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  1. There are a few observations in this which makes the high sensitivity for GHGs rather questionable.

    In the first place, GHGs in the pre-industrial past follow orbital/temperature changes, don’t lead. This is clear from the detailed Epica Dome C ice core, where CO2 trends follow the d18O (temperature proxy) trend in the LGM-Holocene transition, with no measurable feedback from increasing CO2 levels.
    See here (with thanks to André van den Berg for the graph).

    Secondly, orbital changes have their effect mainly in the (sub)tropics and may have a different effect on e.g. cloud cover (which are in reverse correlation with total solar irradiance) than more evenly distributed GHGs. Thus the effect of one W/m2 from GHGs doesn’t necessary equals the effect of one W/m2 from orbital changes…

    [Response: There is plenty of evidence showing that the GHG changes contribute to the amplitude of the ice-age cycles. The graph you show simply demonstrates that the deglaciation was complex. Given the impacts of adding 120 meters equivalent of global mean sea level equivalent of freshwater to the system are unlikely to be negligible on ocean circulation and biological activity. Similarly, the different timescales for land biospheric changes and ice sheet changes will almost certainly give a complex transient scenario. That is very interesting, and indeed, largely uncertain, but as a demonstration there is no CO2 impact on climate it falls very short.

    As to oribital forcing regionally having a different effect to global mean forcings, I specifically state that above and discuss the implications for Hansen's argument. - gavin]

    Comment by Ferdinand Engelbeen — 7 Apr 2008 @ 8:54 AM

  2. This paper has been picked up by this morning’s Guardian newspaper here in the UK, which ran it as the front page lead.

    That report was in turn picked up by The Register, a well-known UK IT (and related issues) site, which has recently been sullying it’s generally excellent record for debunking popular myths or the hype-du-jour by jumping to entirely the wrong side of the popular debate on AGW.

    Comment by A. Simmons — 7 Apr 2008 @ 9:21 AM

  3. I am on an international socials commentary e mail list. We have had discussions on global warming on that list, and I must admit that a few of those on the list have been taken in by the deniers. I have had some very sharp debates with them. In any case, one person posted the following note, which quotes an article from the “Guardian” newspaper. Can somebody explain this for me? Thank you.

    “Hansen’s team studied core samples taken from the bottom of the
    ocean, which allow C02 levels to be tracked millions of years ago.
    They show that when the world began to glaciate at the start of the
    Ice age about 35m years ago, the concentration of CO2 in the
    atmosphere stood at about 450ppm.”

    This makes no sense as it stands in the light of present targets for
    CO2 emissions; I read it as saying that we should be aiming for a CO2
    concentration which would be the SAME at the start of the last Ice
    Age, at the time when the earth started to glaciate.

    But then it goes on:
    “If you leave us at 450ppm for long enough it will probably melt all
    the ice – that’s a sea rise of 75 metres. What we have found is that
    the target we have all been aiming for is a disaster – a guaranteed
    disaster.”

    If 450ppm were compatible with a long, long Ice Age and global
    glaciation 35m years ago, how is it that exactly the same level today or in the future would be expected to cause global warming?

    Comment by John Reimann — 7 Apr 2008 @ 9:32 AM

  4. If someone could give a brief explanation about what an ‘orbital forcing’ is opposed to simply a ‘forcing’ then I’d be very grateful. I’ve got a fair understanding of the latter but don’t understand what the ‘orbital’ part means. Thank you.

    [Response: It refers specifically to the changes in the distribution of solar radiation over latitude and season that occur because of variations in the precession, obliquity and eccentricity of the Earth's orbit. Otherwise known as Milankovitch forcings. - gavin]

    Comment by Chris Rison — 7 Apr 2008 @ 9:57 AM

  5. “A more subtle point is that the ‘efficacy’ of different forcings, especially ones that have very regional signatures might vary, making it more difficult to add up different terms that might be important at any one time.”

    Should this be: A more subtle point is that the ‘efficacy’ of different forcings might vary, especially ones that have very *different* regional signatures, making….? A bit hard to parse as well as a missing word.

    [Response: thanks. I made the correction. - gavin]

    Comment by Keith Clarke — 7 Apr 2008 @ 10:08 AM

  6. #3 – I think the language the Guardian uses is a bit confused. If you look at the ice cores, then over the recent ice-age cycles CO2 goes up to a high-point of about 280ppm in the interglacials and is lower than that during the glacial maximums.

    I think the 450ppm 35 million years ago is referring to a time *before* the current geologic period of ice-age cycles. What they argue is that if the 450ppm is sustained over geologic timescales ie >1000-10000 years then it will lead to the loss of all ice.

    That seems reasonable to me, but I don’t think it has any bearing on policy, since CO2 levels are already above 380ppm and rising rapidly. We have to work out a way of stabilising those levels during this century and *then* we can work out how we’re going to reduce them back down again (or whether the carbon cycle will do it for us quickly enough).

    The East Antarctic Ice Sheet is going to give us more than a century of breathing space to sort things out, and if it doesn’t, well, there’s not much we can do to avoid that, so we’d better hope that it does.

    Comment by Timothy — 7 Apr 2008 @ 10:13 AM

  7. Re #3 The first x million years of antartic glaciation 34 million years ago was unstable and did not become stable until 18 million years ago when CO2 levels had fallen slightly lower I believe. worryingly Northern Hemisphere Ice sheets did not begin to form until 400 ppmv but I do not know when they became stable CO2 levels wise. If we take into account the differences in orbital forcings 34 million years ago and the levels of other greenhouse gases and the amount of vegetation on the planet I would agree with James Hansen that climate sensitivity is possibly higher than it was way bacj then.

    Comment by pete best — 7 Apr 2008 @ 10:14 AM

  8. The six degree long term climate sensitivity seems to largely depend on the CO2 level when Antarctica began to be glaciated about 35 million years ago. I am having trouble understanding how a 425 ppm level of CO2 at that time was arrived at. From looking at the curves, it does not appear any of them really fits very well, so this data is not adequate to arrive at such a conclusion.

    I also want to question the assumption that the temperature (thus CO2 level) at which glaciation begins is the same one that will melt the ice cap entirely. An ice cap creates it own regional climate, as can be seen by the contrast between Antarctica and the Arctic. Therefore I would assume that the temperature required to melt an ice cap is significantly higher than the temperature it formed at.

    On the other hand, this view seems to contradict the observation that the warming period for interglacial periods is shorter than the cooling period of re-entering the ice age.

    Comment by Blair Dowden — 7 Apr 2008 @ 10:42 AM

  9. “I would assume that the temperature required to melt an ice cap is significantly higher than the temperature it formed at.”

    I believe this is the state the Greenland ice cap is in now – ie it is only there because it is already there, and if it melts there’s no way to get it back without another ice age. Indeed, if it starts to melt, then presumably its height will decrease and the melting will accelerate.

    So, yes, I think I would now agree with you that it is a bit of a leap of faith to assume that 450 ppm would see the eventual demise of the Antarctic Ice Sheet.

    Comment by Timothy — 7 Apr 2008 @ 10:48 AM

  10. “So what does this mean for the future? In the short term, not very much”.

    Well, if Hansen is right, that depends on what you mean by “short-term”. To quote from the preprint:

    “Sea level changes of several meters per century occur in
    the paleoclimate record, in response to forcings slower and weaker than the present human-made forcing. It seems likely that large ice sheet response will occur within centuries, if human-made forcings continue to increase. Once ice sheet disintegration is underway, decadal changes of sea level may be substantial.”

    The Guardian article A. Simmons referred to quotes him as saying: “We are talking about a sea-level rise of at least a couple of metres this century.”

    So far as I can see, he could be right about that, without being right about the long-term/Earth System climate sensitivity being as high as 6 degrees C. He’s suggesting that previous ice-sheet melting episodes were slow because the forcing due to orbital change was slow, not due to inherent inertia, and that recent observation suggests ice-sheets can melt much faster if the forcing is faster.

    [Response: I wasn't talking about sea level - but just to make it clear, I share Jim's concern that serious sea level changes are a real possibility. None of the long term sensitivity issues deal with the problem of rates of change, and so the preprint or this post cannot really address that. - gavin]

    Comment by Nick Gotts — 7 Apr 2008 @ 11:00 AM

  11. Do you mean by, “simple mixed layer ocean” that the variations of ocean temperature with depth are not part of the analysis?

    [Response: In the standard estimate of the Charney sensitivity. no. Using fully coupled OAGCMs takes much much longer and has not yet become standard practice. In the GISS models, the difference in eventual temperatures (after hundreds of years) is on the order of a few tenths of a degree. - gavin]

    Comment by Jim Bullis — 7 Apr 2008 @ 11:20 AM

  12. On the issue of the orbital forcing changes though – Hansen isn’t even looking at the forcing going all the way back to the orbital effects in this paper, he’s just looking at the CO2 levels as if they are the forcing. The actual forcing from the orbital changes is presumably smaller (or is it effectively large when you account for latitudinal dependence?) – i.e. if CO2 levels themselves are a positive feedback of a factor 3 or so on the orbital forcings, then doesn’t that further multiply the actual sensitivity to fundamental forcing by a factor of 3, i.e. 18 C instead of 6?

    The point is: it’s widely recognized that CO2 levels in the atmosphere increase as a result of temperature increases, a positive feedback effect. Climate models and Charney analysis effectively ignore this because they’re looking at the effect of increased CO2 itself.

    But if our interest is in the effect of *anthropogenic* CO2 only, which is a real forcing, then the feedback CO2 could be tremendously additive. I.e. if you look at the target for CO2 emissions by humans, rather than just the target CO2 level in the atmosphere, the constraint is that much more stringent. To keep to 350 ppm, which already means a long-term warmer world, we may have to go to zero or less-than-zero human emission levels. But I’d like to see that quantified a bit better…

    Comment by Arthur Smith — 7 Apr 2008 @ 11:32 AM

  13. Re:#3
    John Reimann
    “If 450ppm were compatible with a long, long Ice Age and global
    glaciation 35m years ago, how is it that exactly the same level today or in the future would be expected to cause global warming?”
    Prior 35m years ago the earth did not have large ice sheets like today. As the temperature sinks below a special value the Antarctic ice sheet growth.
    If the temperature rise in the future above a similar (but somewhat higher value, see post#8) value for a long time, the ice sheet will melt.
    The sun is now somewhat brighter the 35m ago, which lowers the CO2 level needed to reach this temperature.
    On the other hand the higher albedo of the ice sheets will rise the level of CO2 needed to this temperature.
    The problem is, that the exact temperature is not well known.

    Comment by Uli — 7 Apr 2008 @ 11:57 AM

  14. I am a little confused. You mention that slower feedbacks are excluded from definitions of sensitivity, which is reasonable; sensitivity must be defined on a relevant time scale.

    However, does this mean that those slower feedbacks are excluded from coupled model formulations? I thought I’d seen mentions of afforestation or predictive vegetation in the IPCC report.

    Could somebody address the sign, magnitude and time scale of feedbacks related to vegetation changes? I’d imagine that increased vegetation would result in a larger carbon sink, but there would be changes in surface albedo and transpiration along with it.

    [Response: Most GCMs do not consider vegetation feedbacks (and all 'sensitivity' numbers you will have seen, do not include them either) - but it is becoming more common and most groups have, or are working on, such modules. Some of the early experiments (by Peter Cox, Pierre Freidlingstein etc.) show positive feedbacks on CO2 levels (of varying degrees) and, presumably, some impact on temperature due to albedo/ET effects. I am not however aware of what they are (maybe someone more knowledgeable could comment?). - gavin]

    Comment by tharanga — 7 Apr 2008 @ 12:04 PM

  15. Gavin,

    While I appreciate your effort to keep the long millennial timescale in consideration, I think it worth stressing that Hansen et al. have been looking hard at the timescale for the response of icesheets and find evidence that it is centuries rather than millennia. And they stress this also now:

    Ice sheet response time is often assumed to be several millennia, based on the broad sweep of
    paleo sea level change (Fig.1A) and primitive ice sheet models designed to capture that change.
    However, this long time scale may reflect the slowly changing orbital forcing, rather than
    inherent inertia, as there is no discernable lag between maximum ice sheet melt rate and local
    insolation that favors melt (7). Paleo sea level data with high time resolution (28, 29) reveal
    frequent ‘suborbital’ sea level changes at rates of 1 m/century or more.
    Present-day observations of Greenland and Antarctica show increasing surface melt (30), loss
    of buttressing ice shelves (31), accelerating ice streams (32), and increasing overall mass loss
    (33). These rapid changes do not occur in existing ice sheet models, which are missing critical
    physics of ice sheet disintegration (34). Sea level changes of several meters per century occur in
    the paleoclimate record (28, 29), in response to forcings slower and weaker than the present
    human-made forcing. It seems likely that large ice sheet response will occur within centuries, if
    human-made forcings continue to increase. Once ice sheet disintegration is underway, decadal
    changes of sea level may be substantial.

    If so, then slow feedbacks may not be all that slow and the present day policy implications rather large.

    It is worth noting that the preprint calls for stabilization below the current concentration of CO2 in the atmosphere and for active measures to remove CO2 from the atmosphere while providing a senario for how this might happen.

    If if a policy of adaptation rather than mitigation is pursued, measures must also be taken now for projects that require 100 year plus planning horizons such as building dykes or sea walls or siting nuclear reactors. And, without a firm committment to mitigation, adaptation measures can’t be left unconsidered, doubling or more the present day cost of response. For example, the NRC is beginning to entertain an application for a new reactor at Calvert Cliffs on the Chesapeake Bay. This might be considered an aspect of mitigation, but it would be foolhardy not to consider what impact 5 meters of sea level rise before the planned end of decommissioning might have and build in adaptation measures now such as siting the plant further inland where the foundation would not be subject to erosion. A dyke to protect Long Island and it’s neighbors might need its foundation laid within a decade and its cost planned for in tax policy within a few years. Transportation planning also has long term aspects such as the interstate highway system. How soon must we start to elevate I-10 even higher to get the job done in time and at what cost?

    So, I would argue that in the short term this work means quite a lot.

    [Response: Please don't misunderstand me - the eventual long term temperature change being 6 deg is the thing that I'm not sure has short term implications. But that is a statement about how changes in T affect ice sheets (etc.) which then affect T again. That is very different from saying that T affects ice sheets (and sea level) which is a much more serious short term issue and would be even if the long term sensitivity was the same as the Charney one. - gavin]

    Comment by Chris Dudley — 7 Apr 2008 @ 12:09 PM

  16. Re 14:

    I am no expert in this and don’t know much about terrestrial ecosystems except that they are generally considered to be substantially more complex than ocean ecosystems. I’ve read a few papers on ocean ecosystem modeling and would argue that our understanding of the crucial processes is still quite primitive. For example one ocean ecosystem model that I know is used in at least one GCM does not include any sort of parameterization related to ocean acidity. If large scale changes in the ocean ecology occur because of acidification the model cannot reasonably be expected to capture the effects. Moreover the key organisms and the dynamics between them is poorly understood at best.

