> Lenton and Vaughan first divide geoengineering proposals into two > sorts: shortwave and longwave.
What gets us into trouble is not what we don't know. It's what we know for sure, that just ain't so. For a long time, everyone knew that the world was too big for us to affect in ways like global climate change. Dilution was the solution to pollution. Among the general public, everyone knows that geoengineering is just a bunch of hare-brained schemes about launching an impossibly huge number of mirrors into space. People just come up with these ideas as an excuse to allow unlimited fossil-fuel use. Anong geoengineering proponents, everyone knows that there can be no possibility of any useful intervention affecting horizontal heat transport within the atmosphere, or affecting transport of latent heat upward. Shortwave/ longwave is a dichotomy because it sounds like one. I'm open to hearing arguments against the third category of geoengineering, but so far I haven't. It's just not considered. On Jan 29, 10:50 am, "John Latham" <[email protected]> wrote: > To All. Comments welcomed. Cheers, John. > > * > > LENTON/VAUGHAN ASSESSMENT OF MARINE CLOUD BRIGHTENING VIA SEAWATER CCN SEEDING > > I think this comprehensive article serves a very useful purpose to the > geoengineering community, in gathering together the various ideas and > subjecting them to well-constructed analytic tests. It is particularly > useful in identifying proposed techniques which could not be of > significant importance. It is reassuring that the authors are careful > to state that the limitations of such an approach can inevitably give > rise to non-trivial quantitative uncertainty, so that some of their > conclusions should only be regarded as tentative. > > In their Abstract (page 2560) the authors state that ?By 2050, only > stratospheric aerosol injections or sunshades in space have the > potential to cool the climate back toward its pre-industrial state.? > This categoric statement makes it clear that they do not regard marine > cloud albedo enhancement via cloud seeding with seawater particles > (Latham et al. 2008, and several earlier papers) as adequate to meet > this criterion. I think this conclusion is not justified for reasons > outlined below. (Please note that I am not arguing that our technique > will definitely work ? there are currently unresolved technological > and scientific questions still under examination ? but that the > computational evidence to date indicates that if these questions can > be adequately resolved, the technique is in principle powerful enough > to stabilize the Earth?s temperature for some decades, and balance the > warming associated with a doubling of atmospheric CO2 concentrations). > > In assessing our scheme the authors focused attention on (largely > elderly) back-of-the-envelope and undeniably deficient calculations, > which were designed to constitute a first-look into the quantitative > power of the scheme, and identify that parameters to which possible > cooling were most sensitive. They did not discuss our most recent work > (at the time of writing the paper, Latham et al., 2008), involving two > wholly separate well-respected GCM (atmosphere-only) models, both of > which indicated ? subject to the caveats mentioned above ? that full > quantitative compensation for CO2 doubling could be achieved. Since > that time our collaborators Phil Rasch and Jack Chen have started > using a highly sophisticated fully-coupled ocean/atmosphere GCM (at > NCAR). Our results to date must be regarded as provisional, as more > and longer simulations are required before categoric statements can be > made, but they provide strong indications that the technique ? again, > subject to the above caveats - could hold the Earth?s average surface > temperature steady, and maintain existing values of the polar ice > cover to beyond the CO2-doubling point. > > We argue, therefore, that this cloud-albedo-enhancement scheme should > be added to the two cited in the Lenton/Vaughan Abstract. > > Reference. J. Latham, P.J. Rasch, C.C.Chen, L. Kettles, A. Gadian, A. > Gettelman, H. Morrison, K. Bower, T.W.Choularton., Global Temperature > Stabilization via Controlled Albedo Enhancement of Low-level Maritime > Clouds. 