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Positive feedbacks from the carbon cycle

Filed under: — david @ 27 May 2006

Two papers appeared in Geophysical Research Letters today claiming that the warming forecast for the coming century may be underestimated, because of positive feedbacks in the carbon cycle. One comes from Torn and Harte, and the other from Scheffer, Brovkin, and Cox. Both papers conclude that warming in the coming century could be increased by carbon cycle feedbacks, by 25-75% or so. Do we think it’s time to push the big red Stop the Press button down at IPCC?

The approaches of both papers are similar. The covariation of temperature versus CO2 (and methane in Torn and Harte) is tabulated for a record in the past. For the Torn and Harte paper, the time frame chosen is the last 360,000 years, while Scheffer et al. focus on the Little Ice Age, from 1500-1600 A.D. In both cases it is assumed that the climate shift is driven by some external thermal driver. As the temperature warms (in the case of the deglaciation) or cools (the LIA), the CO2 concentration of the atmosphere changes in the sense of a positive feedback, rising associated with warming or falling in response to cooling. The changing CO2 drives a further change in temperature.

In general, it is clear that eventually the sense of these articles could be correct. The response of the terrestrial biosphere to rising CO2 could go either way; toward an increase in uptake because of CO2 fertilization or a longer growing season (as we see today) versus an increase in soil carbon respiration in warmer conditions (the reason why tropical soils contain so little carbon). Uncertainties in the response of the terrestrial biosphere to rising CO2 is a major source of uncertainty for the climate change forecast (Cox et al., 2000).

The oceans are presently taking up about 2 Gton C per year, a significant dent in our emissions of 7 Gton C per year. This could slow in the future, as overturning becomes inhibited by stratification, as the buffer loses its capacity due to acidification. Eventually, the fluxes could reverse as with a decrease in CO2 solubility due to ocean warming.

The biggest question, however, before pushing the Stop the Press button at IPCC, is timing. The CO2 transition through the deglaciation took 10,000 years. (Actually this helps to constrain the cause of the CO2 transition, because the air/sea equilibration time scale for CO2 would be considerably shorter than that.) The timescale that seems intrinsic to IPCC is a century or so, during which we should be able to reap only a small fraction of any harvest that takes 10,000 years to grow. The Scheffer et al paper avoids this issue by restricting its attention to a time period of just a century.

Scheffer et al illustrate the potential feedback for the coming century in a figure which looks something like Figure A.

Temperature depends on CO2 concentration via radiative equilibrium in the blue curves, and CO2 concentration in the air is affected by temperature according to the red lines. A rise in CO2 concentration from an external source changes the equilibrium CO2 as a function of T relation toward higher CO2, to the right, labeled “forcing”. The stable final equilibrium is where the two relations cross, with further CO2 degassing from the land or the ocean, so that more CO2 ends up in the atmosphere than would have if there were no feedback (a vertical red line). A climate sensitivity calculated from the coupled system is higher than one that ignores any carbon cycle feedbacks.

The situation today is complicated somewhat by a carbon spike transient. Atmospheric CO2 is rising so quickly that the terrestrial biosphere and the ocean carbon reservoirs find themselves far out of equilibrium. In attempting to keep up, the other reservoirs are taking up massive amounts of CO2. If emissions were to stop today, it would take a few centuries for the atmosphere to equilibrate, and it would contain something like 25% of our emitted CO2.

I would draw our current situation as in Figure B, with CO2 concentration wildly higher than the equilibrium red line, poised to relax toward lower concentrations if emissions stopped. The effect of the carbon cycle feedback is to change the equilibrium atmospheric CO2 that we are relaxing toward. It seems to me that the most important part of the equation for our immediate future is the decay rate of that carbon spike, rather than the equilibrium value that CO2 will relax to in hundreds of years.

122 Responses to “Positive feedbacks from the carbon cycle”

  1. 51

    Re 49, 48 & 47. “Dr. Hansen isn’t running for office. But Mr. Gore might be, and even if he isn’t, he hopes to promote global warming as a political issue. And if he wants to do that, he and those on his side will have to learn to call liars what they are.” Washington Post.

    Re 49, 48 & 47. Shaving 10% of individual energy use will make no difference what so ever. Here in Europe every man women and child uses twice their share of the world’s energy. Reducing that by 10% would still leave we Europeans using 80% more than is fair. In the United Sates the figure is 5 times their share and reducing that by 10% would leave each American with 350% more than they are entiled to.

    Since Kyoto was first proposed, the UK has stabilised its total CO2 emissions at around 600 million tons per annum. Meanwhile the US has increased its emissions by around 700 million tons. In other words, even if we in Britain had stopped burning any fossil fuels, global greenhouse gas emissions would have increased because of the US!

    The good news is that if the US did halve its energy consumption then the standard of living in the US would still be above that of the UK, which is perfectly adequate for a civilised society.

    The bad news is that both the UK and the USA will have to go even further. However, it will be forced on them by soaring oil prices now that we have passed Peak Oil. However, we must have a global agreement to cut fossil fuel use, otherwise when we have used all that expensive oil we will be roasting in a hell of our own making.

  2. 52
    Hank Roberts says:

    Here’s a source I hope the RC contributors or Coby for the ‘ill-considered’ list will check. It may be one of the places some of the odd and unsupported ideas come from — for example the claim that CO2 is already absorbing all the infrared it can. This is all footnoted to early 1990s sources on the site.

  3. 53
    Brian Gordon says:

    To those who argue we cannot make quick emissions cuts, for example #47:

    > 3.)there is no way, no way at all, to “quickly cut carbon emissions in half or more”. That regrettable fact deserves some attention when contributors wing all kinds of carbon-cutting suggestions without trying to imagine and help us see how a credit-strapped America will respond or – even how impractical it might be to plant trees without having, in place, a means to water them.

    Of course there is a way – there are many ways. (I do agree with Mr. McCormick’s contention that the US debt will be a very major problem, because it will severely limit the federal government’s ability to drive or finance change.) It’s just that we don’t like any of them, because they change the current economic structure. Taxes could go way up on GHG-producing products, auto fuel efficiency could be mandated at a very high level, new houses could be net contributors to the grid, etc. Americans are unwilling to consider these options because they are “left-wing,” “socialist,” or in some other way are thought to inhibit individualism. But there are lots of ways we could immediately and drastically reduce our emissions. Or, we could wait for climate change to reduce our emissions by reducing our numbers. Pay now, or pay later. Maybe with your children’s lives.

  4. 54
    Tom Boucher says:

    Re #51 – I don’t see how you define what is a “fair share” of the world’s energy. Are you referring to average individual energy consumption? You then remark on how Europeans and Americans use more than their “fair share” – meaning others use less, and if all people used their “fair share” we would still be at the same level of energy use, right? I don’t understand this at all. Also, it appears you define an “adequate” standard of living for a civilized society as that of the UK. Why is this? Could you give us some insight into the calculus you are using?