    I would also argue that the state of our understanding of the carbon cycle as it operates now is still pretty uncertain. There were papers published last year on the missing sink (the gigaton of CO2 that is taken up by unknown processes) like this one: Stephens, B. et al. Science 316, 1732–1735 (2007).

    Comment by John E. Pearson — 7 Apr 2008 @ 1:02 PM

  17. Re 11 Thanks gavin,

    So we know that there is no accounting for a controlling process whereby an increase in ocean surface temperature causes an increase in storm activity. Hurricane formation is a particularly strong example of this. That increase in storm activity causes mixing of the ocean such that colder waters from deeper regions are brought up such that the “mixed layer” is cooled. This reverses the initial temperature increase of the ocean surface. There is abundant cold water to handle this for a long time.

    If this is the governing process, global warming will be seen as a very slight increase in ocean surface temperature. Only over a long time will there be a measurable increase in surface temperature. Before that happens, there should be a measurable increase in the “mixed layer depth”.

    Since deeper waters will be warmer, there is a possible link to the global ocean circulating currents that results in warmer water in polar regions. This could be related to loss of ice, especially ice that is in ocean contact.

    It seems that a quantitative study might result in better understanding of temperature changes. It does not appear that this is being done. From what you say, it would be prohibitively time consuming?

    Comment by Jim Bullis — 7 Apr 2008 @ 1:20 PM

  18. I’ve been keen to read the Real Climate response to Hansen’s paper for a couple of weeks, and thanks very much for it. I suppose, however, that I remain confused about the implications, even having read Gavin’s response to #15. Please forgive me if I am slow!

    The battle against climate change is based in no small part because of the alaming scientific understanding that we are potentially beginning long-term future processes that cannot be stopped. Short term concerns drive the headlines and insurance companies (and have the most emotive impact), but of course they are not the whole story. The bottom line is – what does the best science now suggest for a target that can be considered safe with reasonable probability? Is 450ppm becoming an inherently unsafe target for a long term habitable Earth? Is 350ppm the new 450ppm? Does the best advice to policymakers need an urgent review?

    [Response: Nobody can say what is safe (in the long term), though we aren't talking about making Earth inhabitable, just seriously uncomfortable for it's existing inhabitants! As the levels rise, the consequences will get worse, and within those consequences will be dozens of thresholds and tipping points related to local or regional ecosystems and climate regimes - some which could have global consequences. We don't know exactly where they are or what their effects will be, so the only prudent course is to try and avoid as many as possible. Thus in my opinion emissions should be lowered as fast and as soon as is technologically and economically feasible. Setting a target now doesn't imply that people will not revise it downward later on in the process and so I don't tend to get hung up on a precise target. - gavin]

    Comment by Guy — 7 Apr 2008 @ 1:34 PM

  19. Jim #17, I think you are jumping to a lot of conclusions here. First, storms–even Cat 5 hurricanes are local and short-lived processes, whereas greenhouse forcing is operative 24/7/365. What is more, while such processes could well be important in the Southern Hemisphere, they will be less so in the Northern Hemisphere. Third, unless storm intensity increases drastically, the storms will foster exchange only down to a certain depth, and as waters at this depth warm, the effectiveness of this mechanism will decrease. Moreover, CO2 solubility will decrease. Thus, one could argue that the mechanism you posit is in fact hiding the warming that is going on, and that in the future (and CO2 persists for hundreds to thousands of years), the warming will be much more severe. In short, given that we already see significant warming occurring, I don’t think we can count on the oceans to save us.

    Comment by Ray Ladbury — 7 Apr 2008 @ 1:37 PM

  20. We might want to know that the discussion is moving to the courts:

    Comer, et al. v. Murphy Oil USA, et al., in which a class of Mississippi property owners blame the environmental impact of energy and chemical companies for Hurricane Katrina damage. The case was dismissed during summary judgment in Mississippi federal court, but has since been appealed to the U.S. Court of Appeals for the 5th Circuit.

    Comment by Richard Pauli — 7 Apr 2008 @ 2:07 PM

  21. RE #3 &

    “Hansen’s team studied core samples taken from the bottom of the
    ocean, which allow C02 levels to be tracked millions of years ago.
    They show that when the world began to glaciate at the start of the
    Ice age about 35m years ago, the concentration of CO2 in the
    atmosphere stood at about 450ppm.”

    This makes no sense as it stands in the light of present targets for
    CO2 emissions; I read it as saying that we should be aiming for a CO2
    concentration which would be the SAME at the start of the last Ice
    Age, at the time when the earth started to glaciate.

    That 450 ppm also jarred me and my initial thought was the same as yours. Then I started thinking (aside from the points already raised), the earth was already in an initial cooling phase from some higher global temp. As denialists so like to point out, CO2 follows temp, and so when the temp (initially triggered by reduced solar irradiation??) lowered to that point at which ice sheets start to form, the CO2 was at 450 ppm. I understand from Lovelock’s REVENGE OF GAIA that plants & life in general do much better in cooler climates, so the plants started flourishing more and absorbing CO2 once the temp started decreasing from its high point, and the ice & snow increased the albedo and reduced temp more, and plants liked it even more with reduced temp from lower CO2 & increasing albedo, and the earth kept getting cooler with these cooling positive feedbacks (or swinging up and down, but on the whole headed down). I’m sort of imagining it as a direction and momentum thing — in the cooling direction.

    Now we are adding CO2 so the effect is a warming trend, which reduces ice and snow albedo and releases carbon from frozen permafrost and ocean hydrates, and the direction and momentum are in the warming direction. And I think plants don’t very hot temps as much, especially the land being dissicated from the warmer air sucking out the moisture, and harm from droughts, floods, heat stress.

    So perhaps there’s this issue of global temperature direction (cooling or warming) and system momentum.

    Maybe that’s what “sensitivity” really has to do with — how much you have to poke the dragon to wake him from his sleep. Very little, it seems.

    Comment by Lynn Vincentnathan — 7 Apr 2008 @ 2:32 PM

  22. I do not understand the second part of this statement from the Hansen paper:

    The most direct GHG feedback is release of CO2 by the ocean due to temperature dependence of CO2 solubility and increased ocean mixing in a warmer climate that flushes the deep ocean of CO2 that accumulated through biologic and physical processes.

    First, I thought a warming climate reduced the temperature difference between the equator and poles, which is what drives most of the winds and ocean currents that cause ocean mixing. I would not think a small increase in hurricanes would compensate. In the deep past it is during warmer climates that you get a stratified and stagnant ocean.

    Second, I did not think there was an excess of CO2 in the deep ocean, rather it would be in equilibrium with the lower CO2 levels of the past few million years. I would think that today’s higher CO2 levels would eventually increase levels in the deep ocean, though of course not quickly enough to solve our problems here on the surface.

    Comment by Blair Dowden — 7 Apr 2008 @ 2:34 PM

  23. Arthur Smith (12) wrote “To keep to 350 ppm, which already means a long-term warmer world, we may have to go to zero or less-than-zero human emission levels.” The world is already at 385 ppm and adding 1–2 ppm per year. So to reach 350 ppm from just the current level requires removing about 185 GtC from the active carbon cycle.

    Proposed methods to accomplish this include burning biofuels with CCS, as well as direct sequestration from the atmosphere, considered in a previous thread (down two).

    And just briefly, without the reasoning, I suggest that even just 315 ppm is too high for long term climate stability.

    Comment by David B. Benson — 7 Apr 2008 @ 3:38 PM

  24. Gavin (in #15),

    I think I see your distinction, we must wait for bare earth in the Antarctic for it to warm the Antarctic through albedo change, but since ice sheets have been grouped in as slow, I would still say that slow may not be so slow. And, this has a large effect. The total amplitude of the sensitivity revises the stabilization target downward, but a not so slow slow feedback also limits the amount of time we can be above that target. So, according to the preprint, we need to be cutting emissions very quickly now to avoid extra effort in cleaning up the atmosphere that would be the result of delay. And, we must perform that cleanup fairly quickly as well to reach the stabilization target soon. Letting the ecosystem do it on its own is not fast enough. If we had thousands of years for the slow feedbacks to come into effect, we might just wait, after cutting emissons, for the atmospheric concentration to fall just as we are doing with CFCs, but with a faster slow feedback, this would not be an option. So, at least for planning, the preprint has two large present day effects: a target below the current concentration and a need to take positive action beyond cutting emissions to meet that target.

    Comment by Chris Dudley — 7 Apr 2008 @ 3:45 PM

  25. Interesting read, but…

    We tend to focus in singular stuff instead of the whole. Sure, discussing CO2 is good, but consider some of the causes, say factories. What are they needed for? A consumption lifestyle. For whom? 6 billion people, who grow and consume more each day. Their lifestyle creates alienating neighbourhoods where we adapt to having cars etc. Can you walk 12 miles to the hospital? Maybe overpopulation is a legitimate concern, since it is not just consumption, but the scale of it, shaping our eco-system and society in a manner dependent on oil/consumption.

    For a discussion on this, see this interview: http://www.corrupt.org/act/interviews/john_feeney

    Comment by DD — 7 Apr 2008 @ 4:54 PM

  26. Gavin wrote:

    “Earth System sensitivity is not stable over geologic time. How much it might vary is very difficult to tell, but for instance, it is clear that from the Pliocene to the Quaternary (the last ~2,5 million years of ice age cycles), the climate has become more sensitive to orbital forcing.”

    i seen to recall GCMs that attempted to model the closing and opening of ocean channels such as the Drake passage between Antarctica and S. America.

    are there any (loooong range)models that take continental drift into account ?

    tanx for another good column
    sidd

    Comment by sidd — 7 Apr 2008 @ 5:28 PM

  27. Re #3 I have an explanation of what was meant by the glaciation starting 35 million years ago. That was when ice first started appearing on the mountain tops of Antarctica.

    It was only about 3 million years ago when ice sheets started forming in the Northern Hemisphere. It is their waxing and waning that produces the glacial/interglacials driven by Milankovitch cycles, which taken together are called the Great Ice Age.

    In other words ice started forming in Antarctica 35 Ma ago, but the Ice Age did not start until the Isthmus of Panama closed 3 Ma ago, and ice sheets started forming in the Northern Hemisphere.

    The level of CO2 at the start of the present inter-glacial 10 ka ago (the Holocene) was 260 ppm, and most of the Laurentian and Scandanavian ice sheets disappeared. See the Antarctic ice cores here for the CO2 level:
    http://en.wikipedia.org/wiki/Image:Co2-temperature-plot.svg

    During the previous inter-glacial (the Eemian) at around 130 ka ago the level of CO2 was at around 290 ppm and the Greenland ice began to melt as well, raising the sea level to about 5 m higher than today.

    Now, with CO2 at 380 ppm both Greenland and the Antarctic Peninsula are melting, but not the Antarctic mountain ice sheets.

    If all of Greenland melts we get a rise of 7 metres (20 feet). If ALL of Antarctica goes we get a rise of 70 m (200 feet, but CO2 levels are not high enough for that to happen yet!

    Comment by Alastair McDonald — 7 Apr 2008 @ 6:56 PM

  28. Gavin,

    Y you wrote “So what does this mean for the future? In the short term, not much. Even if this is all correct, these effects are for eventual changes – that might take centuries or millennia to realise.”

    It seems to me that there is a major flaw when thinking about ice sheets, which means an imminent danger is being ignored. Only the melting of continental ice sheets is being considered as a serious threat, because only they raise sea level. If the Arctic sea ice disappears sea level will change by only a few millimetres, and s it is not considered a danger.

    But it will have a large effect on albedo! And that seems to be what this thread is about. Roughly a third of the multi-year Arctic sea ice disappeared last, and some Russians are predicting it will all be gone in another couple of years time. Whereas the greenhouse effect only increase with the log of gas concentration, albedo has a linear effect.

    If melting ice sheets are a danger because of their effect on albedo, then the melting Arctic sea ice sheet rather belies your claim of what this means for the future when you wrote “In the short term, not much.”

    Cheers, Alastair.

    Comment by Alastair McDonald — 7 Apr 2008 @ 7:23 PM

  29. Ray #19

    Thanks for the response. I am trying not to come to any conclusions, and intended my words to be looking for comment.

    But to clarify, I used the hurricane as a strong example, not meaning to exclude general wind processes.

    Are you saying that ocean circulation patterns in the Northern Hemisphere do not reach Antarctic regions where ice is more in the water?

    Also, why would CO2 solubility decrease if surface water warmed slightly and deeper water warmed more?

    My premise is indeed that storms will foster exchange down to a depth such that the effectiveness of this mechanism will decrease, but then the level of storm activity would increase until the exchange went deeper. And yes, this would be hiding the warming that is going on. So I am suggesting that, maybe, without this process the ocean surface would be warmer than it is. I realize that the ARGO data discussed elsewhere is said to have been misinterpreted, but the actual numbers for surface temperature are not changing that much.

    I also think I have heard that Antarctic ice is breaking up faster than expected.

    Now back to hurricanes. Yes they are local, and short-lived, but they have powerful mixing effects that have a long lasting effect. We have actual knowledge of the strong deep currents in the gulf due to Katrina, from the fact that ocean floor pipelines were seriously damaged. I believe they were in water 1500 meters deep. The impact of this, via the gulf stream, would be spread over the entire North Atlantic, and it would last there quite some time.

    But my point of view goes back to the practice of indirectly measuring the thermocline with a velocimeter as a part of underwater sound studies. This was the best way to relate temperatures to underwater sound propagation effects. More directly, Navy sonar operations used to include, and probably still do, a bathythermograph scan, “BT”, as a part of understanding how to best operate the sonar in a particular region to detect submarines, and the key depth of increased safety was the depth of the “layer.” The layer depth is thus known very well to vary significantly with wind effects, much less in strength than hurricanes. And we are talking about depths around 70 meters. That number is the transition between mixed conditions and rapidly cooling water depths. Below 600 meters, the oceans are almost universally cooler than 5 degrees C. About 85% of the oceans are 3000 to 6000 meters in depth. So we know very well that the reservoir of cold is large.

    But my premise is not that the oceans will save us. If taken into account, it may be seen that they will slow the process as far as ocean surface temperature goes, and hence general air temperature. Further, the process I describe, while making surface temperature slow to change, could relate to ice melting activity.

    But my premise is not that the oceans will save us. If taken into account, it may be seen that they will slow the process as far as ocean surface temperature goes, and hence general air temperature. Further, the process I describe, while making surface temperature slow to change, could relate to ice melting activity.

    Eventually, as the depth necessary to tap into the cold gets lower, the storms will increase. Without benefit of analysis, I venture to guess this would be noticeable much sooner than a hundred thousand years. However, it might not be as soon as some are now saying.

    Comment by Jim Bullis — 7 Apr 2008 @ 8:15 PM

  30. RE #22, & the quote from Hansen’s study, “The most direct GHG feedback is release of CO2 by the ocean due to temperature dependence of CO2 solubility and increased ocean mixing in a warmer climate that flushes the deep ocean of CO2 that accumulated through biologic and physical processes.”

