George B
Extinct but not forgotten Staff Member
One scheme which is not talked about much . . . it doesn't use Sulfur Compounds nor does it use injection into the stratosphere is the following . . . it uses a type of high tropospheric cloud seeding to reduce cirrus clouds and thus reduce the amount of heat retained or reflected back into
You will notice form this same paper (quote above) that the targeted area to mitigate Cirrus Clouds is where Cirrus Clouds naturally form . . . which is the same areas where contrails form via air traffic. So the aircraft do not produce the Cirrus Clouds they only trigger their formation when conditions are ripe . . . The key to this paper is that one could use silver iodine or some other nucleating agent to dissipate Cirrus Clouds in the higher Troposphere not that it is now being done!!!
Seems a possible scenario could be to get permission for each long haul commercial jet to carry a canister of silver iodide (AgI) and when they transverse an area of projected cirrus cloud bank (persistent contrail) activity via a projection by NASA . . . a ground signal could release the contents of the canister . . . this would be a passive system . . . when a canister is expended it would be replaced at the next airport . . . [link to cloudsgate2.larc.nasa.gov]http://cloudsgate2.larc.nasa.gov/cgi-bin/site/showdoc?docid=33&cmd=latest
External Quote:Modification of cirrus clouds to reduce global warming
David L Mitchell and William Finnegan
Desert Research Institute, Reno, NV 89512-1095, USA
E-mail: david.mitchell@dri.edu
Received 1 April 2009
Accepted 12 August 2009
Published 30 October 2009
Abstract.
Greenhouse gases and cirrus clouds regulate outgoing longwave radiation (OLR) and cirrus cloud coverage is predicted to be sensitive to the ice fall speed which depends on ice crystal size. The higher the cirrus, the greater their impact is on OLR. Thus by changing ice crystal size in the coldest cirrus, OLR and climate might be modified. Fortunately the coldest cirrus have the highest ice supersaturation due to the dominance of homogeneous freezing nucleation. Seeding such cirrus with very efficient heterogeneous ice nuclei should produce larger ice crystals due to vapor competition effects, thus increasing OLR and surface cooling. Preliminary estimates of this global net cloud forcing are more negative than–2.8 W m–2 and could neutralize the radiative forcing due to a CO2 doubling (3.7 W m–2). A potential delivery mechanism for the seeding material is already in place: the airline industry. Since seeding aerosol residence times in the troposphere are relatively short, the climate might return to its normal state within months after stopping the geoengineering experiment. The main known drawback to this approach is that it would not stop ocean acidification. It does not have many of the drawbacks that stratospheric
injection of sulfur species has.
http://iopscience.iop.org/1748-9326/4/4/045102/fulltext/
"Substances exist that nucleate ice crystals as effectively as silver iodide (AgI, the best ice nucleant known) at cirrus cloud temperatures, and some are relatively inexpensive and non-toxic (see section 2.1). If significantly larger, these artificially seeded ice crystals would fall faster, and their higher fall velocities may lead to reduced cirrus cloud coverage as predicted in GCM simulations (Mitchell et al 2008, Sanderson et al 2008). The lower cirrus cloud coverage would result in greater OLR and cooler surface temperatures, thus reducing the impact of global warming. It is important to note that the decrease in cirrus coverage would occur where the cirrus greenhouse effect is strongest (i.e. temperatures < –40 °C). This is a key principle for this geoengineering idea."
You will notice form this same paper (quote above) that the targeted area to mitigate Cirrus Clouds is where Cirrus Clouds naturally form . . . which is the same areas where contrails form via air traffic. So the aircraft do not produce the Cirrus Clouds they only trigger their formation when conditions are ripe . . . The key to this paper is that one could use silver iodine or some other nucleating agent to dissipate Cirrus Clouds in the higher Troposphere not that it is now being done!!!
Seems a possible scenario could be to get permission for each long haul commercial jet to carry a canister of silver iodide (AgI) and when they transverse an area of projected cirrus cloud bank (persistent contrail) activity via a projection by NASA . . . a ground signal could release the contents of the canister . . . this would be a passive system . . . when a canister is expended it would be replaced at the next airport . . . [link to cloudsgate2.larc.nasa.gov]http://cloudsgate2.larc.nasa.gov/cgi-bin/site/showdoc?docid=33&cmd=latest
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