Some new climate surprises blow in with the dust

From NASA: Dust’s Warming Counters Half of its Cooling Effect

Dust that routinely rises above the world’s deserts causes a more significant localized warming effect than previously thought, a new study based on NASA field research shows.

In April 2008, atmospheric scientists set up camp in Zhangye, a semi-arid region between China’s Taklimakan and Gobi deserts. They sorted and prepared cargo that included two mobile laboratories housed in trailers, and an array of upward-looking instruments for measuring airborne dust particles. Then, the team waited for favorable conditions – for either of the two neighboring deserts to send clouds of dust blowing over camp before fieldwork wrapped up a few months later in June.

The wait paid off. By early May, a heavy dust episode darkened the skies over camp as scientists and instruments looked on.


Before (left) and after (right) photos of the study site in Zhangye, China, show the magnitude of the May 2008 dust event.

The mineral properties of the aerosol particles and the wavelength distribution of incident light combine to determine whether a dust particle reflects radiation and cools the local atmosphere, absorbs radiation and warms the local atmosphere, or both. While scientists have a good handle on dust’s primary effect of reflecting and cooling at the visible wavelengths, the smaller influence of absorbing and warming at the longer infrared wavelengths has remained more of an uncertainty – and most climate models either underestimate it or do not include it at all.

 

smiling guy at a computer terminal

Atmospheric scientist Richard Hansell works with data that show the location of a spring 2008 dust event (red) measured in Zhangye, China, between the Taklimakan and Gobi deserts. Credit: NASA/Goddard

When the field work concluded, Richard Hansell of the University of Maryland, College Park, and NASA’s Goddard Space Flight Center, Greenbelt, Md., and colleagues combined data collected from the ground-based sensors with computer models to quantify the interaction of visible and infrared light energy.

The analysis showed that over half of dust’s cooling effect is compensated for by its warming effect. The finding, published in the Journal of Geophysical Research, Atmospheres, could clarify scientists’ understanding of how dust influences moisture fluctuations in the atmosphere and surface temperatures around the planet.

The dust dilemma

Dust is just one, but important, type of tiny airborne particle collectively known as aerosols. And while dust has a notable impact on health and visibility, it is also known to have an effect on climate. The question remains: How much of an effect?

As the 2007 assessment report by the United Nations’ Intergovernmental Panel on Climate Change shows, the magnitude of aerosols’ influence on climate is not well understood. That’s where ground-based work like Hansell’s can help. The team’s interest was not in the global coverage of the dust – events frequently observed by satellites – but rather in the individual flecks of dust and their physical and chemical properties.

“Looking at dust from space, the spatial extent is awesome,” Hansell said. “You can see large dust clouds that get stirred up over the desert and transported globally. But I’m looking from the ground-based perspective, collecting a very large volume of data to analyze dust and to look specifically at how it interacts with radiation, in my case with infrared – the longer wavelengths.”

How dust interacts with these longer wavelengths has long perplexed scientists – it’s not an easy thing to study. But with an array of instruments and growing volumes of data from NASA’s Surface-based Mobile Atmospheric Research & Testbed Laboratories (SMARTLabs), scientists are making progress.

The long and short of it

Sunlight is composed primarily of energy at the shorter visible wavelengths known as shortwave. When shortwave radiation arrives to Earth’s atmosphere and encounters dust particles, some of the energy is reflected back to space. Cooling results because Earth’s surface doesn’t receive as much radiation had the dust not been there; an effect that’s relatively straightforward to observe.

The challenge stems from the much weaker signal of the longwave radiation – the invisible, low-energy radiation emitted by the earth, atmosphere, clouds and anything else with a temperature. Dust can absorb this type of radiation and thus contribute to warming. But the process depends on the particles’ size, composition, optical properties, and how those parameters affect the transfer of energy between the particles and the atmosphere.

Compared to small-sized aerosols such as smoke, larger particles including dust are more efficient at absorbing longwave radiation. In addition to size, dust particle composition also matters. Minerals such as silicates and clays are better than others at absorbing longwave radiation.

To determine the warming influence of dust, Hansell and colleagues started by characterizing dust size and composition as measured by instruments in the NASA mobile lab at Zhangye, in addition to data collected from previous field studies there. At the same time, the team in Zhangye used an interferometer to describe changes in the spectral intensity of the longwave radiation.