    When I read it I had in mind the frozen methane hydrates at the bottom of the ocean (from “biologic processes”). But I could be wrong. That’s what it seemed like to me with my limited understanding.

    Also, do warmer oceans tend to turn the CH4 that is being released from the hydrates into CO2? And, if so, wouldn’t that be actually a bit better than the ocean releasing CH4 into the atmosphere where it is a much more potent GHG for the ~10 years until it decomposes into CO2.

    Then, there is the issue to anoxic warming oceans turning this into hydrogen sulfide and poisoning life on earth. I imagine that might be a possibility in the distant future if we don’t mitigate GW enough. But that wouldn’t be a positive feedback, I don’t think, just a nasty effect of GW.

    Comment by Lynn Vincentnathan — 7 Apr 2008 @ 8:47 PM

  31. I don’t know. Can you refute a man’s science if you can’t spell his name?

    http://www.nature.com/ngeo/journal/v1/n4/full/ngeo157.html

    Comment by Mark A. York — 7 Apr 2008 @ 10:11 PM

  32. Just to clarify, are the figures being used in this post and Hansen et al C02 ppm, or C02 equivalent (GHG forcings)?

    Comment by George Darroch — 8 Apr 2008 @ 12:01 AM

  33. I cannot at present see a major issue with Hansens analysis but I see big problem with politicians being able to swallow it. In recent talks I have seen him do he speaks of leaving coal in the ground or using CCS technology within a decade but looking at CCS technology it is either in development for new power plants or it has to be retrofitted at some point to existing power plants sooner which is unlikely to happen.

    He then states that existing oil and gas reserves can be used so long as we leave unconventional oil alone. Anyone been to Athabasca recently? The oil sands there are being developed at a frantic pace, 1 mb/d now rising to 5 mb/d come 2020 and other shale and heavy oils are likely to be developed also once conventional oil begins to peak come 2015 as the head of shell announced recently.

    If we really want to max out our Co2 levels at 450 ppmv (oil and gas usage only) then we has better really start compaigning now. I am sure that the world can do it but its just that lead times are so long for R&D, prototyping, and full commercial release that its doubtful that any significant dent in CO2 emissions can be made for 30 years.

    Comment by pete best — 8 Apr 2008 @ 4:23 AM

  34. Gavin

    I don’t understand Hansen’s assumption.

    How conciliate the global temperature driving by CO2 and the lag between Antarctic temperature and CO2?
    The initial “forcing” for glaciations isn’t, as you know, CO2, but regional summer insolation forcing, even if the global forcing is weak.
    So can you explain, again, why Hansen considers only GHG in his sensitivity calculation?

    Comment by Pascal — 8 Apr 2008 @ 4:55 AM

  35. 1) On a 6degC climate sensitivity in policy relevant timescales or not, having read this paper twice – I am very very unconvinced.

    I’m still reading this para (Page 4) as a gaff:
    “Paleoclimate data permit evaluation of long-term sensitivity to specified GHG change. We
    only assume that the area of ice is a function of global temperature. Plotting GHG forcing (7)
    from ice core data (27) against temperature shows that global climate sensitivity including the
    slow surface albedo feedback is 1.5°C per W/m2 or 6°C for doubled CO2 (Fig. 2), twice as large
    as the Charney fast-feedback sensitivity.”

    I still see roughly equal contributions from GHG and ice sheet albedo (fig 1b), i.e. 1+1=2. And fig 2 after time=0, I see what is in effect a double count of forcing because the GHG alone seems to be equated with the full 3degC excursion, so because there aren’t the extensive ice sheets now 6 degC/2 = Charney’s ~3degC.

    I still subscribe to a 3degC sensitvity, but am willing to be persuaded.

    2) On SLR, since Hansen’s earlier paper where his team looked at the seasonal insolation peak correlations with ice-volume changes, I am now concerned (previously I didn’t count SLR as a major policy timescale threat). That’s especially the case given the Arctic and the potential for secondary impacts on Greenland and news from the Antarctic.

    Comment by Cobblyworlds — 8 Apr 2008 @ 6:10 AM

  36. Alastair #28

    I asked William Connolley about this over at Stoat, as he modelled the impacts of the loss of Arctic sea ice a while back; his answer: “Well, it would lower the albedo, though perhaps not by as much as you might expect due to clouds and sun angle. Our study found little *long term* impact, because the ice largely regrew each winter. That included albedo effects.”

    Hope that’s of interest.

    Comment by outeast — 8 Apr 2008 @ 6:24 AM

  37. http://www.scientificblogging.com/news_releases/putting_the_west_antarctic_ice_sheet_in_proper_global_warming_context

    This article appears to demonstrate that WAIS has been losing mass for a long time at around 2 cm per year but recently it has jumped to 1.6 M per year, a significant increase. And this is with only 0.8C of GW. With 0.6C in the pipeline from ocean latency and another 0.4 from existing infrastructure already in place I really fear for the ice sheets flow rates into the oceans. If we are releasing GHG’s at 30x any known historical rate and 1.6 M become 2 or 2.5 M per year then things are only going to accelerate for the next 60 years at least even if we stop all CO2 emissions significantly in 20 years time.

    Comment by pete best — 8 Apr 2008 @ 6:58 AM

  38. Just so I’m sure I understand, it seems you’re basically saying that the “resting state” of climate in the long run after doubling of pre-industrial CO2 is likely warmer than the shorter-term (100 years or so) response of the system. But you’re also saying that uncertainties in feedbacks etc are very large (perhaps an understatement, actually).

    That would seem to leave high long-term sensitivity in the realm of what Princeton’s Steve Pacala has called “the monsters behind the door” — possible, but not necessarily clear threats. That’s different than coming to a conclusion that 350 ppm is an appropriate long-term limit for CO2.

    For us non-scientists, does this question, because of the uncertainties, still rest in that simple precautionary place (“do no harm”) or has this paper truly narrowed the scope of what’s possible from the human greenhouse intervention?

    [Response: The key point to take home from this study is that the initiation of glaciation likely didn't happen at 550 ppm or 650 ppm or similar - it was likely less. That implies that if you wait long enough with levels that high, large scale glaciation is probably unsustainable. Undefined in all of this is what 'long enough' means, and whether you can get a better lower bound. Those are unfortunately exactly the issues that matter in the short term. I think that it is difficult to rule out definitively that it is as low as 425 ppm or so. However, as I stated above, initial targets that are being set now are not set in stone and are not yet really being worked towards. So does this add to pressure to move ahead on emission reductions? Yes, but there is no shortage of reasons to be working on that already. - gavin]

    [Response: We should also recall the implications of Dave Archer's "long tail" of anthropogenic CO2. Something like 20% of the anthropogenic CO2 will stick around for much more than 1000 years. That tells us something about how much peak CO2 we can tolerate without committing the planet to extreme consequence of the very long term warming. For example, if we reached a peak CO2 of 1200 ppm, then the long term tail contains about 280 + (1200-280)/5 or 464 ppm CO2. That would mean that even if the deglaciation took a very long time to set in, the CO2 would indeed stay above the threshold level for a long time. This is only a crude illustrative calculation, and to do it right would take a proper ocean carbon cycle model, but I hope it gives the idea of what Hansen's calculation implies even if the catastrophic changes require a very long time to act. --raypierre]

    [Response: I'm very pleased I can disagree with Gavin for once (this is hard). The CO2 level at which glaciation started (in a phase of declining CO2 concentration) is very likely not the same as the CO2 level where the ice sheets will vanish again (in a situation of rising CO2 concentration) - the latter very likely is quite a bit higher. This is because of the positive ice albedo feedback which leads to hysteresis - the basic concept is well known since way back (I think Budyko) and this is also found in coupled climate - ice sheet models like our CLIMBER-2 model - see Calov and Ganopolski 2005. -stefan]

    Comment by Andy Revkin — 8 Apr 2008 @ 7:18 AM

  39. I would like to look at this statement from the Hansen paper:

    Climate forcing in the LGM equilibrium state, relative to the Holocene, due to the slow feedback ice age surface properties, i.e., increased ice area, different vegetation distribution, and continental shelf exposure, was -3.5 ± 1 W/m2 (10). The forcing due to reduced amounts of long lived GHGs (CO2, CH4, N2O) was -3 ± 0.5 W/m2, with the indirect effects of CH4 on tropospheric ozone and stratospheric water vapor included (fig. S1). The combined 6.5 W/m2 forcing and global surface temperature change of 5 ± 1°C relative to the Holocene (10b,c), yields an empirical sensitivity ~¾ ± ¼ °C per W/m2 forcing, i.e., a Charney sensitivity of 3 ± 1 °C for the 4 W/m2 forcing of doubled CO2. This empirical fast-feedback climate sensitivity allows water vapor, clouds, aerosols, sea ice, and all other fast feedbacks that exist in the real world to respond naturally to global climate change.

    Climate sensitivity varies as Earth becomes warmer or cooler. Toward colder extremes, as the area of sea ice grows, the planet approaches runaway snowball-Earth conditions, and at high temperatures it can approach a runaway greenhouse effect (8). At its present temperature Earth is on a flat portion of its fast-feedback climate sensitivity curve.

    The calculation above is for a long period of time and includes all the slow feedbacks, so I do not know why Hansen calls it a fast feedback. Since the greenhouse gas portion is about half of the total forcing (ie. 1 + 1 = 2), if you consider them the cause (or at least the main feedback) then you get a GHG sensitivity of about 6 degrees. With ice sheets pushing below 45 degrees of latitude, this looks close to a snowball-Earth condition which has a high climate sensitivity. Luckily the same thing was not also happening in Asia, or we might no be here to write about it. A look at the increasing temperature response to the same orbital forcings as average temperature dropped shows that climate sensitivity became significantly larger during the Pleistocene ice ages.

    I am surprised that Hansen did not use the Pliocene (about 3 million years ago) as a benchmark. Here we have CO2 levels around 400 ppm, global average temperature about 2 or 3 degrees higher, and sea levels 25 to 35 meters higher (think ten story building). The carbon dioxide forcing is about the same ( 280 ppm Interglacial / 180 ppm LGM is close to 400 ppm Pliocene / 280 ppm Interglacial ) for a temperature change about half as much, implying a much lower climate sensitivity, closer to three degrees rather than six for the period we are about to enter.

    I still do not think you can use the temperature (or CO2 level) for the initiation of glaciation to be the same as that sufficient to melt the ice cap. For a large continent like Antarctica I think it will take a few extra degrees to overcome the thermal inertial of all that ice, unless someone can demonstrate why this is wrong.

    Comment by Blair Dowden — 8 Apr 2008 @ 8:26 AM

  40. #22 Blair Dowden,
    This might help:
    “Carbon dioxide is more soluble in cold water, so at high latitudes where surface cooling occurs, carbon dioxide laden water sinks to the deep ocean and becomes part of the deep ocean circulation “conveyor belt”, where it stays for hundreds of years. Eventually mixing brings the water back to the surface at the opposite end of the conveyor belt in regions distant from where the carbon dioxide was first absorbed, e.g., the tropics. In the tropical regions, warm waters cannot retain as much carbon dioxide and carbon dioxide is transferred back into the atmosphere” http://science.hq.nasa.gov/oceans/system/carbon.html
    Scroll down to the first bullet point.

    With regards stronger winds in a warming planet, see Toggweiler & Russell “Ocean Circulation in a Warming Climate.” Nature 17/1/08. That suggests a role for vertical temperature gradients in strengthening winds, such vertical gradients should increase with more global warming. Therefore regionally stronger winds could occur, and in the Southern Ocean that can impact overturning/mixing through Ekman Transport, the Southern Ocean is big! (I wonder if such enhanced wind driven mising would in effect be a negative feedback on warming rates, enhaning ocean thermal damping.)

    #32 George Darroch,
    Where people don’t put units, you can safely assume that if the figure’s in the hundreds it’s probably atmospheric concentration in parts per million, where it’s below or around 10 it’s probably Watts per square metre.Otherwise concentration is “ppm” and forcing “Wm2″.

    #34 Pascal,
    Why not read the actual paper?

    Hansen’s team explain why they consider CO2 to be reasonably considered the primary forcing where they do so. But they also consider the other primary forcing as albedo changes.

    #36 Outeast, thanks for that.

    Comment by CobblyWorlds — 8 Apr 2008 @ 9:28 AM

  41. Andy Revkin, think about doubling times in other areas. Pondweed on a lake. Mussels in cooling water intakes. Scum in a clean water system. Radiation in a fission pile. Epidemic spread compared to background existence of a pathogen.

    Those are all simple compared to climate. All are places where increasing some kind of moderating influence early on prevents a world of trouble by impacting the doubling time, lessening or halting the growth of the problem.

    We have lots of experience with this. We know we don’t notice problems until it’s almost too late — and the more profitable the system externalizing a cost, the more pressure not to notice those costs.

    This might be our final examination.

    Comment by Hank Roberts — 8 Apr 2008 @ 10:31 AM

  42. Antarctica has been glaciated several different periods over the last 600 million years. It didn’t just start 34 million years ago, that is just the start of the latest episode of glaciation.

    Antarctica was likely glaciated 580 million years ago, 450 million years ago, 300 million years ago and 150 million years ago. CO2 levels could have been as high 3000 ppm to 5000 ppm in some of those different periods.

    Antarctica is an unusual case in plate techtonics since continental drift has placed Antarctica around the south pole for most of the past 600 million years including various times when it was locked together with other continental plates.

    So, I don’t think the 6.0C sensitivity estimate is robust throughout the entire geologic record.

    Comment by John Lang — 8 Apr 2008 @ 11:02 AM

  43. #40 Coblyworlds

    If you say:

    “Hansen’s team explain why they consider CO2 to be reasonably considered the primary forcing where they do so. But they also consider the other primary forcing as albedo changes.”

    there is 2 forcings and their sum is 3.5 + 3.0W/m2 = 6.5W/m2

    so the sensitivity is 5°C/6.5W/m2 = about 0.75 °C.m2/W

    No, Hansen consider CO2 forcing alone, to find about 1.5°C.m2/W.

    My question was: why to consider CO2 alone?

    But I think Hansen uses the particuliar case of glaciation to know the impact of ice-sheet as a slow feedback.

    He assumes in his paper that ice-sheet feedback depends only of temperature and global forcing.

    And the alone real global forcing is GHG, even in the case of Pleiostene.

    This is what I understand now.

    Comment by Pascal — 8 Apr 2008 @ 11:59 AM

  44. from Gavin’s article:

    “… it is clear that from the Pliocene to the Quaternary … the climate has become more sensitive to orbital forcing. It is therefore conceivable (but not proven) that any sensitivity derived from paleo-climate will not (in the end) apply to the future.”

    This statement seems to permit opposite interpretations:

    1) The earth has gradually become more sensitive to orbital forcings. This could indicate a greater overall sensitivity, and thus a tendency for paleoclimate-based projections to underestimate the current sensitivity.

