Hi All Language can get us into a muddle. Should we stop using the singular, as in THE half life of CO2?
I think David Archer is saying there are several, even many, removal mechanisms which each have different holding capacities and transfer rates. When the fast ones are full . . . . Stephen -- Emeritus Professor of Engineering Design School of Engineering and Electronics University of Edinburgh Mayfield Road Edinburgh EH9 3JL Scotland tel +44 131 650 5704 fax +44 131 650 5702 Mobile 07795 203 195 [EMAIL PROTECTED] http://www.see.ed.ac.uk/~shs David Schnare wrote: > Ken, John, et al: > > My confidence in our understanding of the carbon cycle has reached > what I hope is a nadir. Attached is a chart of Mona Loa CO2 data and > actual CO2 emissions data. They do not reflect a 100 year dwell time > in the atmosphere. The literature on CO2 half-life suggests a 7.5 > year half-life with the range from about 5 to 15 years. That range is > a better explanation of the actual CO2 data than the modeled estimates > (by a wide margin). > > Thus, one wonders, what are the GCM modelers assuming, and how close > to reality is that? > > David Schnare > Center for Environmental Stewardship > > > > On Sun, Nov 23, 2008 at 6:03 AM, John Nissen <[EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>> wrote: > > > Hi Ken, > > You are forgiven for breaking the rules, because you are not. > What you have posted is extremely relevent - and is what started > me off on taking geoengineering seriously - not the carbon capture > but the aerosol cooling geoengineering. We need to understand > the carbon cycle in order to appreciate the imperative for > geoengineered cooling. > > There is no alternative to geoengineered cooling in the short > term, the awsome problem of saving the Arctic sea ice - which is > ignored in this article. I know you appreciate this [1]. > > When I read the IPCC report in 2007 about stabilisation at 2 > degrees, I could not understand how they arrived at the "climate > sensitivity", on which all their calculations seemed to be based. > When I looked into it, their calculations seemed to use 140 years > as the lifetime for CO2 - the half life for the 50% of CO2 which > is not immediately absorbed. > Your article does not explain that, as CO2 concentration increases > in the atmosphere, the equilibrium concentration in the ocean and > biomass increases. This explains the almost exactly 50% of CO2 > which is immediately absorbed. > > It is the lifetime of the remaining 50% which is of concern. If > we halted all CO2 emissions overnight, what would the effect be? > IPCC gave a mean estimate of around 140 years. Yet I found papers > saying that this lifetime was thousands of years - one gave 32,000 > years as an estimate. Who was right? I suspected the longer time > could be correct, and your research confirms that. So emissions > reduction, however severe, would not halt global warming. > > Your article suggests the answer is geoengineering to remove > carbon. But we do not have the time. We have to apply cooling > techniques, of which only the stratospheric aerosols and marine > cloud brightening techniques offer high feasibility of sufficient > scaleability over the few seasons to save the Arctic sea ice from > disappearing over the next few years. > > Thus your article is highly relevent to geoengineering. > > Cheers from Chiswick, > > John > > > [1] You gave a telling postscript to a recent posting of yours (re > Worldwatch Book): > > PS. By the way, given that changes in CO2 emissions will not > significantly affect temperatures over the next decade or two in > any plausible scenario, it is hard to image how anything other > than climate engineering can significantly reduce climate risk > over this time period (perhaps there are adaptive strategies that > could reduce this risk, but it is hard to see how those would > apply to sea ice, ice sheets, arctic ecosystems, and permafrost). > > > ----- Original Message ----- > *From:* Ken Caldeira <mailto:[EMAIL PROTECTED]> > *To:* geoengineering <mailto:[email protected]> > *Sent:* Saturday, November 22, 2008 3:08 AM > *Subject:* [geo] Carbon is forever (Nature online news story) > > NOTE: I AM BREAKING THE RULE ABOUT POSTING GENERAL > CLIMATE/CARBON POSTS TO THIS GROUP. (BAD, BAD, BAD) > > > http://www.nature.com/climate/2008/0812/full/climate.2008.122.html > > > > News Feature > > Nature Reports Climate Change > Published online: 20 November 2008 | doi:10.1038/climate.2008.122 > > > Carbon is forever > > *Carbon dioxide emissions and their associated warming could > linger for millennia, according to some climate scientists. > Mason Inman looks at why the fallout from burning fossil fuels > could last far longer than expected.* > > Carbon is forever > > Distant future: our continued use of fossil fuels could leave > a CO_2 legacy that lasts millennia, says climatologist David > Archer > > 123RF.COM/PAUL <http://123rf.com/PAUL> MOORE > > After our fossil fuel blow-out, how long will the CO_2 > hangover last? And what about the global fever that comes > along with it? These sound like simple questions, but the > answers are complex — and not well understood or appreciated > outside a small group of climate scientists. Popular books on > climate change — even those written by scientists — if they > mention the lifetime of CO_2 at all, typically say it lasts "a > century or more"^1 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B1> > or "more than a hundred years". > > "That's complete nonsense," says Ken Caldeira of the Carnegie > Institution for Science in Stanford, California. It doesn't > help that the summaries in the Intergovernmental