John- I would think we all agree with you about the urgency to cool the arctic (especially in permafrost regions), and the need to evaluate promising mitigation techniques that could be deployed as soon as possible. I don't know what the process is going to be for evaluating concepts, but I do believe that using Lair or LN2 to reduce humidity at the top of the atmosphere (TOA) warrants further investigation. Just thinking about it from an "engineering judgement" standpoint, it seems that releasing many 100-ton payloads of Lair at the TOA should create very large regions of perfectly dry air, since the Lair expansion ratio is over 7,000 times at 50,000 ft (the ceiling of a KC-135, as an example). This dry air should increase radiation of the earth's heat to space by mixing with the resident TOA air and reducing average humidity. This process should also evaporate existing cirrus clouds, giving a visual confirmation that it's working. I believe a significant improvement to this approach would be to use a heat exchanger that would heat the Lair as it's expelled using heat from the aircraft's engine exhaust (i.e.bleeding off of this. This would heat the Lair into a very hot and dry air before it's expelled, causing the Lair to expand far beyond 7,000 times to reduce humidity over an even larger region. This very hot and dry air has a key benefit of bouyancy, so that Lair released at 50,000 ft, for example, would continue to rise higher in the TOA region, making it significantly more effective.
_____ From: John Nissen [mailto:[email protected]] Sent: Wednesday, September 14, 2011 1:00 AM To: David Mitchell Cc: Mark Massmann; 'Kevin Layton'; Geoengineering; Ken Caldeira; Sam Carana; John Gorman; Emily; Brian Orr; Peter Carter; Tom Barker; Brian Launder Subject: Cooling the Arctic by removing clouds Dear David, I believe you were considering a form of geoengineering that doesn't come under "solar radiation management" (SRM), but rather "thermal radiation management" (TRM), i.e. by removing cloud cover and increasing thermal radiation into space from the surface of land and sea. We need as much negative forcing (i.e. cooling) as we can quickly get in/into the Arctic, because of the perilous state of some of the methane in the Arctic, particularly in the area of the East Siberian Arctic Shelf (ESAS), where the methane could get discharged in huge quantities without warning to immediately boost global warming by many times [1]. Cloud brightening can cool the Arctic through cooling the surface water of currents entering the Arctic from the Atlantic, but there is a limit to how far one can go with that before it starts affecting climate in Europe! And this method could take years to cool the ESAS waters by the several degrees needed to slow methane discharge and stabilise the situation. So we will almost certainly need stratospheric aerosols to produce a general cooling effect over the whole Arctic during the spring and summer months. However cloud removal could be a useful supplement, especially because of uncertainties in the logistics and effectiveness for rapid aerosol deployment [2]. One could remove the clouds either by evaporating them, as Mark Massmann is suggesting (see email appended below), or by making them discharge their H2O content as snow. The latter approach has the advantage of increasing albedo of land and ice surfaces below, where they are not already covered by fresh snow; so it has an SRM aspect - making it a double-edged sword. I look forward to your suggestions for the most effective combination of geoengineering techniques, considering the desirability of readiness for full-scale deployment next spring - if this were possible and shown to be the best risk-minimisation strategy! Best wishes, John [1] Shakhova and Semiletov estimate that up to 50 Gt methane could be discharged "at any time" [3], boosting atmospheric content by around 11 times the present (~5 Gt). The resulting climate forcing would be at least 20 times the present methane forcing (0.48 W/m-2) because of indirect forcing effects [4]. Such a discharge could be produced by earthquake, and part of the ESAS is prone to earthquakes. Thus the probability of such a discharge happening cannot be known exactly, but the risk is enormous because of the fatal consequences, assuming: risk = probability x magnitude [2] The tethered balloon method of stratospheric aerosol deployment could take years to develop, so I assume we'd use stratotankers or similar. It is also conceivable (though extremely unlikely in my view) that some adverse side-effect would appear such as to force a termination of deployment, in which case TRM could become the key technology for general Arctic cooling. Anyhow we need a belts and braces approach in this precarious situation. [3] http://en.wikipedia.org/wiki/Arctic_methane_release [4] http://www.atmos.washington.edu/academics/classes/2011Q2/558/IsaksenGB2011.p df -- On 02/07/2011 11:15, Mark Massmann wrote (under subject "Modified Lair concept") John and Kevin- I've been going through calculations for various Lair strategies, and in the process have found some new strategies for Lair. 1. One is to reduce global cirrus clouds. By releasing Lair over cirrus clouds (say 50,000 ft), it will expand over 7,000 times into perfectly dry air and cause cirrus to sublimate (basically drying them out). This effect could be done on a very large scale and should last much longer than creating new clouds, because once a cirrus region is dry and cirrus free, it would stay that way until new cirrus is formed. 2. The other is to add salt-CCN's to brighten marine clouds (i.e. replace MCB). Here, Lair would primarily be used as a disbursent for salt-CCN's, where the CCN's would be added to Lair so that they mix and are suspended in it, so that when Lair is released the CCN's would be evenly disbursed over a large region. This way you could essentially replace the function of MCB- and do this ASAP to help cool the arctic instead of waiting on a fleet of MCB vessels to be manufactured (at least 5 years down the road). Please let me know what you think of these, and I will make a new posting outlining them to the group. Also John- please let me know what cloud area is needed to help protect the arctic (I'm assuming it's smaller than what's needed to globally offset global warming, though it could be close if you wanted much more cloud coverage per area). Thanks! Mark -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
