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  1. Dear Raypierre,

    There seem to be other, more benign geo-engineering proposals around, more worthy of discussion and modelling than the sulphate into the stratosphere one.

    Prsonally I think there is a bit of mileage in adding extra cloud condensation nuclei (from sea water) into the marine boundary layer to increase low level cloud cover.

    I would be interested in contact details of the people that you mentioned who have done some modelling, in case they could do some more, on other ideas.

    I could supply papers on this, or a summary for your Realclimate site, if you are interested.

    Best Wishes, Colin Forrest

    If you don’t know

    Comment by Colin Forrest — 15 Dec 2007 @ 6:13 AM

  2. Great summary! Unfortunately I have never been at an AGU meeting in spite of being a member.

    Has anybody really doubted that sulfate aerosol geoengineering is anything but a last-ditch attempt at saving our sorry asses after, conform human nature, doing too little too late? It does’t even undo the effects of climate change, just cancels numerically its most conspicuous manifestation. Almost everything else remains unfixed.

    One question though: how would preferential injection at high latitudes help? The stuff stays in circulation for some years. Would it spread much in latitude over that time?

    Comment by Martin Vermeer — 15 Dec 2007 @ 8:35 AM

  3. It is a relief to see some of the possible disadvantages of
    geo-engineering being discussed, and especially some of the effects
    of ‘G-enge’ options on atmospheric chemistry. I’m not sure myself
    it’s a genie we want to let out of the bottle; after all, how do we
    judge the setting of the Earth’s thermostat in the first place? And then
    how do we decide what setting it should be (a trickier issue than it seems –
    just consider ‘Who benefits?’, or ‘Who benefits the most?’ – as not everyone
    sees local or regional warming as a problem). Perhaps worse is the possibility
    that G-enge will be used as an excuse to pollute even more i.e. it will be
    seen as a perpetual way to offset the results of our planetary mismanagement. It
    also has the difficulty that when it comes to proper maintenance, it becomes
    just another ‘built’ system that needs resourcing against other competing options.
    We only have to look at the errors – and negligence? – over the years relating to
    other (much smaller scale, admittedly) systems to appreciate the potential for
    serious mistakes and problems, e.g. as with nuclear power stations (remember Windscale, Three Mile Island, Chernobyl etc?), chemical plants or oil refineries(Flixborough, Seveso, Bhopal,
    BP Louisiana?), river/flood defences (New Orleans?), etc. etc. etc.

    Anyways, thanks for all the AGU posts – very informative. Over to Candide now,
    I think : ‘What’s next?’

    Comment by Nick O. — 15 Dec 2007 @ 8:36 AM

  4. There have been a couple of recent papers (I’ve lost the links, they were in sciencedaily a couple of weeks back) about industrially enhanced silicate weathering. It would seem to me, that if something like this were to be found to be both economically affordable (cost per ton CO2) removed, and environmentally not too destructive, that this would be something we should look into. My gut feeling, we will probably come up with some schemes that remove CO2 at some rate, although that rate is probably much lower than current emissions. Even so it might provide a way for a post fossil fuel world to gradually reign in excess CO2.

    Any discussion of this? Im not equipped to judge whether this is realistic, or just a crude attempt to distract us from concentrating on emissions reductions.

    Comment by Thomas — 15 Dec 2007 @ 10:43 AM

  5. Geo-engineering is possibly an extension of human hubris, the same thing that got us into this mess. We need to restore the planet to pre-industrial state through negative population growth, forest expansion etc along with solar & wind energy. Let nature restore nature.

    Comment by Bird Thompson — 15 Dec 2007 @ 11:00 AM

  6. Reminder: It is near the deadline for submissions to the Blog Articles Book

    What would you like people to know?

    Also, what are your Xmas book recommendations?

    Comment by Pete Dunkelberg — 15 Dec 2007 @ 11:14 AM

  7. Are there any climate models that incorporate permanent
    El Nino conditions?

    Comment by Kevin Byrne — 15 Dec 2007 @ 11:34 AM

  8. It is not global warming per se that is the problem, it is the rate of climate change. At a rate of 0.01C per century we can adapt to huge changes in climate. At a SLR of .02 meter per century we can adapt to almost any sea level change. However, rates of 0.1 C per year for climate change or .2 meter year SLR will destroy our civilization in a short time.

    Geo-engineering seeks to introduce changes in the global system that are so rapid as to reduce our rapid rate of climate change. To be effective in the limited time available, the geo-engineering effects would have to be very intense. This will introduce very rapid, intense, local weather changes.

    It does not help wheat and rice farmers whose crops would be wiped out due to freak weather, that the freak weather was caused by geo-engineering to prevent additional climate change. Are you going to tell all the bees to stay inside because we are going to be “geo-engineering” next spring and there may be some freakish weather? Are you going to take almonds, apples, pears, cherries, squash, melons, potatoes, and etc off the global menu? (Well just for a few years until we get this global geo-engineering thing done, then if any bees and other pollinators have survived, we can get some seeds out of the repository, and go back to eating.)

    It does not help the people that would starve because crops were wiped out by geo-engineering, that the geo-engineering may help avoid the loss of some oil company’s infrastructure. And, if enough people starve, then the oil company will not need the infrastructure, because they will not have the customer base.

    Moreover, since Arctic Ice is melting faster than predicted by the models, we may not have as much time to complete geo-engineering as the models predict.

    If we are going to talk about public policy, we need the think through the details. I am not saying the above will come true in any geo-engineering scheme. I am say that the guys talking about geo-engineering have forgotten where their food comes from, and how it is produced.

    Comment by Aaron Lewis — 15 Dec 2007 @ 12:21 PM

  9. What data/papers point to a permanent El Niño during the Pliocene? How strong is that evidence? I know that some climate models seem show that we will get a permanent El Niño, while others don’t (I remember the RC posting on this a while back seemed to shrug it’s shoulders, suggesting confusion over what will happen to El Niño).

    And what was different about the Pliocene orbital configuration? Are there any reasons that we couldn’t use the Pliocene climate (world 3 degrees C warmer but CO2 only around 400ppm) as an example of what will happen over the long run? I guess, what I am saying, is there any reason that CO2 sensitivity would be higher in the Pliocene than today?

    I guess if I have such questions, I should really go to AGU myself…

    Thanks for all the great updates from conference.

    Comment by David Kroodsma — 15 Dec 2007 @ 12:28 PM

  10. The warnings of scientists about the potential hazards of geoengineering are sobering. What is more sobering is concerns that politicians and industry people who resisted predictions of global warming based on modeling will also resist any predictions of hazards of geoengineering. They refused to acknowledge the predictions of global warming models, why should they acknowledge the predictions of geoengineering models??

    Comment by sue — 15 Dec 2007 @ 12:29 PM

  11. Again, Raypierre, much thanks for sharing.

    In the previous RC discussion of climate engineering, it was pointed out that we are already clearly inadvertently geoengineering climate. Besides CO2, we have urban and agrarian albedo changes; here in California, massive water projects change the desert of Sou Cal a land of lawns and ficus, and in the central valleys, field evaporation from farms change alter the microclimate by increasing the water vapor greenhouse effect–as it was explained to me… the polemics of geoengineering are complicated at best. Anyway…

    A somewhat tangential layman question-comment regarding Ralph Lorenz and Maximum Entropy Production (MEP) models: Has there been any practical application of MEP to Earth climate, in any predictive or practical sense?

    I seem to recall reading papers portraying anthropogenic climate change in less serious terms using MEP as a justification.

    On the other hand, my beginner interpretation of MEP seemed to indicate reasoning that the sustained application of a forcing may be subject to a protracted delay in observation. Until the system (in this case Earth climate) moved to a new equilibrium phase, climate sensitivity would be grossly underestimated.

    In both cases, the stability of climate and very rapid change seemed to fit MEP possibilities. The relative simplicity of MEP is what I found alluring, but wonder if anyone who has more refined thinking about this can comment?

    Comment by Jim Redden — 15 Dec 2007 @ 12:39 PM

  12. Lest anyone think that geoengineering schemes to modify (or stabilize) climate, and concerns about those schemes, are something new, here are excerpts from a paper on this topic published in Science in 1974 [Note: The authors were concerned about food and water shortages ravaging Africa in the early 1970s – they were not talking about the nuclear winter scenarios or a new ice age that AGW skeptics keep suggesting were dominating the thinking of climatologists at that time]:

    W.W. Kellogg and S.H. Schneider (1974) Climate Stabilization: For Better or Worse? Science 186 (No.4170): 1164-1172

    …So far, we do not have a comprehensive climate theory that can explain- much less predict- these trends. Nevertheless, we understand enough about the earth-atmosphere system to recognize that humans can affect it, and surely have already, by pushing on certain “leverage points” that control the heat balance of the system. If we continue to expand our global activities, our influencess on future climates will be still greater.

    If we could forecast climate changes we would be faced with several options. First, do nothing. Second, to alter our patterns of land and sea use in order to lessen the impact of climate change. And third, to anticipate climate change and implement schemes to control it….

    It may be useful now to summarize some important points and questions we have discussed in connection with potential climate-related conflict situations: [Note: a colon was inserted in place of a period in the original text]

    1) The atmosphere is a highly complexe and interactive resource common to all nations.

    2) Decision-making with unsharpened tools (such as climate models) may become necessary.

    3) What if we could trace climatic cause and effect linkages? Accusations would abound.

    4) What if one nation perceived climatic cause and effect linkages? Could this be used as an excuse for hostility?

    5) What if one nation could predict climate? This would change entire international economic market strategies or might lead to pressure for climate control.

    6) Who would decide and who would implement climate modification and control schemes> The cost of miscalculation (or perception of miscalculation) are immense.