Combining the measured parameters in a computer model, the researchers calculated the longwave energy at Earth’s surface with and without dust aerosols present to determine the Direct Aerosol Radiative Effect (DARE), a parameter that describes how aerosols modulate the energetics of the atmosphere.

The warming influence

The team found that dust’s radiative impact, and hence its warming influence, conservatively ranges from 2.3 to 20 watts per square meter of radiation at the surface in Zhangye. Collectively, dust’s longwave warming effect counters more than half of dust’s shortwave cooling effect.

For perspective, the warming influence of 20 watts per square meter is comparable to the low end of longwave radiation’s effect on clouds, which measures about 30 watts per square meter. Warming by greenhouse gases measures about 2 watts per square meter, although the warming occurs globally whereas the warming influence of dust and clouds is regional.

“The influence of dust on longwave radiation is a lot bigger than we expected,” Hansell said.

The magnitude of that influence, however, can vary from one location to another. “Compared to our previous study of Saharan dust measured at Sal Island Cape Verde, the longwave effects of dust at Zhangye were found to be about a factor of two larger, owing to differences in the dust absorptive properties and proximity to the desert sources, he said.

Still, with dust holding on to more heat than previously thought, scientists can begin to reassess dust’s role in changes observed near Earth’s surface, such as air temperature and the moisture budget. For example, dust’s warming effect on the atmosphere could be an underestimated factor driving evaporation, and atmospheric convection and stability.

“We’re now at point where I see trying to link what we’re measuring into work being done by the modeling community, to improve climate predictions and to better understand the dynamical consequences of these radiative effects,” Hansell said.

Related Links:

Dust Dominates Foreign Aerosol Imports to North America
http://www.nasa.gov/topics/earth/features/dust-imports.html

NASA Goddard SMARTLabs
http://smartlabs.gsfc.nasa.gov/

Kathryn Hansen
NASA’s Earth Science News Team

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37 Responses to Some new climate surprises blow in with the dust

  1. Otter says:

    OK! Definite question here: Dust coming off of West Africa, and hurricanes.

    Do the dust clouds coming off of Africa act as a seed for hurricanes, and is it due to cooling effects, or warming effects?

    Have fun with that one!

  2. HenryP says:

    So it never was the CO2. I knew that.

  3. poitsplace says:

    It amazes me how the true believers in climate change think the models are all so similar and perfect…but they make radically different assumptions about things like aerosols (http://www.climatescience.gov/Library/sap/sap2-3/public-review-draft/sap2-3-prd-ch3.pdf), and that doesn’t even include what’s being mentioned in this article

  4. Edohiguma says:

    Otter, I think that’s just the weather? You know, chaotic, non-linear? Something that has been going on for centuries without humans doing anything?

  5. Bloke down the pub says:

    Going out in the field and collecting data? How can that possibly be right?

  6. Matthew W says:

    “new study based on NASA field research shows”

    Based on field research??

    How dare they !!!

  7. Alan the Brit says:

    Very fascinating & interesting post yet again. Full marks!

    How can these people from the UNIPCC get away with this sort of thing? They admit that certain very important things like aerosols are not properly & or clearly understood (just like clouds & water vapour) that the programmers either make an approximation (best guess) in their models of its effects, or ignore it altogether, yet claim significant accuracy for the model outputs! It’s rather akin to me as an engineer admitting that I am modelling materials I don’t fully understand, by using emperical mathematics I don’t fully appreciate, then claim great accuracy & understanding!

  8. tadchem says:

    I will take empirical data over seat-of-the-pants heuristics any day.

  9. Doug Huffman says:

    @Otter; dust may act as nucleation site and not directly in heating/cooling.

  10. Jimbo says:

    The science is settled………….again.

    ………..it is also known to have an effect on climate. The question remains: How much of an effect?

    The same question is being asked by some skeptics about co2. They talk about consensus but they know deep down they don’t know but will not say openly because of possible cuts in funding.

  11. Richard M says:

    Now, if we could only get the climate scientists to study the cooling effect of GHGs and add that to the models. All atmospheric particles have both warming and cooling effects.

  12. markx says:

    As I often like to say:

    1. They have put forward a plausible theory,
    2. ‘Proven(?)’ it by computer modeling,
    3. and are now in the early stages of data collection.

