“Sulfate Lens” Enhances Climate Warming Properties of Atmospheric Soot
30 June 2009
Particulate pollution thought to be holding climate change in check by reflecting sunlight instead enhances warming when combined with airborne soot, according to a new study by researchers at the University of California, San Diego. They report on their work in the Proceedings of the National Academy of Sciences online the week of June 29.
Soot, also called black carbon, absorbs solar energy. Recent atmospheric models have ranked soot second only to carbon dioxide in potential for atmospheric warming. But particles, or aerosols, such as soot mix with other chemicals in the atmosphere, complicating estimates of their role in changing climate.
Until now, scientists have had to assume how soot is mixed with other chemical species in individual particles and estimate how that ultimately impacts their warming potential. Our measurements show that soot is most commonly mixed with other chemicals such as sulfate and this mixing happens very quickly in the atmosphere. These are the first direct measurements of the optical properties of atmospheric soot and allow us to better understand the role of soot in climate change.
— Kimberly Prather, professor in the Department of Chemistry and Biochemistry and the Scripps Institution of Oceanography at the University of California, San Diego
Prather and Ryan Moffet, a former graduate student at UC San Diego who is now at the Lawrence Berkeley National Laboratory, measured atmospheric aerosols over Riverside, California and Mexico City. Using an instrument that measures the size, chemical composition and optical properties of aerosols in real time, they showed that jagged bits of fresh soot quickly become coated with a spherical shell of other chemicals, particularly sulfate, nitrate, and organic carbon, through light-driven chemical reactions.
Within several hours of sunrise, most of the atmospheric carbon they measured had been altered in this way. Particles of sulfate or nitrate alone reflect light, and some have proposed pumping sulfate aerosols into the atmosphere to slow climate change. But these chemicals play a different role when they mix with soot.
The coating acts like a lens and focuses the light into the center of the particle, enhancing warming. Many people think sulfate aerosols are a good thing because they are highly reflective and cool our planet. However we are seeing that sulfate is commonly mixed with soot in the same particles, which means in some regions sulfate could lead to more warming as opposed to more cooling as one would expect for a pure sulfate aerosol.
—Kimberly Prather
Their measurements showed that in the atmosphere the lens-like shell of sulfate and nitrate enhances absorption of light by coated soot particles 1.6 times over pure soot particles.
Efforts to reduce soot would pay off soon. Unlike carbon dioxide, which lingers in the atmosphere for centuries, soot falls from the sky in a matter of days to weeks, making the reduction of soot a quicker option for slowing down climate change.
"Recent atmospheric models have ranked soot second only to carbon dioxide in potential for atmospheric warming. "
What happened to the 85% component of greenhouse gases - H2O? Water vapor? This is a revealing statement about why the models have gone wo wrong. Their weighting is utterly barmy. And they make little room for variability like clouds. Which is probably the reason they fail in predictability.
Posted by: sulleny | 30 June 2009 at 11:09 AM
It is hardly a novel insight that there are clouds in the sky. And of course the effect of atmospheric water vapour and cloud distribution is much studied, and debated in greenhouse science. And the overwhelming consensus (other than by those who know there were 20 Cubans on that grassy knoll) is that the net water vapour and cloud effects are secondary to warming caused by carbon dioxide and other gases like methane.
Posted by: SVW | 30 June 2009 at 03:41 PM
The effect of water vapour as a GHG, is probably around 36-70%. And yes that larger than CO2's effect but smaller than the 85% being quoted.
The problem is the context of the statement of CO2 being the most important GHG. Considering the transient nature of water vapour, some argue quite convincingly, that it is a magnifier of longer lived GHG's in the atmosphere. This would make CO2, the gas with the most impact.
The total forcing all the components in the atmosphere give a positive 33 degree forcing. If the longer lived components didn't raise the temperature enough to allow water to exist in a vapour state easily, then as a component, it would soon be negligible. The radiation earth receives should only heat it to -18C. CO2 traps enough energy to create a atmospheric temperature whose relative humidity is enough to keep enough water vapour in the air to raise the temperature to an average 15C.
A good explaination of this can be found at
http://www.realclimate.org/index.php?p=142
Or the context could be in terms of what people can do or are doing.
As to the soot, well there was the effect of black soot on arctic ice melt article in GCC. But the experimental evidence of soot is of much more recent history and I think should be explored in more detail.
Posted by: aym | 30 June 2009 at 04:59 PM
Actually, there is a way to get around an 85% effect of water vapour. If you include clouds but that is a maximun amount and is a sort of arbitrary pick. By the same token, you could arbitrarily pick the high number for the range that CO2 contributes and gets a GHG combined effect of over 100%. Plus ideal clouds around the earth all the time?
Posted by: aym | 30 June 2009 at 05:10 PM
Oops, time to recalibrate the climate models again.
New factors and parameters are discovered so often that sometimes I get a bit of a queasy feeling about the accuracy of climate models that are supposed to account for nearly everything. I always wonder how much there is still to be discovered about the earth's climate system.
Posted by: Fred H | 01 July 2009 at 07:37 AM
"But the experimental evidence of soot is of much more recent history and I think should be explored in more detail."
I agree. And this is what I am calling on. The definition of warming components is in a constant state of flux these days. It seems no sooner is one "forcing" falsified than someone dreams up a new one. This is not anything more than unproven theory.
"And the overwhelming consensus (other than by those who know there were 20 Cubans on that grassy knoll) is that the net water vapour and cloud effects are secondary to warming caused by carbon dioxide and other gases like methane."
You might want to study a bit about volcanic effects on global temperature and ocean temperature effects such as the PDO. Apparently you believe contrarians Kepler and Copernicus were on the knoll with the "Cubans." Start with Ian Plimer's Heaven and Earth
Posted by: sulleny | 01 July 2009 at 01:01 PM
There is a difference between quantification of a probable GHG component in AGW and it's an existance of a newly considered component invaldating anything.
Looking at the way GHGs behave, the sulfate-soot components may already have reached a plateau contribution to GH warming. They could already be incorporated into the models as forcing components of other gases as a set amount of forcing.
Studying and quantification would bring into focus the benefits , if at all, of what controlling this material would bring.
The theory isn't proven because all theories cannot be proven. To be proven assumes total knowledge of every aspect and that doesn't exist for anything in science. We learn new things about every aspect of our knowledge.
AGW is the best explaination because of the thousands of peer reviewed studies, papers, and observations that support it. It encompasses and uses various physical laws.
The fundamental problem with the denialists is the cherry picking of the data and the ignoring of the thousands of studies and papers. If the denialists cannot release any peer reviewed paper that expains what is happening, and I mean peer reviewed not just believed in, then denialism at its heart is flawed.
Posted by: aym | 02 July 2009 at 08:34 AM