Panel on > Climate Change (IPCC) reports have confused the issue, allege > Caldeira and colleagues in an upcoming paper in /Annual > Reviews of Earth and Planetary Sciences/^2 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B2> > . Now he and a few other climate scientists are trying to > spread the word that human-generated CO_2 , and the warming it > brings, will linger far into the future — unless we take > heroic measures to pull the gas out of the air. > > University of Chicago oceanographer David Archer, who led the > study with Caldeira and others, is credited with doing more > than anyone to show how long CO_2 from fossil fuels will last > in the atmosphere. As he puts it in his new book /The Long > Thaw/, "The lifetime of fossil fuel CO_2 in the atmosphere is > a few centuries, plus 25 percent that lasts essentially > forever. The next time you fill your tank, reflect upon > this"^3 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B3> > . > > "The climatic impacts of releasing fossil fuel CO_2 to the > atmosphere will last longer than Stonehenge," Archer writes. > "Longer than time capsules, longer than nuclear waste, far > longer than the age of human civilization so far." > > The effects of carbon dioxide on the atmosphere drop off so > slowly that unless we kick our "fossil fuel addiction", to use > George W. Bush's phrase, we could force Earth out of its > regular pattern of freezes and thaws that has lasted for more > than a million years. "If the entire coal reserves were used," > Archer writes, "then glaciation could be delayed for half a > million years." > > > Cloudy reports > > "The longevity of CO_2 in the atmosphere is probably the least > well understood part of the global warming issue," says > paleoclimatologist Peter Fawcett of the University of New > Mexico. "And it's not because it isn't well documented in the > IPCC report. It is, but it is buried under a lot of other > material." > > It doesn't help, though, that past reports from the UN panel > of climate experts have made misleading statements about the > lifetime of CO_2 , argue Archer, Caldeira and colleagues. The > first assessment report, in 1990, said that CO_2 's lifetime > is 50 to 200 years. The reports in 1995 and 2001 revised this > down to 5 to 200 years. Because the oceans suck up huge > amounts of the gas each year, the average CO_2 molecule does > spend about 5 years in the atmosphere. But the oceans also > release much of that CO_2 back to the air, such that man-made > emissions keep the atmosphere's CO_2 levels elevated for > millennia. Even as CO_2 levels drop, temperatures take longer > to fall, according to recent studies. > > "The climatic impacts of releasing fossil fuel CO_2 to the > atmosphere will last longer than Stonehenge, longer than time > capsules, longer than nuclear waste, far longer than the age > of human civilization so far." > > David Archer > > Earlier reports from the panel did include caveats such as "No > single lifetime can be defined for CO_2 because of the > different rates of uptake by different removal processes." The > IPCC's latest assessment, however, avoids the problems of > earlier reports by including similar caveats while simply > refusing to give a numeric estimate of the lifetime for carbon > dioxide. Contributing author Richard Betts of the UK Met > Office Hadley Centre says the panel made this change in > recognition of the fact that "the lifetime estimates cited in > previous reports had been potentially misleading, or at least > open to misinterpretation." > > Instead of pinning an absolute value on the atmospheric > lifetime of CO_2 , the 2007 report describes its gradual > dissipation over time, saying, "About 50% of a CO_2 increase > will be removed from the atmosphere within 30 years, and a > further 30% will be removed within a few centuries. The > remaining 20% may stay in the atmosphere for many thousands of > years." But if cumulative emissions are high, the portion > remaining in the atmosphere could be higher than this, models > suggest. Overall, Caldeira argues, "the whole issue of our > long-term commitment to climate change has not really ever > been adequately addressed by the IPCC." > > The lasting effects of CO_2 also have big implications for > energy policies, argues James Hansen, director of NASA's > Goddard Institute of Space Studies. "Because of this long CO_2 > lifetime, we cannot solve the climate problem by slowing down > emissions by 20% or 50% or even 80%. It does not matter much > whether the CO_2 is emitted this year, next year, or several > years from now," he wrote in a letter this August. "Instead > ... we must identify a portion of the fossil fuels that will > be left in the ground, or captured upon emission and put back > into the ground." > > > Slow on the uptake > > Unlike other human-generated greenhouse gases, CO_2 gets taken > up by a variety of different processes, some fast and some > slow. This is what makes it so hard to pin a single number, or > even a range, on CO_2 's lifetime. The majority of the CO_2 we > emit will be soaked up by the ocean over a few hundred years, > first being absorbed into the surface waters, and eventually > into deeper waters, according to a long-term climate model run > by Archer. Though the ocean is vast, the surface waters can > absorb only so much CO_2 , and currents have to bring up fresh > water from the deep before the ocean can swallow more. Then, > on a much longer timescale of several thousand years, most of > the remaining CO_2 gets taken up as the gas dissolves into the > ocean and reacts with chalk in ocean sediments. But this > process would never soak up enough CO_2 to return atmospheric > levels to what they were before industrialization, shows > oceanographer Toby Tyrrell of the UK's National Oceanography > Centre, Southampton, in a recent paper^4 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B4> > . > > Finally, the slowest process of all is rock weathering, during > which atmospheric CO_2 reacts with water to form a weak acid > that dissolves rocks. It's thought that this creates minerals > such as magnesium carbonate that lock away the greenhouse gas. > But according to simulations by Archer and others, it would > take hundreds of thousands of years for these processes to > bring CO_2 levels back to pre-industrial values (Fig. 1 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#f1>). > > > Figure 1: Long lifetime. > > Figure 1 : Long lifetime. 