2008. Phil. Trans. Roy. Soc. A, 366, 3969?3987, > doi:10.1098/rsta.2008.0137 > > John Latham [email protected][1] 01/29/2009 > > *********************** > > Quoting "Oliver Morton" <[email protected]>: > > > > > > > I just posted this at Heliophage (and if anyone known how to get html > > into posts here could they explain it to me?) Meanwhile, to see links > > go to > >http://heliophage.wordpress.com/2009/01/28/geoengineering-by-the-numb... > > > A very useful paper comes out today in Atmospheric Chemistry and > > Physics by Tim Lenton and his student Naomi Vaughan. Tim told me when > > I was reporting the Andy Ridgwell paper on leaf albedo (Nature story| > > blog entry) that he'd become pretty interested in evaluating > > geoengineering schemes, and was setting up a group at the University > > of East Anglia to assess them. This paper presumably represents the > > first fruits of that interest, providing a ranking of most of the > > geoengineering schemes proposed in the literature in terms of the > > amount of radiative forcing they can provide. > > > Radiative forcing is, more or less, the difference in terms of energy > > per square metre that's associated with any given action that changes > > the climate; it's a pretty routine way of expressing things in IPCC- > > land. The IPCC puts the radiative forcing associated with the > > greenhouse gas industrial and industrialising societies pumped into > > the atmosphere from 1800 to 2005 at about 1.6W/m², and the forcing > > for a doubling of CO2 at about 3.7W/m². > > > Lenton and Vaughan first divide geoengineering proposals into two > > sorts: shortwave and longwave. Shortwave schemes seek to reduce the > > amount of energy that gets into the earth system by reflecting away > > incoming sunlight. Longwave schemes seek to increase the amount of > > energy leaving the earth system by making the atmosphere more > > transparent to outgoing infrared radiation -- that is, by reducing the > > greenhouse effect. Then they assess the two with some very simple > > modelling (well, for the longwave there are some wrinkles, but it's > > all in principle pretty simple). They don't claim that the figures > > they come up with are the best available in any particular case, just > > that they are all derived the same way, and so allow fairly > > straightforward comparisons. By standardising the techniques they also > > show up a few errors in previous analyses: for example, if you > > increase the total amount of light reflected back into space by > > clouds, you reduce the amount reflected by the surface, simply because > > less light gets there in the first place. > > > The first and most striking conclusion is that if you want to have a > > big effect, go shortwave. Sulphate aerosols in the stratosphere (which > > were the main topic of this piece and these Climate Feedback posts) > > and mirrors/refractors in space (also in that piece, and in this paper > > by Roger Angel) both have the potential to provide as much by way of > > negative forcing as a doubling of CO2 provides by way of positive > > forcing. Not surprising; if you're not constrained by money or by > > concerns about environmental side effects, you can put mirrors in the > > sky and particles in the stratosphere until it's darkness at noon. > > > When you leave these global technologies behind, the other shortwave > > interventions rank, unsurprisingly, more or less according to the area > > they affect. Increasing the brightness of marine stratocumulus clouds, > > as proposed by John Latham, would affect about 17% of the earth's > > surface, and the Lenton-Vaughan analysis suggests that the whitening > > effect would have to be considerably more marked than previous work > > has assumed; but if that brightening could be achieved then a negative > > forcing that averages more than 3W/m² should be possible. Covering non- > > sandy deserts with aluminium and polyethylene (not an idea I had come > > across before, and a pretty silly one as far as I can see: more here > > if you want it) makes 2% of the surface a lot brighter, and gets you > > an average 1.7W/m² of negative forcing, obviously very unevenly > > spread. Increasing the brightness of the planet's grassland as Robert > > Hamwey has discussed (pdf) gets you 0.64W/m², and the Ridgwell et al > > idea of planting brighter crops gets you 0.44W/m² at best, croplands > > being smaller than grasslands. Lightening everywhere that people > > actually live (another idea from the Hamwey paper) gets you 0.19W/m²; > > increasing the area of plankton blooms that seed the creation of > > clouds in parts of the southern ocean gives you just 0.016W/m² (and > > that may be an overestimate) and restricting yourself to just creating > > shinier cities gives you no more than 0.01W/m². > > > What of the longwave? In principle, capturing carbon dioxide from the > > air (pdf of the Keith et al paper) and burying it in the ground could > > give you whatever radiative forcing you wanted; the limits to such a > > scheme are entirely economic, rather than being imposed on the earth > > system. All the other schemes, though, which involve making changes in > > the natural carbon cycle, are quite constrained, with none able to > > counter a doubling of carbon dioxide, even given the most extreme > > assumptions. > > > The biggest effect comes from really aggressive planting of forests, > > as described in an essay (pdf) by Peter Read on his global gardening > > plans. This involves growing