  5. 55

    Re #54 The figures I quoted were what I remembered from a BBC broadcast, so they may be inaccurate or garbled. If you go to Fig 5 on page 4 of this PDF file from a WWF site, you will see that Western Europe’s ecological footprint is five times that which is sustainable, and North America’s is nine times. . It seems that the average foot print is two global hectares, so as you point out even if Britain and the US restricted themselves to the average then the world would still be consuming at twice the sustainable rate. OTOH if both N. America and W. Europe restriced themaselves to the current average, there would be a huge reduction in the resulting average consumption.

    The main point is that NA and WE consumption is unsustainable and it will have to be curbed by governments, otherwise it will be enforced on us by India and China grabbing thier share. How can you stop them in a free market?

    As far as the UK having an adequate standard of living, in fact it is now too high. A recent survey revealed that compared with 50 years ago when 80% of people were happy, the figure is now 30%. It seems clear to me that we are now too rich for our own good.

  6. 56
    George says:

    At what point do we consider geoengineering as a response to abate global warming? I am specifically thinking of placing screens in space to regulate the amount of sunlight reaching the planet and/or disbursing aerosols above the troposphere to reflect away sunlight. Moreover, what are the risks to the biosphere from such schemes? I would greatly appreciate it if you could direct me to the literature on geoengineering and climate change.

  7. 57
    Hank Roberts says:

    Maybe a big cloud of coal dust launched into space (wry grin). That’d show those photovoltaic people, cut their efficiency ….

  8. 58
    Hank Roberts says:

    Remember natural variation happens. Imagine trying to undo a big cloud of dust in space blocking sunlight, or a big cloud of sulfates in the stratosphere, if the sun happened to become a bit less bright afterwards.

    The good thing about fossil carbon is it could be used in a way intelligently designed — not so much as to push the climate into warming, and enough to avoid slipping into cooling.

    Apparently we did that well until about the 1600s.

  9. 59
    Brian Gordon says:

    Geoengineering is not the answer. Why geoengineering won’t work:

    1. Governments, corporations, and individuals will create what they want, not necessarily what the planet needs, just as occurs now. Planet-scale geoengineering involves worldwide cooperation and agreement – we can’t even agree now that global warming is a threat, never mind agreeing to something as minor as Kyoto, never mind agreeing to governmental environmental control.

    2. When you don’t know all the complexities of your life support system, it is foolish to experiment with it. I doubt we will ever know enough to be able to accurately control our environment (though we may soon be forced to try) because it is an evolving system, and because the complexity of the earth’s systems is truly staggering.

    3. Planet-scale geoengineering is completely out of harmony with the natural world – it makes us God/gods. It assumes that we have a right to live at any cost, but no other species unless it suits us. This is a common developed-world/Judeo-Christian belief, and it is one reason we are in such trouble now. We currently have the creative and destructive powers of minor gods, but not the wisdom to know how to use those powers.

  10. 60
    Coby says:

    Geoengineering may be in the future, as a necessary evil. I agree with Brian’s points above, but I would say this:

    Geoengineering could work, we are resourceful and clever creatures. The problem is it would take a few planets and a few multi-decade trials before we would get it right. Imagine the waste disposal problem, getting rid of the many spoiled planets created in the learning process…

    I can’t help smirking a bit at the irony involved. Surely the geoengineering solutions would be tested out on all those wonky computer models, right? This is what the sceptics think is the prudent course, ignore the model warnings but then design and execute massive planet wide experiments based on same.

  11. 61
    Hank Roberts says:

    “Fix Venus and Mars First” should be our approach.

    Sunshade between Venus and the Sun; mirror on the far side of Mars, at the Lagrange points, eh?

  12. 62
    Doug Percival says:

    George wrote in comment #56: “At what point do we consider geoengineering as a response to abate global warming? I am specifically thinking of placing screens in space to regulate the amount of sunlight reaching the planet and/or disbursing aerosols above the troposphere to reflect away sunlight. Moreover, what are the risks to the biosphere from such schemes?”

    How would you like to take conscious control of your liver, your kidneys, your intestines, your lungs, your lymphatic system, etc, and direct their functioning at the cellular level with your conscious mind? And once you do so, you never get to stop — if you don’t consciously direct them and coordinate them to perform their biological functions at every moment, they’ll simply stop, and if you make an error in your instructions to them, they will fail and you will die.

    Do you think that “you” — your conscious mind — could do a better job of directing and coordinating the functions of these organs than “nature” does?

    With that in mind, do you think that human “engineers” can do a better job of “running” the Earth’s climate, ecosystems, and the biosphere than “nature” does?

    Someone once said of George W. Bush that “he was born on third base and thinks he hit a triple”.

    Sometimes, something like that seems to me to apply to the human species. We were “born” into a rich, diverse, wonderful living Earth, and have been enjoying the vast bounty that it freely bestows upon us for thousands of years, and we have come to think that we are “gods” and we can take over and run the whole show better than billions of years of evolution have made the whole show quite capable of “running” itself without our “help”.

    What hubris cometh before a fall!

  13. 63
    Joel Shore says:

    Re #60 (“I can’t help smirking a bit at the irony involved. Surely the geoengineering solutions would be tested out on all those wonky computer models, right? This is what the sceptics think is the prudent course, ignore the model warnings but then design and execute massive planet wide experiments based on same.”):

    What makes it even more ironic to me is that it seems like you have to know what is going on with the climate due to greenhouse gases to way higher precision in order to do some sort of geo-engineering to counteract act it than you do to counteract it by simply reducing or sequestering greenhouse gas emissions. (And, of course, then in addition, you have to know to high accuracy the effect that your geo-engineering solution will have…and how these effects will interact.)

    Another irony is that many of the people throwing out these ideas are of the libertarian or conservative bent who complain about the evil’s of government intervention and regulation, the U.N., and such. However, their proposed solution seems to be one that can only work on a big government scale with massive amounts of international cooperation. By contrast, while approaches like Kyoto do involve international agreements and government action, they can be (and are being) implemented in market-based ways such as through emissions trading so that they are much more flexible and market-oriented approaches to finding solutions.

  14. 64
    George says:

    Little of what has been said here so far speaks to the viability of geoengineering solutions to the potential of run-away global warming. It is should also be stressed that we have already altered the biosphere through excessive carbon dioxide emissions. Geoengineering could be a rational means to stablize the environment. In the long run, I agree humans must institute appropriate regulations of its changes to the planet.

  15. 65
    Lynn Vincentnathan says:

    Thanx for this entry on positive feedbacks (I’ve been away from the net for a few weeks). I understand that scientists can only work with stuff they can work with (quantify, etc), which doesn’t mean other stuff isn’t happening or might not happen.

    As people living on this planet, OTOH, we should follow the prudent route of thinking the worst could happen, and do whatever we can to stave it off at the personal level; at home, work, school, church; at the various levels of government from local to national to international. I can’t think of a better way for me to spend my spare time…..

    I’m reading Cliffnotes Statistics (gearing up to teach statistics again after a decade), and came across this on p. 70: “A small, but important real-world difference may fail to reach significance in a statistical test. Conversely, a statistically significant finding may have no practical consequence.”

