[geo] SRM geoengineering as soon as possible?

[John Nissen]

Hi all, I argue that we shouldn't wait for the sea ice to disappear, but get on with SRM geoengineering with due haste.  This is what I wrote to John Shepherd and Ken Caldeira on this subject recently: --- So I don't see any alternative to SRM for generally cooling the Arctic and saving the sea ice.  (Reduction of black carbon would also help, as Tim Lenton points out, but I disagree with him that it could be an alternative.)  It will have to be done eventually, but when is the best time?  I would argue that the best time is as soon as possible, for a number of reasons: Positive feedback is building up; Less SRM is required if done sooner; Side-effects will be smaller, and more easily dealt with; There's a lot of uncertainty about how quickly sea ice could disappear; There is a risk that techniques do not work as well as expected; If one technique fails there is more time to modify it or develop alternatives; Deployment might have to be temporarily suspended for some reason, and there would be more time to play with. We do not know how well stratospheric aerosols would work - especially because of unknown droplet size, movement in air currents, and lifetime.  Therefore, I would suggest that some field-trials are started for stratospheric aerosols at high latitudes in spring (to reduce ozone depletion risk) - ideally next spring in/near Arctic, but otherwise next spring in/near Antarctic.  Balloons and/or high-flying aircraft could be used.   Monitoring could be by instrumented balloons, if suitable satellites are unavailable. As you point out, deployment in both north and south high latitudes would be desirable to minimise chance of unbalancing the hemispheres, and because there are threats from polar amplification in both polar regions. Probably the biggest side-effect risk is from disruption of monsoons, and one might want to reduce or suspend SRM in a period of high El Nino for example.  And you would probably want to suspend SRM if there were a major volcanic eruption, ejecting sulphur into the stratosphere. Deploying stratospheric aerosols would then buy time for the development and deployment of safer (even safer) but more expensive techniques, in particular the marine cloud brightening.  Somebody has suggested this technique would take ten years - but with a crash programme, we should aim to have it ready much sooner - not only as an insurance policy, but it opens up options for a mix and match approach to SRM (e.g. stratospheric aerosols for general cooling, cloud brightening for more local cooling). BTW, efforts to reduce sulphate aerosol pollution in the troposphere, e.g. from ships, should be subject to a moratorium, because their masking of global warming is so valuable. --- Do you disagree with any of that? Cheers from Chiswick, John -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineer...@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.