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Aerosols (pollutants, like soot) as a driver of climate change

8 May 2009

It’s common for advocates to focus on a narrative that they believe will convince the public of the urgency of their cause.  Unfortunately this can blind them to research indicating that the problem is more complex then the simple story they push — and hence that their well-intended solutions might be ineffective, or even counter-productive.

I believe that’s become true today about climate science.  This is another in a series of articles about research showing the complexity and uncertainty in the current models of climate change.  Previous articles have focused on solar influences.  Here are a few discussing the role of atmospheric particles.  Brief excerpts appear below for these two articles.

(1)  Impure as the Driven Snow“, Scientific American, 8 June 2007 — “Soot is a bigger problem than greenhouse gases in polar meltdown.”  This discusses “Present-day climate forcing and response from black carbon in snow”, Mark G. Flanner, Charles S. Zender, James T. Randerson, and Philip J. Rasch, Journal of Geophysical Research, June 2007 — Abstract.

(2)  “Climate response to regional radiative forcing during the twentieth century”, Drew Shindell and Greg Faluvegi, Nature Geoscience, March 2009 — Abstract, NASA’s summary.

There is a large body of research about effect of particles on Earth’s climate.  Here are a few other articles, with no excerpts given:

Of course, it’s important not to let the proles know about such research (aerosols possible role as both warming and cooling agents).  Hence Obama’s science advisor, John Holdren, was careful not to mention this during his interview with Associate Press in which he discussed using aerosols to geoengineer the Earth’s climate.  Don’t spoil the simple narrative!

Excerpts

(1)  Impure as the Driven Snow“, Scientific American, 8 June 2007 — This discusses “Present-day climate forcing and response from black carbon in snow”, Mark G. Flanner, Charles S. Zender, James T. Randerson, and Philip J. Rasch, Journal of Geophysical Research, June 2007 — Abstract.  Excerpt:

Belching from smokestacks, tailpipes and even forest fires, soot—or black carbon—can quickly sully any snow on which it happens to land. In the atmosphere, such aerosols can significantly cool the planet by scattering incoming radiation or helping form clouds that deflect incoming light. But on snow—even at concentrations below five parts per billion—such dark carbon triggers melting, and may be responsible for as much as 94 percent of Arctic warming.

… Zender, physicist Mark Flanner and other colleagues built a model to examine how soot impacts temperature in the Arctic and Antarctic regions. Temperatures in the northern polar region have already risen by 1.6 degrees Celsius (2.88 degrees Fahrenheit) since the dawn of the Industrial Revolution.

… Whereas forest fires contribute to the problem—the effect noticeably worsens in years with widespread boreal wildfires—roughly 80 percent of polar soot can be traced to human burning, adding as much as 0.054 watt of energy per square meter of Arctic land, according to the research published this week in the Journal of Geophysical Research. When the snow melts, it exposes dark land below it, further accelerating regional warming. “Black carbon in snow causes about three times the temperature change as carbon dioxide in the atmosphere,” Zender says. “The climate is more responsive to this than [to] anything else we know.”

(2)  “Climate response to regional radiative forcing during the twentieth century”, Drew Shindell and Greg Faluvegi, Nature Geoscience, March 2009 — Abstract, NASA’s summary

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, aerosols 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 aerosols. 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 black carbon — 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

… 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).

… “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 greenhouse gases.”

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.”

For more information

To read other articles about these things, see the FM reference page on the right side menu bar.  Of esp relevance to this topic:

Posts on the FM site about the sun’s effect on Earth’s climate:

  1. Worrying about the Sun and climate change: cycle 24 is late, 10 July 2008
  2. Update: is Solar Cycle 24 late (a cooling cycle, with famines, etc)?, 15 July 2008
  3. My “wish list” for the climate sciences in 2009, 2 January 2009
  4. About the recent conference ”Solar Activity during the onset of Solar Cycle 24″, 3 January 2009
  5. A brief look at the Sun’s influence on Earth’s climate, 4 May 2009
  6. An important puzzle from the National Weather Service’s Space Weather Prediction Center, 10 May 2009
  7. Big news from NASA about the causes of climate change!, 5 June 2009
  8. Peer reviewed science: breakthoughs about the sun’s impact on Earth’s climate, 4 September 2009
  9. Another climate wild card: solar cycle 24, perhaps causing food riots during the next decade, 1 February 2011
  10. Update about the weather – on the Sun. Perhaps coming soon to Earth., 9 February 2011
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11 Comments leave one →
  1. Sera permalink
    8 May 2009 4:38 am

