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A new study indicates that dust from regions boarding deserts has a different composition than previously thought. This in turn can alter the impact of dust on climate change, for example via changing the net heating/cooling effect of dust and its effect glacial melting.  (Source: bachmont, Creative Commons)

The study finds that there's more large dust particles in the atmosphere than previously thought. This may mean that climate change models will need to be rerun and reanalyzed to take into account the complex effects of atmospheric dust.  (Source: UCAR)
More large dust particles are present than previously, thought, may act both to cool or accelerate melting

Some of the Earth's tiniest naturally occurring particles may play a much different role in global climate change than previously thought.  New findings reveal that models scientists have long used to estimate the causes and effects of global warming may be flawed due to errors in one of their significant inputs -- atmospheric dust.

This revelation is an indirect conclusion of a new study published in the journal 
Proceedings of the National Academy of Sciences by Jasper Kok, a climatology researcher with The National Center for Atmospheric Research (NCAR).

I. Ice Melt, Cooling, and Large Dust Particles

The study's key conclusion was to show that the ratio of small soil dust particles (clay), which cool the atmosphere, to large soil dust particles (silt), which may heat or cool depending on their size, may be much lower than previous estimated using empirical (observation based models).  While the number of small dust particles, according to our discussion with Professor Kok, is approximately the same as previously thought, the number of large particles are much higher.

This is a critical finding because it means that current global circulation models (GCMs) used in broader climate change models, may significantly overestimate the net cooling effect per volume of dust (given the greater occurrence of large silt, which favors heating).  The overestimation of the cooling is reported especially high at the top of the atmosphere (TOA), where it may be overestimated by as much as a factor of 15.

It is also critical as these large silt particles tend to precipitate and can play an important role of accelerating glacial melting.  Thus atmospheric dust may not only warm the earth more than previously estimated, but may also lead directly to one of the observed effects often associated with climate change -- glacial melting.

II. A Dusty Surprise

To better understand the study, it's important to get a picture of what these particles are

Mineral dust originates when sand particles are blown by the wind into soil, shattering it into microparticles.  Major sources of mineral dust include the southwestern United States, northern Africa, Northeast Asia (the Gobi Desert) and Australia.

The sand essentially acts like tiny bullets, hammering dirt particles, which tend to be 20 microns or smaller and are thus known as PM20 sediment.  This process, known as saltation ejects a mixed distribution of dust microparticles into the atmosphere, as the cracked particles' aerodynamic forces overwhelm their cohesive forces. 

The smallest resulting microparticles measure less than 2 microns (2000 nm).  These particles are known as clay.  Past studies have shown that they tend to stay in the atmosphere for long periods of time, reflecting light and cooling the Earth.  

Large microparticles, known as silt, can reach 50 microns (50,000 nm) -- about the width of a human hair).  Their weight causes them to quickly fall out of the atmosphere.  Depending on their size they can either exert a net cooling effect or a net heating effect.  Silt larger than 5 microns in diameter tends to warm the earth (as reflection of outgoing radiation back towards the Earth overcomes sun-blocking effects), while silt between 2 and 5 microns tends to cool (as the sun blocking effects are more effective than the reflective effects).  In that regard small silt acts much like clay, albeit being less effective at cooling.

Despite their quick precipitation all types of silt have another significant direct effect on the climate.  After falling through the atmosphere, they tend to accumulate in mountain polar ice, concentrating sunlight, absorbing heat and accelerating melting.

In order to find the true ratio of the particles types, Professor Kok cleverly combined mathematical theory and statistical data.  To determine the breaking method, he used brittle object breaking formulas developed by mathematicians.  Brittle objects, like glass, rocks -- or soil -- break into a predictable distribution of small, medium, and large particles.  

Using these formulas, the researcher turned to statistical information on arid soil, published in a 1983 study Guillaume d'Almeida and Lothar Schüth from the Institute for Meteorology at the University of Mainz in Germany.  By combining the two, he was able to arrive at what is thought to be the most accurate statistical distribution for particle sizes resulting from soil breaking published to date.