  13. Johanus says:

    “Dust that routinely rises above the world’s deserts causes a more significant localized warming effect than previously thought”

    It is well known that solids absorb heat, otherwise the surface temps of all the solid planets, even the airless ones, would be absolute zero. So it’s not surprising that solids suspended in the air (“dust”) keep on absorbing too, modulated by the albedo of the dust cloud which determines how much energy is reflected back.

    So the cooling effect of the dust is cut in half. Wichtig ist es immer noch kühlt!

  14. Alan Watt, Climate Denialist Level 7 says:

    markx says:
    November 1, 2012 at 5:59 am

    As I often like to say:

    1. They have put forward a plausible theory,
    2. ‘Proven(?)’ it by computer modeling,
    3. and are now in the early stages of data collection.
    4. but the danger is too urgent to wait for data, so must agitate for massive social/economic change now.

    As I like to say: Global Warming is bad science used to support dismal economics.

  15. Alan Watt, Climate Denialist Level 7 says:

    It would be interesting to go back and look at how the current climate models treat the great US dustbowl years in the middle 1930′s, presumably without including this effect, and then look at what would have to be “adjusted” to get them to hindcast correctly including this effect.

  16. Rick says:

    OT for this thread but is it true that minute dust particles in the air act as a trigger in the formation of rain drops. If there wasn’t any dust in the earth’s atmosphere there wouldn’t be any rain.

  17. Doug Huffman says:

    No. High degrees of supercooling/superheating (boiling nucleation) may occur.

  18. Bruce Cobb says:

    But, but, any warming influence of dust diminishes the much-ballyhooed warming effect of C02. How inconvenient!

  19. Dennis Gaskill says:

    “Kathryn Hansen
    NASA’s Earth Science News Team”

    Any relation to the “great AGW propagandist” James Hansen ?

  20. Chuck Nolan says:

    markx says:
    November 1, 2012 at 5:59 am
    As I often like to say:

    1. They have put forward a plausible theory,
    2. ‘Proven(?)’ it by computer modeling,
    3. and are now in the early stages of data collection.
    ————–
    But, isn’t that how climate science has always been done?
    cn

  21. Willis Eschenbach says:

    OK, so the dust causes cooling … although the headline is curious. Rather than saying that the cooling effect of the dust is twice as large as the warming effect, they focus on the warming being large, half as large as the cooling.

    Please note that this is the same claim that I made regarding black carbon, that it cools the surface. See “Extremely Black Carbon” and “Ramanathan and Almost-Black Carbon“. I took lots of heat for saying that.

    Yeah, I know, I’m posting this to note that I was right … but on the other hand, a lot of folks are very happy to trumpet the fact when I’m wrong. So since nobody else will point it out, I’m just going to be genteel and quietly note that, at least upon occasion, I get it right once in a while.

    w.

  22. DesertYote says:

    Otter
    November 1, 2012 at 3:47 am
    ###

    I don’t know about that, but dust from Africa does cause coral bleaching in the Bahamas, something that has been known to for 30 years, but conveniently forgotten today.

  23. One of the key points seems to get lost. The effect, absorbed or reflected, has to do with mineralogy as well as particle size. If you are going to understand this stuff in any way at all, you need to find ways to collecting empirical data on both components. This goes to Willis’ point, fine black carbon or any color carbon, is nothing more then another mineral. The mineralogical composition in things like dust and soils is often an underrated or ignored component.

  24. Zeke says:

    Except, when coal is transported in open cars, they get it wet in order to reduce the coal dust. There is more dust on a simple dirt road than from transporting coal.

    But, since the scientific study has been completed with such accuracy and with the sheer amount of data collected, legislation will need to be written up, and scientists will need to be flown in to testify before Congress. The Precautionary Principle will need to be invoked, because scientists should be protecting people from any possible harm, if there can be sufficient doubt raised by scientists. And somewhere, some scientist stands to gain reputation, grants, honors, plane tickets, a scientific meeting at a nice location with fancy guests, being published – “for the public good” of course, not that the humble, objective scientist wanted reputation, grants, honors, plane tickets, conferences with the right people.

    So for the public good, scientists will next be terrifying the public about dust. Likely from coal. I do hope more scientists would resist the obvious charms and glories of using science for public good. Perhaps more will.

  25. markx says:

    Chuck Nolan says: November 1, 2012 at 7:43 am

    quotes me: “…… and are now in the early stages of data collection…..”
    ————–
    and says “…But, isn’t that how climate science has always been done?….”