    We have the impression that more schemes will be proposed for climate control than for control of the climate controllers. Whether or not purposeful climate control is ever needed or realized, the problems of inadvertant climate modification, climate prediction, and feeding a growing world population suggest the timeliness of studying potential climate-related crisis and conflict scenarios. This is the first step. In any case, the objective of understanding and anticipating natural, inadvertent, or purposeful climate change and its consequences for society must, in our view, continue to be a major interdisciplinary goal. While it is essential to work out international mechanisms to guarantee that any new knowledge of our climate system will have only constructive uses, the price of human suffering of continued ignorance of the causes of climate change may already have become unacceptably high.

    Comment by Chuck Booth — 15 Dec 2007 @ 12:40 PM

  13. Another thanks for your reporting on the recent results from this meeting!

    Regarding geo-engineering, was there any discussion, or opinions, on the viability of producing biochar for carbon sequestration? From what I have seen it offers potential for significant help if it can be demonstrated that the charcoal remains stable as long as its backers claim. It has the potential to be widely implemented from the scale of single farms to much larger operations. Biochar also appears to be a highly valuable soil amendment, improving fertility with lower fertilizer and water requirements. Large scale implementation probably will rely on the IPCC, or other appropriate body, to recognize it as a validated carbon sequestration technology in order for its use to be eligible for carbon credits.

    I was wondering if the climate community has begun to discuss or evaluate this possibility. At this time I mostly only see its enthusiastic promotion by a smaller community.

    Comment by Anthony Leonard — 15 Dec 2007 @ 1:04 PM

  14. Thomas (3) — Emissions reductions are important, but there is a completely viable scheme to permanently and safely sequester carbon: produce biocoal via hydrothermal carbonification and bury the stuff in abandoned mines or carbon landfills. I don’t know about the cost, but it would be environmentally anti-destructive.

    Comment by David B. Benson — 15 Dec 2007 @ 1:45 PM

  15. Oops. Hydrothermal carbonization.

    Comment by David B. Benson — 15 Dec 2007 @ 1:58 PM

  16. (11) I would be interested in learning about the process. Especially if it could be made a byproduct of say geothermal power, or some other energy generating scheme. I’m not of the opinion that any of the schemes are a substitute for emissions reductions, but they might have a part to play in mitigating the damage after we discover we did too little too late.

    Comment by Thomas — 15 Dec 2007 @ 4:50 PM

  17. Thomas (13) — Yes, the reaction is exothermic.

    Popular accounts:,2144,2071791,00.html

    A demonstration plant, using forestry wastes, is described in the following link.

    A more technical article:

    M.-M. Titrisci, et al.,
    Back in the Black: hydrothermal carbonization of plant
    material as an efficient chemical process to treat the CO_2
    New Journal of Chemistry, 207, 31, 787–798 (25 references). (Linked below)

    or as a .pdf file


    Comment by David B. Benson — 15 Dec 2007 @ 5:43 PM

  18. The 100,000 year cycle of Pacific sea surface temperatures might have something to do Milankovitch cycles.

    The overall cycle switched from 41,000 years to 100,000 years about 1.5 million years ago. Maybe it was sooner according to this data.

    I always thought the glaciation cycles started about 2.5 million years ago.

    Comment by John Wegner — 15 Dec 2007 @ 6:47 PM

  19. It is important not to assign specific definitions to the very general term “geo-engineering”. As David Benson suggests, sequestering carbon is a form of geo-engineering with no worries about unintended atmospheric effects. Methods may be developed to remove carbon from the atmosphere.

    “Cooling” the climate by blocking solar energy would be an extreme measure, to be taken only if the worst stage of the crisis has been reached.

    Realistic measures to transform the grid off of fossil fuels in a cost efficient way, combined with imaginative geo-engineering efforts, might end up being the cocktail that successfully balances science and social policy.

    Comment by Walt Bennett — 15 Dec 2007 @ 7:12 PM

  20. Re # 11 David B. Benson: “a completely viable scheme”

    Viable in what sense? Technologically? Environmentally? Economically? All three? How about providing some documentation on this?

    Comment by Chuck Booth — 15 Dec 2007 @ 8:48 PM

  21. Just wanted to reiterate the thanks as a “lay public non-scientist (Librarian)” – I appreciate your summaries and doubt any standard news outlet covered much, if any, of this conference (I heard nary a peep). I was particularly excited to be able to see Dr. Lonnie Thompson’s speech, as he’s a bit of a hero for me.

    Comment by Andy Wickens — 15 Dec 2007 @ 9:51 PM

  22. Geo-engineering is the topic in the energy and environmental arenas that scares me spitless. If you look at where much of our CO2 emissions come from–coal-fired electricity generation–and how hard it will be to sequester those emissions or replace that generation with CO2-free ways to move electrons, it becomes clear that even with an enormous amount of political will and funding we’ll have one heck of a hard time reducing emissions in a reasonable time.

    I fear that we’re on a collision course with geo-engineering, and that much of the talk about it in mainstream circles will make it sound like a (relatively) cheap and safe fix, and therefore a “good” argument for us not to do the hard (and politically distasteful) work of reducing emissions aggressively.

    Comment by Lou Grinzo — 15 Dec 2007 @ 10:33 PM

  23. Reply to 2 Nick O. and 5 Pete Dunkelberg
    On Chernobyl: Alex Gabbard wrote to me: “The reactor that had the accident at Chernobyl was very out-of-date (1st generation) design that has to be precisely controlled to prevent cooling water from boiling. Water carries away heat and moderates far better than bubbles, and as bubbles form in water, the reactor goes increasingly unstable. What caused Chernobyl to blow its top was residual water in the core suddenly going to high pressure steam and erupting into a steam explosion. Since the building top was simply resting by its weight on the walls, not a containment vessel at all, the steam explosion burped the top off its position allowing outside air in, subsequently igniting a carbon fire.” The United States and other Western countries DO NOT now build and do not now posses or operate ANY reactors of such primitive design. Nor do we allow containment buildings to have easily removable tops. Containment buildings in the Western hemisphere are required to be pressure vessels.
    The Chernobyl accident released only 200 tons of radioactive material, as much as a coal-fired power plant would release in 7 years and 5 months. The Chernobyl accident had a shorter “stack” than coal-fired power plants. The radioactive material was released in a short time at ground level. That is why the Chernobyl accident had impact. Only 52 people died at Chernobyl , mostly fire fighters, a hazardous job in any case. The Three Mile Island incident did NOT release a noticeable amount of radiation into its neighborhood, it was just expensive to clean up the inside of the reactor. Nobody died and nobody was injured at Three Mile Island.

    To read more from Alex Gabbard, go to:

    Please give this book for Xmas: “Environmentalists for Nuclear Energy”, by B. Comby
    English edition, 2001, 345 pp. (soft cover), 38 Euros
    TNR Editions, 266 avenue Daumesnil, 75012 Paris, France;
    ISBN 2-914190-02-6
    order from:
    Read a review of this book by the American Health Physics Society at:
    Association of Environmentalists For Nuclear Energy [EFN]

    Please give this book for Xmas as well: “Six Degrees” by Mark Lynas. Read a summary at:

    Please give this book for Xmas: “How to Tell Which New Car Will Last Longer” by Edward Greisch. It is available only as an Adobe Acrobat (.pdf) download from:

    We don’t recycle nuclear fuel because spent fuel is valuable and people steal it. The place it went that it wasn’t supposed to go to is Israel. This happened in a small town near Pittsburgh, PA circa 1970. A company called Numec was in the business of reprocessing nuclear fuel. I almost took a job there, designing a nuclear battery for a heart pacemaker. [A nuclear battery would have the advantage of lasting many times as long as any other battery, eliminating many surgeries to replace batteries.] Numec did NOT have a reactor. Numec “lost” half a ton of enriched uranium. It wound up in Israel. The Israelis have fueled both their nuclear power plants and their nuclear weapons by stealing nuclear “waste.” It could work for any other country, such as Iran or the United States. It is only when you don’t have access to nuclear “waste” that you have to do the difficult process of enriching uranium.

    There are other climate engineering options, such as placing mirrors or other obstructions at the first Earth-Sun Lagrangian Point to block sunlight. Doing this would use up as much money as our military budget. I would guess that it would result in less food because there would be less sunlight reaching the Earth.

    Comment by Edward Greisch — 15 Dec 2007 @ 11:12 PM

  24. Reducing GHG emissions to the atmosphere is necessary but not sufficient because atmospheric GHG concentrations will still increase, albeit at a slower rate. Solar input to Earth already exceeds IR radiation to space, so the oceans will continue to store heat. Ice melting will continue to accelerate.

    We need additional help, like pumping up deep cold water and distributing it at the surface at the rate of one million cubic meters per second. In addition to surface cooling, the up-welled water will supply nutrients to increase food production and slow down ocean acidification.

    Comment by Dick LaR — 16 Dec 2007 @ 1:35 AM

  25. David #11, wouldn’t the process you are talking about also remove nutrients from the soils for each ton of carbon sequestered? Would that not render it ultimately unsustainable? And if we are relying on biofuels as well as bio-sequestration, isn’t that going to tax the abilities of agriculture to feed 12 billion people as well?

    Comment by Ray Ladbury — 16 Dec 2007 @ 8:55 AM

  26. Raypierre, thanks for your reports – for me, reading them was in at least two ways better than being there: no transatlantic flight, and an expert interpreter of the science.

    Comment by Nick Gotts — 16 Dec 2007 @ 9:08 AM

  27. Me too, Raypierre.

    I’ve been reading your blogging from AGU in parallel with Tom Athanasiou’s blogging from Bali, for example

    Some week the scientists and government representatives should do one of these events in the same place at the same time with a shared program.