    2) Because the earth is more sensitive to orbital forcings, and because orbital forcings are headed in the cooler direction, paleoclimate-based projections could overestimate the sum of forcings we’re likely to experience.

    Are either or both of these readings in error?

    Comment by Daniel C. Goodwin — 8 Apr 2008 @ 1:09 PM

  45. Andy (#38),

    I think the the precautionary level is 280 ppm. What this preprint (and it is a preprint, not a paper) is arguing is that the sensitivity is larger than has been assumed up until now and so a “safe” temperature (a la Exeter) corresponds to a lower concentration (350 rather than 450). It does so so much that a scenario is developed to show how 350 ppm might be achieved (fig. 6). So, the preprint takes the risk quite seriously. We don’t know what it will be once it is a paper. Hansen has a habit of being right, but there may be some flaw in the analysis that a referee catches.

    To some extent, the argument has already been published in Pilosophical Transactions. There is more detail here though.

    Gavin (also #38),

    I think that we are working up to meeting targets. Some countries will meet Kyoto compliance, though if they do this through biofuels, this will be a mirage. So, there is some progress. Your point that all we need to know for sure right now is the direction (emissions cuts) makes some sense, but the manner in which we cut emissions might be influenced by the present work. Greater efficiency cuts emissions, but it does not leave energy to do sequestration while shifting energy sources might make a difference. Solar power is expected to be cheaper than coal in less than a decade, but biochar may never be as an energy source. Yet, we might start planning to absorb the opportunity cost and promote biochar production in order to make progress on sequstration even though it might slow emissions cuts a little. Right now, that would mean supporting research into biochar, its effectiveness in sequestration and its utility as an energy source.

    Comment by Chris Dudley — 8 Apr 2008 @ 1:40 PM

  46. #43 Pascal,

    Sorry, I had thought you were talking about the Cenozoic.

    I think Hansen is only fixing on CO2 because that is the major issue the paper addresses. There are statements throughout the paper about other mainly albedo based changes, and there’s reference to methane with regards the PETM (page25).

    #44 Daniel Goodwin
    The variation in climate sensitivity could in theory be higher or lower. From what I read (and I am only an amateur) orbital forcings are too slow to be a factor in sub-centennial processes. Orbital factors can initiate, but the insolation rate of change due to orbital factors would not drive the detailed processes at a centennial scale (Dansgaard Oeschger etc).

    As an aside:
    Hansen’s earlier paper “Climate change and trace gases” refers to the spring as a key factor in melt, page 8 under figure 3. http://pubs.giss.nasa.gov/abstracts/2007/Hansen_etal_2.html Then proceeds to outline the claim that ice-sheet melt is actually a rapid process.

    In Gerard Roe’s “In Defence of Milankovitch”, http://earthweb.ess.washington.edu/roe/Publications/MilanDefense_GRL.pdf he shows that the rate of change of global ice volume tracks beautifully with 65degN insolation.

    Hansen’s team have been building up a case that ice-sheet loss is in fact a relatively rapid process so is relevant to policy timescales. I think they have a strong point on this, but am still not convinced about this 6degC sensitivity. I’ll butt out and see what others have to say.

    Comment by CobblyWorlds — 8 Apr 2008 @ 2:40 PM

  47. Blair, I would guess that the last glacial maximum, LGM, some 19-30 kyr ago, was chosen instead of the Pliocene, 3 million years ago, because there is a lot more data on conditions during the LGM (no ice core measurements from the Pliocene, for example).

    The whole notion of the surface temperature response to 2X CO2 climate sensitivity as the main publicly discussed benchmark seems misleading, however. It was originally just a climate model benchmark, wasn’t it? Mostly for the convenience of modelers when comparing their different models.

    An equally important variable is the ocean temperature response to increased CO2, which has suffered from large uncertainties. According to Levitus et al (GRL 2004):

    We present new estimates of the variability of ocean heat content based on: a) additional data that extends the record to more recent years; b) additional historical data for earlier years. During 1955–1998 world ocean heat content (0–3000 m) increased 14.5*10^22 J corresponding to a mean temperature increase of 0.037C at a rate of 0.20 Wm2

    Compare this to a more dated estimate (Science 2000):

    We quantify the interannual-to-decadal variability of the heat content (mean temperature) of the world ocean from the surface through 3000-meter depth for the period 1948 to 1998. The heat content of the world ocean increased by ~2 × 10^23 joules between the mid-1950s and mid-1990s, representing a volume mean warming of 0.06°C.

    That is a large change in estimates. A number like 0.06C might seem tiny, but it represents far more energy storage in the oceans than a 0.6C increase in the surface temperature field. So, what’s the current best estimate of the ocean temperature sensitivity? What’s the best estimate of the amount of heat the oceans have absorbed?

    Based on the evidence in polar regions, where warming rates and ice melt rates have outstripped model predictions, (not much net albedo change yet, is there?), it seems that polewards heat transport by oceans (and atmosphere) might be accelerating the rate of response (not the equilibrium response, but the rate of approach to equilibrium).

    This from Levitus 2001:

    We compared the temporal variability of the heat content of the world ocean, of the global atmosphere, and of components of Earth’s cryosphere during the latter half of the 20th century. Each component has increased its heat content (the atmosphere and the ocean) or exhibited melting (the cryosphere). The estimated increase of observed global ocean heat content (over the depth range from 0 to 3000 meters) between the 1950s and 1990s is at least one order of magnitude larger than the increase in heat content of any other component.

    So, if that’s correct, the ocean is what we want to watch. If we had launched the Triana/DSCOVR climate satellite ten years ago, instead of mothballing it, we’d probably have robust answers to the energy budget question, and we could get the ocean heat change by calculating the (total energy change)-(atmospheric warming).

    Regarding the “monsters in the box”, what that points to is the “labile carbon store” which is currently in soils, sediments, and permafrost: the carbon in the freezer. Warm up the freezer, and all of a sudden microbes can start converting it all to CO2, H2S, etc. Stinky. Obviously the biosphere will play a huge role in that – but we shouldn’t expect the biosphere to absorb that excess carbon. It seems that during stable climate periods the biosphere operates mostly in steady state, pushing 100 gigatons of carbon through the system each year via photosynthesis and respiration, but in balance. That’s the big looming issue.

    Comment by Ike Solem — 8 Apr 2008 @ 4:26 PM

  48. RE #36 & “Our study found little *long term* impact, because the ice largely regrew each winter. That included albedo effects.”

    I’ve sort of always thought (reducing) albedo might not be much of a long term issue, esp once all the ice/snow is melted.

    However, it seems to me that ice forming in winter in the Arctic wouldn’t have a tremendous +albedo (cooling) effect either, since there’s not as much sun up there in the winter as in the summer. OTOH, I think that the sun’s energy gets used up a lot in the melting process of that ice each summer, rather than in warming the planet, so if there were no or little ice formation in the winter and not much to melt in the summer, that would have an impact (like a jump up in temp). Not a continual one, once equilibrium is reached.

    I’d think its the lesser or greater ice cover during those long summer days that would should the greater albedo effect.

    Comment by Lynn Vincentnathan — 8 Apr 2008 @ 4:53 PM

  49. Albedo is the one thing we will have great control over in the future, with the 10 billion people all wanting a modern and comfortable lifestyle. That’s going to take a lot of solar panels and other two dimensional surfaces, in fact, combining agriculture, land use and biodiversity preservation, one can make the assumption that it is going to take ALL of the available surfaces. Here is where material science and condensed matter physics again comes into play – these surfaces can be exceeding thin, and they can be engineered to either be reflective, transparent, transmissive or emissive, with an electronically controlled and very fast response times.

    Work that into your global models. We need a very large area for energy anyways, and if you add up the dead areas we have created already, there’s plenty of room here.

    Comment by Thomas Lee Elifritz — 8 Apr 2008 @ 5:01 PM

  50. Re #49 solar power would not take all that much space. A concentrated solar system in desert area 250km by 250km would supply all the Worlds current electricity demands.

    Comment by D Price — 8 Apr 2008 @ 5:54 PM

  51. Since Hansen’s latest estimate is bound to arouse controversy, I’ve posted a revised graphic precis of past sensitivity estimates- Levenson’s 2006 compilation did not include Arrhenius second thoughts, published a decade after he produced the Victorian estimate that set the roller coaster in motion:

    http://adamant.typepad.com/seitz/2008/04/target-of-fear.html

    Comment by Russell Seitz — 8 Apr 2008 @ 5:57 PM

  52. Re #36 where outeast wrote:

    “… William Connolley … modelled the impacts of the loss of Arctic sea ice … “Well, it would lower the albedo, though perhaps not by as much as you might expect due to clouds and sun angle. Our study found little *long term* impact, because the ice largely regrew each winter. That included albedo effects.”

    Hope that’s of interest.”

    It is interesting but not surprising. It sounds as though Connolley limited the SST to -1C and so a major positive feedback from the greenhouse effect of water vapour would have be suppressed. Moreover, as CEP Brooks explained, it is highly unlikely that the sea ice will reform in winter if there is no multi-year ice there to provide a surface where the air can be cooled well below the freezing point of sea water.

    Moreover, he was using an atmosphere only model, and even the full Ocean-Atmosphere model cannot replicate the melting Arctic ice. Vellinga and Wood (2002) had already tried to replicate the rapid warming at the end to the Younger Dryas with that model but its forcing was insufficient.

    The problem is that the modellers are using the wrong paradigm! See http://www.realclimate.org/index.php/archives/2008/04/target-co2/index.php?p=509#comment-84027

    I think I would rather take Hansen and Broeckers ideas than Connolley. Broecker believes that sea ice caused the Younger Dryas http://www.amnh.org/sciencebulletins/earth/f/glaciers.20050331/essays/59_1.php
    and Hansen believes that albedo is the main forcing. So although I am interested to hear of Connolley’s work I am far from convinced that loss of the Arctic sea ice will not lead to disaster :-(

    Comment by Alastair McDonald — 8 Apr 2008 @ 5:59 PM

  53. A concentrated solar system in desert area 250km by 250km would supply all the Worlds current electricity demands.

    Ok, fair enough. Now simulate what the local effects of such a large array would be when going to the reflective, the black to transparent state on nanosecond time scales.

    Such will be the state of condensed matter physics very shortly. If we can do that locally, we should be able to do it globally. Not only does that solve the power problem, but that also solves the thermostatic problems.

    Comment by Thomas Lee Elifritz — 8 Apr 2008 @ 7:04 PM

  54. Re #40: Thanks for the Toggweiler & Russell paper. I had not realized the importance of the increasing vertical temperature gradient on wind speeds. One would expect a different global wind (and ocean current) pattern than the current one driven by the polar-equator temperature difference. This could have important effects on some regional climates.

    However, I think increased ocean circulation would reduce CO2 levels by removing it from the atmosphere faster than it can be returned on the other end of the cycle. The deep ocean is presumably under saturated relative to the high atmospheric CO2 levels of today and the future, and would therefore absorb some of the CO2. So I still do not fully understand Hansen’s statement that I quoted.

    My main problems with the Hansen paper remain:

    1) I think he is extrapolating a high glacial era climate sensitivity into that for a warmer climate where it will be significantly less.

    2) He is using the conditions for ice sheet formation as the criteria for ice sheet melting, not taking the thermal inertia of the ice sheet into account.

    [Response: Regarding your second point, you are confusing thermal inertia with hysteresis. The thermal inertia of the ice sheets says that to deglaciate, the warming must persist for a sufficiently long time. As Gavin notes, it is uncertain how long "long" is, but it's probably a good bit more than a century. Hysteresis, on the other hand, would say that no matter how long you wait, the deglaciation happens at a lower CO2 threshold than the initiation, since the ice sheet creates conditions that tend to maintain itself. Rob DeConto's work shows there is some hysteresis in this problem, but not much, when Milankovic effects are taken into account. In fact, if the initiation happened during Milankovic conditions that are favorable to glaciation, while you increase CO2 at a time that's favorable for deglaciation, the deglaciation could well happen at a lower CO2 level than the initiation (though that's not a case Rob computed explicitly). --raypierre]

    Comment by Blair Dowden — 8 Apr 2008 @ 8:05 PM

  55. For anyone who’s more or less convinced by Hansen, please join us at 350.org. Our slightly insane goal is to make 350 the most well-known number on the planet in the next 18 months. We need artists and musicians and political organizers (on Saturday 350 bicyclists rode in circles in Salt Lake City). It’s not completely insane, either–our team organized 1400 rallies in all 50 states last April for domestic climate action. Now we’re just trying to do it for the, you know, whole planet

    For my money, Hansen’s paper is the most important development in the climate debate since the IPCC 1995 report. I think it’s going to turn out to be our last real shot at turning public opinion, and with it political action, away from incremental change and towards transformative action. Many thanks to realclimate for keeping us all apprised, and please join us at 350.org

    Comment by bill mckibben — 8 Apr 2008 @ 8:09 PM

  56. Re # 29 Jim Bullis: “…why would CO2 solubility decrease if surface water warmed slightly and deeper water warmed more?”

    Because CO2 solubility is inversely related to temperature (http://jcbmac.chem.brown.edu/myl/hen/carbondioxideHenry.html)

    Comment by Chuck Booth — 8 Apr 2008 @ 10:46 PM

  57. 53:
    If we are using solar power, then at least for the active wavelength of the device(s) we will have high absorption, i.e. panels will have very low albedo. The best way to mitigate this is to decrease overall energy demand, and increase the PV efficiency. Max efficiency today is around 40%. But current human energy needs are roughly 1 part in 10,000 of insolation, so even at 10% efficiency we are only increasing solar heat absorbed at the surface by .1%.

    But the larger point, that our species controls a substantial surface area of the planet, and perhaps if albedo management were made a priority, we could provide sufficient negative shortwave forcing by this means? For affecting the earths climate system, there is no need for short time scale albedo changes. Of course in a science fiction sense, coupling a weather model, with the ability to rapidly control the albedo of a significant part of the earths surface would allow some degree of control over the weather.

    Some other comments, for the experts to reply, as I’m not capable of properly evaluating:

    regarding paleoclimate icesheet decay rates: it can be argued that Northern ice sheets were highly vulnerable to collapse into the sea, i.e. a significant chunk of the Laurentide was grounded over Hudsons bay, and also major parts of the European over the North Sea? GIS does not seem to possess this sort of vulnerability to rapid collapse, although the WAIS might be vulnerable. Another thing I don’t hear discussed is how the albedo of a melting part of an ice sheet might evolve over time. If buried dust accumulates on the surface of the ice as it melts (this is common in Alpine glaciers, which are very much dirtier in general -and probably have larger dust particles) how low might the summertime albedo become?

    I was unconvinced by Connolley’s ice free arctic summer runs. I think he treated the ice/ocean as a fixed boundary condition for the GCM. I would think that the greatest energy anomaly would be the increased solar absorption, which is largely absorbed by the ocean. Some of this heat will be “liberated”, by the later freezeup in the fall. But probably more importantly the incremental heat would likely be transported deeper into the ocean. I suspect it would take decades for this change in oceanic circulation to have much of a global impact.

