March 15, 2009
Global Dimming Caused By Rising Aerosol Pollution

Rapid economic growth has driven up emissions of aerosols so much that the amount of light hitting the surface has declined globally. I really hate pollution.

COLLEGE PARK, Md -- A University of Maryland-led team has compiled the first decades-long database of aerosol measurements over land, making possible new research into how air pollution changes affect climate change.

Using this new database, the researchers show that clear sky visibility over land has decreased globally over the past 30 years, indicative of increases in aerosols, or airborne pollution. Their findings are published in the March 13 issue of Science.

"Creation of this database is a big step forward for researching long-term changes in air pollution and correlating these with climate change," said Kaicun Wang, assistant research scientist in the University of Maryland's department of geography and lead author of the paper. "And it is the first time we have gotten global long-term aerosol information over land to go with information already available on aerosol measurements over the world's oceans."

Different aerosols have different effects on temperatures. Black soot aerosols will absorb more sunlight and reduce the amount of light that reflects back into space. Therefore they should cause warming. Whereas sulfur aerosols will cause cooling. The effects of these aerosols are troubling because they have much shorter half-lives than CO2. Once Asian countries become advanced enough to want to clean up their air they'll cut back on aerosols emissions and very quickly the effect these aerosols have on climate will end. Maybe the aerosols are canceling out some of the effects of CO2. We'll find out eventually.

But the sun is shining brighter in Europe.

According to the authors, a preliminary analysis of the database measurements shows a steady increase in aerosols over the period from 1973 to 2007. Increased aerosols in the atmosphere block solar radiation from the earth's surface, and have thus caused a net "global dimming." The only region that does not show an increase in aerosols is Europe, which has actually experienced a "global brightening," the authors say.

The largest known source of increased aerosols is increased burning of fossil fuels. And a major product of fossil fuel combustion is sulfur dioxide. Thus, the team notes, that their finding of a steady increase in aerosols in recent decades, also suggests an increase in sulfate aerosols. This differs from studies recently cited by the Intergovernmental Panel Climate Change showing global emissions of sulfate aerosol decreased between 1980 and 2000.

I am surprised that in this database the US doesn't show a decline in aerosols given US emissions regulations. The shift toward use of Western US coal was driven in large part by emissions regulations to cut sulfur emissions. The Western coal is lower in sulfur than Eastern coal.

Share |      Randall Parker, 2009 March 15 10:03 PM  Pollution Trends

Pollution said at March 16, 2009 6:07 AM:

For the first time, a large study shows the deadly effects of chronic exposure to ozone, one of the most widespread pollutants in the world and a key component of smog, according to a study in today’s New England Journal of Medicine.

Doctors have long known that ground-level ozone — which is formed when sunlight interacts with pollution from tailpipes and coal-burning power plants — can make asthma worse. This study, which followed nearly 450,000 Americans in 96 metropolitan areas for two decades, also shows that ozone increases deaths from respiratory diseases.

Bob Badour said at March 16, 2009 7:14 AM:

Brighter in Europe? Something smells fishy in Denmark. Don't the Europeans burn a lot more diesel? Doesn't that release a lot more particulate pollution?

JoeKing said at March 16, 2009 8:17 AM:


Will you be so kind as to explain the conradiction between your statement & EPA's... "Between 1975 & 2006 8-hr ozone exceedance days declines >85%, while 1-hr exceedance days declined >95%", yet at the same time hospital emittances for asthma increased. Studies have actually shown a slight "decrease" in school absenses as ozone levels INCREASED...

Do you accept the possibility of any other causal factors?

As air pollution becomes less & less of an issue organizations like the Amer. Lung Assoc. have to resort to cherry-picking statistics, distortions of studies, & outright lies to justify their existances (& continued funding). "Global Dimming" studies are another manifestation. The air pollution "problem" was solved 20 years ago...we have long since passed the point of diminishing returns.

b said at March 16, 2009 9:06 AM:

I am surprised that in this database the US doesn't show a decline in aerosols given US emissions regulations.

It's possible that the dwell time is long enough that we stand in the downwind shadow of China and the rest of Asia (at temperate northern latitudes, the winds flow east around the globe). In which case our emissions cutbacks would help Europe; and while they would help us, too, that effect would be compensated for by the increase in industry in the East (and most especially the massive amount of coal the Chinese are burning).

bbartlog said at March 16, 2009 9:09 AM:

Oh, and one other thing: one of the main constituents of smog isn't even a direct output of industry. It's microscopic bits of auto tires. That component of pollution will keep increasing as long as more miles are driven (barring some change in tire composition).

Shannon Love said at March 16, 2009 1:49 PM:

Europe's brightening might be largely explained by Frances heavy use of nuclear power. Statistically, the difference of pollution prevented by those plants is significant over the entire region. France gets 80% of its electricity from nukes. If all those plants were coal powered instead, you would see a lot more pollution even with contemporary safeguards.

crosspatch said at March 17, 2009 2:54 PM:

"I am surprised that in this database the US doesn't show a decline in aerosols"

The US gets a lot blown over from China. As China's fossil fuel usage increases, our aerosol counts will likely rise. Much of it gets washed out by the time it gets to Europe. Europe experiences a lot of US emissions which are much lower than they were, say, 30 years ago.

happyfeet said at March 17, 2009 6:25 PM:

This is me over here finding the aerosols troubling.

Syl said at March 17, 2009 10:07 PM:

"Unlike aerosol particles, carbon dioxide and other greenhouse gases are transparent and have no effect on visibility."

Now that's just silly. Can the rest of the article be trusted? I don't know about you but I have a hard time seeing through fog, and darned if those clouds don't hide the sun. I guess water vapor ain't no greenhouse gas according to some.

C3H Editor said at March 18, 2009 6:57 AM:

One can't claim "global dimming" and "global brightening" in the same article. There may be "regional" dimming and "regional" brightening but using the word "global" is incorrect. This is also true for the concept of "global warming" and "global cooling" as either one can exist at same time and are more regional oriented than true global conditions.

With that said, and if the science of this study holds up, then the study indicates the total inadequacy of global climate models (GCMs), which have never accounted for aerosols correctly because of the CO2-myopia the models encapsulate. It may explain the truly awful prediction capabilities of these models 5 years and out.

Of course, this study does suggest a rather inexpensive solution to "global warming": burn more coal. Versus spending trillions of dollars for unproven techniques, the coal solution just seems more "natural" and affordable. Since the world's human life expectancy has increased during the period of the study, it would suggest a modest amount of coal aerosol pollution is acceptable trade-off if it keeps the planet cooler.

Finally, the researchers are concluding an aerosol causation from an apparent reduction of light hitting the surface. However, there is a great body of sun/solar science that is currently suggesting that the amount of solar energy hitting the earth has been decreasing since 1998, which their study may also be an indication of.

For more solar & climate info, go here:

C3H Editor,

Randall Parker said at March 18, 2009 6:31 PM:

C3H Editor,

Burn more coal and put more cancer-causing particulates in the air? Put more mercury in the air? Cause more respiratory-damaging ozone? Surely you jest.


fog represents a small fraction of all H2O in the atmosphere.

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