John: I keep saying this and someday someone will bother to look at www.scotese.com and click on climate to see the 540 million year climate history of the earth derived from proxy records. There is a strong positive greenhouse feedback effect that is operative until the positive feedback saturates which is when the greenhouse layer becomes a black body. The temperature saturates at around 25 C. Your position is totally correct unless someone finds an alternative explanation to positive feedback and heating, which I doubt they will. AGW is just a minor perturbation speeding up the long, not monotonic, temperature rise. We need geoengineering to save the climate from disaster.
_____ From: [email protected] [mailto:[email protected]] On Behalf Of John Nissen Sent: Friday, June 12, 2009 7:56 AM To: Tom Wigley Cc: [email protected]; Geoengineering; [email protected]; [email protected] Subject: [geo] Re: Back to Nature Dear Tom, Let us first set aside considerations of tipping points in the Arctic, and focus of the CO2 effect on temperature. This is a fundamental question: which of us is right about the effect of zero CO2 emissions! The whole basis of the forthcoming Copenhagen meeting is that, if we reduce global CO2 emissions sufficiently, and sufficiently quickly, then it will reduce global warming such as to keep the temperature below a ceiling - suggested as 2 degrees below the 1900 temperature level by some, 1 degree below the 2000 level by professor Jim Hansen (equivalent to 1.7 degrees below the 1900 level). I query that whole basis. You said your model is "consistent with the science of the AR4". Now, when I looked at the models being used by IPCC and Hansen, it seemed that they assumed a relatively short effective CO2 lifetime, somewhere in the range 50-200 years. However effective lifetime of a proportion of the excess CO2 (above pre-industrial 280 ppm level) is now thought to be many thousands of years [1]. Indeed David Keith, in his talk to us at the RGS on May 14th [2], emphasised that the effective half-life of anthropogenic CO2 was many thousands of years - much longer than nuclear waste! There is certainly sufficient to continue a net forcing for global warming, currently at 1.6 W/m-2. So I just don't believe that reducing emissions can halt global warming. I said so to professor Hansen when I met him very briefly before a lecture, but he said he was sure that negative feedback would cut in quickly. Where is this negative feedback coming from? There is a small amount from increased infra-red heat radiation, as the average global temperature increases. Against that, there is mounting positive feedback, e.g. from increased water vapour (a greenhouse gas) and from the "albedo effect" in polar regions. So now if we bring in the Arctic, the melting of the Arctic sea ice will add a globally-averaged forcing of between 0.5 and 1.5 W/m-2. If then the massive amounts of methane, currently trapped in frozen structures, start to get released, then we would have forcing quickly climbing to many Watts/m-2, and we could be in for a warming event on a par with the Paleocene/Eocene thermal maximum (PETM), 55.8 million years ago [3]. That would be my scary "Back to Nature" scenario! So, even if you are right about the effectiveness of emissions reduction, it is academic if we do not cool the Arctic by geoengineering. Can you at least support that message for Copenhagen? Best wishes, John [1] http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B3 According to Archer, some of the excess CO2 (fossil fuel component) will be gradually absorbed by deep ocean over a few hundred years, but the remaining 25% will last for many thousands of years. Here is his model simulation of atmospheric CO2 concentration for 40,000 years following after a large CO2 release from combustion of fossil fuels. Different fractions of the released gas recover on different timescales. Reproduced from The Long Thaw: Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact [email protected] [2] http://www.21stcenturychallenges.org/challenges/engineering-our-climate-is-t here-a-role -for-geoengineering/media-gallery/video/professor-david-keith/ [3] http://en.wikipedia.org/wiki/Paleocene-Eocene_Thermal_Maximum Tom Wigley wrote: John, You are wrong. If we stop all emissions immediately, the warming trend will stop and reverse. In the attached ms I set all emissions to zero from 2021 onwards. Tom. +++++++++++++++++++++++ John Nissen wrote: No, it's all wrong - about the CO2 being absorbed from the atmosphere and the planet cooling. On the contrary, if we were all to drop dead tomorrow, global warming would continue for thousands of years, as I explain in the thread I started, about the GREAT LIE. There'd also be an immediate warming spurt, as the sulphur aerosol pollution (which has a cooling effect) would be quickly washed out of the atmosphere. And,within a few decades, on top of the CO2 warming would be the warming from methane as permafrost melted, and the sea level would rise 60-70 metres as Greenland and Antarctic ice sheets melted. Thus, if we disappear, or just carry on as we are for that matter, the Earth will continue tipping into a super-hot state, which probably won't be habitable for humans, even at the poles. However it is unlikely that the Earth will go the way of Venus, with the oceans boiling away, if that's any comfort. Cheers, John --- Alvia Gaskill wrote: http://en.wikipedia.org/wiki/Aftermath:_Population_Zero I recently saw the Nat. Geo program "Aftermath: Population Zero," one of several hypothetical accounts of what the world would be like without people. Not less people, no people. These seem to have been inspired by the work of Alan Weisman, author of the book "The World Without Us." http://en.wikipedia.org/wiki/The_World_Without_Us In addition to describing what would happen to domesticated animals and pets left without humans to take care of them, the fate of infrastructure is also presented. This particular program (there is another one that has been turned into a series on the History Channel called, appropriately enough, "Life After People" http://en.wikipedia.org/wiki/Life_After_People ; http://en.wikipedia.org/wiki/Life_After_People:_The_Series [for those people still not depressed enough after watching the original documentary]) also explores changes in the Earth's climate without its number one interferent, us. After 150 years, winters are colder than during the last days of humans with greater snowfall, indicating declining GHG levels. It is stated that the oceans will remove 13.5Gt of CO2 per year. Is this correct? After 200 years, the excess CO2 from human emissions is completely eliminated by plants and trees. Don't tell David Archer. Perhaps the increase in plant growth will speed the removal. Or won't that matter? After 500 years, forests return to the state they had 10,000 years ago. I doubt that one, as that would have been at the tail end of the ice age. After 25,000 years, the interglacial is over, the ice sheets return and erase NYC along with most of the areas wiped out before. Which raises an interesting question for the geo haters. If it became apparent that the interglacial was ending, would you be in favor of artificial means of prolonging it to ensure the planet's habitability for billions of humans? If you say no, then I think I'm going to propose to Nat. Geo or History a new series, Life After YOU People! --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
<<inline: climate.2008.122-f1.jpg>>