    Comment by Thomas — 8 Apr 2008 @ 10:51 PM

  58. Re #53: I’m not sure what you’re trying to get to with that question. An actual 250km x 250km solution wouldn’t work for myriad reasons, so trying to figure out what good or bad things would happen with it are pointless.

    Re #45: What sequestration points to is that we have to stop recycling anything that contains carbon and comes from renewable sources. We also need to come up with the Backyard Carbonizer, that can replace the trashcan and recycle bin as the disposal place of first resort. A small parabolic reflector pointed at the bottom of a large cast iron pot should reduce most carbon based rubbish to carbon in short order. Better yet, get those thermal depolymerization guys rolling out their plants faster.

    Comment by FurryCatherder — 8 Apr 2008 @ 11:59 PM

  59. Re #42, I believe it is in relation to where Antartica is today, ie the south pole. 600 million years ago, it did not exist officially and probably not 300.150 million years ago either. Plate tectonics and all that.

    Comment by pete best — 9 Apr 2008 @ 3:59 AM

  60. http://video.google.co.uk/videoplay?docid=9171659355384722877&q=james+hansen&total=186&start=0&num=10&so=0&type=search&plindex=1

    If we just use all of the conventional oil and gas reserves we will hit 450 ppmv of CO2 and risk a different planet. James Hansen.

    Comment by pete best — 9 Apr 2008 @ 4:36 AM

  61. RE #54: I think there is a major component of hysteresis just due to the thickness of the East Antarctic ice. Melting starts only when the temperature at the surface altitude of 3 km rises above 0 degC for some substantial time each year.

    I believe a balmy summer day there means presently about -15 degC. A 6 degC rise in global average might just about cause some surface melting at that altitude because of polar amplification. Maybe this is one of the tipping points.

    Return of the ice cover will start on the bare ground at a low altitude and will then require lower global average temp conditions.

    Greenland and Western Antarctica are likely to melt first precisely because of their low altitude surfaces.

    Comment by Pekka Kostamo — 9 Apr 2008 @ 5:56 AM

  62. Russell Seitz posts:

    [[Since Hansen’s latest estimate is bound to arouse controversy, I’ve posted a revised graphic precis of past sensitivity estimates- Levenson’s 2006 compilation did not include Arrhenius second thoughts, published a decade after he produced the Victorian estimate that set the roller coaster in motion:]]

    I note that you have Hansen’s estimate as the final one. Did you miss the repeated notice that that was a long-term sensitivity and not a short-term sensitivity? Apples and oranges, buddy.

    Comment by Barton Paul Levenson — 9 Apr 2008 @ 6:37 AM

  63. After reading the paper, I note it is interesting that the only CO2 proxies around the 34 million year ago Antarctic glaciation period are in fact …

    … 1500 ppm (not 450 ppm) ???

    The only references within 10 million years of the period are from Pagani et al 2005 (1,500 ppm +/- 500 ppm) and Retallic 2001 (1,000 ppm +/- 500ppm).

    Comment by Lowell — 9 Apr 2008 @ 8:01 AM

  64. Possibly of relevance to this discussion:

    Stanford Report, April 2, 2008
    Phytoplankton species deviates from norm: No CO2 absorbed in photosynthesis-
    Findings could affect scientists’ understanding of amount of carbon dioxide phytoplankton pull from atmosphere

    A widespread species of ocean-dwelling microorganisms has been found to employ a never-before-seen alternative method of photosynthesis…The discovery has implications not only for scientists’ basic understanding of photosynthesis—arguably the most important biological process on Earth—but also for the amount of carbon dioxide that phytoplankton pull from the atmosphere….
    “There is a new twist on photosynthesis here, and that has to be accounted for when it comes to CO2 modeling,” Bailey said, adding that, in some cases, the models may overestimate the amount of carbon fixation that occurs in nutrient-poor waters.
    It is not yet clear what the finding might mean to studies of long-term global warming, he said, but it will have to be incorporated into any models that include carbon fixing by phytoplankton as a factor…
    http://news-service.stanford.edu/news/2008/april2/plant-040208.html

    Comment by Chuck Booth — 9 Apr 2008 @ 8:49 AM

  65. Isn’t the question of a “target CO2″ level moot, given that anthropogenic CO2 emissions are not only increasing every year, but accelerating, and all indications are that global fossil fuel use and associated emissions will continue to increase for years or decades before they peak and begin to decline?

    The “target” that really matters is the year in which global CO2 emissions will be less than the previous year and will thereafter rapidly decline to near zero. It seems implausible that humanity will achieve that “target” in time to prevent catastrophic warming and climate change.

    Comment by SecularAnimist — 9 Apr 2008 @ 9:07 AM

  66. Re #53 when I say 250km by 250km that’s just the total area. They do not all have to be in the same piece of desert. They can be scattered in smaller units if need be.

    Comment by D Price — 9 Apr 2008 @ 10:30 AM

  67. Re #47 Ike. According to James Annan the number for ocean heat content rise in the Levitus Science 2000 paper was an arithmetic error, see end of http://julesandjames.blogspot.com/2008/04/frogs-and-blogs.html

    Otherwise I agree that ocean warming is a key issue, but its now problematic in that Argo is not showing any warming since 2004 while the combination of Jason and Grace finds the warming to be continuing at the same rate as earlier. The latest presentation on this issue is here http://ibis.grdl.noaa.gov/~leuliett/presentations/osm_2008.pdf

    Comment by Erik Hammerstad — 9 Apr 2008 @ 10:33 AM

  68. It seems implausible that humanity will achieve that “target” in time to prevent catastrophic warming and climate change.

    In 1908 it seemed implausible that one could step onto a modern jetliner and fly anywhere in the world, or that man could walk on the moon. There was this one guy, Konstantin Tsiolkovsky who thought it might be possible.

    The fact that now people understand that not only do we need to reduce carbon output to zero, but we have to remediate the atmosphere back to a previous CO2 level, is the first step. If we can do that, 300 or 320 ppm is just as reasonable, indeed, most people studying the problem understand that 350 is probably the upper limit. Hansen et al. have merely quantified it to the best of their abilities, and within the state of the art of science.

    You’re on a spaceship, carbon dioxide is increasing, you know you have a problem, yet you continue to breathe. Breathing is necessary to solve that problem that you know exists, and you know you do have to solve it.

    There is of course a time limit with this problem.

    Anyone that now claims there isn’t a problem to be solved have been adequately warned, and the minimum bar is set.

    Good luck! On this post I linked to my blog. I don’t come in here much, only when something of significance happens or is published. Hansen again has risen to the challenge.

    Comment by Thomas Lee Elifritz — 9 Apr 2008 @ 10:49 AM

  69. We’re doomed. Move inland ;)

    Comment by GeologyJoe — 9 Apr 2008 @ 10:59 AM

  70. > moot
    Nope. Else we’d be living with whatever level of pollution industry gave us at their high points.

    You never know what is enough until you know what is more than enough.

    Comment by Hank Roberts — 9 Apr 2008 @ 11:21 AM

  71. Re Raypierre’s response to #54: Thank you for clarifying the difference between thermal inertia and hysteresis. Orbital forcings are obviously critical to the formation of the Laurentian Ice Sheet, but on the timescale of the ice sheets of Antarctica and Greenland, would they not just be noise in the average temperature signal?

    I am trying to get a feel for how much hysteresis there is in the Antarctic ice sheet. Three million years ago CO2 was at 400ppm, temperatures were 2 or 3 degrees higher and sea level was about 30 meters higher. Since CO2 is now almost 400ppm, does it follow that if it stays at that level we will get 30 meters, or is it more like 15, 20 or 25?

    Comment by Blair Dowden — 9 Apr 2008 @ 12:04 PM

  72. What I get from this latest paper on estimating a climate sensititivity factor is that it’s a moving target.It reinforces the fact that there are many un-certainties involved. Feedback parameters are complex in their relationships.

    Increasing surface temperature increases evaporation and adds to atmospheric H2O which is a greenhouse gas that adds to temperature rise, but this can also increase cloud cover which increases albedo which has a cooling effect and leads to temperature decrease. Go figure! It’s a problem, and must add to the headaches already confronting climate modelers.

    Comment by Lawrence Brown — 9 Apr 2008 @ 2:09 PM

  73. #54 Blair Dowden,

    I agree that at first glance it might seem that increased overturning should increase CO2 uptake because of high current CO2 levels, but the deeps actually have high concentrations of CO2.

    Have you read David Archer’s post on reduced ocean uptake? http://www.realclimate.org/index.php/archives/2007/11/is-the-ocean-carbon-sink-sinking/
    specifically 5th para down.

    It would have been better for me to have linked to it earlier, but I got distracted and forgot. Sorry.

    Comment by CobblyWorlds — 9 Apr 2008 @ 2:35 PM

  74. One thing a poster mentioned is the location of Antarctica. While all the other continents have shifted position over millions of years Antartica doesn’t seem to have moved at all from the South Pole. Is there a reason for this?

    Comment by D Price — 9 Apr 2008 @ 5:07 PM

  75. Re #73: CobblyWorlds, thanks, I read that article but I guess it did not sink in (pardon the pun). The idea is that the deep ocean has excess carbon dioxide because of decaying organic matter. The present ocean circulation is not sufficient to recycle it back to the atmosphere quickly enough. But I have just learned that wind speeds, and presumably ocean circulation, are higher with warmer temperatures. Therefore CO2 must have been building up in the deep ocean for millions of years. If that rate is not very slow there must be a large imbalance.

    As is often the case, I get a piece of information, but not the whole picture. I hope someone can make sense of it for me.

    Comment by Blair Dowden — 9 Apr 2008 @ 8:25 PM

  76. Here is my picture of the global wind – ocean current system. There are two main sources of atmospheric circulation. The horizontal gradient (temperature difference between equator and poles) decreases with increasing global temperature, while the vertical gradient increases. It is not clear which one is stronger. Ocean circulation depends on wind strength, although maybe the vertical gradient is more effective. Ocean circulation appears to have been weaker at the last glacial maximum. This would suggest that increasing greenhouse gases will increase ocean circulation. But in the Cretaceous, when CO2 levels were very high, the ocean circulation was so weak that the ocean became stratified, and led to ocean anoxic events where the lower levels had no oxygen. There is a piece of the puzzle missing here.

    Comment by Blair Dowden — 9 Apr 2008 @ 9:44 PM

  77. > deep ocean
    Blair, I’d be real curious to know the sources for any actual observations — since there are a fair number of photographs of whale skeletons on the deep ocean floor, that suggests there’s not enough CO2 dissolved there to make the pH effective at dissolving bone, so I’d wonder where measurements were taken.

    There are a few, for example this fascinating observation:

    http://www.pnas.org/cgi/content/full/103/38/13903
    Lakes of liquid CO2 in the deep sea

    (footnotes there all worth following)
    But that’s associated with a hydrothermal system, not decaying material.

    Comment by Hank Roberts — 9 Apr 2008 @ 10:09 PM

  78. Is not often that Dr Gavin Schmidt is wrong about something with respect to climate. But I just learned that he failed on his prediction that world wide warmer temperatures will come back at year end.
    They will not, It came back full force in March just past with a staggering +1.4 C anomaly for the Northern Hemisphere. http://data.giss.nasa.gov/gistemp/ . My respect for Gavin as a tireless advocate of good climate is however not lowered at all, he taught many of us about sensitivity, and so we shall remember that temperatures are not so hard to predict , with sensitivity in mind there can be variances….

    Comment by wayne davidson — 10 Apr 2008 @ 12:29 AM

  79. Re: #73: D Price Says: “One thing a poster mentioned is the location of Antarctica. While all the other continents have shifted position over millions of years Antartica doesn’t seem to have moved at all from the South Pole. Is there a reason for this?”

    I think you are referring to what John Lang wrote in #42: “Antarctica is an unusual case in plate techtonics since continental drift has placed Antarctica around the south pole for most of the past 600 million years including various times when it was locked together with other continental plates.”

    Unless I am missing something, I thought much of what became Antarctica was equatorial from the Neoproterozoic Era until sometime after Gondwana drifted southward (late Ordovician). It wasn’t until the Mesozoic that Antarctica made its way down to the south pole (about 140my).

    Comment by Jim Eaton — 10 Apr 2008 @ 1:53 AM

  80. Re #74 where D Price ask why Antarctica has not moved.

    I have never seen a a reason given, but then I have not seen that question asked before.

    My own idea is that it is due to centrifugal/centripetal forces. Because Antarctica is centred on the South Pole the centripetal forces cancel each other out. India, on the other hand, moved away from the region of the Southern Ocean and was accelerated as it approached the equator. That acquired momentum has resulted in it crashing into Asia and building the Himalayas.

    Cheers, Alastair.

    Comment by Alastair McDonald — 10 Apr 2008 @ 4:02 AM

  81. Re D Price

    The thought is essentially incorrect. However, it hasn’t moved much compared with how far the other continents have moved since ~90 Mya though. See the powerpoint animation on the linked page.

    It seems to me (possibly wrongly, since tectonics isn’t my bag) that the movement of the other continents has constrained Antarctica’s movement over that last period.

    Comment by P. Lewis — 10 Apr 2008 @ 4:32 AM

  82. raypierre

    you say:

    “[Response: We should also recall the implications of Dave Archer’s “long tail” of anthropogenic CO2. Something like 20% of the anthropogenic CO2 will stick around for much more than 1000 years. That tells us something about how much peak CO2 we can tolerate without committing the planet to extreme consequence of the very long term warming. For example, if we reached a peak CO2 of 1200 ppm, then the long term tail contains about 280 + (1200-280)/5 or 464 ppm CO2. That would mean that even if the deglaciation took a very long time to set in, the CO2 would indeed stay above the threshold level for a long time. This is only a crude illustrative calculation, and to do it right would take a proper ocean carbon cycle model, but I hope it gives the idea of what Hansen’s calculation implies even if the catastrophic changes require a very long time to act. –raypierre]”

    this is logical.

    But Hansen’s calculation gives us a CO2 target at 350ppm.

    If I use your equation, I find a short term target at 630 ppm to get a 350 ppm tail.

    If I use 450ppm now, we get without problem, a 314 ppm tail.

    So why 350 ppm now or in few decades?
    Because 314 ppm is a dangerous concentration?

    I understand that the phenomenons are non-linear, but we know that a long time ago.

    So what is the deep interest of this new Hansen’s article?

    Comment by Pascal — 10 Apr 2008 @ 5:26 AM

  83. hum

    following my precedent post.

    314ppm implies 5.3 ln(314/280) = 0.607W/m2 forcing.

    even with 1.5°C.m2/W temperature increase is, “only”, 0.9°C since preindustrial age, close to today increase.

    It’s very surprising that such a minor temperature anomaly is so dangerous.