    Comment by Hank Roberts — 16 Dec 2007 @ 11:51 AM

  28. Raypierre,

    Thank you very much for all of the time, knowledge, and energy you gave to your reports. In a country where GW is virtually ignored by the major news oganizations your reports were a treasure for the layman. I’m saving them as information sources for my high school lectures on AGW and its consequences. Have a good rest and a happy holiday.

    Comment by Mike Tabony — 16 Dec 2007 @ 12:28 PM

  29. Re #11: […produce biocoal via hydrothermal carbonification and bury the stuff in abandoned mines or carbon landfills.]

    Might be interesting in the long term, but it seems kind of pointless, even wasteful, to bury biocoal at the same time other people are busily digging up natural coal and burning it.

    Comment by James — 16 Dec 2007 @ 12:28 PM

  30. Chuck Booth (16) — Technically and environmentally. As I stated, I don’t know the costs. See my post #14.

    Ray Ladbury (18) — No more than cutting down trees to make logs does, which is very little. (Most nutrients are in the leaves.) One can always fertilize as required. I don’t know about 12 billion people, but feeding 9 billion plus bio-fuels leaves a sizable excess capacity of non-agricultural (too degraded), non-bio-fuel land which could be utilized for the produce of biocoal.

    Comment by David B. Benson — 16 Dec 2007 @ 2:11 PM

  31. Re #11

    Hydrothermal carbonized biocarbon is by the way, due to it’s supercritical washed out quality, sometimes used as absorbant of smelly volatile organic compounds found in drinking water; chlorine, petrol fumes etc.. and should not be buried untill loaded with the maximum amount of smelly pollutants.

    Comment by per — 16 Dec 2007 @ 5:08 PM

  32. “Since the Northern Hemisphere ice sheets had not yet formed at this time (Pliocene)”

    Raypierre, your statement is likely not correct. There is considerable sedimentary evidence that glaciation was firmly established on Greenland during the Middle to Late Pliocene, and its beginnings can be traced all the way back to at least the Middle-Late Miocene. If not, then one has some explaining to do. During the Late Miocene, global sea levels fell 50-100 meters below present during at least one short event. With no ice sheet in the NH, it begs the question of where is the missing ocean volume? To some degree, it is likely taken up in the Antarctic Ice Sheets, but possibly to a lesser degree in the NH. It is also important to note that as a whole, the Miocene was even warmer than the Pliocene, but was nevertheless typified by rapid growth of the SH Ice sheets.

    [Response: Written somewhat in haste. I should have made it clear that the transition period under discussion is the stretch beween about 3.1 million years ago and 2.5 million years ago, and it would be fairer to say the Northern hemisphere ice sheets were not yet fully formed, as there is indeed evidence for some NH ice at this time. I suppose there’s the question of how big the NH ice sheets have to get before they can have the kind of rectification effect that some people have proposed for selecting out a 100Kyr cycle. In any event, a 100Kyr cycle in tropical temperature is very interesting in the Pliocene, since 100K doesn’t set in as an important rhythm in ice volume until the mid-Pleistocene. –raypierre]

    Comment by Bryan S — 16 Dec 2007 @ 5:15 PM

  33. “I continue to think that geoengineering is a big and unfortunate distraction, but since the cat is out of the bag, it is good that some people are doing the work to head off rosy and over-optimistic projections of sulfate geoengineering as a magic bullet that could substitute for the hard but necessary work of mitigation of CO2 emissions.”

    There really isn’t a qualitative difference between a “geoengineered” solution and reduction in GHG emissions.

    You have an imperfectly known high dimensional nonlinear system in front of you, and you have some things that you can regard as control inputs (sulfate or CO2 emissions, etc.), and some things (e.g. global average temperature, arctic ice volume, etc.) that can be regarded as outputs. Even if you are skeptical of AGW, you can at least agree that the problem can be formulated this way – presumably skeptics just feel the transfer function from some inputs is smaller than other people think.

    Now the plant is imperfectly known, and the future of the control inputs is not certain (hence the scenario based approach we have seen with GHG projections).

    So fine. I think everyone can agree that this is a formulation that leaves out nothing and includes nothing extraneous. It is particularly well suited to plants that have feedbacks that are not completely identified.

    What does it get you? Well, when we consider the question of whether “geoengineering” or GHG reduction is preferred, it is really in terms of the cost of control for some performance specification. This formulation allows you to objectively and rigorously compare, to the extent that your knowledge supports such inference, different approaches to climate control.

    One really important thing that you would get from this formulation is that it would provide with estimates of the cost of uncertainty – in other words, you get bounds on the cost of control which include the effect of uncertainty; you can view this as a lower bound on the value of reducing the uncertainty. For parties who had differences in their idea of what is the right performance specification (“why should WE pay to preserve YOUR climate”) they can use this as a guide to how they should invest their resources.

    The thing that I would look for first in this sort of approach is whether one or another time scale ended up dominating the contollers that got synthesized for various reasonable performance specifications. That would tell you a lot about which atmospheric species to pay attention to. Offhand I would guess that the long lifetime of CO2 would make it the most economical control variable, but at least this would be an objective way to test that notion.

    [Response: There’s a huge difference between sulfate geoengineering and CO2 mitigation. In the latter, you’re restoring the system to a previous state, whose behavior was known. In the former, you’re taking it into a new kind of state, with a fundamentally different kind of energy balance, and you have no good analogue in nature to help you make sure there isn’t a disaster lurking. Now if by “geoengineering” you’re including things like pulling CO2 out of the atmosphere and sequestering it, there I’d agree with you; there’s not much difference there between mitigation and CO2 removal. The decision between the two comes down to cost, feasibility and side effects –raypierre]

    Comment by Andrew — 16 Dec 2007 @ 6:29 PM

  34. I like the biocoal idea. What this all seems to boil down to, for me anyway, is this: CO2 still has positive uses no matter the fact that we seem to have too much of it. It’s part of the carbon cycle system, we need to determine how much is too much or too little. I would guess that means deterimining how much to burn or store over a 2 year cycle assuming we have some decent feedback as to the density of CO2 and methane in the atmosphere. Does it produce methane if stored for long periods of time?

    The idea of using aerosoles to control the greenhouse effect is… well, about as good an idea as saying global warming is ok. The aerosoles would, as I understand it, erode our atmosphere’s natural tendancy to block harmful cosmic rays which is said to be a source of natural mutations. It sounds like aerosoles would help make the planet a microwave. My tax dollars could be spent better elsewhere.

    Anywho, I’m still in favor of this process, whatever it is: growing plants such as trees and grass to collect CO2 and using the mature trees for building or store them with the decaying in a natural gas collector. Various stages of decay would yield products that could be used in farming. The idea being not to increase the time of decay but to store the carbon in the form of decaying grass and wood chips/trees. The natural gas produced would have to be burned, oh darn, probably to produce electricity or somthing.

    Comment by Harold Ford — 16 Dec 2007 @ 7:44 PM

  35. Raypierre,
    Thanks for the time, experience, and energy you have given for your reports. I’m saving them as references for my high school lectures on AGW. At a time when the major news organizations say so little about the subject your posts have been very educational.
    Thanks again.

    Comment by Mike Tabony — 16 Dec 2007 @ 10:25 PM

  36. Ray #18 – No, it’s exactly the opposite. Biochar was initially created in an attempt to reproduce the Terra Preta soils found in the Amazon Basin. These soils are uncharacteristically productive and have very high naturally occurring nutrient levels because of biochar.

    If biochr can be produced efficiently and economically, it will be a win-win for everyone involved.

    Wiki has some good info on Terra Preta.

    Comment by Ferris — 16 Dec 2007 @ 11:32 PM

  37. It’s just been pointed out to me that one of the AGU geoengineering talks I missed — the historical talk by James R. Fleming on Harry Wexler, the ozone hole, and geoengineering ideas circa 1962 — actually presented new material beyond what I’d seen before. I really regret having missed this, as James is always illuminating to listen to. You can find some of the contents of his talk at

    Comment by raypierre — 17 Dec 2007 @ 12:00 AM

  38. Terra Preta, biochar…
    This can be done efficiently and economicly, but perhaps not in the large scale super duper tech that big biz likes: Teach the poor small farmers to make charcoal instead of burning down forests. There are ovens where to put in wood and get out char coal. Wood gas driven automobiles are known since WWII. The next real innovation in car technology after Ford’s Model T (1909) would be the wood gas hybrid: Get wood pellets at the gas station, dump the charcoal there, and voila: Drive carbon negative.

    Comment by Florifulgurator — 17 Dec 2007 @ 5:00 AM

  39. I bet that at some point over the next 50 years having failed to mitigate CO2 enough we will attempt geoengineering projects of some kind. James lovelocks recent attempt via tubes places in the ocean with valves to allow colder waters to rise to the surface to stop the oceans from stopping abosrbing CO2.

    how much CO2 could be removed from the atmosphere and what would power the machines that did it (even if it is possible)?

    Comment by pete best — 17 Dec 2007 @ 5:57 AM

  40. I thought the bali meeting was a virtual waste of time, with the usa as usual showing absolutely no leadership and almost vetoing the whole process. It clearly shows the white house still doesn’t understand it’s responsibily in the issue. For the vast part of last century the usa was the single biggest emitter of greenhouse gasses therefore it should stand to reason that it is also the usa that should take greatest responsibilty in initiating meaningful emission cuts. Yes! Mr Bush- emission cuts might slightly strain the economy..but it was largely that same reckless polluting economy that has plunged the world to the edge of the abyss. So if any country should take the lead in this dilemma it’s america. If the usa only had displayed more guts and leadership rather than it’s typical self serving approach- china and india would have probably have had the confidence to go with achievable and immediate emission targets.