    [Response: Welcome back. I was wondering why we hadn’t heard from you in a while. When looking at significance tests, make sure to keep an eye out for the distinction between those that assume a Gaussian underlying distribution and those that are independent of the underlying distribution (or rely on some a priori estimate of it). Also, one must keep in mind that if one looks at a hundred results, it’s a pretty sure bet that one of them will be significant at the 1% level. –raypierre]

  16. 66
    John McCormick says:

    RE: #64, George mentions a “potential run-away global warming”. It is more than a potential if we continue to “engineer” the planet’s atmosphere. That said, correcting our folly will never (time, money and confidence level are not there) include a geoengineering solution.

    We must get this thread back onto the reality track

  17. 67
    Rod Brick says:

    re #52 by Hank Roberts
    I don’t understand your dismissing T.J. Nelson out of hand. Because he had some cited references from ancient 1992? Is the science of Beer’s Law, e.g., now outdated? Is it “odd” just now, or was it always odd?? Actually, while I don’t have the bona fides to credibly assess, I found his article extremely learned, intuitively believable, and devoid of snide and strident comments. The latter, btw, while cute, unfortunately detract from what otherwise what might be valid science.

    [Response: A lot of rubbish is written in a way that seems learned. The problem isn’t that science has changed, but that a lot of the material on the web site mentioned in #52 is based on a fundamental misunderstanding of basic physics. For example, it’s not Beer’s law that is at issue but that the greenhouse effect depends on how much radiation gets out the top of the atmosphere for a given surface temperature, and that relies not on the saturated part of the CO2 band but the unsaturated part in the wings. The reference to the old “1990’s” literature, I think, was not meant to imply that the fundamental physics has changed, but that the site refers to “old” skeptics arguments that have for the most part fallen out of fashion. Skeptics keep recycling lies and misleading statements long after they’ve been debunked, but even these arguments wear out after a while, so the skeptics have to move on to new and better ways of misleading the public. –raypierre]

  18. 68
    allun says:

    Maybe i didn’t understand the rules? I didn’t want to discuss economic impacts, etc. but it still apears we have an elephant in the room that isn’t being considered in any of the articles here or wikipedia.
    My concern is we appear to be releasing between 1% (absolute best case) to 3-5% of solar influx in hydrocarbon and nuclear heat sources, (at the moment, growing steeply). Since it appears that orbital variations can account for about 6.8% solar variation,
    ( ) aren’t we talking about a significant challenge to Gaia?
    (and everybody else that lives on this rock?)
    Wasn’t trying to be a smartass, really think this should concern us?
    Please be so kind as to educate me if my ‘facts’ err?

    [Response: Your energy numbers are all wrong. A little more care in looking around on the web would have given you reliable numbers. These are easy numbers to get, so there’s no excuse for being so speculative. From Eric Weinstein’s Physics World, ( ) the world power use is 1.28 x 10**13 Watts. Using the surface are of the Earth, this amounts to .025 Watts per square meter. Absorbed solar radiation is on the order of 250 Watts per square meter. The heating from energy use, averaged globally, is utterly insignificant compared to solar energy, and also unimportant compared to the indirect effect of industry via the CO2 radiative effect (about 4 W/m**2 for a doublling). As for your comment regarding Milankovic (also partly wrong in the numbers because you fail to distinguish seasonal local variations from global means) I don’t understand that at all. –raypierre]

  19. 69
    Dan Robinson says:

    I’m getting into this a bit late, and guess what, I haven’t read it all yet. At this level of conversation I’ll stick to asking “questions”.

    Considering that H2O is a, or ultimately the, major GG, will we see a turnaround in runaway greenhouse (the point where natural forces dominate, and even total economic collapse won’t stop it) while there’s still more water to evaporate from the oceans? What natural forces will stop it before that point? Could this mean the end of all life on earth? Are we looking at why we’ve never been (provably) contacted by ETs, because they all followed similar paths and never made it much beyond us?

  20. 70
    Coby says:

    No Venus runaway possible here. There is a post on this site specifically about Venus, you should have a look.

  21. 71

    Re 69 & 70 I don’t think Dan was proposing that Earth would turn into a Venus. They are very different. Venus is heated by carbon dioxide and kept cool by sulphur dioxide clouds. Earth is heated by water vapour and kept cool by water clouds. Thus Earth has a built in thermostat which prevents it heating above about 40C. The greater the greenhouse effect, the thicker the clouds that are produced. It is a negative feedback. That is why life has existed for 3,500,000,000 years :-)

    But it has only held on by the skin of its teeth on several occasions, and one of these is about to occur again, when the Arctic sea ice melts and Arctic temperatures jump by 12 C or more, just as they have in Svaldbard this year :-(

    [Response: I’m not aware of any built in thermostat mechanism that keeps the Earth below 40C. In fact, I’ve run plenty of simulations that get warmer than that, given enough CO2. What did you have in mind? Lindzen’s paper from the 1980’s is based on incorrect radiation, questionable models of convection and an unrealistic assumption about the vertical distribution of water vapor. –raypierre]

  22. 72
    allun says:

    Excuse me? You may be right, however, most of my numbers cames straight from this site, and ( ). My estimate on insolation is not really speculative, as i used the solar constant (429 btu/sq.ft./hr.) shining on a normal disk of earth radius – 35% reflectance, (obtained from my Halliday & Resnicks), and must only be a quite high ballpark. The reality has to be (much?) lower. Your reference to ( ) doesn’t seem to address this at all?
    Still, it would be great if you’d show me where i err, as i really don’t see how seasonal variations, due to incidence angle, affects the integrated whole earth energy balance.

    [Response: Ray is right. The solar energy incident on the Earth’s surface is the solar ‘constant’ (~1365 W/m2 – can we stick to metric units please?) divided by 4 (to account for the surface area of the disk vs. the sphere) and multiplied by the co-albedo (~0.7 – your 35% albedo number is slightly too high), giving around 240 W/m2. Total energy consumption is around 412 quadrillion Btu / yr = 412*1055*10^15/(5.1*10^14 area of the earth)/(3600*24*365 seconds in a year) = 0.027 W/m2 – 4 orders of magnitude smaller…. -gavin]

  23. 73
    allun says:

    I’m an engineer. We lack the large brains inherent in earth scientists, so we deal in complexity reductions. Let me attempt one here? We live in a large insulated box, that has an internal and external heat source? This box has achieved a thermal equilibrium of sorts. We’re at the moment increasing the r factor of the boxes insulation at the same time releasing 300-500 quadrillion btu’s/yr of extra internal heat source. Lets not quibble about magnitude, the fact that we’re messing with (thank you for the 4 orders of magnitude, some relief there!), a (moderated by feedback?) equilibrium still concerns me. (But less now, thanks!)
    And i still don’t see any way seasonal variations effect an integrated whole earth balance.