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] > > Model simulation of atmospheric CO_2 concentration for 40,000 > years following after a large CO_2 release from combustion of > fossil fuels. Different fractions of the released gas recover > on different timescales. Reproduced from /The Long Thaw/^3 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B3> > . > > Full figure and legend (18 KB) > > <http://www.nature.com/climate/2008/0812/fig_tab/climate.2008.122_F1.html> > > > Several long-term climate models, though their details differ, > all agree that anthropogenic CO_2 takes an enormously long > time to dissipate. If all recoverable fossil fuels were burnt > up using today's technologies, after 1,000 years the air would > still hold around a third to a half of the CO_2 emissions. > "For practical purposes, 500 to 1000 years is 'forever,'" as > Hansen and colleagues put it. In this time, civilizations can > rise and fall, and the Greenland and West Antarctic ice sheets > could melt substantially, raising sea levels enough to > transform the face of the planet. > > > New stable state > > The warming from our CO_2 emissions would last effectively > forever, too. A recent study by Caldeira and Damon Matthews of > Concordia University in Montreal found that regardless of how > much fossil fuel we burn, once we stop, within a few decades > the planet will settle at a new, higher temperature^5 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B5> > . As Caldeira explains, "It just increases for a few decades > and then stays there" for at least 500 years — the length of > time they ran their model. "That was not at all the result I > was expecting," he says. > > But this was not some peculiarity of their model, as the same > behaviour shows up in an extremely simplified model of the > climate^6 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B6> > — the only difference between the models being the final > temperature of the planet. Archer and Victor Brovkin of the > Potsdam Institute for Climate Impact Research in Germany found > much the same result from much longer-term simulations^6 > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#B6> > . Their model shows that whether we emit a lot or a little bit > of CO_2 , temperatures will quickly rise and plateau, dropping > by only about 1 °C over 12,000 years. > > "The longevity of CO_2 in the atmosphere is probably the least > well understood part of the global warming issue." > > Peter Fawcett > > Because of changes in the Earth's orbit, ice sheets might > start to grow from the poles in a few thousand years — but > there's a good chance our greenhouse gas emissions already may > prevent that, Archer argues. Even with the amount of CO_2 > emitted so far, another ice age will almost certainly start in > about 50,000 years. But if we burn all remaining fossil fuels, > it could be more than half a million years before the Earth > has another ice age, Archer says. > > The long-term effects of our emissions might seem far removed. > But as Tyrrell says, "It is a little bit scary, if you think > about all the concerns we have about radioactive wastes > produced by nuclear power. The potential impacts from emitting > CO_2 to the atmosphere are even longer than that." But there's > still hope for avoiding these long-term effects if > technologies that are now on the drawing board can be scaled > up affordably. "If civilization was able to develop ways of > scrubbing CO_2 out of the atmosphere," Tyrrell says, "it's > possible you could reverse this CO_2 hangover." > > Top of page > > <http://www.nature.com/climate/2008/0812/full/climate.2008.122.html#top> > > > > References > > 1. Flannery, T. The Weather Makers: The History and Future > Impact of Climate Change 162 (Atlantic Monthly Press, > New York, 2005). > 2. Archer, D. /et al/. Ann. Rev. Earth Pl. Sc. (in the press). > 3. Archer, D. The Long Thaw: How Humans Are Changing the > Next 100,000 Years of Earth's Climate (Princeton Univ. > Press, 2008). > 4. Tyrrell, T., Shepherd, J. G. & Castle, S. Tellus 59, > 664–672, doi:10.1111/j.1600-0889.2007.00290.x (2007). > 5. Matthews, H. D. & Caldeira, K. Geophys. Res. Lett. 35, > L04705, doi:10.1029/2007GL032388 (2008). > 6. Archer, D. & Brovkin, V. Climatic Change 90, 283–297 (2008). > > /Mason Inman is a freelance science writer currently based in > Pakistan/. > > > > Ken Caldeira > Department of Global Ecology > Carnegie Institution > 260 Panama Street > Stanford, CA 94305 USA > +1 650 704 7212; fax: +1 650 462 5968 > > [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> > [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> > > http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab/ > > > > > > The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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