enough plant material in the next 50 > > years to more than completely make up for all the arbon dioxide lost > > through deforestation and land use change over the past few centuries, > > which is really remarkably ambitious, especially if people are still > > going to have some space to grow food. By 2050 this strategy gets you > > an effective 0.49W/m² of negative forcing thanks to 88 gigatonnes of > > carbon dioxide being stored away. A variant of the idea in which you > > grow the biomass and burn it in power stations fitted out for carbon > > capture and storage does even better: 0.69W/m² by 2050 and almost 2W/ > > m² by 2100 (For the longwave calculations, the radiative forcing > > depends on how long the programme has been going on. It also depends > > on what assumptions you make about how effective carbon-emissions > > control is; Lenton and Vaughan calculate all the forcings in terms of > > what extra relief the carbon-dioxide drawdown provides in a world that > > is already making serious cuts in emissions). > > > A lower tech idea that Read is fond of, as for that matter am I, is > > turning biomass into biochar and ploughing it into the ground. Jim > > Lovelock, Lenton's mentor and friend, was extolling this as a possible > > way of making things better in New Scientist last week, speaking to > > the in-this-case-aptly-named Gaia Vince. This may make sense for all > > sorts of reasons, and the fact that making the charcoal also provides > > you with fuel (see Johannes Lehmann's commentary in Nature a few years > > ago) is obviously a plus, but even a really aggressive campaign along > > these lines gives ou a negative forcing of only 0.40W/m² by 2100. > > > After that come a bunch of ocean fertilization schemes, using > > phosphorous, nitrogen and iron, all of which offer something in the > > region of 0.1-0.2W/m². A system of pumping nutrient-rich water up to > > the ocean surface sketched out by Lovelock and Chris Rapley (earlier > > blog entry) delivers a truly meagre 0.003W/m² by 2100. > > > None of this, as Lenton and Vaughan are at pains to make clear, counts > > as an endorsement; all the schemes have side effects and risks, as > > well as in some cases (ahoy there, vast fleet of space parasols) > > quite remarkable costs. But looking at the options this way does allow > > a sense of what might be possible, and a way of seeing what might be > > done in a mix and match sort of way. And the fact that the paper is > > published in the discussion section of ACPD means that the various > > researchers whose work is discussed will have a chance to answer back, > > correct any poor assumptions, and carry the debate forward. > > > Cross-posted to Climate Feedback > > -- > John Latham > > [email protected] & [email protected] > > Tel. 303-444-2429 (H) & 303-497-8182 (W) > > Links: > ------ > [1] mailto:[email protected] > > ----- End forwarded message ----- > > -- > John Latham > > [email protected] & [email protected] > > Tel. 303-444-2429 (H) & 303-497-8182 (W) > > > > > > To: Oliver & Co. Cheers, John. > > * > > LENTON/VAUGHAN ASSESSMENT OF MARINE CLOUD BRIGHTENING VIA SEAWATER CCN SEEDING > > I think this comprehensive article serves a very useful purpose to the > geoengineering community, in gathering together the various ideas and > subjecting them to well-constructed analytic tests. It is particularly > useful in identifying proposed techniques which could not be of > significant importance. It is reassuring that the authors are careful > to state that the limitations of such an approach can inevitably give > rise to non-trivial quantitative uncertainty, so that some of their > conclusions should only be regarded as tentative. > > In their Abstract (page 2560) the authors state that ?By 2050, only > stratospheric aerosol injections or sunshades in space have the > potential to cool the climate back toward its pre-industrial state.? > This categoric statement makes it clear that they do not regard marine > cloud albedo enhancement via cloud seeding with seawater particles > (Latham et al. 2008, and several earlier papers) as adequate to meet > this criterion. I think this conclusion is not justified for reasons > outlined below. (Please note that I am not arguing that our technique > will definitely work ? there are currently unresolved technological > and scientific questions still under examination ? but that the > computational evidence to date indicates that if these questions can > be adequately resolved, the technique is in principle powerful enough > to stabilize the Earth?s temperature for some decades, and balance the > warming associated with a doubling of atmospheric CO2 concentrations). > > In assessing our scheme the authors focused attention on (largely > elderly) back-of-the-envelope and undeniably deficient calculations, > which were designed to constitute a first-look into the