I came upon this study and find it interesting . . . the research indicates that Cirrus Cloud reductions (through a type of high tropospheric cloud seeding) could result in slowing global warming and that commercial aviation could be the easiest and cheapest way to accomplish such geoengineering without much of the side effects of sulfur injection for example . . . the amount of cloud seeding material would be small in comparison to the sulfur injected into the stratosphere . . . Modification of cirrus clouds to reduce global warming
David L Mitchell and WilliamFinnegan
Desert Research Institute, Reno, NV89512-1095, USA
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.
[link to iopscience.iop.org