The other atmospheric aerosols

NOAA study finds particles in the air slowing climate change


Increasing particles in the atmosphere may be slightly slowing climate change, according to a study released by the National Oceanic and Atmospheric Administration. These particles, called aerosols — which have nothing to do with hair spray or spray-on deodorants — have been shown to reflect sunlight back into space and have decreased the expected temperature increases.

“The models in the past have included aerosols, but when the projections were run for the 2000s or in the big climate report that came out in 2007, those model projections were unaware of the effect,” says study coauthor Ellsworth Dutton, who works in the global monitoring division of the Earth System Research Laboratory at NOAA and has been involved with aerosol research for years. “[This study] partially offers an explanation as to why those models haven’t worked out as expected.”

The aerosols at hand are particulate matter — dust or smoke particles.

Their effect is small, but in a scenario where a 2-degree change is expected to have a dramatic effect, they could amount to a change of 0.1 to .15 less per decade than predicted, John Daniel, a physicist at the NOAA Earth System Research Laboratory and an author of the new study, says in a press release.

“We are continually collecting information from our observatories that are spread around the world, and we just noticed this developing trend over the last several years,” Dutton says.

The study combined data from various tools on the ground that measure the sun and atmosphere and match that with information on the atmosphere collected by NASA satellites, which offer a brief glimpse of the globe.

Over the past decade, as aerosols in the stratospheric atmosphere have nearly doubled, they’ve applied a cooling effect of about 0.1 watts per square meter, offsetting some of the 0.28 watts per square meter warming effect from carbon dioxide in that same period.

“Aerosols are kind of a major uncertainty in what’s going on, and they are highly variable from many different sources, both natural and manmade,” he says. “They’re difficult to characterize, as opposed to gas molecules that are fairly well identifiable and understood.”

They come in different sizes, shapes and quantities, which makes it difficult to quantify their atmospheric impacts. What they saw during the 2000s, he says, most likely come from natural volcanic sources. Possible human sources for increased aerosols include coal-burning power plants, though they are less likely to have had a significant cooling effect, and not one that outweighs the detriments to the atmosphere of the carbon dioxide they emit, according to Dutton.

“There’s a lot of concern about burning coal as well as producing carbon dioxide, which is the main culprit in the global warming models,” he says. “It probably won’t have much of an impact changing the way that people think about coal.”

Because volcanoes and their outputs, the main player in this effect, are by nature unpredictable, it would have been difficult for climate-modeling scientists to have included this variable in their predictions, and, even knowing that they have an effect now, it’s impossible to estimate what their future impact will be.

“It’s certainly something interesting.

I think the biggest potential societal impact is probably on some of the debates as to how well some of the climate predictions have been faring and how the public has accepted some of these suggestions as to what the climate might be doing because of the greenhouse gases,” Dutton says. “Over the last decade or so the temps haven’t increased as much as those projections, […] and it’s not because there’s anything wrong with the basic theory of global warming.”

The study offers an alternate, physically based observed phenomenon to explain why the climate hasn’t changed to match models that weren’t aware of this variable.

“It’s still a good idea to keep working toward renewable energy applications to help reduce the carbon footprints,” Dutton says.

And those infamous aerosols of the ’80s are still not a great idea — stylewise or environmentally. The fluorocarbons they contain have a chlorine compound that eats through the atmosphere.