  24. 74

    Ray, surely you are aware of my scepticism of the models. It is the paleoclimatic record which shows that the global mean temperature has never risen above 40C. Moreover, if Lindzen were right with his “Iris theory” then the warmth of the Eemian could never have happened. My ideas are original, but not new. I have since discovered that they had already been proposed by
    Ou ,
    Wally Broecker (of course) , and G.C.Simpson [
    (1928). “Some Studies in Terrestrial Radiation.” Memoirs of the Royal Meteorological Society 2(16): 69-95.,
    (1928). “Further Studies in Terrestrial Radiation.” Memoirs of the Royal Meteorological Society 3(21): 1-26.]

    [Response: I’m not aware of geological evidence that would preclude temperatures over 40C ever having occurred over the past 3.5 billion years. There’s no positive evidence for such warm temperatures, but it’s too strong a statement to say that it couldn’t happen. The prevailing theory for the generally moderate temperatures over the long term is the CO2 weathering thermostat, though there are suggestions that a methane regulation mechanism might have been dominant instead before the oxygenation of the atmosphere. That’s very different from saying the temperature wouldn’t exceed 40C no matter how high the CO2 or methane got. The Broecker press release you linked states only that he thought water vapor reductions could have accentuated LGM cooling (more precisely stated, that reductions in relative humidity could have lead to more cooling than the standard models). This could well be true, but not on the basis of Broecker’s evidence, which rested on a rather faulty interpretation of the Andean mountain glacier data (see my GRL paper on Huascaran isotopes). In any event, there’s no suggestion there of a thermostat at the high end. Ou’s paper rests on a highly questionable assumption regarding maximization of entropy production., and in the end is a kind of low-cloud thermostat mechanism; he does predict a limitation on maximum temperature, but neither the reasoning nor the predicted behavior of low clouds is borne out by any cloud-resolving dynamical simulations I’m aware of. None of these things have anything to do with the matters regarding radiative transfer fundamentals you used to bring up earlier in the history of RealClimate. I haven’t read these two old Simpson papers, which date back to the early days of radiative transfer when people were still sorting out some very basic points, but if they deal with the subject matter I think they do, it is discussed and disposed of in Goody and Yung’s book, under the heading of “Simpson’s Paradox.” –raypierre]

  25. 75
    Brian Gordon says:

    On another thread on this site, I asked for the data showing that we (humanity, civilization) have 10 years to make significant reductions in GHGs; after that, the degree of climate change will (sooner or later) be sufficient to end life and lifestyle as we know it. This thread seems a much more appropriate place to talk about that, as climate change inevitability is all about feedbacks and tipping points.

    Hank Roberts pointed me to this article:
    which was helpful. From the article:

    “The Earth’s climate system has great thermal inertia, yielding a climate response time of at least several decades for changes of atmosphere and surface climate forcing agents [Hansen et al., 1983].” p. 2

    Is this still considered to be true? If so, then the Arctic is melting due to GHGs from decades ago. Uh oh. Or pollution (ozone, methane, and soot) as the authors suggest?

    For the Arctic sea ice to melt, its temperature must rise above the freezing point of sea water. For that to happen, the ice must absorb energy to rise to the freezing point, then must absorb more energy to change state. If we weren’t measuring the ice temperature/heat content, we don’t know how long the time lag has been before the ice actually started melting. Has anyone been measuring the temperature of the sea ice? More from the article:

    “Satellite data indicate a rapid decline, ~9%/decade, in perennial Arctic sea ice since 1978 [Comiso, 2002], raising the question of whether the Arctic has reached a ‘tipping point’ leading inevitably to loss of all warm season sea ice [Lindsay and Zhang, 2005]. Indeed, some experts suggest that “…there seem to be few, if any, processes or feedbacks that are capable of altering the trajectory toward this “super interglacial” state – free of summer sea ice” [Overpeck et al., 2005].

    “Could the Greenland ice sheet survive if the Arctic were ice-free in summer and fall? It has been argued that not only is ice sheet survival unlikely, but its disintegration would be a wet process that can proceed rapidly [Hansen, 2004, 2005]. Thus an ice-free Arctic Ocean may have implications for global sea level, as well as the regional environment, making Arctic climate change centrally relevant todefinition [sic] of dangerous human interference.” p. 24-25

    “We suggest that the conclusion that a ‘tipping point’ has been passed, such that it is not possible to avoid a warm-season ice-free Arctic, with all that might entail for regional climate and the Greenland ice sheet, is not warranted yet. Better information is needed on the present magnitude of all anthropogenic forcings and on the potential for their reduction. If CO2 growth is kept close to that of the alternative scenario, and if strong efforts are made to reduce positive non-CO2 forcings, it may be possible to minimize further Arctic climate change.” p. 25

    It seems that some experts think a tipping point has already been passed for the Arctic, and therefore, Greenland, while the authors of this paper do not. Further, they feel this tipping point can be avoided if strenuous action is taken immediately (see the last sentence of the quote). However, they make no claims of having scientific evidence to ‘guarantee’ this. From another article (sorry, I do not have the original reference):
    “In early 2004, a surprising course [sic] began to publicize the risk of one such event, the U.S. Department of Defence, the Pentagon, released to Fortune magazine its analysis of the security implications of “a plausible scenario for abrupt climate change.”

    “It suggested that it was plausible that the Gulf Stream could stall by 2010. This would be caused by rapidly melting polar ice changing the salinity of the ocean. The ice is fresh water and its release would push down on the more saline currents, slowing and potentially stopping the vast ocean conveyor belt of currents. If the Gulf Stream were to stall, the Pentagon study anticipated widespread social and institutional collapse as droughts led to collapses in food production, displaced environmental refugees pressed on other borders for resources, soil erosion increased and wind speeds across Texas picked up … The Pentagon concluded that the risks of climate change were more significant than the risk of terrorism.

    “To avoid the “tipping point” described above, we need reductions of [GHGs of] 80% by 2050, of 30% by 2020.”

    I don’t understand at all how reducing GHGs by 2020 and 2050 will avoid a tipping point that will occur in 2010? This scenario was described as “plausible,” and 2010 is only four years away; even if it’s not 2010, but 2020, surely there are enough GHGs currently in the atmosphere to accomplish this?

    Thanks for your patience…and let no one construe that passing tipping points is an excuse for doing nothing.

    [Response: The “tipping points” refererred to above are somewhat speculative but within the realm of possibility — though the “European ice age” response to a thermohaline shutdown begins to look somewhat less plausible as a consequence in light of recent thinking on the role of sea ice in past responses, though there may be other serious consequences of thermohaline shutdown. Remember, though, that if there are tipping points, nobody is sure precisely where the thresholds are, so reducing emissions at any time gives you a better chance of not having passed one. Moreover, it is highly likely that there are several thresholds in the climate — melting of Greenland, melting of the West Antarctic ice sheet, some major shift in El Nino (perhaps), desertification of the Amazon, clathrate release, carbon release from arctic soils, probably many more we haven’t thought of yet. Each of these would have a different threshold. The less far we go from the familiar climate range of the past two million years, the less likely we are to encounter something really bad. Thus, even if we couldn’t do better than stabilizing at 2xCo2, there are still a lot more impacts that will set in between 2xCO2 and 4xCO2, so it’s still worth the effort to stabilize at 2xCO2. I do hope we can do better than that. –raypierre]

  26. 76
    Dan Robinson says:

    “Re 69 & 70 (& 71) I don’t think Dan was proposing that Earth would turn into a Venus. They are very different. Venus is heated by carbon dioxide and kept cool by sulphur dioxide clouds.”

