Hi All
You must have a contrast change of at least 20% to be able to see a ship
track. We can do useful cooling with contrast changes that you would
not see. If we know where not to spray we can avoid decreased albedo
unless we get in a panic about the overdue ice age.
Is the reduction in albedo due to making the clouds rain or drizzle?
Stephen
Emeritus Professor of Engineering Design. School of Engineering.
University of Edinburgh. Mayfield Road. Edinburgh EH9 3JL. Scotland
[email protected] Tel +44 (0)131 650 5704 Cell 07795 203 195
WWW.see.ed.ac.uk/~shs YouTube Jamie Taylor Power for Change
On 14/08/2014 17:21, Ken Caldeira wrote:
I am not sure of the quality of this reference (attached) but it is
relevant:
Occurrence of lower cloud albedo in ship tracks
Y.-C. Chen^1 , M. W. Christensen^2 , L. Xue^3 , A. Sorooshian^4 ,
G. L. Stephens^5 , R. M. Rasmussen^3 , and J. H. Seinfeld^1,6
^1 Division of Engineering and Applied Science, California Institute
of Technology, Pasadena, California, USA
^2 Department of Atmospheric Science, Colorado State University, Fort
Collins, Colorado, USA
^3 National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA
^4 Department of Chemical and Environmental Engineering/Atmospheric
Sciences, The University of Arizona, Arizona, USA
^5 Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, California, USA
^6 Division of Chemistry and Chemical Engineering, California
Institute of Technology, Pasadena, California, USA
Abstract. The concept of geoengineering by marine cloud brightening is
based on seeding marine stratocumulus clouds with sub-micrometer
sea-salt particles to enhance the cloud droplet number concentration
and cloud albedo, thereby producing a climate cooling effect. The
efficacy of this as a strategy for global cooling rests on the extent
to which aerosol-perturbed marine clouds will respond with increased
albedo. Ship tracks, quasi-linear cloud features prevalent in oceanic
regions impacted by ship exhaust, are a well-known manifestation of
the effect of aerosol injection on marine clouds. We present here an
analysis of the albedo responses in ship tracks, based on in situ
aircraft measurements and three years of satellite observations of 589
individual ship tracks. It is found that the sign (increase or
decrease) and magnitude of the albedo response in ship tracks depends
on the mesoscale cloud structure, the free tropospheric humidity, and
cloud top height. In a closed cell structure (cloud cells ringed by a
perimeter of clear air), nearly 30% of ship tracks exhibited a
decreased albedo. Detailed cloud responses must be accounted for in
global studies of the potential efficacy of sea-spray geoengineering
as a means to counteract global warming.
*Citation:* Chen, Y.-C., Christensen, M. W., Xue, L., Sorooshian, A.,
Stephens, G. L., Rasmussen, R. M., and Seinfeld, J. H.: Occurrence of
lower cloud albedo in ship tracks, Atmos. Chem. Phys., 12, 8223-8235,
doi:10.5194/acp-12-8223-2012, 2012.
_______________
Ken Caldeira
Carnegie Institution for Science
Dept of Global Ecology
260 Panama Street, Stanford, CA 94305 USA
+1 650 704 [email protected]
<mailto:[email protected]>
http://dge.stanford.edu/labs/caldeiralab
https://twitter.com/KenCaldeira
Assistant: Dawn Ross <[email protected]
<mailto:[email protected]>>
On Thu, Aug 14, 2014 at 8:59 AM, Andrew Lockley
<[email protected] <mailto:[email protected]>> wrote:
Ship traffic terminates in busy ports, but on the high seas, they
are relatively dispersed, and cross winds serve to distribute the
sulphur and / or resulting aerosols.
I remain of the opinion that making this change without good
science is an extremely risky thing to do.
A
On 14 Aug 2014 16:43, "Mike MacCracken" <[email protected]
<mailto:[email protected]>> wrote:
I was asked by a colleague about what is expected to happen as
marine bunker
fuels are desulfurized over the coming several years. My first
response was
that it would reduce the SO2 emissions and so the sulfate, and
since sulfate
adds to cooling, this would suggest the desulfurization would
lead to a
warming influence.
But then, the key to cloud brightening is addition of CCN in
relatively
unpolluted regions (so yes, over remote oceans), but is not
much of the ship
traffic in relatively polluted regions? Experiments do seem to
indicate that
over-saturation of CCN tends to lead to cloud clearing--so
basically we are
in the Goldilocks situation--one needs to have neither too few
CCN nor too
many to get cloud brightening.
So, might it be that in some polluted regions, reducing the
SO2 emissions
from marine sources might actually lead to an increase in
clouds/cloud
brightness? Has anyone done a really careful analysis of this?
Do we really
have good quantitative estimates of what might happen? And how
might all of
this play out as the other sources of SO2 are changing?
Perhaps Stephen Salter, John Latham, Alan Gadian, et al. have
a paper(s) on
this that I have missed.
Mike MacCracken
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