    Comment by Lawrence Coleman — 17 Dec 2007 @ 8:03 AM

  41. Re Jim #8:

    There are of critisms of the MEP principle, when it was used by Patridge (1975) it was novel and the theoretical under-pinnings weak. Also it was criticised for being a little light on both mechanism and results. I feel it became a bit of a backwater.

    Since then the MEP and the maximum caliber principles have gained much stronger foundations.

    I do not think that there is much of a problem with the principles any longer.

    MEP does involve a shift in the way that problems are handled. Particularly the reduction of information to its relevent content. For instance, it was shown by Paltridge that the zonal temperature distribution and the corresponding fluxes could be reproduced assuming a very small number of constraints. The implication being that the vast amounts of nitty-gritty that are the hallmark of the best climate models are irrelevent “when considering zonal distributions”. They are however vital when predicting the weather.

    An implication of the principle is that the difference between our initial MEPP values and observed values are a measure of the unknown constraints. As the initial fit can be viewed as pretty close then the major constraints must be as used by Paltridge. I think that many find the idea that an important measure of the general climate can be largely explained in such a simple way to be unplatable.

    At the basis of MEPP is how to make inferences from partial information and may represent a brickwall as to what can be inferred regaring the climate given our limited knowledge. That is it could have something to say about the limits of predictions.

    That sounds a bit negetive. On a more positive note it will be of interest to see if the output of various models do conform to the MEPP and to maximum caliber and if they don’t why not.

    Alexander Harvey

    Comment by Alexander Harvey — 17 Dec 2007 @ 9:46 AM

  42. Andrew, you claim there is no difference between CO2 reduction and sulfate/aerosol geoengineering. Hmmm, if we look at the IPCC summaries, where are the biggest uncertainties? Yup, aerosols. Where are they among the smallest? GHG forcing. I’d call that strike one against aerosols.
    What timescale do GHGs act on? Hundreds to thousands of years. And sulfates? months to years. Strike 2.
    And sulfates will likely be much more effective in acidifying the oceans than CO2. Strike 3. Thanks, for trying.

    Comment by Ray Ladbury — 17 Dec 2007 @ 10:00 AM

  43. Raypierre: “There’s a huge difference between sulfate geoengineering and CO2 mitigation. In the latter, you’re restoring the system to a previous state, whose behavior was known. In the former, you’re taking it into a new kind of state”

    From the point of view of control theory, and for that matter, from the point of view of public policy, there is no qualitative difference between geoengineering and “mitigation”. You have a system which will approximately do X, you want it to do something closer to Y instead, and you want to know if that can be achieved, and if so, how should it be most efficiently done, and what will it have to cost?

    Now you claim that the behavior of the previous state is “known”. I would suggest that it is preferable to regard the previous state as possibly less uncertain. This uncertainty is probably much larger than might be thought at first sight. Suppose we thought it were as simple as choosing a year and “dialing the climate back to that year”. Well if you pick a year in the industrial era, then that “climate state” is a point on a trajectory of a forced system, not necessarily having any unforced stability properties (and in fact very likely not having any). So to control the system to that state (extended perhaps as a constant in time), you may have to spend a lot to stabilize it. Yes it’s nice to know that we have attempted to measure the sensitivity of that sort of state to forcing, but that is not the same as computing the minimum cost of artificially stabilizing that state.

    Suppose on the other hand you dial your wayback machine back further, then the cost likely increases and your knowledge of that state and the dynamics decreases.

    I think you might be pretty optimistic about what “previous state” actually entails in terms of the entire climate system – who is going to “reset” the abyssal circulation to that previous state? This is an example of part of the system which is very expensive to control, unless we are cognizant of controlling that part of the system on a different timescale than we seek to control other parts of the system such as the global average temperature.

    But as soon as we recognize that we are going to control different parts of the system on different timescales, then we also recognize that it will be a very long time before we actually return the system to a close analog of any past state that we know to any great degree. But over the longer timescales that it will necessarily require to get close to any previous state, the biosphere is going to change quite a bit. In particular, how many humans will be there when we arrive at that previous climate, and what gases will they choose to emit? Will there be an asteroid impact over that timescale?

    What occurs here is a situation called “recourse”. It means that the control policy itself is sensitive to the system under control. The computational complexity of controllers with recourse is often prohibitive. In human reality, the politics probably do not admit controllers that are held constant over centuries, let alone millenia. So it appears necessary to restrict attention to a relatively short time – such as a century, during which time it is unlikely that we are going to control the system to anything close to a constant state, and over which period large and important aspects of the climate system will be essentially uncontrolled.

    So we will not be “going home again”. At least not any time soon.

    Comment by Andrew — 17 Dec 2007 @ 11:26 AM

  44. #43 Andrew,

    if you strayed into a minefield, what would you do? Carefully retrace your steps? Step where there are other footprints? Or rush the shortest — or any plausible-looking — way out?

    What Raypierre meant by previous/known state, was a collection of states or ‘regime’. Even the current state of the climate system is still similar to, or within the regime, where it operated during periods of time in the recent geological past. Nothing very weird happened then, which is somewhat comforting.

    Continued build-up of GHG would put us deeper and deeper in ‘uncharted territory’, with no real (recent) paleo analogues. Some of that will happen anyway, because of what’s in the pipeline. Yes, it is about risks and probabilities. Not mitigating (which is actually well affordable if you start in good time, cf. IPCC AR4 WG3) is simply not on the table for prudent decision makers, with or without geo-engineering.

    The only valid reason I see for using aerosol geo-engineering would be as a semi-desperate symptomatic treatment, like giving the patient a fever suppressant to keep him alive until the antibiotics start having their effect. Aerosols work immediately, mitigation is a long term systematic effort.

    Comment by Martin Vermeer — 17 Dec 2007 @ 2:45 PM

  45. As a college student in one of these cities:, I feel it is my duty to help publicize this list. If everyone in the country went and got their Carbon Footprint score from and then took just one pledge I think we could stop global warming. Not only is it fun to see where you land compared to these cites, but you can compare to your state, US etc…This tool is vital to the international fight against global warming.

    Comment by Greg — 17 Dec 2007 @ 3:03 PM

  46. Hey can you believe Chicago is number one on this list of top green cities? This article talks about the greenest cites. put together this list; it is a sample of like over a million people. I took my personal carbon test and blew the national average out of the water! I took some of their pledges too so I will be getting further and further below the average. It feels good being one of the people helping to lower my cities average rather than raising it, and I think all people can contribute if they take a pledge or two.

    Comment by Greg — 17 Dec 2007 @ 3:20 PM

  47. Andrew (43) — That was a well-done warning. Thank you.

    As an example, it will be feasible, even economically so according to Biopact, to remove about 350 Gt of carbon from the active carbon cycle in the next 70 years, while at the same time not adding any by the use of bio-fuels, etc. However, this may well not restore the ocean chemistry and biology, hence not returning the planet to the state enjoyed during the 1950s.

    Comment by David B. Benson — 17 Dec 2007 @ 4:07 PM

  48. Couldn’t we remove CO2 from the atmosphere by increasing the amount of biomass and topsoil to create a greater sink fairly easily? What does the research into AGW say about how much is now being sunk and how to increase that (and one would imagine, food production if the biomass is edible).

    Comment by Ralph Smythe — 17 Dec 2007 @ 5:00 PM

  49. > 350 Gt
    Net, or gross?
    That would be almost half the total CO2 in the atmosphere, if they mean net. It sounds like magic.

    Comment by Hank Roberts — 17 Dec 2007 @ 5:20 PM

  50. Hank Roberts (49) — My understanding is that since the beginning of the industrial revolution, humans have added about 500 Gt of carbon to the active carbon cycle. As 350/500 = 0.7, this means the removal of about 70% of what has been added since 1750 CE.

    Not magic. Biopact’s assumption is that carbon capture (in the form of carbon dioxide) and sequestration (as liquidfied CO2 in deep saline formaions) is going to work, both technically and economically. Then using biocoal in CCS coal reactors is carbon-negative as indeed are any of the means of producing bio-fuels which has a utilized CCS capacity.

    For simplicity, assume it was possible to instantly convert completely now. Then removing 350 Gt in 70 years only requires successfully sequestering 5 Gt per year.

    Comment by David B. Benson — 17 Dec 2007 @ 6:46 PM

  51. Gavin,
    Just a little housekeeping, could you please update with your comments. Also, could you please clear up a couple of points. Is it generally agreed that the Earth has warmed .8c since the 1900? What portion of that warming, whatever the number may be, is currently ascribed to CO2 forcings? Also, in your comments to EOS you state that the current forcing of CO2 is 2.6 w/m^2. Is that figure based from 1750 and thus 2.34 w/m^2 is a better estimate per the IPCC’s recommendation of using 1860 as a starting point for forcing calculations? Or do you not agree with the IPCC, and could you please provide the reason why.
    Thank you.

    [Response: 2.6 W/m2 comes from IPCC AR4 and is the forcing for all long-lived greenhouse gases since 1750. The argument is not affected in the slightest by using 1850 or whatever as a starting point. Your question about attribution is not very well posed, see here – gavin]

    Comment by Ellis — 17 Dec 2007 @ 8:01 PM

  52. Thank you, Ray and David for taking the rest if us along for the ride. It’s the next best thing to being there.
    I’m glad that energy policy was included as a topic. It’s critically intertwined with the future of Earth’s climate. Business as usual, as a policy, is no longer a rational option, yet Under Secretary Dobriansky and her delegation in Bali, acted pretty much as if this is their preferred course.