And the results yielded a major surprise.  They showed that the ratio of larger particles to small particles (responsible for heating) was two to eight times higher than originally thought.  In other words, this additional large dust may be both exerting more of a net warming effect on the atmosphere and more of a melting effect on glacial ice.

The difference in ratio is large enough that previous models may have even missed the sign of the net forcing from dust (there may have been a net warming due to global dust, rather than a net cooling).  At the least, the dust's per unit cooling effect is much smaller than previously though.

This raises puzzling questions about historic cooling, which traditionally is accompanied by an increase in global dust.  According to Professor Kok, "We know from paleo-records, such as ice cores and lake/ocean sediment cores, that the atmospheric dust concentration during, for example, ice ages, was several times higher than it is now."

The author believes that this is because current GCMs and climate change models significantly underestimate the current volumes of atmospheric dust circulation, and thus come close to the correct net forcing, despite overstating the dust's per-unit net cooling effect.  If true, this could have important ramifications in the biology field, as the Earth's nutrient circulation model would change.

Another possibility not fully analyzed in the paper is that the cooling effect could instead be lesser, but the warming effect from other inputs e.g. carbon aerosols could be less than previously thought.  This would be very significant if true, as it could have a bearing concerning to what degree current emissions need to be regulated.

A crucial question not discussed by the author, but that also seems apparent, is whether warming can trigger an increase in dust, which in turn reins in the system and results in a cooling.  That is a critical question to assessing the possible impact of aerosol emissions, as it could indicate that the planet as the ability to counteract aerosol emissions, via an increase in dust, at least to an extent.

Again, Professor Kok emphasizes that how atmospheric dust levels change over time is still poorly understood.  But based on our discussion with him, we received the impression that this is absolutely critical to determining how our climate will change in response to a variety of factors, including carbon dioxide emissions.

III. Back to the Drawing Board

The new findings by no means devalue the idea of using computer modeling to study the Earth's climate.  But they are an important reminder that climate models are only as good as their inputs, and in many cases those inputs are based on information that's lacking.

It would be rash not to reevaluate at least some of the modeling work done to date, taking into account this new perspective on atmospheric dust.

How much or how little impact this study has on modeling will rest largely on determining more accurately how atmospheric dust levels vary with time.  According to a brief conversation we had with Professor Kok, the levels of atmospheric dust and how they change with time is a poorly "understood" topic.  Thus the study could potentially invalidate currently collected data from current warming models, or leave it largely unscathed.  But it does indicate that a new round of data collection and verification is necessary to determine which is the case.

Despite the controversy that peripheral effect of the study will bring in the non-scientific community, which is preoccuppied with the kind of instant, absolute answers that can justify billion dollar policy decisions, most objective members of the climate change community will likely take the need for correction in stride. 

The author states:

Climate scientists are acutely aware of the many uncertainties in climate models. They are an imperfect tool to estimate future climate, but they are probably the best tool we have. However, despite the many uncertainties, climate scientists are still able to say that, over long time periods (decades) over which greenhouse warming will overwhelm natural climate variability, the Earth will very likely warm. Exactly how much this warming will be, and how this varies regionally, is still uncertain... For this reason, much of the research in the climate sciences is directed towards reducing uncertainties in climate models by both better understanding processes that are already in the models (such as what my study has done), and by adding additional processes that had not yet been accounted for (the glacier melting by dust deposition has for example been added to some climate models in the last few years). My study is thus a small part of this much bigger effort.

And moreover, Professor Kok thinks that its important not to forget the results' beauty from a mathematical perspective, in the rush to apply them to improving modeling.  He states in the previous NSF press release, "As small as [the particles] are, conglomerates of dust particles in soils behave the same way on impact as a glass dropped on a kitchen floor.  Knowing this pattern can help us put together a clearer picture of what our future climate will look like.  The idea that all these objects shatter in the same way is a beautiful thing, actually.  It's nature's way of creating order in chaos."