    Comment by Pascal — 10 Apr 2008 @ 6:46 AM

  84. Blair, The deep oceans are quite isolated from the surface. The water is colder, saltier and denser. CO2 dissolves more readily under pressure and at low temperature, and this further increases density and stratification. In the very deep ocean, CO2, CH4 and H2O condens out and form clathrates. I’ve had friends on submarines, and they confirm that even in a hurricane, things are very quiet in deep water. You hear about damage to drilling platforms and pipes, etc. What people forget is that that is all pretty shallow. The ocean is another world.

    Comment by Ray Ladbury — 10 Apr 2008 @ 8:52 AM

  85. The value of climate sensitivity should inform important economic and political decisions. As a decision tool, Hansen’s more conservative value may be a more prudent and wiser value to use than a lower value, which might be more consistent with the body of atmospheric science.

    The value we select will affect how we deal with climate warming. A larger number says that, “Now, we must act more aggressively!” A smaller number says,”We can procrastinate and survive.”

    If we pick a larger number, and act now, later we can say, “Oh, the actual climate sensitive number is a littler smaller.” If we pick a smaller number, and thereby fail to act in time, there will be no later. Hansen’s larger value is more prudent.

    The kind of Arctic Sea Ice retreat that we have had over the last 3 years, was predicted by the IPCC models not to occur for another 40 years. If the IPCC says 40, and the correct answer is 4 years, then we cannot do engineering based directly on the IPCC predictions and projections. We must incorporate safety factors of 100 or 1,000, or even a 100,000 where large populations are at risk. Even Hansen’s number may not include a sufficient safety margin for direct use as an engineering basis of design where large numbers of people are at risk.

    Our climate sensitivity number is not merely a matter of what can be defended in a publication; it is a matter of what the wise policy is.

    Comment by Aaron Lewis — 10 Apr 2008 @ 9:22 AM

  86. It is interesting to note that Dr Hansens new work suggesting an increased climate sensivivity of limiting GHG emissions to no higher than 450 CO2e which corresponds to a average temperature increase of less than 2C (high probability) means that he is taking the stance (politically) that we can use all of the conventional oil and gas but must leave the coal in the ground.

    Coal is not being left in the ground just as unconventional oil sources arn’t either. Oil is currently fetching $110 a barrel on the open world market and that is making people want to produce more of it inline with global economic growth of between 2% and 3% per annum. CTL is coming online this year outside of south africa, China, Indiam, USA etc all have projects of this nature and come 2020 a billion barrels a year could be coming from this source. The Athabasca tar sands are also going to end up supply around 1.5 to 2 billion barrels a day come 2020. As conventional oil surges in price due to the effects of peak so do alternative oil sources come online from fossil fuel sources. This is why we must have a biofuel solution that takes oil away in order to have any chance of not reaching 450 CO2e in record time.

    New coal fired power plants are coming online to without CCS at the present time, retrofitted by 2020, lets hope so but it is a tall order.

    James Hansen just seems to of reduced our chances of limiting sea rise and atmospheric warming somewhat.

    Comment by pete best — 10 Apr 2008 @ 10:08 AM

  87. I have a question:

    How confident are we that the the Co2-temperature lag is ~800 years?

    My understanding is that it is difficult to estimate the ice age-gas age difference in ice core records. I have found a recent article that is suggesting that the 800 years lag is maybe overestimated.

    http://www.clim-past.net/3/527/2007/cp-3-527-2007.pdf

    I think it is an important question because this lag is the main evidence supporting the GHG amplification theory, am I right?

    Can you point me to pertinent peer-reviewed literature?

    Comment by Khebab — 10 Apr 2008 @ 10:18 AM

  88. The 6 C rise is no more than a guess. It has authenticity since this is the figure that Arrhenius arrived at in his calculations. However, Arrhenius also calculated that the rise in CO2 we have experienced since around 1900 when he published the paper should have produced 2 degrees of warming and it just hasn’t. What is not pointed out is that Arrhenius withdrew his predictions when the nature of infrared absorption became better understood and he realised that his projections were far too big.

    Comment by Wotan — 10 Apr 2008 @ 11:29 AM

  89. Americans today (being the worlds primary energy consumers) are an example of the kinds of organisms that evolve in a degraded energy system. Evolution being only the transformation of matter-energy from an available into an unavailable state. As matter-energy becomes depleted or degraded recessive genetic characteristics grow more frequent.

    Comment by John Smith — 10 Apr 2008 @ 11:38 AM

  90. Since you’re talking about CO2 sensitivity, maybe this concept of mine works better on this thread. It does involve “tactical” issues not just the science: One thing to pin skeptics on, considering their rejection of the clearness of “global warming”: Ask, “OK, so you’re not sure that global warming is definitely occurring, or that if it is, not sure it is mostly man-made. But do you at least accept the action and presence of “greenhouse gases?” Water vapor is one GHG [some skeptics like to talk of how the effects of water vapor swamp those of CO2], do you also accept that CO2 is also a “greenhouse gas?” And if so, shouldn’t we at least concerned about a long-term rise in its concentration, even if we can’t agree on just what the outcome has been and will be?” That would take away a lot of steam from their evasions, and force some acknowledgment of the causal stresses in any case.

    BTW, with possible solar cooling etc. we really should IMHO take a closer look at the interaction of all stimuli and not focus narrowly on the CO2 issue.

    tyrannogenius

    Comment by Neil B. — 10 Apr 2008 @ 12:06 PM

  91. Re: #54 (specifically Ray Pierrehumbert’s comment on that post)

    Ray says:
    “Hysteresis, on the other hand, would say that no matter how long you wait, the deglaciation happens at a lower CO2 threshold than the initiation, since the ice sheet creates conditions that tend to maintain itself.”

    Should that not be:
    “Hysteresis, on the other hand, would say that no matter how long you wait, the deglaciation happens at a HIGHER CO2 threshold than the initiation, since the ice sheet creates conditions that tend to maintain itself.”
    (caps only to show the suggested change)

    It sounded like Ray was trying to present a general case in the preceding to explain hysteresis, before going on to outline a particular possibility where the hysteresis effect would disappear, and you could get a scenario that appears to be contrary to hysteresis:

    “In fact, if the initiation happened during Milankovic conditions that are favorable to glaciation, while you increase CO2 at a time that’s favorable for deglaciation, the deglaciation could well happen at a lower CO2 level than the initiation”

    I think I understand this later point by Ray. So to toss out numbers (made up by me, for illustrative purposes only) to see if I understand:

    Perhaps in one set of conditions, the glaciation trip point is 350ppm CO2 and the deglaciation trip point is 375ppm. CO2 drops below 350ppm and glaciation occurs. And perhaps CO2 continuess to drop, say to 275ppm. Then a long time after glaciation occurs, other things change (for example: orbit, precession, etc.) and the new glaciation trip point is down to 300ppm, and the deglaciation trip point is 325ppm. So even though there is still hysteresis in the new trip points, any apparent hysteresis with respect to the original glaciation event has effectively disappeared, and you could get deglaciation with CO2 only rising back to 325ppm, even though the original glaciation occured at the higher level of 350ppm.

    Am I following OK?

    -Kevin

    Comment by Kevin Underhill — 10 Apr 2008 @ 2:40 PM

  92. #76 Blair Dowden,
    “As is often the case, I get a piece of information, but not the whole picture. I hope someone can make sense of it for me.”

    Same here.
    Understanding “reality” is like chasing the horizon. However far you go, you’ve always got further.

    To add to what Ray said, check out Ekman Transport: http://oceanmotion.org/html/background/ocean-in-motion.htm and note in particular:

    “At a depth of about 100 to 150 m (330 to 500 ft), the Ekman spiral has gone through less than half a turn. Yet water moves so slowly (about 4% of the surface current) in a direction opposite that of the wind that this depth is considered to be the lower limit of the wind’s influence on ocean movement.”

    Then try to imagine that in the context of figure 1 of Toggweiler & Russell.

    #78 Wayne Davidson,
    La Nina’s can be very hard to predict, check out the spread on this current model ensemble forecast: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/figure5.gif

    This year will be a cool one globally: http://news.bbc.co.uk/1/hi/sci/tech/7329799.stm

    My favourite from Dr Schmidt was his “further education in radiation physics.”
    http://www.realclimate.org/index.php?p=58
    IMHO the result is a very informative and thought provoking discussion.

    Comment by CobblyWorlds — 10 Apr 2008 @ 3:23 PM

  93. Cobbly, ENSO being difficult? I guess so, in some ways…. But I am a bit
    perplexed by why there are no Density Weighted Temperature charts out there, anywhere? DWT’s would be the equivalent of a sun disk measurement, a snapshot of the temperature of the entire atmosphere, much less variable than surface temperatures, extremely useful for trend making. As far as 2008 being cold,
    I don’t think so, not anymore.

    Comment by Wayne Davidson — 11 Apr 2008 @ 1:16 AM

  94. Just a comment for those who can’t understand why CO2 levels at several hundred parts per million can be significant.

    This week, Hawaii Volcanos National Park was shut down because sulfur dioxide levels reached 9.1 parts per million in the atmosphere. That’s well above the 2 parts per million that triggers a declaration of Hawaii County’s highest alert level, a Code Purple.

    Some compounds can have major effects, even at seemingly low percentages.

    Comment by Jim Eaton — 11 Apr 2008 @ 1:35 AM

  95. http://blogs.reuters.com/environment/2008/04/11/coaly-smoke-green-ire-over-huge-india-coal-plant/

    4GW coal fired power plant to be built in India using super critical coal technology for cleaner burning. No CCS in sight. It will produce upto 23 million tonnes of CO2 per annum and is partly sponsored by the IMF/WB.

    With a shelf life of 60 years we are are sure looking like we are tackling climate change don’t we.

    Comment by pete best — 11 Apr 2008 @ 9:32 AM

  96. Before I finish reading this excellent piece, can I propose a second, economic, based sensitivity.

    If we had a trend for storm damage from global warming, as a percentage of all storm damage, then we have a liability reserve account for mitigation. The sensitivity of CO2, therefore, becomes whether the mitigation payments made to “green” individuals is sufficient to induce enough individuals into green mode, and what level of storm damage will we accept over the long term..

    In other words, does co2 liabilities equal mitigation costs.

    Comment by Matt — 11 Apr 2008 @ 10:58 AM

  97. Could you do a post on the subject suggested by your sentence “Secondly, it subsumes the very special nature of orbital forcing – extreme regional and seasonal impacts but very little impact on the global mean radiation.”?

    Comment by Earl Killian — 11 Apr 2008 @ 11:38 AM

  98. On 10th April 208, Khebab wrote:

    “this [icecore T-CO2] lag is s the main evidence supporting the GHG amplification theory, am I right? ”

    i do not think this is the case, that the lag is the main evidence supporting GHG amplification. the physics is fairly well understood, that the main mechanisms for removal of volcanic CO2 are photosynthetic fixing, weathering of rocks and CaCO3 formation by oceanic life. These are suppressed during glaciation, resulting in accumulation of CO2 in the atmosphere.

    but i could be wrong, ifso i await correction.

    sidd

    Comment by sidd — 11 Apr 2008 @ 1:00 PM

  99. #93 Hello Wayne,

    With regards this years global average temperature, my opinion would still be swayed most by the behaviour of this La Nina, and as the model spread shows, that’s likely to persist, but how intense seems to be unsure. I am aware of the trends in the Northern Hemisphere last year it’s warming was still on an upward exponential, despite a slight cooling on a global basis. See the three latitude plot from GISS: http://data.giss.nasa.gov/gistemp/graphs/Fig.B.lrg.gif

    So whilst I still think that the proposition that we’re going to have a slightly cooler year this year than last is reasonable. I think this year is likely to be greater than or (almost) equal to 1 degree anomaly for GISS 23.6-90degN.

    DWT data – I’d have to think about it, but not now, my learning curve looks something like the GISS northern hemisphere anomaly on the link above. ;)

    Whichever way the Arctic goes this year it’ll be fascinating, but I still wouldn’t bet against Orheim’s previous statement.

    PS Ben Saunders has been stymied by kit failure in his bid for the North Pole speed record: http://north.bensaunders.com/journal/entry/the-fortress-02-04-2008-18-38-00/
    “The ridge was monstrous: nowhere was it less than two stories high, it stretched as far as either horizon…
    …as I turned to face north, I was greeted with a troubling sight: another giant ridge, then beyond that an endless view of rubble ice so smashed up that it made anything I saw at the start of this expedition seem like child’s play…
    An interesting thought occurred as I scrambled on. It’s quite possible that no one else has seen multi-year sea ice (ice that’s thick enough to survive the summer) in this state before… The consensus among the experts at Eureka was that the ice on the Canadian side this year was more fractured than they’d ever seen before.”

    Comment by CobblyWorlds — 11 Apr 2008 @ 1:14 PM

  100. Re Matt @ 96: “If we had a trend for storm damage from global warming, as a percentage of all storm damage, then we have a liability reserve account for mitigation….
    In other words, does co2 liabilities equal mitigation costs.”

    Why limit the account to storm damage? Why not account for loss of agricultural output due to heat and water stress and salinization? Or the collapse of fisheries? Or the displacement of populations due to flooding of low-lying coastal regions and spreading desertification?

    Storm damage is only one dimension of the future impact of climate change.

    Comment by Jim Eager — 11 Apr 2008 @ 3:02 PM

  101. To my mind good theory creates more good theories. It seams that our predictions of future climate changes more or less becomes truth. This is why it is of great importance that we start to understand the Universal Law of Attraction and start saying the good things that we want to happen to our planet.

    The We Project is a good start. They state: We can solve the climate crisis. Telling what we want make all the difference.

    Comment by Søren Kjær Vestergaard — 12 Apr 2008 @ 6:49 AM

  102. Ferdinand Engelbeen:

    CO2 trends follow the d18O (temperature proxy) trend in the LGM-Holocene transition, with no measurable feedback from increasing CO2 levels

    If it was the other way around, i.e. temperature lagged CO2 by several hundred years, that would actually be very strong evidence that sensitivity to CO2 was low (because the temperature delay should be less than 100 years). However, as the record stands, you cannot rule out CO2 causing warming because warming always occurs when the CO2 rises (with perhaps some short term variation).

    Comment by Chris O\'Neill — 12 Apr 2008 @ 3:25 PM

  103. Khebab (87) — Already by 1862 CE Tyndall wrote regarding the amplification effect of global warming (so-called greenhouse) gases. The history is in “The Discovery of Global Warming”, linked here:

    http://www.aip.org/history/climate/index.html

    Comment by David B. Benson — 12 Apr 2008 @ 5:08 PM

  104. Re #94, Jim, a simple household experiment can be carried out to show the significance (in terms of numbers only) of the levels of Carbon dioxide in the atmosphere that we are dealing with.

    Get 10 litres of water, then add 27 grams of Potassium permanganate. In terms of parts per million, this will give a solution that is of about the same number of parts per million as CO2 in the 1960′s. Then add 1 gram for each 10 year period up to the present. Quite rough, it is actually a little more than 1 gram per 10 years equivalent, however it does show that what we are dealing with is certainly not insignificant.

