"This study provides basic information for future climate studies," Wang said in a telephone interview.

The scientists blamed increased industrial activity in places like China and India for some of the decreased visibility, while they said air quality regulations in Europe helped improve visibility there since the mid-1980s.

The aerosols can have variable cooling and heating effects on surface temperatures, reflecting light back into space and reducing solar radiation at the Earth's surface or absorbing solar radiation and heating the atmosphere, they added.

(Editing by Maggie Fox)
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Reply Fri 13 Mar, 2009 05:42 pm
@Walter Hinteler,
re walter's post :

They described a "global dimming" in particular over south and east Asia, South America, Australia and Africa, while visibility remained relatively stable over North America and improved over Europe, the researchers said.

i believe i read somewhere that some scientists are concerned about the air over europe becoming "too clean" , and not filtering out enough UV rays ?
if i recall correctly , it was expected that this "anomaly" would correct itself within a few years/decades ?
can airmasses really be that stable ?

i always assumed that the air all over the world was constantly shifting .

i know that at certain times of the year , air pollution from coal fired power stations in the southern U.S. moves all the way into northern canada .
we also have been effected by large forest fires in northern quebec when north-westerly winds have brought smoke all the way into eastern ontario and new york state .

i also recall that swedish authorities claimed that "exhaust" from the large nickle and copper smelters near sudbury/ northern-ontario drifted as far as sweden and caused their lakes to acidify .
(i know that the smokestacks at the smelters were fitted with "extensions" after a few years of operation to allow the exhaust "to punch" through the lower atmosphere and prevent the dirt and dust from falling on adjacent land around sudbury - apparently it worked very well - for a while .
all smokestacks have now been fitted with scrubbers and sudbury has truly become a "green community " . i remember driving up there in the 70's and there wasn't much in the way of grass , living trees etc. to be found within 30 miles of the smokestacks) .

any scientific explanation for these conflicting occurences ?

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Reply Fri 13 Mar, 2009 07:10 pm
There is a butterfly in Patagonia that keeps making a breeze in the U.S.
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Reply Fri 13 Mar, 2009 07:14 pm
Visible pollution, dimming the sky as it does, is the answer to global warming, such as it is. Not that we want to breathe the stuff, and it could lead to global cooling.
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