    Should we not wait for conclusive research before making policy? Every day, it seems, we are learning more and making new discoveries that contradict ealier beliefs (nothing new there!) Why are we in such a hurry anyway? I thought science was slow, steady and exacting- with the occasional eureka moment. Flavor of the day is not a modis operandi. One hundred years ago, our best scientists claimed the sun was a giant lump of coal…

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  2. OldSkpetic permalink
    8 May 2009 10:03 am

    FM Thank you so much for mentioning this. The positive/negative effects of these have been (except in some esoteric scientific literature) been largely ignored.

    It’s like the issue of localised pollution. Depending on your local geography/weather patterns/etc plus local industry they can have massive effects on what you, as a local, experiences .. far greater or lesser than ‘overall averages’ would indicate. In some cases even distances as small as a few 10′s of km can make all the difference between choking or breathing easy, or having mercury brain damaged children.

    Take another example, what side of a ‘rain shadow’ are you on (very topical Australian issue), on one side you are reasonably fine, the other, maybe even just a few km away .. the proverbial ‘sucking on….’ applies.

    The high altitude aerosols are another example .. with a global twist: “your industry (from country X 000′s of kms away) are producing aerosols that are harming us” (if it helps they won’t complain of course) .. how do you sort that out in international courts?

    Whatever global or regional effects of pollution .. and whatever the causes .. what we, as individuals, experience will depend on the local environment and how these effects combine, which will dwarf any large scale effects that are happening (good or bad).

    FM: we are on the same page .. much, much more research needed on this. Here in Oz there is a debate about using UAV’s for scanning bushfires and bushfire prone zones using advanced sensors .. as far as I’m concerned there should be no debate … just buy the things. But this concept also offers some interesting pollution monitoring options for other areas as well .. and opens a very interesting door to local ‘fixes’ and/or management/mitigation efforts.
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    Fabius Maximus replies: The effect of aerosols was a primary driver of the global cooling fears in the 1970′s. It was not a consensus, but a significant element in the climate literature. This was one of the major themes on NOAA’s history page, before they re-wrote it (putting all that in the memory hole).

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  3. 8 May 2009 4:20 pm

    What would happen if we added up all the theoretical affects? Ie – this article says 45% of warming in the Arctic caused by aerosols and black carbon. Other studies do similar projections including the IPCC models. The Argo bouys and satellites show that the ocean circulation caused a huge warming in the arctic along with a weather system that seems to have been stuck over the arctic drawing in warm southern air.

    I think if I added up all the theoretical causes of warming we would get a number in excess of 100%. It is warmer. I am guess it could be decades before we figure out why …. if ever.
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    Fabius Maximus replies: My point in posting these articles is to demonstrate that the science is not settled. Saying otherwise is just agitprop. It’s a debate, taking place in many fields on many levels — from the adequacy of the data up through the models of these complex interrelationships.

    I don’t understand what it means to “be a warmer.” These are not rival baseball teams. Unless you are a scientist specializing in these fields you opinion means zip. It’s fun to have an opinion on these things and to debate them, but non-scientists taking their own opinions seriously puts them on the anti-science “team” — just chaff in the effort to understand these complex dynamics.

    By the way to say “it is warmer” is absurd. Over what time scale? Over generational or century-long time scales we are rebounding from the Little Ice Age. During this decade it appears that temperature is stable or cooling. Over intermediate time scales the data is confused. Due to inadequate funding, the surface temperature network is a mess, both from a data collection standpoint (stations moving, and not following the siting guidelines) and analytical perspective (e.g., unclear adjustments for the urban heat island effect).