quantitative > power of the scheme, and identify that parameters to which possible > cooling were most sensitive. They did not discuss our most recent work > (at the time of writing the paper, Latham et al., 2008), involving two > wholly separate well-respected GCM (atmosphere-only) models, both of > which indicated ? subject to the caveats mentioned above ? that full > quantitative compensation for CO2 doubling could be achieved. Since > that time our collaborators Phil Rasch and Jack Chen have started > using a highly sophisticated fully-coupled ocean/atmosphere GCM (at > NCAR). Our results to date must be regarded as provisional, as more > and longer simulations are required before categoric statements can be > made, but they provide strong indications that the technique ? again, > subject to the above caveats - could hold the Earth?s average surface > temperature steady, and maintain existing values of the polar ice > cover to beyond the CO2-doubling point. > > We argue, therefore, that this cloud-albedo-enhancement scheme should > be added to the two cited in the Lenton/Vaughan Abstract. > > Reference. J. Latham, P.J. Rasch, C.C.Chen, L. Kettles, A. Gadian, A. > Gettelman, H. Morrison, K. Bower, T.W.Choularton., Global Temperature > Stabilization via Controlled Albedo Enhancement of Low-level Maritime > Clouds. 2008. Phil. Trans. Roy. Soc. A, 366, 3969?3987, > doi:10.1098/rsta.2008.0137 > > John Latham [email protected][1] 01/29/2009 > > *********************** > > Quoting "Oliver Morton" <[email protected]>: > > > > > > > I just posted this at Heliophage (and if anyone known how to get html > > into posts here could they explain it to me?) Meanwhile, to see links > > go to > >http://heliophage.wordpress.com/2009/01/28/geoengineering-by-the-numb... > > > A very useful paper comes out today in Atmospheric Chemistry and > > Physics by Tim Lenton and his student Naomi Vaughan. Tim told me when > > I was reporting the Andy Ridgwell paper on leaf albedo (Nature story| > > blog entry) that he'd become pretty interested in evaluating > > geoengineering schemes, and was setting up a group at the University > > of East Anglia to assess them. This paper presumably represents the > > first fruits of that interest, providing a ranking of most of the > > geoengineering schemes proposed in the literature in terms of the > > amount of radiative forcing they can provide. > > > Radiative forcing is, more or less, the difference in terms of energy > > per square metre that's associated with any given action that changes > > the climate; it's a pretty routine way of expressing things in IPCC- > > land. The IPCC puts the radiative forcing associated with the > > greenhouse gas industrial and industrialising societies pumped into > > the atmosphere from 1800 to 2005 at about 1.6W/m², and the forcing > > for a doubling of CO2 at about 3.7W/m². > > > Lenton and Vaughan first divide geoengineering proposals into two > > sorts: shortwave and longwave. Shortwave schemes seek to reduce the > > amount of energy that gets into the earth system by reflecting away > > incoming sunlight. Longwave schemes seek to increase the amount of > > energy leaving the earth system by making the atmosphere more > > transparent to outgoing infrared radiation -- that is, by reducing the > > greenhouse effect. Then they assess the two with some very simple > > modelling (well, for the longwave there are some wrinkles, but it's > > all in principle pretty simple). They don't claim that the figures > > they come up with are the best available in any particular case, just > > that they are all derived the same way, and so allow fairly > > straightforward comparisons. By standardising the techniques they also > > show up a few errors in previous analyses: for example, if you > > increase the total amount of light reflected back into space by > > clouds, you reduce the amount reflected by the surface, simply because > > less light gets there in the first place. > > > The first and most striking conclusion is that if you want to have a > > big effect, go shortwave. Sulphate aerosols in the stratosphere (which > > were the main topic of this piece and these Climate Feedback posts) > > and mirrors/refractors in space (also in that piece, and in this paper > > by Roger Angel) both have the potential to provide as much by way of > > negative forcing as a doubling of CO2 provides by way of positive > > forcing. Not surprising; if you're not constrained by money or by > > concerns about environmental side effects, you can put mirrors in the > > sky and particles in the stratosphere until it's darkness at noon. > > > When you leave these global technologies behind, the other shortwave > > interventions rank, unsurprisingly, more or less according to the area > > they affect. Increasing the brightness of marine stratocumulus clouds, > > as proposed by John Latham, would