    Yes, actually I was thinking of a “Venus syndrome”, and for the moment, still am. Has the negative feedback effect of H2O clouds been proven to happen? I’m thinking higher temperatures, probably throughout the atmosphere, would mean H2O would have to go to a higher altitude to condense to clouds, putting a thicker blanket between us and the drier air above, maybe meaning the percent of cloud cover would remain about the same. Also (and maybe part of the cause of the previous effect) condensation to clouds causes heating, just as evaporation causes cooling. I’ll accept your view as long as all this has been considered.

    “That is why life has existed for 3,500,000,000 years”

    But keep in mind that in about that span of time, the sun has grown hotter by about 25% (James Lovelock), so all bets are at least in doubt.

  27. 77
    llewelly says:

    Yes, actually I was thinking of a “Venus syndrome”, …

    Dan, please see Lessons From Venus , which explains why the Venus syndrome can’t happen here.

    [Response: At least not for a billion years or so. I should provide a clear disclaimer that the discussion Rasmus and I provided in the Venus article was based on clear-sky water vapor feedback. Nobody has brought clouds into the picture in a convincing way, and it’s a matter that badly needs to be rectified. It’s actually hard to rule out a runaway cloud-based greenhouse effect on Earth, because clouds are so optically thick in the infrared. I don’t think it’s at all likely, but whether it happens is a race between the cloud cooling and the cloud warming effect. The reason I say it’s hard to rule it out on first principles is that some of the parameter sets in the ensembles do seem to run away. These were just discarded for the most part, but they ought to be looked at so as to provide a better understanding of the physics involved in the runaway. (well, we don’t know whether it’s a real runaway, since the runs were stopped before equilibrium). As I said, I don’t think this is a likely scenario, and it’s probable that the runs with a “runaway” cloud feedback would fail to match 20th century temperatures. However, we’d learn something by finding out what was going on in those runs, and refining our picture of why we don’t expect real clouds to behave that way. On the other hand, given recent evidence of a very warm early Paleocene Arctic, I wouldn’t completely discount a surprise cloud warming effect we haven’t factored in. –raypierre]

  28. 78
    Ron says:

    I think geoengineering (e.g., increasing polar albedo by large-scale spraying of titanium dioxide, possibly on some kind of flotation device for the polar seas) merits research as a component of our response to climate change. Of course it should not become an excuse to continue unsustainable carbon emissions, nor an excuse to cut climate research (as some deniers would argue). But, at the same time, geoengineering should not fall victim to the idea that “we shouldn’t play God;” alas we already are playing God via our carbon emissions.

    We should evaluate potential solutions primarily on their technical and economic merits. That doesn’t mean losing sight of Earth as our spiritual home, but it does mean not letting dogma become our primary guide.

  29. 79
    John L. McCormick says:

    Re: #78. Ron, I know from nothing about titanium or your idea (suggestion) to increase polar albedo by large scale spraying of titanium dioxide. You say it merits research as a component of our response to climate change.

    Here is what I know of the Arctic ice: it is melting rapidly. Over the past 30 years the annual average sea-ice extent has decreased by about 8 percent, or nearly one million square kilometers.

    Here is what I learned from a USGS 2005 report on Titanium Statistics and Information about the cost of titanium on the world market:


    Because of a significant increase in demand, prices of titanium metal products rose considerably. The year end unit value of titanium sponge ranged from US$3.55 to US$6.44 per pound in 2004, a significant increase compared with that of 2003. The yearend price range for titanium scrap also reflected market conditions, increasing to between US$3.80 and US$4.00 per pound in 2004 from between US$1.50 and US$1.70 per pound in 2003.

    So, titanium sponge ranged in 2004 from $7100 to $12,880 per ton and titanium scrap from $7600 to $8000 per ton. I wonder what it would cost to spread titanium dioxide on the Barrows airport runway?

  30. 80
    llewelly says:

    Ray, thank you for your long response. I hadn’t guessed the cloud unknowns were of such importance to a potential runaway greenhouse effect. It helps that you mention the Arctic, where cloud warming is expected to outweigh cloud cooling. Now I’ve a question: Is Arctic cloud cover increasing?

  31. 81
    Almuth Ernsting says:

    I gather from Raypierre’s comments that the recent study on the Arctic 55mya gave some rather alarming results. Is there any chance of a blog-post about the study, the results and what the implications may be? That would be extremely helpful!

    [Response: Writing an article on this is next on my queue. I’ve bumped it ahead of Part III of the circulations and warming post. Very, very interesting stuff. Those who want to get a peak at it should look for recent papers authored by “Brinkhuis” on –raypierre]

  32. 82


    Please allow me to expand on a few points I made in my previous short post #74 by responding to your response.

    Lack of geological evidence for global mean temperatures ever exceeding 40C seems to me to be good grounds for assuming it to be true. Moreover, if temperatures above those levels had occurred in the past, then life as we know it would have been destroyed, as nearly happened during the PT mass extinction.

    As you say, mechanisms associated with atmospheric CO2 are generally regarded as having controlled past climates, but I an arguing, like Wally Broecker, that ” … most thinking has focused on water vapor changes as secondary; that is, as the earth warms or cools, evaporation rates change and the amount of moisture in the air rises and falls,” he said. “We opt to turn this thinking around and make water vapor the driver that changes global temperatures.” Although he was referring to Quaternary climates, the Principle of Uniformitarianism means that this hypothesis should also apply to all of Earthâ??s history. Since it does solve many problems, not least those posed by Veizer, then this should be seen as confirmation of its validity.

    My thinking is not based on what Broecker said in the Daly lecture. Like you, I only have the account from the press release. However, since the basis of my ideas is that rapid climate change is caused by the runaway effect of water vapour, I have to admit that Wally got there first. However, I go further than your view of his ideas, and claim that both rapid coolings and rapid warmings can be caused by that effect. All that is needed is the sudden formation of sea ice as happened at the start of the Younger Dryas, or a massive release of methane as happened at PETM event to trigger a cooling, or warming event, respectively.

    I gather from reading the abstract of your paper, (all that is readily availble to me at present,) that you do not deny that there was a reduction in humidity during the last glacial maximum. The drying of the atmophere during glacial periods is well known, but in a Science paper Maslin & Burns showed that it also happened in the Amazonian basin during the Younger Dryas. In a recent BBC TV program you could see where in the Greenland ice the Younger Dryas had ended, by the abrupt change in colour of the snow due to the ending of wind blown dust when the climate suddenly became wetter.

