Aerosols May Drive a Significant Portion of Arctic Warming

Aerosols May Drive a Significant Portion of Arctic Warming
Researchers used an electron microscope to capture these images of black carbon attached to sulfate particles. The spherical structures in image A are sulfates; the arrows point to smaller chains of black carbon. Black carbon is shown in detail in image B. Image C shows fly ash, a product of coal-combustion, that's often found in association with black carbon. While black carbon absorbs radiation and contributes to warming, sulfates reflect it and tend to cool Earth. Credit: Peter Buseck, Arizona State University

( -- Though greenhouse gases are invariably at the center of discussions about global climate change, new NASA research suggests that much of the atmospheric warming observed in the Arctic since 1976 may be due to changes in tiny airborne particles called aerosols.

Emitted by natural and human sources, can directly influence climate by reflecting or absorbing the sun's radiation. The small particles also affect climate indirectly by seeding clouds and changing cloud properties, such as reflectivity.

A new study, led by climate scientist Drew Shindell of the NASA Goddard Institute for Space Studies, New York, used a coupled ocean-atmosphere model to investigate how sensitive different regional climates are to changes in levels of carbon dioxide, ozone, and .

The researchers found that the mid and high latitudes are especially responsive to changes in the level of aerosols. Indeed, the model suggests aerosols likely account for 45 percent or more of the warming that has occurred in the Arctic during the last three decades. The results were published in the April issue of Nature Geoscience.

Though there are several varieties of aerosols, previous research has shown that two types -- sulfates and -- play an especially critical role in regulating climate change. Both are products of human activity.

Sulfates, which come primarily from the burning of coal and oil, scatter incoming solar radiation and have a net cooling effect on climate. Over the past three decades, the United States and European countries have passed a series of laws that have reduced sulfate emissions by 50 percent. While improving air quality and aiding public health, the result has been less atmospheric cooling from sulfates.

At the same time, black carbon emissions have steadily risen, largely because of increasing emissions from Asia. Black carbon -- small, soot-like particles produced by industrial processes and the combustion of diesel and biofuels -- absorb incoming solar radiation and have a strong warming influence on the atmosphere.

Aerosols May Drive a Significant Portion of Arctic Warming
Since the 1890s, surface temperatures have risen faster in the Arctic than in other regions of the world. In part, these rapid changes could be due to changes in aerosol levels. Clean air regulations passed in the 1970s, for example, have likely accelerated warming by diminishing the cooling effect of sulfates. Credit: Drew Shindell, Goddard Institute for Space Studies

In the modeling experiment, Shindell and colleagues compiled detailed, quantitative information about the relative roles of various components of the climate system, such as solar variations, volcanic events, and changes in greenhouse gas levels. They then ran through various scenarios of how temperatures would change as the levels of ozone and aerosols -- including sulfates and black carbon -- varied in different regions of the world. Finally, they teased out the amount of warming that could be attributed to different climate variables. Aerosols loomed large.

The regions of Earth that showed the strongest responses to aerosols in the model are the same regions that have witnessed the greatest real-world temperature increases since 1976. The Arctic region has seen its surface air temperatures increase by 1.5 C (2.7 F) since the mid-1970s. In the Antarctic, where aerosols play less of a role, the surface air temperature has increased about 0.35 C (0.6 F).

That makes sense, Shindell explained, because of the Arctic's proximity to North America and Europe. The two highly industrialized regions have produced most of the world's aerosol emissions over the last century, and some of those aerosols drift northward and collect in the Arctic. Precipitation, which normally flushes aerosols out of the atmosphere, is minimal there, so the particles remain in the air longer and have a stronger impact than in other parts of the world.

Since decreasing amounts of sulfates and increasing amounts of black carbon both encourage warming, temperature increases can be especially rapid. The build-up of aerosols also triggers positive feedback cycles that further accelerate warming as snow and ice cover retreat.

In the Antarctic, in contrast, the impact of sulfates and black carbon is minimized because of the continent’s isolation from major population centers and the emissions they produce.

"There's a tendency to think of aerosols as small players, but they're not," said Shindell. "Right now, in the mid-latitudes of the Northern Hemisphere and in the Arctic, the impact of aerosols is just as strong as that of the ."

The growing recognition that aerosols may play a larger climate role can have implications for policymakers.

"We will have very little leverage over climate in the next couple of decades if we're just looking at carbon dioxide," Shindell said. "If we want to try to stop the Arctic summer sea ice from melting completely over the next few decades, we're much better off looking at aerosols and ozone."

Aerosols tend to be quite-short lived, residing in the atmosphere for just a few days or weeks. Greenhouses gases, by contrast, can persist for hundreds of years. Atmospheric chemists theorize that the climate system may be more responsive to changes in aerosol levels over the next few decades than to changes in greenhouse gas levels, which will have the more powerful effect in coming centuries.

