Re: [geo] Re: Rejected - a simple argument for SRM geoengineering AND did you get that right?Hi Mike
Don't think so. Rereading my message I see that I did not omit to mention both the deposit and withdrawl mechanisms for the "biosphere carbon bank" i.e. photosynthesis for deposit into the biosphere 'bank' and decay for withdrawl from it. The gross flows of about 110 Gt each into ocean and terrestrial biosphere are netted off in the numbers I quoted, with about 50Gt respired immediately by plant life and about as much released by warm oceans as is absorbed in cold ocean regions (more exact numbers at Fig 4 [3?] of the RS geo-engineering report that I don't have to hand). The 60 and 20 for land and ocean photosynthetic fixing that I mentioned are the amounts taken out of the atmosphere each year. These were balanced by an equal amount released by decay processes when the biosphere was in pre-industrial equilibrium. With only about 800 Gt in the atmosphere, this means the average CO2 molecule in atmosphere can expect to get fixed (and later released) about once every ten years The time constants in the Bern model relate, I believe, to quick adjustment with the oceans, slower adjustment with the biosphere and long term adjustment with the very limited benthic and lithosphere quasi-final resting places. These time constants slowly adapt to shifts from the pre-industrial numbers as enhanced CO2 levels impact on the rate at which CO2 is fixed (CO2 fertilisation - a phenomena that finally resolved the IPCC second assessment report's mystery sink problem) and the rate it decays (Peter Cox's work on the impact of warmer climate on the biosphere sink). So the lifetime of an incremental CO2 molecule depends on the scenario - in a rapidly warming world an increment of CO2 will provoke further warming and intensify decay processes and possibly leave several CO2 molecules in the atmosphere in 10000 years. In a slowly warming world it will provoke further CO2 fertilization and possibly be removed in a few decades. >From the scientific perspective the point I am making is that the atmospheric >chemisty-physics effect of a CO2 increment cannot be separated from the >biological effects, which may well be much more important over a meaningful >policy horizon.. But my main concern is the policy implication of giving the 10000 year figure prominence since it tends to give the impression that reducing emissions is the overwhelmingly important thing to do. If on the other hand policy makers can be brought to realize that a molecule of CO2 revisits the biosphere every ten years or so then they can maybe be brought to realize that this gives 1000 opportunities to do something about the problem before 10000 years are up. It is a simple matter, over a few decades, to manage the earths landscape so that 63 Gt are photosynthesized annually and only 57 Gt allowed to decay to CO2, yet that does as much good as reducing fossil fuel emissioins to zero, which nobody believes is feasible this side of 2100 Cheers Peter ----- Original Message ----- From: Mike MacCracken To: Peter Read ; Martin Hoffert ; David Keith ; Greg Rau ; Geoengineering ; John Nissen ; Ron Larson ; David Hawkins Sent: Sunday, November 22, 2009 2:56 AM Subject: Re: [geo] Re: Rejected - a simple argument for SRM geoengineering AND did you get that right? Hi Peter-Problem with your analysis is that biosphere also gives off something like 60 GtC as well. Preindustrial with steady CO2, as much was being taken up and given off. The net uptake, driven by the gradient created by emissions is now something like 1 GtC/yr and would equilibrate well before all of the perturbation is removed for this net uptake is occurring mainly as the new emissions are distributed among the fast reservoirs (atmosphere something like 50%, upper ocean that is well mixed 20-25% (and this includes the maybe 1 GtC/yr or less headed to the deep ocean), and terrestrial biosphere something like 25-30%. My upper ocean and terrestrial biosphere numbers may be off a bit, but close. You are counting the gross flux-sort of like saying how much cash is going into the stock market by only counting the dollars used to buy the stocks without subtracting off the money coming out due to sales. Mike On 11/21/09 3:20 AM, "Peter Read" <[email protected]> wrote: I must be off the map somewhere I guess, but in my view you guys have got it wrong This is because the calculations pertain exclusively to atmospheric physics/chemistry. In fact the biosphere fixes about 60 Gt C annually plus another 20 including oceanic photosynthesis So with less than 800 GT in the atmosphere, incremental CO2 stays in the atmosphere for around 10 years, not 10,000 Of course, if natural and anthropogenic fixation is exactly balanced by decay for 10,000 years then the physical-chemical processes are all that matters. But is that likely?? An increment of CO2 will cause an increment of CO2 fertilization, allowing for which would lead to a smaller lifetime I suspect [can anyone do the sum please?]