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  4. Gary Rondeau permalink
    8 May 2009 4:25 pm

    That aerosols are a big contributor or climate heating/cooling is not new, but perhaps is getting a fresh look as to its importance. Volcanic eruption has always been know to be a short-term climate driver. I guess what we are realizing is that the activity human civilization generates enough aerosols to be a significant chronic effect. The good news is that response to policy changes can be rather rapid because the life time of the aerosols in the atmosphere is short compared to the century time scale for CO2.

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  5. anna nicholas permalink
    9 May 2009 12:43 am

    Its due to heat escaping from the earth’s core due to volcanic activity and seabed drilling .
    The increase in human population ( heat generating ) and decrease in amphibian poulations ( heat absorbing ) are no doubt also critical , as was the invention of refrigerators , air conditioning , computors ,and the EU , all pumping out heat on hot days .

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  6. 9 May 2009 2:05 am

    Consistent with my newly attained state of infinitely jaded consciousness, I believe the reason there is less interest in soot as a driver of climate is that soot is readily removed from stack gasses from coal burning. There is already essentially zero soot generated by coal combustion. Where’s the regulatory fun, the opportunity for tax mischief in that?
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    Fabius Maximus replies: I doubt that the coal burned in 2nd and 3rd world nations is “essentially zero” — and anything remotely like zero. Plus the other sources of soot, such as engines (e.g. trucks, ships), waste incineration, deliberate burning of fields and forests, etc.

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  7. 9 May 2009 3:10 am

    Re:6

    Yes, agreed, but the eradication of all these sources of particulate emissions is at least routine, and at pretty low cost. Contrast this with CO2, whose removal and sequestration is, at minimum, very expensive, and worst case, impossible.

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  8. birchman2 permalink
    9 May 2009 2:06 pm

    See “The Great Global Warming Swindle”. I’m curious what you guys have to say about it.
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    * See the video here.
    * Here is a website with stills and transcript of the video, plus supporting materials.
    * Here is the Wikipedia entry (note that Wikipedia is a source of assertions and links, not a reliable source of information on controversial issues).

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  9. Robert Speirs permalink
    10 May 2009 1:16 am

    I think it interesting that 19th century temperatures were affected by at least three worldwide huge volcanic eruptions – Tambora, Krakatoa and the New Madrid, Misouri, earthquake. All three expelled huge quantities of aerosols and soot, cooling the climate, presumably. Wasn’t the year after Tambora (1816) called the “year without a summer”? Or, more colloquially, “Eighteen Hundred and Froze to Death”? In the twentieth century I don’t recall any truly large volcanic eruption, on the Krakatoa scale. One could happen anytime. But the records from the 19th century, spotty as they are, are doubtlessly affected by these unpredictable volcanic events. And records from previous centuries are also distorted to some extent. So the level of temperatures we are comparing present-day temperatures to is artificially – volcanically – depressed. Therefore, assuming a large eruption can be expected at least every century, the twentieth and twenty-first centuries’ temperatures are artificially high, because of the absence of mega-eruptions. But if Yellowstone goes up, that may not continue to be the case.

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  10. Persimine permalink
    10 May 2009 5:45 pm

    China is building another 1 MW coal plant every 10 days. Not the clean technology, but the soot blasters that have poisoned the ocean and melted icecaps and glaciers for decades. We hope you enjoy the taste of mercury with your fish. The Northwest Passage comes free, at no charge to you.
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    Fabius Maximus replies: You did read the post, didn’t you? About the uncertainty as to the effect of particles in the air. Global cooling or warming?

    Either way, China’s actions pretty much mocks the pretentions of the Kyoto treaty.

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  11. erasmus permalink
    11 May 2009 12:08 pm

    Re 9, it would be helpful to see a comparison of the particulates thrown out by Mt St. Helens and all our similarly particulate contributions the previous 50 years and since. Of course, it’s not all the same stuff, but from material I read back in the early 90′s I think, the quantity from St. Helens dwarfs most of what we had been contributing. There is also forest fire particulates which I suspect due to man-caused deforestation has been greatly reduced the past couple of millenia, albeit especially the past two centuries.
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    Fabius Maximus replies: There is a large literature on this subject, and all these questions have been studied. Look around and you will find it.

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