Andrew, Looking at global historic data of warming, one might at first glance conclude that only a relatively small amount of global warming did cause the arctic melting we're witnessing now. So, the conclusion would then be that we similarly needed to reflect just a small amount of sunshine back into space to have the reverse effect.
However, what complicates things is that global warming is amplified in specific areas, notably around the North Pole. East Siberia was at times 7°C warmer than normal during the summer of 2007 and the East Siberian permafrost region alone contains 500 billion tonnes of carbon. So, we would need to achieve much more cooling there to avoid further melting. In other words, it's going to be hard to come up with exact amounts of water vapor or aerosols that needed to be released to achieve the same amount of cooling worldwide. And of course, we don't need to achieve the same amount of cooling everywhere. What is most urgent is the arctic melting of sea-ice and permafrost. Therefore, I suggest to make a start by getting ships as proposed by Stephen Salter to cruise as close to the arctic as possible. Such a proposal should be discussed and considered at the Major Economies Forum on Energy and Climate, set in Washington this month, followed by a summit in Italy in July. Obama has invited the leaders of 16 major economies, as well as the secretary general of the United Nations, to participate in this forum. http://voices.washingtonpost.com/44/2009/03/28/obama_sets_international_clima.html This Forum seems to focus only on energy. We should present the forum with a similar Open Letter that we recently presented to Dr Pachauri, head of the IPCC, in which we suggested that a comprehensive approach to global warming should consist of three parts: Part A: Emissions reduction Part B: Carbon stock management Part C: Heat transfer and radiation management I hope to convince further members of this group to become signatories to such an Open Letter to this Forum. Cheers! Sam Carana On Wed, Apr 1, 2009 at 8:31 PM, Andrew Lockley <[email protected]> wrote: > I'm not so concerned about the absolute physical limits of the process (as > in max temperature or forcing reached). What concerns me is the ability to > avoid dangerous climate change by using geoeng to arrest or reverse > dangerous effects. > I'd be really interested to see calculations that show whether geoeng can or > cannot 're-freeze' the Arctic. If it cannot, then maybe John Nissen is > right and we have a very short time to act. If it can re-freeze it, then > the risks of 'full scale' SRM geoeng probably outweigh the benefits by a > substantial margin at this stage, and for some time to come. (Much further > research is needed into geoeng and also ice dynamics and carbon cycle > feedbacks). > I think that this is one of the most fundamental things we have to > demonstrate when considering the case for geoeng. Is there anyone on this > list who'd be willing to bring forward a paper or informal research on the > interaction between ice-albedo feedback and SRM geoeng. > A > > 2009/4/1 Eugene I. Gordon <[email protected]> >> >> As you probably know greenhouse gas is a positive feedback on global >> surface temperature but saturates when it becomes a black body. As the >> concentration of greenhouse gas goes up the layer become blacker and blacker >> (in the IR that is) As it becomes blacker the amount of radiation sent back >> to the Earth's surface saturates. IT IS NOT A REFLECTOR NOR IS THE LAYER >> GOING TO GET HOTTER AND RADIATE MORE ENERGY BACK AS THE EARTH WARMS UP. So >> there is a concentration of CO2, methane, water vapor etc. above which the >> greenhouse layer sends back a maximum amount of energy independent of the >> concentration. The positive feedback saturates. Does anyone know what that >> level is and what fraction of the radiation from the surface is currently >> returned? In any case there is no tipping point and there may be a limit to >> how high the surface temperature can go (of course there is a limit, it is >> about 24 C). Geoengineering other than CO2 removal controls the forcing >> function (the sun intensity at the Earth's surface). There is a lot of loose >> talk about tipping points that needs to be eliminated. >> ________________________________ >> From: [email protected] >> [mailto:[email protected]] On Behalf Of Andrew Lockley >> Sent: Tuesday, March 31, 2009 6:49 PM >> To: geoengineering >> Subject: [geo] the limits of geoengineering? >> >> There's been quite a few suggestions on this list that we need to use >> geoengineering whilst we still can. >> I'm not convinced by this argument, and I'd like to investigate how long >> the 'window of opportunity' for geoeng is. >> Lenton and Vaughan found that Aerosols could counter a doubling of natural >> CO2, and space sunshade (if possible) could go much further >> This seems to suggest that we have quite a while to act. Even in the even >> of the start of a methane pulse which gives a doubling of co2 equivalent, we >> can still ramp up geoengineering intervention quickly if needed. I suggest >> that we'd have at least 5yrs or so warning, even of a really sudden methane >> pulse from permafrost. >> However, the big risk, as I see it, is that ice-albedo feedback will be >> too strong in the arctic to overcome with geoeng. I know that re-freezing >> will occur in winter, but the thickness of the ice may not be sufficient to >> last all year, even with geoeng. If this happens, we may be unable to stop >> the methane pulse from permafrost occuring (if it indeed does). >> I don't have the skills needed to do the complicated sums, nor do I have >> access to clever computers that can do them for me. Could someone therefore >> suggest how long we've got before the 'window of geoengineering opportunity' >> closes - if it indeed does? >> A > > > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