. But an increment of CO2 will cause incremental warming and incrementally hasten decay, possibly lengthening the 10,000 years . However, I am much more concerned with the presentational aspect of the 10,000 years number. This lends credence to the overwhelming importance of reducing emissions [[unless, that is, you happen to think that shorter term climatic impacts, like the risk of Greenland collapsing, are important]]. I believe the science should be stated in a way that emphasizes the carbon cyle as a whole, and the ease of getting CO2 out of the atmosphere, not the very difficult (costly) problem of stopping it being emitted. Peter ----- Original Message ----- From: Marty Hoffert <mailto:[email protected]> To: [email protected] ; [email protected] ; [email protected] ; [email protected] Sent: Saturday, November 21, 2009 12:00 PM Subject: RE: [geo] Re: Rejected - a simple argument for SRM geoengineering David et al: True, Jim Kasting's work on the long-term carbon cycle as impacted by human fossil fuel CO2 emissions is decades old. But brilliant though Jim is, he was not the first. See, e.g., the attached paper published in 1974 when it first dawned on me and others at NASA/GISS that we might be on to something important with the fossil fuel O2 greenhouse-climate issue. Who would have thought that Steve Schneider, Richard Sommerville, Jim Hansen and yours truly would be pounding the table in 2009 for the world to act to limit emissions? (Remember, the planetary climate was still cooling in the '70s.) My '74 Atmos Env. paper admittedly has (minor in the overall scheme of things) errors. Not too surprising for an early probes into the far horizons of humankind's future. (Still, Dave Keeling liked it.) Finding those conceptual errors might be fun exercise for a carbon cycle savvy reader 35 years later. But mostly, I think, I was right about the longevity of the impacts of the fuel era of human history through persistent elevated CO2 levels. Nobody much listened at the time and the paper was buried in in the resting place of specialized academic journals, though I was able to resurrect it with the help of the Internet. But Hey: Is anyone listening now? Will they care in Copenhagen? Cheers, Marty Hoffert Professor Emeritus of Physics Andre and Bella Meyer Hall of Physics 4 Washington Place New York University New York, NY 10003-6621 --- ----- Original Message ----- From: Ken Caldeira <mailto:[email protected]> To: Ron Larson <mailto:[email protected]> Cc: [email protected] ; [email protected] Sent: Friday, November 20, 2009 2:08 PM Subject: Re: [geo] you got that right 1 digit calculations just for orders of magnitude: If we assume a doubling of CO2 is 4 W / m2 and the earth is 5 x 10^14 m2, a doubling of CO2 traps about 2 x 10^15 W. If we assume 2 GtC / ppm, and think it takes say 300 ppm to double CO2, that is 600 GtC, 600 x 10^12 kgC = 6 * 10^14 GC, so each kgC in the atmosphere traps around 3 W. Oil is about 4.5 x 10^7 J / kg. If we pretend oil is CH2, then we can assume that most of this mass is carbon, but a lot of the energy comes for the hydrogen. So by this reckoning it would take ( 4.5 x 10^7 J / kg ) / (3 W / kgC) = 1.5 * 10^7 s or less than half a year for the greenhouse gas to heat up as much as the thermal heating from the oil. Of course, this CO2 is accumulating in the atmosphere. If you think the airborne fraction on the margin, is around 0.5 over the first thousand years, giving you about the radiative heating each year equivalent to the chemical heating from burning. Then you get a few hundred thousand years with several fold less heating, with a cumulative radiative heating on the order of 100,000 times the direct chemical heating. (I am not going to quibble about small integer multipliers one way or the other.) Of course, all of this heat will not go into melting ice. (I think that 75 was the ratio of current atmospheric CO2 radiative forcing to direct heating from fossil fuel burning, but I would need to go back to check.) ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [email protected]; [email protected] http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 On Thu, Nov 19, 2009 at 3:08 PM, Ron Larson <[email protected]> wrote: Dave (cc Ken and list): Thanks to Dave. 1. Since I doubt very much that the computation shown included anything on CO2 effects, I hope Ken can weigh in on this, per the discussion last week re: http://climateprogress.org/wp-content/uploads/2009/11/Warming-burning-091018.pdf 2. The answer might be 100,000 times larger - but that might exhaust the supply of glaciers. 3. Would Exxon today say that one day's worth of melting was calculated properly. That we are only talking of an insignificant addition of only about 75/365 (only about another 20%, assuming we don't worry about whether today's energy consumption is impacting any glacier tomorrow.) (Ken had a factor of 75 for 1 year). 4. I haven't had any luck logging on to to leave a comment at the Grist site, so hope someone will. One chap has shown a multiplicative factor of 65 - which looks like he has calculated for a year. Ron ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.425 / Virus Database: 270.14.76/2517 - Release Date: 11/21/09 07:47:00 -- 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=.