"This is an important model study, raising lots of great questions that will need to be investigated with field research," said Loretta Mickley, an atmospheric chemist from Harvard University, Cambridge, Mass. who was not directly involved in the research. Understanding how aerosols behave in the atmosphere is still very much a work-in-progress, she noted, and every model needs to be compared rigorously to real life observations. But the science behind Shindell’s results should be taken seriously.

"It appears that aerosols have quite a powerful effect on climate, but there's still a lot more that we need to sort out," said Shindell.

NASA’s upcoming Glory satellite is designed to enhance our current aerosol measurement capabilities to help scientists reduce uncertainties about aerosols by measuring the distribution and microphysical properties of the particles.

Provided by NASA's Earth Science Team

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Apr 08, 2009
Whoa! Whoaaaaa! I thought the consensus was clear? I thought there was no more research or science to be analyzed on global warming? How can aerosols suddenly be thrust into the mix?

This research must be BURIED, SUPPRESSED, IGNORED! Dear AlGoracle help us all!

Apr 08, 2009
I'm still waiting for the AGW deniers to offer low-cost AGW insurance. I'd love to be able to see the deniers pay out on huge claims in the coming years as they continue to deny that humans have anything to do with changing climate. Perhaps we can also trade in AGW insurance derivatives - what a concept!!

Apr 08, 2009
An aerosol is any particle small enough to be lofted about by air currents. This article doesn't mention the percentage of total aerosols generated by human sources.

A reasonable guess is that human produced aerosols account for a single digit percentile of the total amount. Pollens, dust, vulcanism and dust from space probably account for the vast majority of all airborne particles.

With this in mind, what possible action could provide any "remedy" for this "problem"? Tree condoms for pollen? Smokestacks and scrubbers for volcanic vents? Paving over the deserts and arid areas of the earth? Rebuking comets and space with a colassal windshield?

The madness continues. . .

Apr 08, 2009
The only problem I have is that the research is coming out of GISS and their integrity has been compromised.

Apr 09, 2009
"Arkaleus" might want to consider the billions of tons of hydrocarbon contaminated ice crystals deposited in the stratosphere by jet aircraft.
Most of the rest of worlds "natural aerosols" are not directly injected into the stratosphere.
This massive hydrocarbon injection, year after year, cannot be benign.

Apr 09, 2009
Yet more evidence that the state of the art in global warming is that we at best have a vague and incomplete understanding of the complexity of the system. That hasn't stopped the hysterics from rushing in and demandng we destroy the world economy in fealty to their unproven computer models.

Apr 09, 2009
Excellent reporting.

Apr 09, 2009
We were told to stop using aerosols to prevent global cooling (remember the ozone hole?). Now we're told they're causing global warming!!!

We were told burning coal and oil was a major cause of global warming. Now we're told they cause global cooling!!!

Assuming this isn't an April fools' joke, it just goes to show that the whole Global Warming hoax was there just to divert taxpayer funds into the hands of the God-less!

Apr 09, 2009
It's a good point you make about jet exhaust. Doubtless, every action has a reaction. It's the magnitude of the effect that must be honestly and accurately reported.

We have to remember that man made emmissions account for only very small parts of the particles and gases present in the atmosphere. Obviously, natural processes are the major drivers of climate by simple quantitative analysis.

AGW articles often emphasize the activities of man without putting them in the proper context of proportion - nature simply exceeds man by sheer scale and all analysis should begin first with nature, not man.

Apr 12, 2009
I'm still waiting for the AGW deniers to offer low-cost AGW insurance. I'd love to be able to see the deniers pay out on huge claims in the coming years as they continue to deny that humans have anything to do with changing climate. Perhaps we can also trade in AGW insurance derivatives - what a concept!!

Oh so you change the subject. How stupid of you LariAnn. You AGW hyperventilators have huffed and screamed for years now that all the science was done and the consensus was clear, yet no one ever mentioned aerosols before... How can such a huge new variable come out if all the science and consensus is in...

Those of us who ARE scientists and researchers use logic and scientific methodologies to continue to study phenomenon like the melting of some glaciers, the retreat of polar ice caps, etc, but since we are not religious fanatics like you, we don't just fall down and tremble at the impending doom that your religious leaders use to get you worked up into your lathers.

I know our cold and dispassionate ways of thoroughly analyzing empirical data is boring and makes you so so mad, but so what?

The earths climate is always changing. How much impact humanity has right now and in the past is not known. Cannot even be accurately speculated at in purely scientific reasoning because there are too many unknown variables..

I know how hard that is for your tiny little intellect to handle, so please do come back at me with some more changing the subject or some nice ad hominem attacks that will make me laugh.

Apr 16, 2009
QubitTamer: If you were paying attention you would know that people have been studying aerosols for nearly a century. This article just adds to the knowledge base. This is part of the scientific process of investigation of the influence of each part of the climate puzzle. You might want to try to read some of the earlier work on aerosols to understand how this fits in. Calling people names does not make your statements any more believable. Try using facts.

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