Beautiful indeed.  Professor Kok's ability to focus on truly objective mathematical and scientific analysis with regard to what is an increasing politicized topic is exemplary as well.  Given recent revelations [1] [2] [3], this kind of objective dedication to scientific truth is not always present in this field, so it's as refreshing to see that as it is fascinating to observe the symmetry that underlies many laws of our universe.

Update: Dec 31, 2010 11:10 a.m.-

We had a lengthy discussion with Professor Kok to clarify a couple of conclusions that the NSF press release seemed to be pointing at.  Most importantly, Professor Kok explained to us that the levels of small dust was not less than previously expected, rather they were the same and the levels of large dust were higher.

He also explained that solar variance (generally within the range of +/- 0.1 percent of total energy transfered into the atmosphere) and dust's reflectivity (about +/- 0.3 percent of total energy transfered into the atmosphere) indicate that any correlation between dust and the impact of solar activity would be very weak (around 3 ppm).  At 3000 ppm, dust's direct effects via atmospheric dust levels are the more important topic to look at, as confirmed by our further discussions with Professor Kok.

That said the key conclusion of this article -- that warming models need to be re-run with accurate dust info or risk offering misleading conclusions -- still stands, albeit via a different mechanism than we previously thought.  We apologize for the confusion concerning the relationship between solar activity and dust levels.

We'd also like to thank Professor Kok for taking the time to discuss some of this study's finer points.  We're looking forward to doing an interview with him on the topic of climate modeling in the near future.

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Doesn't change a damned thing
By Philippine Mango on 12/29/2010 6:21:18 PM , Rating: -1
Still have to not only eliminate CO2 output but also take out what CO2 we've already emitted and put it back. Reason for this is because it's destroying the oceans, specifically the coral which is really the life of the ocean. No coral reef=no fish=dead ocean. Too much CO2 creates carbonic acid which along with nitrogen runoff from farming, means a destroyed coral.

RE: Doesn't change a damned thing
By jmunjr on 12/29/10, Rating: 0
RE: Doesn't change a damned thing
By Fraggeren on 12/29/2010 6:44:49 PM , Rating: 2
It's true that CO2 levels correlates with destruction of corals, this acidification of the oceans could turn out to be a big deal.

RE: Doesn't change a damned thing
By wordsworm on 12/29/2010 7:13:12 PM , Rating: 2
If mankind's actions had no effect on the planet, there would be no such thing as an environmentalist.

Environmentalists have saved countless birds from fighting DDT. They have fought lead in gasoline. The air in cities I recall from the 80s was a thick smog that used to block out the sun to the extent I couldn't see it in bigger cities. Though smog hasn't been entirely eradicated, the progress is welcomed. We still have a long way to go. There's much that needs to be done to help save our planet.

Environmentalists would love nothing better than to find out that we have no impact on the earth. But, sadly, this is not so. We know that deforestation and dragnet fishing needs to be fought. We also know that there is a finite supply of fossil fuels and that we're on the verge of a nuclear fuel shortage (of course, the new arms reduction deal might stave that off for another period). While some environmentalists are extreme, the majority just want to make sure that the environment in which we live in, today and tomorrow, is healthy and clean as much as we can make it.

There's something else. A single volcano has been shown to have the capacity to either drastically warm or cool the earth depending on the chemical makeup. Either direction can have a negative impact. By continually applying ourselves to environmental studies, we might one day find a way to save ourselves in the event of some catastrophic natural event.

RE: Doesn't change a damned thing
By Spuke on 12/29/2010 10:36:33 PM , Rating: 2
we might one day find a way to save ourselves in the event of some catastrophic natural event.
Or we just may all die.

RE: Doesn't change a damned thing
By Flunk on 12/30/2010 11:31:58 AM , Rating: 2
Actually, that's a certainty. We will all die.