    Comment by Lawrence McLean — 13 Apr 2008 @ 1:56 AM

  105. RE 91. I still think the main factor in hysteresis is the altitude change.

    The Antarktis is not commonly perceived as a high plateau. This is due to the map makers’ unfortunate break-down of logic in the area. Instead of the dark brown hues justified by the surface altitude readings, all maps show this continent as white, same as any sea level ice fields.

    To destabilize the Eastern Antarktis, extensive surface melt must start. This is critical as it changes the thermal processes radically. The surface albedo goes down and more solar energy is captured. Another very important fact is that the excess energy is stored in the meltwater as latent heat. Through cracks in ice, some water percolates inside the glacier. In the early phases of the process, the water re-freezes liberating the latent heat and the glacier internal temperature increases. Uneven temperature fields result in uneven thermal expansion and further breakage.

    When the interior temperature has warmed to 0 degC, water remains in liquid form, eventually lubricating the glacier base. It also lubricates the interfaces between ice blocks. Wet ice against wet ice is very slippery indeed. A two mile high pile of wetted ice blocks is definitely unstable. Surface melting occurs now up to 1,5 km above sea level, which is a major concern for Greenland and the Western Antarktis.

    Surface melting in Eastern Antarktis obviously starts when temperatures rise above 0 degrees at the altitude of 10 000 ft (3 km) above sea level. Assuming the average lower atmosphere lapse rate of 6,5 degC/km, this roughly means +20 degC temperatures at sea level. When the Antarctic ice is gone, re-glaciation must start at a substantially lower altitude. The sea level temperatures must then be much lower, based on the lapse rate cited.

    How this translates into CO2 ppms, I am not able to say, considering all the short-term and long-term feedbacks. My quite un-educated initial guess is that the hysteresis might be as large as 100 ppm.

    Antarktis is a huge area with a climate of its own, and may have some quite special features. For instance, does it have a troposphere? Tropopause altitude on the Equator ranges from 12 to 15 km, on high latitudes just between 3 to 7 km. At 3 km altitude (ASL) and near the pole there is at least at times just a boundary layer interfacing directly with the stratosphere. No evaporation, no convection, no fronts, just some jet streams experienced as surface winds. Externally forced intrusions of humid air masses provide occasional snowfalls.

    The Eastern Antarktis will be stable for a long time ahead – which can not be said of Greenland and West Antarktis where the destabilization processes are underway already.

    Comment by Pekka Kostamo — 13 Apr 2008 @ 2:28 AM

  106. Pekka, I think there are a few misconceptions in what you wrote.
    1) under pressure (inside the glacier) ice melts already at a lower temp than 0C.
    2) also the EAIS will start melting at the edges, not
    the top. But the whole ice sheet is like a plastic blob
    of putty, slowly deforming under pressure. Snow gets
    added at the top, gets compacted on the way down, and
    then gets squeezed out sideways towards the coasts.
    This in spite of ice being a solid. As a result, the
    annual layers in the ice get paperthin towards the
    bottom.
    Ice cores are always drilled from the summit, where there
    is no sideways movement even at depth, and you retrieve the
    longest history down to the bedrock.
    In this picture of a slowly deforming pancake, the flow
    is stationary. As much ice leaves at the edges into sea,
    as is added at the top by precipitation. But if you
    remove ice (shelf or coastal glaciers) from the
    edges (processes you sketched), pressure equilibrium is
    disturbed and deformation (ice flow) speeds up also further inland.
    These phenomena are poorly understood currently.
    3) about hysteresis, I believe that on a time scale
    long enough to accomodate isostatic re-adjustment,
    there will be no hysteresis for ordinary glaciations/deglaciations.
    It is different for the “snowball Earth” episodes,
    where the ice reaches 45 deg latitude resulting in a
    runaway glaciation. And later, a runaway deglaciation. Hysteresis
    and runaway feedback go together: they mean that there
    are two stable ice geometries for the same
    CO2 forcing.

    Comment by Pinguiinimies — 13 Apr 2008 @ 5:13 AM

  107. How well does science understand non linear systems, or how well do climate scientists understand non linear systems. The climate systems is a complex one we are told consisting of many interacting elements, outputs of some inputs to others, the systems making up the climate or earth system are coupled and hence complex. But how much of this is linear and how much no linear and if non linear how long before we see dare I say it, strong behaviour away from the norm?

    I learned that in a complex dynamical system have several inputs to a system (simple predator and prey scenarios seem to work) whereby when the input is within a certain range all is well, predator and prey are nicely balanced. However perturb one or more of the inputs and the system can start deviate from the norm in terms of its behaviour. Large scale change is observed when prey die out (virus or too many predators) or vice versa. Birth range of animals change etc and fall out of balance whihc causes some very interesting dynamics to occur. Normally the systems find its way to chaos under certain paramater conditions.

    So is climate modelled this way? Is James Hansen non linear fears for albedo feedback and others leading us to more unpredictable patterns of weather the same as Lovelocks GAIA in which the balance is being perturbed. The Sunshine parameter remains the same, but GHG and land use changes have changed, so have dimming particles for that matters. Is it too difficult to model? Does we need to rely on rea world data more then what the models show us.

    Are these nonlinearities understoodm is 6C from 3C something than scientists missed until now because we are too focused on the linear in science?

    Comment by pete best — 13 Apr 2008 @ 8:39 AM

  108. Re 56 re 29

    Chuck Booth, Thanks for the solubility data.

    Sorry for not making a better question. I was meaning to get at something about temperature and depth effects in combination.

    If you think about my premise that the ocean surface will warm only slightly but the heat energy will be shifted to ever greater ocean depths, then the needed information would be a function of pressure as well as temperature.

    The importance of solubility at the ocean surface as a function of temperature still exists, but the impact would be much moderated if that temperature increase was only slight.

    Comment by Jim Bullis — 14 Apr 2008 @ 12:48 PM

  109. Jim (94), interesting comparison, but it’s kinda apples v oranges; concentration significance ala physiology and human health has no bearing or relation to concentration significance ala radiation absorption.

    Comment by Rod B — 14 Apr 2008 @ 3:29 PM

  110. Re # 108 Jim Bullis

    Jim,
    If I understand your point correctly (CO2 solubility at depth will be a function of both temperature and pressure), the following may have the information you are wondering about:

    Zeebe, R. E., and D. A. Wolf-Gladrow, Carbon dioxide, dissolved (ocean). Encyclopedia of Paleoclimatology and Ancient Environments, Ed. V. Gornitz, Kluwer Academic Publishers, Earth Science Series, in press 2008.
    http://www.soest.hawaii.edu/oceanography/faculty/zeebe_files/Publications/ZeebeWolfEnclp07.pdf
    (Dr. Richard E. Zeebe, Department of Oceanography, University of Hawaii School of Ocean and Earth Science Technology; http://www.soest.hawaii.edu/oceanography/faculty/zeebe.html)

    See also:
    Science 16 July 2004:
    Vol. 305. no. 5682, pp. 362 – 366

    Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans

    Richard A. Feely, Christopher L. Sabine, Kitack Lee, Will Berelson, Joanie Kleypas, Victoria J. Fabry, Frank J. Millero
    http://www.sciencemag.org/cgi/content/abstract/305/5682/362

    Science 10 January 2003:
    Vol. 299. no. 5604, pp. 235 – 239

    Anthropogenic CO2 Uptake by the Ocean Based on the Global Chlorofluorocarbon Data Set

    Ben I. McNeil, Richard J. Matear, Robert M. Key, John L. Bullister, Jorge L. Sarmiento1

    http://www.sciencemag.org/cgi/content/abstract/299/5604/235

    Comment by Chuck Booth — 14 Apr 2008 @ 9:26 PM

  111. Re #109 Rod B: You’re right, but yet… the general argument that small numbers of molecules can have a big effect, stands. Whether the interaction is with photons or with other molecules, is more like a technical detail.

    Another spectacular example is uranium 235, only occurring at 0.7% in natural uranium. Still thermal neutrons can maintain a chain reaction in it due to its huge fission cross-section.

    The permanganate example in #104 is also a good one (although I think the amount should be 2.7 g per 10 litres). The colour will clearly show… that’s interaction with photons :-)

    Comment by Martin Vermeer — 14 Apr 2008 @ 11:53 PM

  112. Re: #111 Martin,

    The way I figured it is:

    H2O: 18 grams/mole
    KMnO4: 158 grams/mole
    Which is 8.8 times the mass/mole of water

    1960′s CO2 ~ 320 ppm

    For something with the same molar mass as water that would equate to:
    (in 10 litres of water = 10,000 grams)
    (10,000 ÷ 1,000,000) * 320) grams = 3.2 grams

    Potassium permanganate is 8.8 times the molar mass of water that gives:
    3.2 * 8.8 = 28 grams

    How am I wrong?

    Comment by Lawrence McLean — 15 Apr 2008 @ 8:24 AM

  113. Re #112 Lawrence: I see you did it by molar ratios. I did it in my head by mass ratio (and miscalcuated).
    Hmmm. Yes, by molecule (actually, anion) count your approach is the right one.

    Comment by Martin Vermeer — 15 Apr 2008 @ 11:57 AM

  114. Martin (111) said, “…You’re right, but yet… the general argument that small numbers of molecules can have a big effect, stands. ..”

    Reasonable point.

    Comment by Rod B — 15 Apr 2008 @ 2:28 PM

  115. Has anyone got a preprint of the paper referred to in the following link ?
    http://news.bbc.co.uk/2/hi/science/nature/7349236.stm

    Svetlana Jevrejeva et al predicting sea level rise range of 0.8-1.5 m by century end.

    Comment by sidd — 15 Apr 2008 @ 2:42 PM

  116. This is comforting:

    Bush plans White House speech Wednesday on climate change
    By DEB RIECHMANN

    WASHINGTON (AP) — In a Rose Garden speech Wednesday, President Bush will outline the way he things the United States can reduce greenhouse gas emissions, and challenge lawmakers on climate change legislation up for debate in June.

    White House press secretary Dana Perino said Tuesday that Bush will not outline a specific proposal, but instead will lay out a strategy for “long-term” and “realistic” goals for curbing emissions.

    Bush wants every major economy, including fast-growing nations like China and India, to establish a national goal for cutting the emissions believed responsible for global warming.

    “This will ensure that all major economies, like France, Germany, China and India play a role in any international agreement so as to avoid a future Kyoto-like mistake,” Perino said.

    A new global warming pact is being crafted to succeed the first phase of the 1997 Kyoto Protocol. It requires 37 industrialized nations to reduce greenhouse gas emissions an average of 5 percent below 1990 levels by 2012. The United States is the only industrialized nation not to have ratified Kyoto, but it agreed with nearly 200 other nations at a conference in Bali in December to negotiate a new agreement by the end of 2009.

    Bush also is to talk about his concerns with legislative proposals likely to be considered during Senate floor debate in June, as well as frame a discussion about pending action in the regulatory arena, she said.

    “We believe there a right way and a wrong way to address this problem,” Perino said, adding that there is no legislative proposal on the hill that the administration supports.

    Comment by Jim Galasyn — 15 Apr 2008 @ 2:56 PM

  117. And re the Bush speech mentioned in 116, who could be surprised at the outcome:

    Bush Announces Greenhouse Gas Strategy — Surprise! It’s Bad
    By Alexis Madrigal

    President Bush delivered a speech today in which he outlined a new strategy to “effectively combat climate change.” Unfortunately, on my initial read of excerpts from his speech, it seems deeply, deeply flawed.

    Bush is finally publicly admitting that emissions should be curbed because they affect the climate. That’s fine, but his proposed response doesn’t logically follow from that statement of fact. If you think the greenhouse gas emissions are a problem, then you should craft a solution that reduces them. But Bush, instead, is suggesting that no mandatory caps be put in place, that no specific targets be fixed in the near term, and that no moratorium be called on coal plant production.

    Essentially, he just says, let’s wait ten years and then do something. The initial IPCC draft roadmap called for rich nations like the US to make reductions of “25-40 percent below 1990 levels by 2020.” Bush’s plan would not only result in no reductions, but would actually allow for continued growth in emissions until 2025!

    This speech strikes me as a desperate, half-baked ruse to stave off the real climate change legislation that is almost sure to come down the pike during the next Presidential Administration. On this issue, a new President cannot take the Oval Office fast enough, be it Obama, McCain, or Clinton.

    Bush also consistently conflates energy security goals–mythical independence from foreign oil, say–with climate change goals–primarily reducing carbon dioxide emissions from burning hydrocarbons. Don’t get it twisted: ethanol is about growing our own, not kicking our habit.

    Comment by Jim Galasyn — 16 Apr 2008 @ 4:03 PM

  118. re: 116 and 117. It is of course no small coincidence that Bush made the speech now because Earth Day is Saturday. Each April is when politicians such as Bush throw the environment a supposed bone.

    Comment by Dan — 16 Apr 2008 @ 4:44 PM

  119. Would it be fair to say that this increased Earth Sensitivity of 6C is of concern or is too speculative to usurp the standard measure as yet? Is the jury still out or has Hansen improved the standard measure of CO2 sensitivity. I mean that a doubling of preindustrial CO2(e?) to 560 ppmv is going to result in a more likely 6C rise!

    400 ppmv of CO2 then means in increased sensitivity from 0.2C per decade or nothing much for a much longer period, ie; this increased sensitivity is not here yet but will make itsels know as we climb towards some currently unknown (2 to 3C) tippng point?

    Comment by pete best — 20 Apr 2008 @ 9:52 AM

  120. Hi folks

    Thanks for the comments, site recommended by Tyndall Centre UK as worth a look.

    Can anyone ponder a guess? Even if stability is achieved at +6 degree Celsius, surely there will be quite fast melting of land-supported ice once the Arctic floating ice has melted i.e less than 50% of ice surface remaining in the Northern hemisphere. During the summer months the sun’s energy is relatively trapped in the North due to climate cells, so will not the mountain ice be melting at double the rate it is today? So will not that result in less melt-water and less irrigation possible/stability in the river systems fed by that mountain melt-water? Has this been included for in the modelling so far? Look out USA/EU/Asia for further food price rises as this ice rapidly reduces in the Rockies/Alps/Himalayas?

    I’d appreciate any comments, Thanks. (Global citizen)

    Comment by Ian Greenwood — 24 Apr 2008 @ 6:50 AM

  121. Moved from the current thread.

    There’s some pretty libelous things said in this Esterbrook interview by that opponent of mine. Doesn’t take long to find them either. Downright shameful. Somebody should hand them their hat.

    http://icecap.us/images/uploads/DonEasterbrookInterviewTranscript.pdf

    Comment by Mark A. York — 24 Apr 2008 @ 9:22 PM

  122. What about methane?

    While it is certainly a much smaller factor in the GCM (at least currently), why have no targets been set for it? Besides being so much more potent a GHG, though with a much shorter lifetime in the atmosphere, it also has the added danger of leading to a positive feedback loop, and hence, wouldn’t a so called “tipping point” for methane in the atmosphere be much more of a concern? Locking in a target for CO2 at whatever level, seems like only half a victory if methane continues to rise.