    The BAU approach almost insures that the Greenland and the West Antarctic ice sheets will continue to melt more rapidly than predictions called for, with a severe rise in ocean mean sea levels. More efficient energy use, alternative sources, and running vehicles on renewable electricity is mandatory to avoid inevitable disaster.

    Further explorations on Europa and Titan, and the possibilies of extra Solar Earthlike planets have to stir anyone’s imagination, who isn’t comatose.

    Comment by Lawrence Brown — 17 Dec 2007 @ 9:10 PM

  53. David, you write:
    > assume it was possible to instantly convert
    > completely now.

    You mean assume a zero net increase of greenhouse gases from human activity, as of right now?

    Comment by Hank Roberts — 17 Dec 2007 @ 9:21 PM

  54. “Andrew, you claim there is no difference between CO2 reduction and sulfate/aerosol geoengineering.”

    I did not say that.

    Comment by Andrew — 17 Dec 2007 @ 10:02 PM

  55. QUESTION – …”stratospheric warming in a geoengineered world increased ozone destruction — by a factor of 2-3 in the Arctic — even if”…

    Shouldn’t the second word in the above be ‘cooling’ or am I wrong?

    [Response: No. Increasing the amount of stratospheric aerosol leads to a significant stratospheric warming (as the aerosols absorb solar radiation from above and long wave radiation from below). You can see the volcanic warm spikes in the MSU4 record. – gavin]

    [Response: Something that wasn’t discussed in the talk, and which I didn’t have the opportunity to follow up on, is why the temperature increase lead to an increase in ozone destruction. Certainly, all sorts of chemical reactions proceed faster at higher temperature, and increasing stratospheric water vapor could make a difference. My previous understanding, though, was that the occurrence of polar stratospheric clouds had the big leverage, and I’d think they’d become less prevalent with a warmer stratosphere. I’ll have to try to follow this up once the paper is available, but meanwhile maybe one of the atmospheric chemistry experts can chime in. Remember, these talks are only 10 to 15 minutes each, leaving little opportunity for presenting details. –raypierre]

    Comment by Patrick 027 — 17 Dec 2007 @ 10:02 PM

  56. $44: #

    #43 “Andrew,

    if you strayed into a minefield, what would you do? Carefully retrace your steps? Step where there are other footprints?”

    Depends on how I got there. If you skiied downhill into a minefield, would you carefully ski backward uphill?

    And that is sort of the point. To stretch your analogy to the current situation, explain what “retracing steps” means. Does it mean getting rid of the Clean Air Act so we get sulfate aerosols back up? Or returning to a pre-industrial population? Depopulating the Americas?

    But we aren’t slowly walking into this minefield. We skiied down pretty far before we suspected it. We aren’t really going to literally retrace our steps. We are going to go foward with attempts to change various chemical species in a very big reactor that we happen to live in. The way that humans successfully control complicated large scale chemical reactions is not normally through minefield analogies. It is much more often to apply modern control theory.

    I suspect that some people here might believe that some proposed approaches to climate control are silly and others are realistic. Well, if that is true, you would expect that to arise naturally from attempting to compute the control.

    [Response: You’ve got to talk specifics. What you have in mind is some kind of hysteresis loop that we’ve crossed. Can you provide evidence of this kind of hysteresis from increasing CO2 and decreasing it back? Certainly, hysteresis is possible, and becomes more likely as we go to higher and higher CO2. The whole point of CO2 mitigation is to avoid the very high levels of CO2 over long time scales, which could get us into a high risk of hysteresis. I don’t see any basis for comparing that to the situation where you let CO2 get very high, and then try to limit the damage by sulfate-based albedo management. -raypierre]

    Comment by Andrew — 17 Dec 2007 @ 10:30 PM

  57. Gavin your response is a bit strange to me. You link to a post that says

    the total forcing from 1750 to 2000 is about 1.7 W/m2 (it is slightly smaller for 1850 to 2000, but that difference is a minor issue).

    And now you say

    The argument is not affected in the slightest by using 1850 or whatever as a starting point.

    Whereas IPCC 4 says on page 12 of 106

    The RF calculations usually take 1750 as the pre-industrial
    index (e.g., the TAR and this report). Therefore, using 1750
    may slightly overestimate the RF, as the changes in the mixing
    ratios of CO2, CH4 and N 2O after the end of this naturally
    cooler period may not be solely attributable to anthropogenic
    emissions. Using 1860 as an alternative start date for the RF
    calculations would reduce the LLGHG RF by roughly 10%.

    Now, I am sure you are right that this does not effect your argument, but it will definately effect the numbers. With that said, I just want to know your justification for using 1750 as a jumping off point, and please, I really want to know, don’t tell me it is because the IPCC uses that date.

    As for ill-posed questions, it is no secret that I am not a scientist, I believe that every keystroke gives me away a little more. I will be blunt, because I do not know the right question to ask, how does a forcing at the tropopause effect the surface? I am sure you have a post that already answers the question, perhaps you could point me in the right direction.

    Comment by Ellis — 17 Dec 2007 @ 11:18 PM

  58. “What you have in mind is some kind of hysteresis loop that we’ve crossed.”

    I think there are lots of changes to the biosphere which can occur which are a lot harder to reverse than the effect of CO2 on temperature.

    For example there is a possibility that climate change could essentially destroy the Amazon rain forest. Well suppose that happens. OK now drop the CO2 back down. Will that rain forest grow back the same as before or might some other ecosystem displace it?

    The real point here is what is the problem with posing the question in a way that can objectively assess what the most efficient control for the climate is?

    Next guy that thinks we just have to look at the sensitivities to figure out what to do? I got this helicopter I want to see your computer fly.

    Comment by Andrew — 18 Dec 2007 @ 12:59 AM

  59. Next guy that thinks we just have to look at the sensitivities to figure out what to do? I got this helicopter I want to see your computer fly.

    Comment by dhogaza — 18 Dec 2007 @ 3:52 AM

  60. Re #45 [Greg] “If everyone in the country went and got their Carbon Footprint score from and then took just one pledge I think we could stop global warming.”

    You appear to make the implicit assumption, remarkably common among US residents, that nothing outside the USA could possibly make a difference. I’m sure if you had stopped to think a moment, you would have realised this is not so, but such automatic assumptions are very revealing, and can be very damaging. AGW cannot be halted without the USA, but neither can it be halted by the USA alone, nor will the USA necessarily lead the effort. It’s time to think globally.

    Comment by Nick Gotts — 18 Dec 2007 @ 5:26 AM

  61. Re #58. How long does it take a tree to become a forest naturally, probably some 300 years anyway. Once lost, lost for a long time even if we did somehow remove CO2 down to 1750 leves.

    Comment by pete best — 18 Dec 2007 @ 7:00 AM

  62. And that is sort of the point. To stretch your analogy to the current situation, explain what “retracing steps” means. Does it mean getting rid of the Clean Air Act so we get sulfate aerosols back up? Or returning to a pre-industrial population? Depopulating the Americas?

    Not exactly… no need to traverse dead ends or loops on the way back, as you wouldn’t in a real minefield either. Also no need to re-play old television programs from past eras backwards… we’re talking climatology here (is it an American specialty to equate/confuse driving SUVs with physically existing? In that case yes to the last question :-) )

    But we aren’t slowly walking into this minefield. We skiied down pretty far before we suspected it. We aren’t really going to literally retrace our steps.

    But it would be wise to try. Of course you won’t be able to precisely ski in the same tracks, due to the dynamics of skiing… and that makes for some excitement in life.

    Comment by Martin Vermeer — 18 Dec 2007 @ 9:56 AM

  63. Andrew, climate mitigation is not simply a matter of twiddling knobs. There are many knobs where we have only a limited understanding of how sensitive they are–and aerosols are among them. On the other hand, we have quite a good understanding of CO2 forcing. Now given that we are monkeying with the only habitable planet we have yet discovered in any planetary system, does it not make sense to mitigate first where we fully understand the efficachy and consequences of what we are doing?

    Comment by Ray Ladbury — 18 Dec 2007 @ 11:07 AM

  64. Hank Roberts (53) — Yes. Obviously conterfactual, just an attempt to keep the post short and simple.

    Comment by David B. Benson — 18 Dec 2007 @ 3:07 PM

  65. > sensitivities … I got this helicopter
    > I want to see your computer fly.

    “Airplanes want to fly. Helicopters want to crash.”

    The climate system has been remarkably resistant to crashing; I suspect it’s more like an airplane than a helicopter in that regard.

    But remember, there’s only so many rivets you can take out of an aircraft in flight and have it hold together. The important thing about tinkering is … you know.

    They say in flying you need two of three things — airspeed, altitude, and ideas.

    We have the first two, gift of nature and a longterm quiet climate. So we’ve pushed the envelope.

    Now? We’re going to put the planet into something exciting this century (hammerhead stall? flat spin?).

    Next? We step aside, put our nieces and nephews, children and grandchildren in the pilot’s seat, and they take over — to perform the recovery portion of the exercise.

    Good luck, kids. Hope you have good ideas.

