Yes, I think we should stop using the singular as in "THE half-life of CO2." (I'm the one who wrote the article that Ken posted at the start of this thread.) But it also doesn't make any sense to say it has multiple half-lives. If you were to say "the first half life is X years, the second half life is Y years, ...," it seems to me that undermines the whole concept of a half-life.
As I understand it, the concept of half-lives comes from nuclear physics, describing how long unstable atoms (such as uranium) stick around. Each atomic isotope's half-life is determined by basic physics, and there's little that we can do to alter that. Carbon dioxide, and the complex geologic and living processes it's tied up with, are a whole different story, though. David Archer--along with all other climate scientists--agree that there are multiple processes that pull CO2 out of the air, and can release it back to the air as well. (This is why, as Ken explained, that the dwell time of an individual carbon dioxide molecule is only a few years, whereas a pulse of CO2 raises the gas's levels for a much longer time.) These various processes each operate at different rates now, and these rates may each change by different amounts as we pump more greenhouse gases into the air, and as air and sea temperatures change. That's what makes it so complicated, and why I had to write 1500 words to try to explain all this. Cheers, Mason <><><><><><><><><><><><><> Mason Inman freelance science journalist based in Karachi, Pakistan [EMAIL PROTECTED] http://masonmade.com <><><><><><><><><><><><><> On Nov 23, 9:14 pm, Stephen Salter <[EMAIL PROTECTED]> wrote: > 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]://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 > > ... > > read more » --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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