    [Response: I have my full Huascaran paper, like most of my papers, posted on my publications site. I wasn’t at the Daly lecture, but from the abstract it’s pretty clear that the substance of the lecture was the same as what was in Wally’s paper in global biogeochemical cycles. The idea that the Huascaran oxygen isotopes gave paleo-humidity was based on a faulty interpretation of the data, and I don’t think Wally subscribes to that idea anymore. There are indications of paleo precipitation, but that’s not the same as having a proxy for mid-tropospheric humidity — which is what affects the radiative feedback. The main reason for my inference that water vapor goes down at least as fast as the constant relative humidity assumption predicts is that it is essentially impossible to account for the observed LGM tropical cooling without an amplifying feedback of at least this magnitude. I can think of dynamical reasons the drying might be greater than Clausius-Clapeyron predicts, but they’re still in the nature of making water vapor a feedback to other drivers, not a primary driver. Things like aerosol supply could change atmospheric humidity through microphysical processes, but so far that’s just speculation, with neither paleo-observations nor theory to back it. Not impossible, and worth a look, but there’s no real support for it yet. ]

    A tipping point has been reached, and that is in the belief that rapid climate change, as proposed by Broecker, is caused by switches in the Atlantic branch of the THC. That belief is now an article of faith for everyone even with only a passing interest in climate science. This is despite the fact that Wally now believes â??the shutdown of the THC was exacerbated by a positive feedback in the form of enhanced winter sea-ice formation.â?? [Schiermeier, Nature 439 p 259] It is as difficult to roll back the idea that the THC causes abrupt climate change, as it will be to reform the Arctic sea ice once it has melted!

    In the two Simpson memoirs, as well as postulating his Paradox, he also dismissed the greenhouse effect of carbon dioxide because he considered it negligble compared with the effects of water vapour and clouds. Water vapour overlaps the CO2 bands, and clouds would limit the temperature increases. As you are probably aware it was Callendar who reintroduced the idea of CO2 being important and causing global warming. Where Simpson was obviously wrong is in the Arctic. There, there is little water vapour because of the cold, and also little cloud in the polar vortex. In that case, CO2 can dominate the greehouse effect, and cause the rapid melting of the ice we are seeing.

    [Response: Simpson wasn’t just wrong in the Arctic. CO2 bands are important even in tropical conditions, and his ideas about clouds were just not very well thought out. Entirely defensible models of tropical clouds can actually yield an amplifying effect on climate change. It’s an interesting question in history of science as to why many early 20th century climate people thought water vapor opacity would overwhelm CO2. That was not even well supported by the spectroscopy of the time. The discussion was muddied by the fact that the various ideas about how to incorporate the radiation into a prediction of surface temperature weren’t incorporated into a consistent model. That was done by Manabe and Strickler and Manabe and Wetherald in the 1960’s, which settled the issue once and for all, at least given the assumption of constant relative humidity in a warming world. ]

    BTW as far as I know Simpson’s Pradox has not been solved. Am I correct?

    [Response: Yes. It wasn’t much of a paradox. What Simpson considered a problem, Ingersoll turned to advantage in his theory of the runaway greenhouse. The crude radiation modelling of the time just didn’t allow Simpson to conclude that the OLR limitation by water vapor wasn’t a problem for Earth’s situation. It’s well-discussed towards the end of Goody and Yung –raypierre]

    Cheers, Alastair.

  33. 83
    Ron says:

    Re: #79:

    So, titanium sponge ranged in 2004 from $7100 to $12,880 per ton and titanium scrap from $7600 to $8000 per ton. I wonder what it would cost to spread titanium dioxide on the Barrows airport runway?

    You don’t need much, since the coating can be extremely thin. Titanium dioxide is the primary reflective constituent of white paint. I don’t imagine it’d cost more than $10,000 retail to paint the Barrow runway (6500 ft x ~ 50ft = ~325,000ft^2) white. But…

    Over the past 30 years the annual average sea-ice extent has decreased by about 8 percent, or nearly one million square kilometers.

    Current paint tech (assuming 350 ft^2 coverage/gal and $10/gal) would cost ~$306 billion to cover that area — about what the U.S. so far has spent on the war in Iraq. (Of course you’d still need some durable floating medium to support the paint on sea areas, which would add significant costs). Still, we should be able to contrive more efficient ways to use Ti02 for this purpose, or find other materials that would be more practical.

    I am assuming that we would want to use ground-based reflectants instead of aerial ones (e.g., atmospheric dispersal of SO2) because they are far easier to control and their effects are more predictable.

  34. 84
    Gareth says:

    Ahem. The Arctic melts, so we paint it white. And this is meant to be a serious response? Gives us climate alarmists a bad name…

  35. 85
    Ron says:

    Re: #83:

    Ahem. The Arctic melts, so we paint it white. And this is meant to be a serious response? Gives us climate alarmists a bad name…

    I am not a climate alarmist, but a climate realist. We’re going to need to use all the tools at our disposal to deal with the climate change we’re causing. We’ve got to go on a carbon diet — yesterday. And we’ve also got to consider other ways to reduce the effects of excess atmospheric carbon. Increasing arctic albedo is, I suggest, one such approach.

    Refute it if you can. But mockery without data hardly helps us solve a very real problem.

  36. 86
    John L. McCormick says:

    Ron, what you are reading from the several responses to your initial offer at #79 is shock at the thought of what you propose without your providing an ounce of specifics that show you or others have actually begun to give that idea serious scientific and international consideration.

    You offer no glimpse at what you are suggesting. so, we can only conclude you are about spreading white paint on flat surfaces around the north Polar region.

    Perhaps you could take a moment and go past your suggestion:

    “I think geoengineering (e.g., increasing polar albedo by large-scale spraying of titanium dioxide, possibly on some kind of flotation device for the polar seas) merits research as a component of our response to climate change.” and tell us who (you perhaps) have been seriously considering such a scheme and have given due consideration to unforseen consequences such as toxic contamination of water, vegetation, species, etc.; the physical application of (what) and at what cost; and, perhaps, the shelf life of any such application of (what).

    When you provide some detail or —better– lead us to some sites and links that go into the discussion with great detail and references, then I can better understand your suggestion.

    Your comment: Refute it if you can. But mockery without data hardly helps us solve a very real problem. is correct in one sense…we have a VERY REAL PROBLEM and very little time and (even US federal money) to devise remedies and adaptation.

    I do not doubt your resolve to make a positive contribution to saving us and our children from the calamity ahead. But, YOU need to provide or lead us to the data, the research, environmental impact statements, cost-benefit analysis, etc.

    Then, we can talk.