    Precisely correct. And this is where they are right now with the whole AGW story. They did the modelling, said case proven. Now they are in the early stages of collecting data.

  26. Anthony Scalzi says:

    Otter says:
    November 1, 2012 at 3:47 am
    OK! Definite question here: Dust coming off of West Africa, and hurricanes.

    Do the dust clouds coming off of Africa act as a seed for hurricanes, and is it due to cooling effects, or warming effects?

    Have fun with that one!

    —-
    Dust layers actually inhibit hurricane formation because that air tends to be be dryer and warmer, making it more stable and thus preventing convection.

    Rick says:
    November 1, 2012 at 6:38 am
    OT for this thread but is it true that minute dust particles in the air act as a trigger in the formation of rain drops. If there wasn’t any dust in the earth’s atmosphere there wouldn’t be any rain.
    —–
    Don’t forget the cosmic ray generated aerosols.

  27. Zeke says:

    And speaking of China, what does happen when the government uses science to suddenly alter agriculture and the economy? The Great Leap Forward did not have particularly good results. So I would think that anyone wishing to apply the Precautionary Principle must include episodes like the Great Leap Forward and Lysenko’s destruction of the food supply using science for the public good.

    Evenly applied, the Precautionary Principle is meaningless.

  28. Kelvin Vaughan says:

    And what does farming, driving, wind etc. throw up into the atmosphere.

  29. Johanus says:

    Kelvin Vaughan said:
    “And what does farming, driving, wind etc. throw up into the atmosphere.”

    Are you suggesting that man-made dust can compete on a level with a full-blown Sahara (Gobi, Taklimakan or whatever) sandstorm?

    So why did Hansell and his team bother to visit a remote desert?

    “Then, the team waited for favorable conditions – for either of the two neighboring deserts to send clouds of dust blowing over camp before fieldwork wrapped up a few months later in June.”

  30. Otter says:

    Edohiguma says:
    Otter, I think that’s just the weather? You know, chaotic, non-linear? Something that has been going on for centuries without humans doing anything?

    ——–

    Humans have absolutely NOTHING to do with this skeptic’s question. Try again!

  31. Otter says:

    Doug, Desert, Anthony S, thanks for the answers!

  32. Rick says:

    Thanks Anthony Scalzi
    physics.aps.org/story/v7/st14
    Here is an article that had me thinking about dust and the formation of raindrops.

  33. stefanthedenier says:

    dust storms in Sahara and any other place; create warmer in upper atmosphere – cooler on the ground. Unfortunately, because they don’t last for long – affect is close to zero.

    Nevertheless, the effect is same as with any other gases that are not opaque, as CO2 + water vapor. When some sunlight is intercepted high up, where cooling is much more efficient; on the ground days are cooler / nights warmer! Grow up guys, common sense famine the ”skeptics are suffering from; is Viagra for Hansen, Mann, for screwing the western democracies and economies. shame, shame!

  34. Willis Eschenbach says:
    November 1, 2012 at 8:08 am

    Please note that this is the same claim that I made regarding black carbon, that it cools the surface. See “Extremely Black Carbon” and “Ramanathan and Almost-Black Carbon“. I took lots of heat for saying that.

    And the corollary is that reductions in black carbon cause warming. Black carbon emissions have greatly reduced through much of the developed and developing world since the 1960s, with India as a notable exception, where studies have shown a cooling trend over the 20th century, except during the monsoon season, when black carbon is washed out of the atmosphere.

    http://www.sciencedirect.com/science/article/pii/S1352231005006540

    They could have done the same measurements in any city in the world measuring the effects anthropogenic aerosols and particulates, and with the known weekly cycle in their emission and levels, come up with an accurate quantification of their effects on the local climate. But that would risk some very damaging consequences for the climate models. Which is why these studies are never done, except a handful referring to the climatically meaningless DTR.

  35. Rick says:

    That should have been:

  36. Rick says:

    Please delete 7:27 am comment. WordPress has automatically linked any URL in the past. Do I need greasemonkey to make that work now?

  37. Evan Thomas says:

    I observe there is quite a deal of dust in any western urban atmosphere. I speculate that it is mainly carbon whose origin is vehicle rubber tyres as they wear travelling along bitumen and concrete roads. Something else to measure without leaving town? Cheers from chilly Sydney.

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