affect about 17% of the earth's > > surface, and the Lenton-Vaughan analysis suggests that the whitening > > effect would have to be considerably more marked than previous work > > has assumed; but if that brightening could be achieved then a negative > > forcing that averages more than 3W/m² should be possible. Covering non- > > sandy deserts with aluminium and polyethylene (not an idea I had come > > across before, and a pretty silly one as far as I can see: more here > > if you want it) makes 2% of the surface a lot brighter, and gets you > > an average 1.7W/m² of negative forcing, obviously very unevenly > > spread. Increasing the brightness of the planet's grassland as Robert > > Hamwey has discussed (pdf) gets you 0.64W/m², and the Ridgwell et al > > idea of planting brighter crops gets you 0.44W/m² at best, croplands > > being smaller than grasslands. Lightening everywhere that people > > actually live (another idea from the Hamwey paper) gets you 0.19W/m²; > > increasing the area of plankton blooms that seed the creation of > > clouds in parts of the southern ocean gives you just 0.016W/m² (and > > that may be an overestimate) and restricting yourself to just creating > > shinier cities gives you no more than 0.01W/m². > > > What of the longwave? In principle, capturing carbon dioxide from the > > air (pdf of the Keith et al paper) and burying it in the ground could > > give you whatever radiative forcing you wanted; the limits to such a > > scheme are entirely economic, rather than being imposed on the earth > > system. All the other schemes, though, which involve making changes in > > the natural carbon cycle, are quite constrained, with none able to > > counter a doubling of carbon dioxide, even given the most extreme > > assumptions. > > > The biggest effect comes from really aggressive planting of forests, > > as described in an essay (pdf) by Peter Read on his global gardening > > plans. This involves growing enough plant material in the next 50 > > years to more than completely make up for all the arbon dioxide lost > > through deforestation and land use change over the past few centuries, > > which is really remarkably ambitious, especially if people are still > > going to have some space to grow food. By 2050 this strategy gets you > > an effective 0.49W/m² of negative forcing thanks to 88 gigatonnes of > > carbon dioxide being stored away. A variant of the idea in which you > > grow the biomass and burn it in power stations fitted out for carbon > > capture and storage does even better: 0.69W/m² by 2050 and almost 2W/ > > m² by 2100 (For the longwave calculations, the radiative forcing > > depends on how long the programme has been going on. It also depends > > on what assumptions you make about how effective carbon-emissions > > control is; Lenton and Vaughan calculate all the forcings in terms of > > what extra relief the carbon-dioxide drawdown provides in a world that > > is already making serious cuts in emissions). > > > A lower tech idea that Read is fond of, as for that matter am I, is > > turning biomass into biochar and ploughing it into the ground. Jim > > Lovelock, Lenton's mentor and friend, was extolling this as a possible > > way of making things better in New Scientist last week, speaking to > > the in-this-case-aptly-named Gaia Vince. This may make sense for all > > sorts of reasons, and the fact that making the charcoal also provides > > you with fuel (see Johannes Lehmann's commentary in Nature a few years > > ago) is obviously a plus, but even a really aggressive campaign along > > these lines gives ou a negative forcing of only 0.40W/m² by 2100. > > > After that come a bunch of ocean fertilization schemes, using > > phosphorous, nitrogen and iron, all of which offer something in the > > region of 0.1-0.2W/m². A system of pumping nutrient-rich water up to > > the ocean surface sketched out by Lovelock and Chris Rapley (earlier > > blog entry) delivers a truly meagre 0.003W/m² by 2100. > > > None of this, as Lenton and Vaughan are at pains to make clear, counts > > as an endorsement; all the schemes have side effects and risks, as > > well as in some cases (ahoy there, vast fleet of space parasols) > > quite remarkable costs. But looking at the options this way does allow > > a sense of what might be possible, and a way of seeing what might be > > done in a mix and match sort of way. And the fact that the paper is > > published in the discussion section of ACPD means that the various > > researchers whose work is discussed will have a chance to answer back, > > correct any poor assumptions, and carry the debate forward. > > > Cross-posted to Climate Feedback > > > > -- > John Latham > > [email protected] & [email protected] > > Tel. 303-444-2429 (H) & 303-497-8182 (W) > > Links: > ------ > [1] mailto:[email protected] --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