    [Response: I like to allow wide-ranging discussion of geoengineerig proposals not because I think that any of them is likely to be a cheaper and better solution than the known and available technologies for reducing CO2 emisssions, but because they offer a playful way to think more deeply about the way the climate system operates. Ken Caldeira’s analysis of the effect of orbital mirrors is a good case in point (with regard to climate dynamics; I don’t think the mirrors are a very workable idea as technology but I won’t speak for Ken). However, it’s good to keep a bit of an idea on reality here. The idea of somehow painting the liquid ocean surface white is pretty silly. If you want to think about more constructive and practical uses of albedo engineering, the urban and suburban environment is really a much better place to start. it could have a small but useful contribution even on the global scale, but more importantly it reduces the urban heat island effect, so there’s less electricity demand for air conditioning. To keep the solar heating you’d want in the winter, you’d need to combine this with passive solar features allowing heating when you want it (heating an
    insulated black roof is not good passive solar heating!). Now here’s an important architectural question: which is better a “green roof” (living plants and moist soil) or a “white roof” (dead white panels without any moisture-holding capacity)? Is there some way to combine the benefits of both — i.e. the high albedo of the white roof with the evaporative cooling of the green roof? –raypierre]

  37. 87
    Ron says:

    Re: #86

    You are exactly correct that I’ve provided few specifics on deploying albedo-increasing materials, and you’re right to ask about what would be deployed, what the downsides might be, what it would cost, how it would be perceived politically, and so forth. And you are also correct that it’s my responsibility to defend any ideas I propose. But I would also point out that criticism of the form “and this is meant to be a serious response?” does not advance the debate one iota.

    That said, I am a rank amateur at understanding climate and I certainly do not have anything like a complete proposal. My point was not to present such a thing, but to diversify the debate on remediating climate change by contributing an offbeat idea that I had not heard discussed before.

    Re: raypierre comment on #86:

    Thank you for the reference to Ken Caldeira’s paper. I’ll check it out.

  38. 88
    Ron says:

    Re: raypierre comment on #86:

    The idea of somehow painting the liquid ocean surface white is pretty silly.

    The idea is not to dye the water, but to deploy reflective materials on some kind of strong, durable floating substrate (wild e.g., mylar).

    [Sorry about not including this in my prior comment.]

  39. 89
    Almuth Ernsting says:

    I wonder if anybody else has read Fred Pearce’s new book ‘The Last Generation’ yet. It’s a terrifying prediction of a virtual breakdown of the carbon cycle, a series of abrupt climate changes leading to massive warming – it reads very much like the scientific details behind the Revenge of Gaia (and has been praised by Lovelock), except that it makes Lovelock sound quite optimistic.

    (looking at the melting permafrost, methan hydrates, the possible Amazon die-back, tropical peat fires, oceans turning acid and killing marine life, most forests turning into carbon sources, etc).

  40. 90
    Gareth says:

    RE #87: “But I would also point out that criticism of the form “and this is meant to be a serious response?” does not advance the debate one iota.”

    Sorry if you’re feeling a bit sensitive about my comment, Ron, but it does advance the debate, if only because it suggests you might like to refine not only the physical basis for your idea, but also its public presentation.

    On the other hand, painting my roof white might well be a good idea…

  41. 91
    John L. McCormick says:

    RE/ #86

    Ray, you are most generous with your time and constructive, if necessarily nudging, replies to the many not-so-carefully-tuned submittals.

    Ron does open a door, however, that I also would like to see RealClimate invite more entry. How to diversify the debate on remediating climate change by contributing offbeat ideas not heard discussed before? â?¦ paraphrase Ron.

    Offbeat ideas can and should include how to expand the audience attracted to this quality discussion on the science of climate change. I would like to see more participation from individuals living in South Asia; in Nepal, India, Bangladesh, Pakistan, and Kashmir. I’d like to hear first hand accounts of the melt back of the Himalayan glaciers and the threat of overflowing glacial lakes and the affect on steam flow into the Ganges and Bramaputra Rivers.

    That region of the world is so very critical to stability of the Southern Hemisphere and, with rare coverage in at least the UK press, we in the North can only imagine what their world will become if water resources for farming and domestic use become critically imperiled.

    It would not be too difficult to encourage participation of knowledgeable people in that region if they were aware of the RealClimate web site. Perhaps the international NGO network could post a link, on their pages, to RealClimate. Perhaps I will explore this with InterAction located in Washington DC. It is an umbrella for most of the Northern humanitarian organizations such as Oxfam, Caritas, etc.

    Does anyone have suggestions how the existence of RealClimate could easily be broadcast deep into the Southern Hemisphere? Language need not be a barrier as translation software, to a degree, is easily obtained.

  42. 92
    Brian Gordon says:

    As someone who has benefitted greatly from raypierre’s (and other’s) comments, I also want to thank the RC scientists and contributors. Thank you. :-)

    My understanding of the purpose of this site is that it is to provide some education about climate science, especially necessary given the disinformation from various sources. Having a forum for untried ideas detracts from this purpose, and possibly also the site’s credibility.

  43. 93
    Florifulgurator says:

    Here´s another layperson´s perhaps offbeat idea on remediating climate change. A low-tech solution. Good work perhaps for the poor. It´s about black, not white. I already posted somewhere else but got no feedback. So,

    Carbon sequestration by producing charcoal from forests: 1) Use the pyrolysis oils for “green fuel”. 2) Leave (most of) the charcoal on site (mix it into the ground for soil enhancement a la Amazonian terra preta) and/or store it underground. 3) Let new trees grow. 4) Repeat.

  44. 94
    Geoff Coe says:

    Until very recently, I had done no real investigating of the global warming issue on my own, but had pretty much accepted the idea that human activity (the burning of fossil fuels and things like the destruction of the rainforsts) were most likely a driving force behind the situation. At the moment, however, due to a short but intensive period of reading, I’m no longer of that opinion. I have not yet seen Al Gore’s movie. At this point, however, I feel that his movie is not likely to give me any information that I haven’t already encountered. The “tipping point” in my mind occurred when I read a blog entry where someone said that his college professor laughed (out loud) at the idea that human beings were the cause of global warning. My first thought was to think that maybe this writer had been to college over 10 or 20 years ago. He gave the name of his professsor, however (Bill Gray), and so I looked him up assuming that more recent information probably caused the professor to change his mind. What I found, however, was a climate scientist who A) doesn’t believe that human behavior is a significant factor in global warming, and B) isn’t being paid by anyone to have that point of view. (For more information on William Gray, here are a couple of articles:

    One climate scientist alone, of course, wasn’t going to convince me. At this point, however, I feel that I can no longer accept Al Gore’s opinion that there’s a scientific consensus on the subject of global warming because obviously there isn’t. Everyone agrees that things are getting warmer, but Gore was saying that the scientific community was in agree that human activity was the central force (all one needs is a single desenting climate scientist who’s NOT being paid by some big business interest and the idea of “censensus” in my mind is bound to go out the window.)