    PS, want to learn to fly that helicopter, or write a program that can fly one? Here’s a start: and instructions

    Comment by Hank Roberts — 18 Dec 2007 @ 3:37 PM

  66. #48 Ralph Smythe

    We can remove Co2 from the atmosphere by increasing biomass and soil organic matter. Broadly speaking, continuous cover is the best thing for soils so woodland has the soils with the highest stored carbon, and annually cultivated arable farmland has the least. Approaches to creating sustainable human agroecosystems which preserve soils and biomass and which have been implemented around the world include organic farming, agroforestry and permaculture. Some prominent researchers are Peter Smith (Aberdeen University) for carbon sequestration in soils and J. Pretty for the benefits of organic farming methods in developing countries. Peat soils (also known as ‘organic’ but in a different sense to the farming method) deserve a special mention as they are often metres thick as opposed to centimetres in normal ‘mineral’ soils, and are correspondingly more important as a carbon store. Which brings us to the real world and politics: there are not yet specific measures within the Common Agricultural Policy to encourage carbon sequestration, although other policies on biofuels and set-aside may have an effect. So in the EU there is not a big increase in carbon stored in agricultural areas, more likely a gradual decline. Forest cover is increasing moderately. Comparable situations exist in other developed countries. However, as you are no doubt aware, some parts of the planet are losing forest cover and agricultural soils through logging, desertification and the introduction of intensive farming. In carbon terms, the draining and destruction of peat soils in Indonesia is of critical concern. In human terms, decreasing productivity around the sahara may cause big problems, as high temperatures are a threat to carbon storage in soils.

    Comment by Ed Sears — 18 Dec 2007 @ 8:46 PM

  67. Andrew,

    What are the likely dynamics of the carbon-climate-human system into the future, and what points of intervention and windows of opportunity exist for human societies to manage this system?

    This is the rather all-encompassing title of a UNESCO-SCOPE policy brief no.2 October 2006 (pdf available online) which I think comes at the climate change problem from the angle you would like. Sulphate geoengineering is in fact mentioned in the list of rapidly deployable technologies, although it is one of 16, and most of the others have far more definable and manageable risks. This has to be emphasised: raising vehicle fuel efficiency standards or reforestation of degraded land (the Chinese have planted 49.2 billion trees since 1980) is a whole different level of safety/risk/lunacy compared to simulating a major volcanic explosion in the atmosphere. The cost of doing sulphate geoengineering is nothing compared to the possible cleanup costs when (if?) it goes wrong. For what it’s worth, if I was in charge of a country, I would see it as a matter for national security that other countries *don’t* carry out ill-planned climate engineering.

    Comment by Ed Sears — 18 Dec 2007 @ 9:32 PM

  68. Somewhat offTopic: I wondered how much energy acceleration, i.e., warming plotted over time, we are witnessing in the record setting retreat of summer arctic ice in 2007; i.e., in a modelled environment with scores of variables, it might be possible to characterize the weight of discretely expressed elements in such an aggregate equation.
    Also only slightly OffTopic, appreciation to the author for the glimpses into AGU’s challenging presentations at the yearly meeting*.
    *The city where the AGU meeting just folded its tents is in an area that has received only 3/5 its yearly average rainfall so far in its currently ongoing wet season.

    Comment by JohnLopresti — 19 Dec 2007 @ 2:20 PM

  69. I would like to give some short background then pose some interesting questions to the Real Climate team.

    During the Upper Miocene, it is generally understood that NH ice sheets were not yet formed (maybe beginning as isolated small sheets). However by the beginning of the Upper Miocene, both the WAIS&EAIS were present. Even without the Greenland Ice sheet however, sea levels in the Upper Miocene (5-11 million years ago) averaged very near present levels, with four distinct lowstands, one of which (10 mya) stood 100 meters below present levels. Only one significant highstand of sea level is present in the Upper Miocene sequence strat record (approximately 6 mya, and it only stood maybe 20-30 meters above present. The d18O proxy certainly points to the global Miocene climate being much warmer than the present climate. In light of these observations:

    Questions: 1) Why were Upper Miocene sea levels averaging about what they are presently, puctuated by several significant drops well below present levels? b) How is this possible without a NH ice sheet during the Upper Miocene (a global climate much warmer than present)?
    2) Does this tell us something important about the long term stability and even possible growth of the SH ice sheets in a warmer world?
    3) Why is not more attention being given to research this? It seems particularly relevant to me, given that the paleogeography was much closer to our modern world than further back in the record such as during the PETM.

    Comment by Bryan S — 19 Dec 2007 @ 6:31 PM

  70. Bryan S (69) — Good questions! The only pieces of evidence I can offer is that the Panama Isthmus closed during 3–5 million years ago and the ‘Wall of Africa’, dividing east from west rose during this same time interval (approximately). Both affected climate, but I amateurishingly opine these changes cannot alone account for your observations.

    Comment by David B. Benson — 19 Dec 2007 @ 6:56 PM

  71. Re 55 Responses – Thanks. (I hadn’t read the abstract for that presentation; I guess I was thinking more of a space-based sunshade or troposphere/surface based albedo enhancement, granted that depending on wavelengths and cloud cover, etc, the later one could also increase solar heating of the stratosphere.) (PS I thought that the stratospheric aerosols themselves would be an ozone depletion issue.)

    Re 69 – Not sure about this particular case, but I do know that over long-enough geologic timescales, geological processes contribute significantly to sea level variations. The rate of sea floor spreading can vary a bit, and faster sea floor spreading leads to wider mid-ocean ridges (elevated by heat – the crust subsides as it cools, which occurs at further distance if spreading is faster), which will displace ocean water – effectively, the average sea floor elevation rises relative to the continents, so they ‘sink’ beneath the water. Also, when continents collide and uplift mountains, that adds to the volume of crust above sea level and leaves a larger ocean basin, allowing sea level to drop. Erosion dumping sediments onto continental shelves and slopes would reverse that, as would spreading and thinning of continental crust. There may be other factors; individual continents may ride over parts the mantle with variations that cause them to sink or rise, for example.

    But those changes may not happen fast enough to explain this case, though I’m not sure – maybe. Also, the Mediterranean sea dried up significantly at some point (more than once?), due to temporary closure of the Strait of Gibralter.

    Re 57 last paragraph – I have some other posts elsewhere that go into the matter in some depth, to which I might refer you at a later time; for now:

    lapse rate = rate of temperature decrease with height

    dry adiabatic lapse rate = the rate of temperature decrease with height that occurs during dry adiabatic convection, wherein no net diabatic heating (via radiation or latent heating/cooling, or for that matter, frictional heating or chemical reaction, etc.) occurs.

    moist adiabatic lapse rate = similar to dry adiabatic lapse rate except that this is for when the water vapor is saturated and condensing during ascent. The latent heating causes the air to cool off less rapidly with height (but it still cools off).

    In a very thin layer near the surface, where convection occurs but large motions are inhibited by the surface, the lapse rate can become larger than dry adiabatic, but on larger scales the dry adiabatic lapse rate sets an upper limit on lapse rates, because any larger lapse rate is unstable and will lead to rapid overturning that would then reduce the lapse rate.

    The distribution of radiative heating and cooling in the atmosphere is such that radiation alone would tend to drive the lower atmosphere near the surface towards being unstable; this and horizontal heating/cooling variations drive the convection that define the troposphere, the lowest layer of the atmosphere (which happens to contain a large majority of the mass of the atmosphere). Because of the moisture available, this convection tends to maintain a lapse rate lower than a dry adiabatic lapse rate.

    To be precise one would have to go into the horizontal and temporal variations – and there are such variations in the above. But one can get a good basic idea of how the greenhouse effect works by considering a one-dimensional model, which is just a column of atmosphere that is representative of the Earth’s atmosphere (or the atmosphere of whatever planet one wants):

    There is a distribution of solar heating (SW radiation) – a majority is concentrated near the surface but some does heat the atmosphere directly. Convection redistributes this heat. (Some SW radiation reflected or scattered back to space and so does not participate in this heating.)

    LW radiation is the radiation the Earth’s surface and atmosphere can emit at their temperature ranges; this is a band of wavelengths longer than SW wavelengths (PS SW does extend into the infrared a bit, so it is incorrect and confusing to consider solar radiation to be UV and visible only).

    The atmosphere can be divided arbitrarily into a number of layers; each layer emits and absorbs some LW radiation, as does the surface. Some LW radiation escapse to space. Proportionally more LW radiation can escape to space from upper layers because the layers can absorb what is emitted by other layers and so radiation from lower layers is more easily absorbed before escaping. The surface can also absorb LW radiation from the atmosphere.

    In an equilibrium climate, LW radiation escaping to space must balance the SW radiation that is absorbed. SW radiation is absorbed, that heat energy is redistributed by convection and by the LW radiation that is emitted and absorbed, and ultimately leaves by that portion of LW radiation that escapes.

    Optical properties vary by wavelength, and it is helpful first to consider what would happen at just one wavelength. At any wavelength, for fixed optical properties, emission of LW radiation increases with increasing temperature. Thus, the net flow of LW radiation tends to be from hot to cold, as with conduction of heat… But I have to go now; stay tuned.

    Comment by Patrick 027 — 19 Dec 2007 @ 10:38 PM

  72. Re 57 part II: With that introduction, I refer you now to my comments 184 and 189 in

    And then, note that radiative forcing at the tropopause is defined for after equilibrium is restored in the stratosphere (and above, presumably), but before any climatic response at the surface or within the troposphere. Of course, as the troposphere and surface respond, the stratosphere will again adjust, and the tropopause will also tend to move.

    PS other comments I made in the same thread (some but not all applying to this subject):

    171 – 176

    and at


    and I also have some comments pertaining to the topic at: (as in a geologic time column, the comments there go from the bottom up.)

    Comment by Patrick 027 — 19 Dec 2007 @ 11:41 PM

  73. Patrick 027 (71) and Bryan S (69) — It seems that the Mediterranean dryed up ten times in the Late Miocene! Here is a line to an abstract:

    Comment by David B. Benson — 20 Dec 2007 @ 2:37 PM

  74. Bryan S (69) — The sea high stand appears to be at (approximately) the same time as the Mediterranean desiccations. The paper linked below suggests the possibility of NH ice sheets during the sub-epoch in question, being titled Reconstructing the late Miocene climate and oceanic heat transport flux…:

    Comment by David B. Benson — 20 Dec 2007 @ 5:39 PM

  75. The abstract by Tripati et al. contained in

    on page 22 concludes with The … storage of ice in both the Northern and Southern Hemisphere[sic] … after 34 Ma.

