Hi David--I have run the MAGICC model of Wigley turning off all emissions (all GHGs, all aerosols)--so an impossibly aggressive limiting case. The black carbon and sulfate effects go away virtually immediately, tropospheric ozone almost as fast, methane over 1-2 decades, and then one is left with the slowly decreasing forcing of the long-lived species--CO2, N2O and halocarbons (with no cooling offset). This leads to several decades of forcing not unlike net forcing today, so one would get continued ocean warming.
You can also look at the IPCC Fourth Assessment and their case of constant forcing (that goldish curve). They kept all concentrations and aerosol loadings the same--which is actually not self-consistent as to keep the CO2 concentration constant, emissions would have to drop by 80% or maybe more, and so SO2 emissions would be expected to drop equivalently, reducing the cooling offset by 80% or so. Of course, so would the black carbon warming influence, which may almost offset the sulfate loss. As the IPCC temperature result shows, one would get about a half degree of further warming. One would thus expect the Arctic to warm more and likely mean there would be virtually no summer sea ice, and this would lead to quite thin winter sea ice that would melt earlier in the spring, and so more solar absorption, etc.--so warming in Arctic would be greater than global average (as is now the case). Now, I happen to think (see my ERL paper) that the reduction in sulfate loading in the Arctic (the cleaning up of Arctic haze) as a result of reduced SO2 emissions from Europe and Russia (at least springtime air into the Arctic typically passes over these regions) is likely contributing to the accelerated melting of the Arctic as compared to models (which don't typically treat this effect, especially as global SO2 emissions are likely headed back up). Thus, in my view we have an analog for a reverse geoengineering experiment--I admit this is a hypothesis, but given all the data that has been taken over the last few decades in cleaning up Arctic haze, there is likely an observational data base for exploring this possibility. While I know some attribute the accelerated melting to soot, Quinn et al in Tellus show, at least for some months, that soot deposition has been going down along with the sulfate decline. What needs to be looked at are data for changes in sunlight and downward IR onto the sea ice as a function of season--and NOAA and others may at least have some data on this. Less springtime sulfate may well lead to earlier melting of surface snow cover, lowering the albedo and then increasing the loss. If all of this is the case, then, indeed, we might want to put the sulfate back over the Arctic--in the troposphere where during summer lifetime might be up to 2 weeks or so [Alan Robock's lower Arctic stratosphere injection had a lifetime of 2 months--far below the global average 2 year versus one week ratio for stratospheric (volcanic) to tropospheric sulfate.] Injection could be done from a few mountain locations on days when winds are headed into the Arctic and need only occur for a the few sunlit months starting when the snow cover albedo drops, so geoengineering injection would likely be a small fraction of recent surface emissions and we thus likely could estimate impacts on sea ice, ecosystems, etc. from past records as well as from models. And, done cleverly, it is not at all clear that just cooling the summertime Arctic would lead to summertime cooling of the surrounding continental areas and suppress the monsoon. What we need to get at all of this is a solid research program where efforts are made to refine and develop ideas, seeing if adjustments can overcome the worst of the side effects (injections on one or the other side of the Arctic, at various times during the sunlit season, injections at additional locations, and so on) rather than just assertions like mine and model simulations that aren't directly representing the proposed intervention. Best, Mike On 12/10/09 7:12 PM, "John Nissen" <[email protected]> wrote: > > Curiously, I can't find you any references. But it's rather obvious if > you think about the relative timescale - and I've challenged many top > climate scientists to dispute it, and nobody has managed! The Arctic > sea ice is indeed the "Elephant in the room", that nobody chooses to > notice, because the prospect of having to deploy geoengineering is so > uncomfortable for them. > > Perhaps it's cowardice. But it's potentially tragic because > geoengineering could be left too late. > > John > > -- > > Hawkins, Dave wrote: >> Hi John, >> In your note you say, "The undisputed fact that emissions reduction cannot >> save the Arctic sea ice, at its current rate of retreat..." >> Can you provide a reference or two that reaches this conclusion? >> (I'm not asking to dispute what you say but would like to see what you have >> in mind as support for the proposition.) >> Thanks >> David >> >> ----- Original Message ----- >> From: [email protected] <[email protected]> >> To: Geoengineering <[email protected]> >> Sent: Thu Dec 10 16:46:31 2009 >> Subject: [geo] Population control, emission cuts, but geoengineering? >> >> >> Hi all, >> >> Two excellent programmes on the environment and mankind's impact: >> >> David Attenborough: >> http://www.bbc.co.uk/iplayer/episode/b00pdjmk/Horizon_20092010_How_Many_Peopl >> e_Can_Live_on_Planet_Earth/ >> >> >> Iain Stewart: >> http://www.bbc.co.uk/iplayer/episode/b00jf6md/Hot_Planet/ >> >> Unfortunately, although Iain had sympathetic mention of Klaus Lackner's >> artificial trees, solar radiation management was represented by sulphur >> being fired into the stratosphere by guns - mention of ozone disruption >> - and the programme ended with punch line "geoengineering is too >> expensive and too dangerous". This was an unwarranted dismissal of the >> technology with probably the best chance of saving the Arctic sea ice. >> The undisputed fact that emissions reduction cannot save the Arctic sea >> ice, at its current rate of retreat, was not mentioned. >> >> Cheers, >> >> John >> >> >> >> -- >> >> 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. >> >> >> > > -- > > 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. > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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