RE: Doesn't change a damned thing
By FITCamaro on 12/30/10, Rating: 0
RE: Doesn't change a damned thing
By Suntan on 12/30/2010 12:15:59 PM , Rating: 2
I know the popular, knee-jerk reaction for a lot of people is to down rate you for saying DDT might be useful, but I tend to agree with you.

I too have read a couple of studies that discovered that *responsible* usage of DDT in poor countries vastly diminished the deaths caused by malaria and other insect borne diseases with little to no impact on the local egg laying animals.

It is just unfortunate that 1) a number of (vocal) environmentalist groups tend to prefer solutions that make a bold statement, even if it indirectly costs human lives in favor of furthering their “cause” and 2) most everyone else just chooses the easier method of outright stopping the use of DDT instead of looking to use it responsibly in places where the human benefit far outweighs the environmental impact because it shuts up the whining environmentalists.


RE: Doesn't change a damned thing
By zozzlhandler on 12/29/2010 7:38:54 PM , Rating: 3
While damage coral is of concern, the co2 levels have been much higher in the past and the sea survived. I believe we need to understand better what is going on before spending billions trying to fix what may or may not be the cause. What if it wasn't co2? The limits on our knowledge and ability to predict have been shown by this study. Should we not learn from this? The (fascinating) book The Black Swan shows clearly how difficult predictions of this kind are. It is foolish to conduct an experiment putting co2 into the atmosphere in an uncontrolled manner, but just as stupid to spend huge sums trying to reduce it when we do not know for sure if it is the cause of our problems.

RE: Doesn't change a damned thing
By raddude9 on 12/30/2010 5:21:09 AM , Rating: 1
While damage coral is of concern, the co2 levels have been much higher in the past and the sea survived.

Not this manure again. Yes, CO2 levels were much higher, but you are talking hundreds of millions of years. In the last million years or so, CO2 levels were always lower than today. And this is what matters to the plans and animals that are currently alive.

CO2 is a greenhouse gas, there is no getting around the physics of it. From that I conclude that it is more stupid to "put CO2 into the atmosphere in an uncontrolled manner" than it is to try to reduce it.

By EricMartello on 12/30/2010 11:46:53 AM , Rating: 2
Yes, for hundreds of millions of years, the earth was warm with higher CO2 levels in the atmosphere...only recently have things began to cool down. Simple logic would suggest that that "norm" for this planet is in fact elevated CO2 levels and global temperatures...and that the current state is the 'fluke'.

CO2 is not the only gas that has a greenhouse effect, and its effects are lower than water making it into some kind of scapegoat to stake a flawed theory upon is a really good way to make sure nobody with something more than a room temperature IQ takes you too seriously.

RE: Doesn't change a damned thing
By zozzlhandler on 12/30/2010 3:04:01 PM , Rating: 2
You Sir, need a lesson on how to discuss in an intelligent manner. Calling something "manure" does not disprove it. Maybe we can use it to fertilize an intelligent discussion?

Anyway, we have seen how supposedly accepted theories can have huge gaping holes, How do we know that its the CO2 causing the coral die-off? What if its something else like silt? We need to know before spending billions on remedies that may or may not work.

By raddude9 on 1/2/2011 6:39:18 AM , Rating: 2
I'm calling it manure because looking at the CO2 levels on earth hundreds of millions of years ago and expecting those levels to have relevance today is patently stupid.

How do we know that its the CO2 causing the coral die-off

higher CO2 --> more acidic oceans --> dead coral

Coral cannot tolerate more acidic water, there's plenty of research to show that if you are bothered to look. What's the point in spending money on research if people are too blinkered to read or understand it.

RE: Doesn't change a damned thing
By GatoRat on 12/30/2010 1:59:52 PM , Rating: 2
Actually, pretty good studies have found a much stronger correlation with ocean silt and coral die off. This is directly related to over deforestation on many islands and the resulting mud flowing into reefs and blocking sunlight.

"There is a single light of science, and to brighten it anywhere is to brighten it everywhere." -- Isaac Asimov

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