    Comment by David B. Benson — 20 Dec 2007 @ 7:15 PM

  76. 63: “Andrew, climate mitigation is not simply a matter of twiddling knobs.”

    From the point of view of control theory, it is. You can substitute the word “control input” for “knob” but that’s basically all it amounts to. Want to call it a manifold? Fine. But it’s still really just knobs.

    Comment by Andrew — 23 Dec 2007 @ 5:20 PM

  77. “The climate system has been remarkably resistant to crashing”

    Is that why it has done it so often in history?

    Comment by Andrew — 23 Dec 2007 @ 5:22 PM

  78. 59: “”

    No not that helicopter. This helicopter:

    The reason to point at this paper is because it is a case where exact linearization leads to an unstable controller.

    So it is a relatively precise demonstration of my point – that it is NOT sufficient to know sensitivities of a nonlinear system in order to control it.

    In the climate control case, the analogy would be unnecessarily large seasonal (or perhaps decadal) oscillations.

    Sure you might get the overall average level where you want it but it is worth asking whether the road we travel to get there is the smooth one.

    Comment by Andrew — 23 Dec 2007 @ 5:31 PM

  79. “What are the likely dynamics of the carbon-climate-human system into the future, and what points of intervention and windows of opportunity exist for human societies to manage this system?”

    It’s worse than that. I am not convinced that we know the likely trajectories for the future. This is pretty much what gets you to the realization that we have to deal with robust control – the question of how to control something when you do not have good knowledge of the dynamics, (and in this case, you do not have good knowledge of the control inputs either). If we take into account the skeptics of the world, we will actually be arguing over the knowledge of the plant outputs as well.

    The huge advantage of control theory is that it is not really a new problem of how to control a system where there is imperfect knowledge of the plant. And it is possible in these methods to be able to know how much of the uncertainties can be tolerated, and which cannot. There are many aspects of climate where the “error bars” are a pain in the butt to nail down. Well, it is entirely possible that not all of them need to be nailed down.

    Comment by Andrew — 23 Dec 2007 @ 5:43 PM

  80. Andrew, if you apply control theory, you will find that either:
    1)We have no control over many parameters (e.g. insolation)
    2)That we do not have sufficient understanding of the parameters to predict how they will affect climate.
    3)That the duration of the effect is too short to really help us much (e.g. aerosols)
    4)That we cannot rule out adverse consequences for the manipulation on the scale that would be needed to have an effect (e.g. sulfate injection).

    In fact, the level of assurance we require that the technique will be effective and that we will not make things worse pretty much precludes anything but reducing CO2 in the atmosphere.

    Comment by Ray Ladbury — 23 Dec 2007 @ 6:27 PM

  81. 81. “Andrew, if you apply control theory, you will find that either:
    1)We have no control over many parameters (e.g. insolation)
    2)That we do not have sufficient understanding of the parameters to predict how they will affect climate.
    3)That the duration of the effect is too short to really help us much (e.g. aerosols)
    4)That we cannot rule out adverse consequences for the manipulation on the scale that would be needed to have an effect (e.g. sulfate injection).”

    1) Parameters which cannot be controlled are no problem. In fact, there are some parameters which are too costly to be part of efficient control. What is more important (and somehow continues to elude you) is that this is why you don’t want to just start pulling levers – you really do want to look at this from the point of view of control theory.

    2) How do you know it is insufficient if you do not have an estimate of an efficient controller? There are going to be many things which are irrelevant to an efficient controller; and it will be really helpful to know which things those are. I would guess that geoengineering would be in that box, but it is a real bad mistake not to come by that conclusion honestly. If you think about trying to seriously show that geoengineering is a waste of time, you will have to demonstrate something more or less along the lines that control theory would make precise.

    3) This is not at all obvious; my suspicion is that it is dead wrong. If you end up having to carefully sculpt seasonal or decadal oscillations it’s nice having some things which act on a fast time scale.

    4) Adverse consequences are included, either in the cost of control, or in the deviation of the trajectory from the specification. For the adverse consequences you are talking about here, I think it more likely that having them in the specification of the controlled trajectories would be more useful.

    Comment by Andrew — 23 Dec 2007 @ 7:52 PM

  82. Andrew, those knobs evolve under selection pressure from that twiddling, and with very short generation times. You don’t know what they’re changing into yet. Look at the paleoecology for natural rates of change in past excursions; the current rate of change is likely to be as fast as the current excursion a couple of orders of magnitude faster, assuming nature can keep up with us, and much faster and less predictable if not.

    I’m just an amateur reader, but I suggest you try reading this:

    The problem with NPZD models is that their representation of biological fluxes is entirely dependent on physical processes. These models do not include many of the ecological processes that are known to be sensitive to, for instance, changes in temperature or pH, such as bacterial remineralization (Rivkin and Legendre, 2001Go), zooplankton grazing rates (Buitenhuis et al., 2006Go), the aggregation role of mucus secreted by some phytoplankton (Engel et al., 2004Go), the ballasting of organic particles by plankton shells (Klaas and Archer, 2002Go) and pH sensitivity of calcifying phytoplankton (Riebesell et al., 2000Go) and zooplankton (Orr et al., 2005Go).

    … One of the great values of large-scale modelling is that it enables us to examine the consequences of physiological differences between PFTs for large-scale phenomena such as spatial distributions and seasonal successions. We will not understand ecology until we have built models that include the necessary processes.

    ——–end excerpt——-

    Found here:

    Comment by Hank Roberts — 23 Dec 2007 @ 8:38 PM

  83. Andrew, I recommend to you the counsel of H. L. Mencken:
    “Explanations exist: they have existed for all times, for there is always an easy solution to every problem — neat, plausible and wrong.”

    Comment by Ray Ladbury — 23 Dec 2007 @ 11:20 PM

  84. “Andrew, those knobs evolve under selection pressure from that twiddling, and with very short generation times. You don’t know what they’re changing into yet.”

    Yes, that is one of the things that makes the modern robust control theory approach attractive. Remember I’m the one that pointed out the possibility of fast and possibly irreversible responses (like loss of the Amazon rain forest) being a potential outcome.

    What seems to be completely ignored though, is my repeated explanation that the less you know about the system, the more you really ought to take advantage of the tools which have recently become available for controlling systems which have large uncertainties. In particular, the main reason that you want to think about robust control for climate is that you do not completely know the plant, you do not completely know the control inputs, and it is even possible that people will not be able to agree on the measured system outputs. When you have a high dimensional nonlinear system with feedbacks as one of the happier things you can say about the problem (and this is not really that happy a thing to have to say) then you really don’t want to screw around with guessing which knobs to turn and which to ignore.

    Comment by Andrew — 24 Dec 2007 @ 2:45 AM

  85. “Andrew, I recommend to you the counsel of H. L. Mencken:
    “Explanations exist: they have existed for all times, for there is always an easy solution to every problem — neat, plausible and wrong.””

    Well Ray, you could crack the odd book yourself. In particular there is probably a proceedings of the 2004 AGU 2004 Fall Meeting where there might be a paper from this invited talk:

    A13C-07 INVITED 15:20h

    “Control Theory and Analysis of Feedback Systems

    * Murray, R M ( , California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125 United States

    Control theory has developed a collection of tools that can be used to better understand the behavior of complex, interconnected systems. This talk provides an introduction to some of the control theory tools relevant to climate dynamics. Specific concepts that will be described include input/output modeling, modeling reduction, and analysis in the presence of unmodeled dynamics.”

    Now I doubt that Murray would have exactly the same take on control synthesis that I would, since I use a lot of stuff that isn’t in the open literature, but he’s definitely in the business. You probably know guys at JPL who know him. I am pretty sure that what he means by “analysis in the presence of unmodeled dynamics” is a version of what I am trying to get across here.

    So it’s not so bad as I thought. At least one guy in climate figured out they should get hip to control theory.

    Comment by Andrew — 24 Dec 2007 @ 2:58 AM

  86. Andrew, you misunderstand my criticism. I am not challenging the use of control theory. Rather I am pointing out that control theory dictates that you must take into account the uncertainties and potential adverse outcomes in deciding which knobs you can twiddle. The fact of the matter is that we cannot change most of the variables that affect climate. Of those we can change, weunderstand well precisely one–greenhouse gasses. So what your little control theory analysis will wind up telling you is “Hey, maybe better back off on the CO2, huh?”
    Since we have precisely one habitable planet, any control-theoretical analysis will have to adopt only those solutions where there is extremely high confidence we will not irreparably screw things up. Since we cannot eliminate the possibility of severe consequences or establish the efficacy of, say, using sulfate aerosols, that is not an option.
    Iron fertilization to cause algal blooms has been shown not to be viable.
    Got any other tricks up your sleve?
    Andrew, the reason control theory is not used more in climate remediation is not because climate scientists are all a bunch of stodgy, conservative, ignorant twits. Rather it is because the only viable solution is obvious.

    Comment by Ray Ladbury — 24 Dec 2007 @ 8:15 AM

  87. Another interesting discussion on control systems, however, I just can’t imagine building such a large “control system” without a reasonably accurate simulation, and a physically representative prototype, and I can’t fathom how we’d do that. We wouldn’t allow that leap of faith for a nuclear power plant control system, a much smaller gambit, would we?