    At this point, therefore, I guess I sort of decided that I could no longer trust what anyone is or was saying and had to start thinking and looking at the problem from the beginning (if you want anything done right, you’re going to have to do it yourself, etc. etc.) I therefore started to ask some very basic questions that most non-scientists would probably not bother to ask. Questions such as “Exactly how much air do we have on the planet?” and “How much CO2 relative to air are we putting out?” The information on this page was a bit too technical for me (I was reading through this page before I stumbled onto the opinions of Dr. Gray) so I went to Wikipedia where a simple pie charts showed me that the amount of CO2 in the atmosphere is several hundred times less than what I thought it would be (here’s the address's_atmosphere) As a non-climate scientist, I’ve been completely converted away from the idea that we human beings are causing global warming even though the political side of my being would almost rather that that argument be true. Politically, I’m much more at home with an environmentalist (as opposed to a capitalist) point of view. What really convinced me, however, were two pages I just sort of happened to stumble upon in a separate search after reading through the Wikipedia site…

    Global Warming: A Chilling Perspective

    Global Warming: A Closer Look At The Numbers

    The second page in particular (the one with the numbers) is the one that really made the most sense and led me to conclude that Dr. Gray’s position is, in the end, probably the one that’s right. I’m no climate scientist, but I’d say that I’m some who’s pretty good with your basic concepts and numbers. Would anyone care to take a stab at telling me, at this point, after reading the things I’ve shown you here, why everyone shouldn’t be laughing at the idea the human behavior is the cause of global warming? From an uneducated point of view, I was ready to accept the human cause idea hook, line and sinker. If we accept the numbers given on the second web page I provided above, however, then the TOTAL effective human contribution to the global warming greenhouse gases is so small (less than 3/10ths of 1% or 0.29%) that it makes no sense to assume that it makes any genuine difference. To suggest that human beings are causing global warming, therefore, would be like suggesting that throwing a match into a raging fire once a minute is what’s causing it to get steadily bigger and hotter.

    The earth is slowly getting warmer. Based on the pages evidence I’ve just cited, however, it’s seems very unlikely that anything we’re doing is having any real effect at all. 0.29% effectiveness, in my opinion, is very little effect. If someone told me that I was being only 0.29% effective at work, for example, I think I’d probably get fired fairly quickly after that.

    Naturally, I wouldn’t be posting here if I wasn’t hoping that someone would come back and explain exactly what (if anything) I’m missing. Am I missing something? If you believe that human behavior is driving global warming today, how would you answer the information given on the last two page (specifically the second one) that I just read? Explain to me why the human contribution to global climate forces shouldn’t be compared (as a friend of mine use to like to say) to a fart in a hurricane? Thank you. (I’m sorry if that last analogy was a bit crude, but I’ve always thought it was fairly descriptive of two things not in the same order of magnitude. Thanks again.)

    [Response: Speaking of laughing out loud, I would laugh out loud myself at the idea that Bill Gray understood even the basics of climate change physics, if it weren’t so tragic. If you want to get an inkling of just a few of the ways that Gray is confused, take a look at the post “Gray and Muddy Thinking about Global Warming.” This is a man who doesn”t even understand energy conservation, or the basic nature of the Earth’s energy budget. You ought to look at the full spectrum of evidence, try to learn what really makes climate tick, and make a decision based on sound science. And yes, Gore’s movie is a very good place to start. The science, as we said in our review of the movie, is very accurate, and quite free from exaggeration. The answer to your last question is present not just in Gore’s movie and book but in the numerous books reviewed by Gavin under “MY Review of books,” as well as spread over virtually all the articles that have appeared on RealClimate. The numbers regarding the proportion of human influence on climate forcing, on the web site you cited, are completely bogus (see Gavin’s post on the “Water Vapor Feedback,” and also the links to the illlconsidered site given in Comment #96 below). I’ll believe that your question is in earnest when I see you actually make an effort to look at the science and understand it. I’ve seen a lot of posts like this where someone pretends to be wide-eyed and having been a true green believer (like Lomborg in the old days) until they saw the light on hearing from (YOUR FAVORITE SKEPTIC HERE) and the scales fell from their eyes. Most of these starry-eyed posts are just from people whose minds are already made up. So please prove me wrong. –raypierre]

  45. 95

    Re Ray’s response: I like to allow wide-ranging discussion of geoengineerig proposals not because I think that any of them is likely to be a cheaper and better solution than the known and available technologies for reducing CO2 emisssions, but because they offer a playful way to think more deeply about the way the climate system operates.

    I have a suggestion which I have not seen anywhere else, and might even be practical. The idea is to farm coral on flooded deserts. I would start with the Negev desert which is below sea level, so the costs of pumping sea water into it would be low.

    This idea has several advantages: First the growth of coral would remove CO2 from the atmosphere. Second, the coral, which is white, would reflect sunlight and so increase planetary albedo. Third, the flooding would be done with sea water, which would not deplete global fresh water resources, and in fact might increase them through the inevitable evaporation.

    Suitable corals which grow quickly and near the surface could be developed using genetic modification, and since the sites would be isolated from the oceans there is little danger of the new strains upsetting the natural world.

    Finacing of the projects could be achieved by issuing carbon credits for each ton of coral produced, so making it profiatble for polluting industries to finace or implement such schemes.

    Although it might seem that the pumping of sea water upto the deserts migh be expensive, in fact much of the surface of the continents is fairly low having been below sea level during the Cretaceous, in other words only a few hundred feet above present sea level. If Antarctica melts, then we may not need to pump the water as the Nullabor Desert in Australia and Arizona will be flooded anyway :-)

  46. 96
    Hugh says:

    Alastair, if memory serves me correctly I think you’ll find that coral is only white…when it’s dead.

  47. 97
  48. 98
    Coby says:

    Geoff Coe, #94

    You should have a look in the dictionary for a definition of consensus, it does not mean unanimity. Please check here for just how strong the consensus is:

    Your clearlight web page is not reliable, the numbers it use for H2O etc greenhouse impact are, as near as I can tell, made up. Have a read here for some sourced numbers and also here for a disection of the basic implied attack on climate scientists that page delivers.

    As Ray suggests, we will see if you are as sincere as you sound, unfortunately many people make very similar presentations but then never follow through on their professed sincere interests. If you really want to get a handle on the scientific basis of this issue you can not do better than starting here:

    [Response: Indeed, I’ve been through something like this several times. The usual sequence is that, in response to what looks like a sincere request to clear up confusion, we and our readers provide a wealth of accurate material to look at. A remarkably short time later a response comes back from the original inquirer saying words to the effect that ” I’ve read all the material you’ve recommended, but I’m still not convinced.” Then, if patience hasn’t given out entirely, I usually ask, “Could you be more specific. For example, just what aspect of the water vapor vs. CO2 argument do you find unconvincing?” Usually at that point the sincere inquirer disappears entirely. Once one said to me “It’s people like me you have to convince, so don’t just tell me to read the material and think harder about it.” As I said, I would be delighted to see things take a different course in this particular instance. Hope springs eternal. –raypierre]

  49. 99
    Mark A. York says:

    It’ll take hope and then some to get rid of this same bogus source. I get it handed to me every time somewhere, and then a newspaper writes a zinger and it starts all over again. Even Charlie Rose asked Gore a littany of stupid questions like these.

  50. 100
    Florifulgurator says:

    Re 94 etc. etc. p.p.
    I recently read about blog trolls paid by “PR” firms specializing on such guerilla propaganda.
    #94 kinda sounds like one, and almost surely Ray & Mark have encountered such folks. Not worth much typing (from my European standards of discourse) – luckily there´re those great resources like realclimate or illconsidered.

    Just throw them links at the ostrich: If you get a reply, she might be seriously interested in the real world & worth some more of your precious time & brainlard.

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