    Comment by TheWonderer — 24 Dec 2007 @ 9:56 AM

  88. > Now I doubt that Murray would have exactly the same take
    > on control synthesis that I would, since I use a lot of
    > stuff that isn’t in the open literature

    What justification is used for keeping tools secret that could help, in this situation?

    Comment by Hank Roberts — 24 Dec 2007 @ 11:10 AM

  89. “Rather I am pointing out that control theory dictates that you must take into account the uncertainties and potential adverse outcomes in deciding which knobs you can twiddle”

    Well it doesn’t, actually. This may be the reason I don’t understand where you are coming from.

    Comment by Andrew — 24 Dec 2007 @ 12:39 PM

  90. “So what your little control theory analysis will wind up telling you is “Hey, maybe better back off on the CO2, huh?””

    It might end up with that result. But the advantage of getting it via control synthesis is that you would be explain to explain not only why that would achieve your goals, but why it would be likely to cost less than other approaches. So if you don’t like geoengineering, this would at least be an objective way to do that.

    In actual fact, I am pretty sure that the schedule of action that would result from a serious application of control theory would have a few interesting twists; sure you will probably want to deal with CO2, but the quantitative details of how and when are probably not something that would be obvious.

    The certification of minimum cost would help with skeptics who think it is going to be expensive – it would present them with essentially a verifiable claim that in order for the climate to be within some acceptable bounds, then the least we must do is X.

    There is something very suspicious with the idea that we can solve the most complex control problem ever attempted with the simplest imaginable controller.

    And frankly, there are quite obvious experiments which could be done. There are what, a dozen or so GCMs out there? For one thing, you could synthesize a minimum cost controller that can handle them all. If you can’t even do that, what reason is there to believe that we will control the real climate with anything approaching minimum cost?

    And if you don’t try to determine the minimum cost, that leaves you open to all sorts of charges of ruining the world economy. (Charges which already are pretty familiar from some quarters).

    Another very important aspect of a control theory approach would be that you would also be able to evaluate things like a market-based control. Different parties may have different desired trajectories for climate. This would provide a way to put that into economic terms – so you would know how much to charge for deviation. I believe that there are a lot of parties in the picture who seem to think entirely in economic terms.

    Comment by Andrew — 24 Dec 2007 @ 12:56 PM

  91. > There is something very suspicious with the idea that we can
    > solve the most complex control problem ever attempted with the
    > simplest imaginable controller.

    No, you’re confusing the leverage point with the controller.

    Getting people to reduce fossil fuel use is inordinately complicated, and if your control theory is being applied by the political science folks it’d be interesting.

    Comment by Hank Roberts — 24 Dec 2007 @ 1:39 PM

  92. Andrew, any application of control theory would have to take into account what we know about climate. That is contained in the models. If control theory does not take into account uncertainties, potential adverse outcomes and likely efficacy of the remediation at some required confidence and probability of success, then it is not suited to the task. If it does, it will tell us that reducing carbon is the only way to move at present given our state of knowledge about the climate.
    One of the reasons for this is because we would have to require a high degree of certainty that we would not be making things worse. Go ahead and do the analysis–I’m pretty sure what your outcome will be.

    Comment by Ray Ladbury — 24 Dec 2007 @ 3:07 PM

  93. Comment on Late Cenozoic Ice Sheet Variability and Control on Global Sea Levels

    Thank you David B. Benson for your interest in my comments, and your links.
    A powerful way to gain insight into the role of ice sheet dynamics and their control on global sea levels is to superimpose a smoothed d18O proxy (or composite of several individual cores) over a composite eustatic sea level curve. As a greater number of deep ocean cores are recovered, and the sequence stratigraphic record across stable platform areas is further refined, a fascinating picture is emerging. Although there is broad correlation between the records, there are also periods when the records are out of phase. As the record improves, these may come into closer agreement.

    As an example of correlation, a large sea level lowstand (50-100 meters below present) near the beginning of the late Miocene (10 ma) corresponds to a dramatic shift in the d18O proxy. Even so, the d18O proxy provides compelling evidence that the overall global climate throughout the Late Miocene (5-11 ma) was certainly much warmer than our modern climate, but also similar in warmth to that of the Early Pliocene (3.5-5 ma), when the most significant sea level highstand of the last 10 million years occurred. During the Early Pliocene highstand, sea levels were perhaps 100 meters higher than present. The Pliocene high sea level event contrasts to average sea levels throughout the Late Miocene which averaged near present levels, but were punctuated by four distinct lowstands 20-100 meters below present levels, and only one significant highstand near the Miocene/Pliocene boundary (Haq et. Al. 1987; Mitchum et al. 1994).

    That being said, Denton et al. (1991) argued that the ice volume on Antarctica was roughly half of the present volume by 15 ma, and perhaps exceeding the present volume by roughly 12 ma. The EAIS has now been traced back into the Early Cenozoic (Barron et al., 1991; Hambrey et al., 1991). There is also evidence that the WAIS was present by the Late Miocene (Abreu and Anderson, 1998). Both the EAIS and WAIS were certainly present during the Pliocene (Denton et al., 1991; Webb and Harwood, 1991; Barrett et al., 1992). Surprisingly, the beginning of the NHIS is now placed by several workers in the Early Pliocene, during an extremely warm global climatic event, and may have been intermittently present in the Late Miocene. During the pronounced Late Miocene low sea levels, there is little evidence of a significant ice sheet present on Greenland.

    From a contemporary perspective, the combined records summarized above should give considerable confidence that a catastrophic decrease of the Southern Hemisphere Ice Sheet volume is not likely even in a severe modern global warming event. In fact, it may be argued that SH ice volumes significantly greater than present have occurred during global climates much warmer than we are likely to see even with a high climate sensitivity to added greenhouse gases. The highlighted record shows that the ice sheets respond in a very non-intuitive (non-linear) fashion to global warming, and in large part may be controlled by regional changes in oceanic heat transport and weather patterns which are especially challenging to accurately model and predict. The Greenland Ice sheet has not been around nearly as long, so its response is less certain. It should be pointed out however, that decreased ice volumes in the NH might seemingly be balanced by growth in the SH ice sheets.
    The Early Pliocene event was not likely to have been driven by significant NH melting, but rather a possible regional response to ocean circulation and weather patterns allowing changes to the SH ice volumes. In summary, the ancient record of ice sheet dynamics and correlation to eustatic sea level paints a complex picture, and illustrates a consistent theme of how the earth system is very non-linear and difficult to predict. It does show however, that the SH ice sheets are likely the key driver of global non-thermosteric sea level variation.

    It is my hope that these comments will provoke interest among the readers and contributors of Real Climate, and hopefully motivate all to recognize the significance of the paleo and geologic record in helping gain a better perspective in the issues involved with global sea level variation its response to climate change.

    Comment by Bryan S — 24 Dec 2007 @ 7:44 PM

  94. RE #41 Alexander Harvey

    Just a short note to thank Alexander Harvey for the expansion of the MEP principles in context.

    Seeing the climate system as a heat engine in process, and noting that increasing CO2 increases the retained energy of the system, might have more than academic implications.

    Bets are on any results will not violate any well established laws of thermodynamics, nor classical physics.

    Comment by Jim Redden — 29 Dec 2007 @ 1:15 AM

  95. Gavin, I read with some interest the article in the December 2007 EOS summaring the January 2007 NOAA workshop on ice sheet modeling. In the second paragraph, your group cites the IPCC Fourth Assessment Report, stating [the understanding of rapid dynamical changes in ice flow “is too limited to assess their likelihood or provide a best estimate of an upper bound for sea level rise”]. Yet, in the first paragraph, your group states flatly “poorly represented physical processes in the ice sheet component *likely* lead to an underestimation of sea level rise forced by a warming climate”. It seems curious that no reference of anyone’s specific work was cited, but only this rather sweeping proclamation. Would you please clarify in more detail why such an important hypothesis is presented without any reference to supporting data. If the reference was inadvertantly left out,could you please supplement the paper here so that we may become better informed on this hypothesis.

    In the section Underlying Problems, it is pointed out that key processes should be incorporated into the models in order to make reliable prediction of future ice sheet change. The first included iteraction of ice sheets with the ocean, requiring models of regional oceanic circulation. Presumably such would require that multi-decadal predictive skill of ocean circulation changes on a very fine scale, and in just the right areas to be able skillfully model their effect on ice discharge. It seems to me that such is a daunting challenge. Could you give some further insight.

    Thanks in advance for the reply.

    [Response: The reason why the uncertainty is predominantly on the up-side is related to the dynamical changes that have been seen in Greenland, West Antarctica and the Antarctica peninsula – none of which are well captured in current ice sheet models. The surface mass balance changes (where you conceivably have counteracting forces) are much easier to model and capture and so the uncertainty is less. At the workshop, the ice sheet people there – Tony Payne, Shawn Marshall, Christina Hulbe etc. – all made it clear that their models were not up to the task – they didn’t have the rheology that would allow them to predict accelerations of ice streams due to lubrication effects or collapse of the floating ice sheet, they didn’t have the water balance to allow them to keep track of the surface melt (the moulins), and they didn’t have the ocean/sub-ice sheet interaction and so on. So they are in a very uncomfortable position of having models that clearly don’t show what is already happening. That, let me tell you, is not a good place for modellers to be. There are however a lot of good ideas and improvements that could be made relatively quickly that don’t require huge advances in regional modelling (though some kind of downscaling is necessary). – gavin]

    Comment by Bryan S — 8 Jan 2008 @ 9:37 PM

  96. What is an extra-solar Large Earth? Is that a planet like Saturn or Jupiter only Earth-like?

    Comment by Jason — 7 Feb 2008 @ 1:13 PM

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