    Comment by R. Gates — 27 Apr 2008 @ 12:15 AM

  123. From some of the responses I understand that if we would use up all oil and gas reserves, but leave coals in the ground, the result would be a CO2 level of 450 ppm. Is that correct? What if we would burn all fossile fuels, including coal? How high could the CO2 level get, in a worst case scenario?

    Comment by Vincent van der Goes — 6 May 2008 @ 7:03 AM

  124. Re #123, if we convert coal to liquids, gas to liquids, mine heavy tar and oil sands then we might do even more damage CO2 wise. Coal is not going to stay in the ground of any kind as it is a local resource in around 70 countries and means energy security for them.

    Scary eh.

    Comment by pete best — 7 May 2008 @ 4:34 AM

  125. R. Gates, what we can target is what humans produce that gets into the atmosphere. Methane as natural gas? Fix the leaky pipes. Doable, being done.

    Comment by Hank Roberts — 7 May 2008 @ 9:59 AM

  126. Does CO2 amplify temperature and if so can you briefly explain how?

    Comment by Ross — 2 Jun 2008 @ 11:20 PM

  127. Sure. Click the “Start Here’ link at the top of each page, and click the first link under Science at the right side.

    Use the Search box, also at the top of the page, for any terms you want explained.

    How much math and science have you had in school so far?

    Comment by Hank Roberts — 3 Jun 2008 @ 12:01 AM

  128. #126

    Yes it does. Check out A saturated gassy argument and Physics of the Greenhouse Effect

    Comment by Chris Colose — 3 Jun 2008 @ 12:34 AM

  129. Ross, Ever hold your hand under a heat lamp at a burger joint, etc.? The heat you are feeling is infrared radiation being absorbed by your skin. CO2 absorbs infrared radiation that would otherwise radiate away from Earth’s surface and atmosphere and back into space. Since more energy is coming in (via sunlight) than is leaving (via outgoing IR radiation–the only energy leaves the climate) the planet must heat up. Does this help?

    Comment by Ray Ladbury — 3 Jun 2008 @ 7:14 AM

  130. There are claims, eg in http://co2science.org/articles/V3/N23/C1.php ,
    that the inferred low correlation between temperature and C02 concentrations (based on the article by Paul N. Pearson and Martin R. Palmer, “Atmospheric Carbon
    Dioxide Concentrations over the Past 60 Million Years,” /Nature/, *206*
    (17 August 2000), 695-99) over the last 60 million years somehow invalidates all the work of the IPCC and the rest of the climate science fraternity. I am a scientist, but my PhD was in exploration geophysics–I would be grateful if you could explain where this line of reasoning goes off the rails.

    [Response: Look at figure 6.1 in IPCC AR4 - that has an updated set of all the CO2 estimates pre-Quaternary (including Pearson and Palmer's work). First thing you notice is that there is a lot of variability among the different methods so P&P aren't likely to be the last word on this. Secondly, if you try and do a detailed comparison where the data are good enough (see Royer et al, 2006), then as best we can judge, there is a correlation between temperature and CO2 over long time scales where the CO2 is changing because of tectonic or weathering effects etc. - gavin]

    Comment by Scott Holladay — 17 Jun 2008 @ 5:33 PM

  131. Thanks, Gavin–your comment and reference were very helpful. As a follow-up, I understand that ice core data and other sources clearly indicates a phase lag of C02 relative to temperature during pre-industrial times. I have read that it is well-known that this lag has reversed during the industrial period due to anthropogenic GHG emissions, but I have not been able to find a graph that clearly shows this. Can you point me to a suitable reference (preferably one that I don’t need a journal subscription to read–IPCC would be great!)

    Comment by Scott Holladay — 18 Jun 2008 @ 1:23 PM

  132. # 131 Scott

    Might I suggest that you’re thinking about this relationship wrong. There has been a lot of emphasis on the blogosphere about “what comes first in the Vostok record” but the two are tied into an intrinsic relationship. CO2 causes temperature rise through well documented radiative principles, specifically inhibiting the efficiency at which the planet loses heat. CO2 will also respond to temperature because of ocean chemistry principles (i.e., gas solubility is lower in warmer water, and that goes in the atmosphere) and also vegetation and other responses. Once you get ocean outgassing though, you’ll also get a positive feedback whereby CO2 amplifies whatever the initial warming effect was (maybe milankovitch orbital variations). But thinking about the two dichotomies too hard is like trying to decide if the chicken or egg comes first.

    Throughout most of the ice core record, you’re going to expect CO2 to lag temperatures because there is not much reason to expect a massive external release of carbon to happen by itself. It should be rare in the geologic record, and random, not cyclic. If you look hard enough in the ice core record though you’ll find instances where CO2 comes first (Marine Isotope Stage 14.2) or precedes a deglaciation, etc. If you look back farther, to say the Paleocene-Eocene boundary there appears to be a massive release of CO2 which caused a large spike in temperatures.

    Today, CO2 is clearly causing (so preceding) a large chunk of the temperature rise. If you want a supporting reference see this paper. What’s more, the magnitude and rate of CO2 rise is far beyond what you’d get with just a CO2 outgassing feedback, and we also have isotopic evidence which unequivocally establishes the source of CO2 release, and it’s fossil fuels, not the oceans (which are a net sink now) or terrestrial biomass. The fact that levels are highest in at least 800,000 years (and likely longer!) is not a coincidence.

    Comment by Chris Colose — 19 Jun 2008 @ 12:44 AM

  133. Thanks, Chris. I had a look at the paper that you referenced (Caillon et al, 2003). While it does discuss paleoclimatic temperatures and CO2 levels in the context of ice core results, I could not find within it direct support for your statement that “CO2 is clearly causing (so preceding) a large chunk of the temperature rise.” Perhaps this was not the paper that you intended to reference.

    The isotopic evidence that you cite for the fossil-fuel origin of high and increasing CO2 concentrations in the atmosphere seems unequivocal. Similarly, it seems well established we are well beyond the highest CO2 concentrations seen in the last 800k years. Thank you for pointing me to that material.

    Regarding the rest of your comments–yes, it is obvious that there is a feedback process at work and that it must factored in–we’ll take that as read. What I’m getting at is that, while it has been repeatedly stated (in many comments at RealClimate, and in the IPCC report, and in media reports) that there exists an unequivocal lead in CO2 concentrations over temperature increase (which we can contrast with the well-established paleoclimate temperature lead over CO2 levels), a graphical or tabular representation of this linkage would be much more helpful from an educational standpoint than verbal statements.

    So this is what I’m looking for: a plot (or a pair of stacked plots with a common time scale) that shows both a well-established temperature versus time series (or a collection of such series) with a corresponding set of CO2 concentration vs time estimates running for the last (say) 500 years. The icing on the cake would be a similar plot with a longer time scale that runs back to the end of the last ice age.

    While such figures would not tell the whole story of radiative forcing and feedbacks, they would be immensely valuable tools for non-experts like me to use in explaining the difference between the pre-industrial and post-industrial GHG-temperature regimes to others.

    Comment by Scott Holladay — 20 Jun 2008 @ 3:11 PM

  134. #133, Scott

    The conclusion in Caillon et al is pretty clear:

    ……
    differs
    from the recent anthropogenic CO2 increase.
    As recently noted by Kump (38), we
    should distinguish between internal influences
    (such as the deglacial CO2 increase) and external
    influences (such as the anthropogenic CO2
    increase) on the climate system. Although the
    recent CO2 increase has clearly been imposed
    first, as a result of anthropogenic activities, it
    naturally takes, at Termination III, some time
    for CO2 to outgas from the ocean once it starts
    to react to a climate change that is first felt in the
    atmosphere. The sequence of events during this
    Termination is fully consistent with CO2 participating
    in the latter 4200 years of the warming.
    The radiative forcing due to CO2 may serve
    as an amplifier of initial orbital forcing, which is
    then further amplified by fast atmospheric feedbacks
    (39) that are also at work for the presentday
    and future climate.
    …………………….

    The Kump paper they mention is also a good read that goes over this.

    http://www.globalwarmingart.com is a good site with the graphs you may be looking for.

    Comment by Chris Colose — 20 Jun 2008 @ 3:44 PM

  135. Scott Holladay (133) — While I ccan’t show you strictly pre-industrial, the following three plots ought to do.

    Decadal average temperatures since 1850 CE:

    http://tamino.files.wordpress.com/2008/04/10yave.jpg

    Keeling curve of atmospheric CO2 concentrations:

    http://www.esrl.noaa.gov/gmd/ccgg/trends/co2_data_mlo.html

    Human-caused emissions of CO2:

    http://cdiac.ornl.gov/trends/emis/tre_glob.htm

    A serious attempt to put these together:

    http://www.scs.carleton.ca/~schriste/data/Carbon-Atmosphere-Mass_files/State%20of%20the%20World_28025_image001.gif

    and for dessert, a light-hearted attempt to put these together:

    http://www.leif.org/research/DAleo2.png

    Comment by David B. Benson — 20 Jun 2008 @ 3:47 PM

  136. After David posts these graphs I probably want to make a further point (I still don’t think the right question/request is being made). I think you’re trying to eyeball a graph and see if CO2 started rising around 1850 or something, and make sure that temperature started rising later (maybe 1900). The better question is probably, from a radiative forcing perspective, what’s the magnitude of the anthropogenic forcing compared to natural forcings? Or, what is the lag time in the climate system between forcing and a full realization of the temperature response? Or, what is the rate and magntitue of CO2 outgassing for a given temperature rise over a specified time period, and the possibility of massive releases from the ocean/biosphere in a warmer world?

    A few things though– a lot of warming before 1950 had to do with natural variation, such as increases in solar, lack of volcanoes, and other things. A clear anthropogenic signal that diverges from the noise of natural variation is not clear until the ’70s or ’80s. Secondly, the climate system takes decades to come to equilibrium and see the full response (or most of it) realized. What’s more, the “warming in the pipeline” (which is what we are commited to even if atmospheric concentrations stabilize) is proportional to the climate sensitivity, so if sensitivity were a lot higher than we think (say the high end at 4.5 C), a stabilization at 385 ppmv would not result in a temperature stabilization for a while, and we’d still be in store for another degree or so. So, a side-by-side comparison of CO2 and temperature as function of time over the industrial era will not give a complete picture to answer your question.

    Comment by Chris Colose — 20 Jun 2008 @ 4:30 PM

  137. Re 134: Chris, I had seen and understood the passage that you quote here. I guess that I should have used the words “graphical” or “numerical” support in 133 rather than “direct” support–sorry for my lack of clarity.

    Re 135: David, thank you very much–the fourth plot is just what I was looking for.

    Comment by Scott Holladay — 20 Jun 2008 @ 4:51 PM

  138. Re 136: I was convinced long before we had this discussion, Chris, but you’ve broadened my understanding considerably. Thanks for taking the time to help me out.

    Comment by Scott Holladay — 23 Jun 2008 @ 8:55 PM

  139. Are these papers/Journals serious?:

    http://arxiv.org/abs/0707.1161

    http://arxiv.org/abs/physics/0601051

    http://arxiv.org/abs/physics/0210095

    Comment by José M. Sousa — 29 Jun 2008 @ 4:21 AM

  140. In view of the present discussion of the role of carbon dioxide in effecting global temperature I would like to know of any laboratory or bench experiments that show a temperature- CO2 concentration curve within the range of currently measured atmospheric CO2 levels.
    You would think it fairly easy to set up multiple containers with different gas concentrations and similar incident radiation.
    Some crude runs have been reported with 100% CO2 or with increased but unreported or unmeasured CO2 concentrations but I know of none with a precise CO2-temperature relationship in the climactically important range.

    I realize that the laboratory scenario is simple in the extreme but it would prove useful in thinking about atmospheric CO2 effects, or for the effects of any other GHG for that matter. I would appreciate any comments, references, or help.

    Comment by Robert Stenson — 10 Jul 2008 @ 4:45 PM

  141. I came late to this thread, finding it due to an interest in climate policy recommendations. Simply put, to me the urgent question currently is, “What should be humanity’s atmospheric CO2 target?” And that is quickly followed by the question, “How do we get there from here?”

    There is no discussion in this thread (nor elsewhere on realclimate.org, apparently) of Cox and Jones, Illuminating the Modern Dance of Climate Change, Science, 19 September 2008 pp. 1642-44. Using additional data, Cox and Jones constrain earth’s climate sensitivity to what previously had been the high end of the range.

    The Cox and Jones article requires that the subject matter of this thread be re-opened and reconsidered.

    IPCC4 concluded the debate about, “Is human-caused global warming real?” to most reasonable people (even though open to revision based on later evidence). So realistically and pragmatically, climate science now must provide policy advice on what to do about it (even though that answer, too, is tentative and subject to revision).

    So I would like to re-open or re-invigorate this discussion in view of recent developments.

    I apologize if I should be asking this instead in another discussion thread. If so, you can simply “tell me where to go.” ;-)

    -Mark

    Comment by Mark Singer — 14 Nov 2008 @ 10:52 AM

  142. Mark Singer (141) — My amateur opinion is that CO2e needs to be reduced to about 300 ppm. One way to get there, the least expensive known to me, is via enhanced mineral weathering (enhnced carbonate formation). Here are some links.

    Olivine weathering:

    ftp://ftp.geog.uu.nl/pub/posters/2008/Let_the_earth_help_us_to_save_the_earth-Schuiling_June2008.pdf
    http://www.ecn.nl/docs/library/report/2003/c03016.pdf

    Peridotite weathering:
    “Rocks Could Be Harnessed To Sponge Vast Amounts Of Carbon Dioxide From Air”:

    http://www.sciencedaily.com/releases/2008/11/081105180813.htm

    Comment by David B. Benson — 14 Nov 2008 @ 3:07 PM

  143. Mark Singer, try:
    – the “Start Here” link at the top of each page
    – the first link under Science in the right hand sidebar
    – the Search box at the top of the page (try “target” as the search)

    Target Atmospheric CO : Where Should Humanity Aim?

    http://www.columbia.edu/~jeh1/2008/TargetCO2_20080407.pdf/

    http://arxiv.org/abs/0804.1126/

    Comment by Hank Roberts — 14 Nov 2008 @ 3:20 PM

  144. Thanks, Dave (No. 142). I also saw that article in Nov. 6 Science. Maybe when the price of carbon gets high enough someone will commercially exploit that. But that leaves the question of what price carbon, which makes target CO2 very relevant.

    Thanks, Hank (No. 143), but I’m aware of Hansen et al., and there are numerous references to Hansen earlier in the thread. I assumed it was no coincidence that this thread started 7 April 2008, the very day Hansen et al. (v1) was submitted. (It was last revised 15 Oct 2008, version v3.)

    So, not being a climate expert, I’d like the experts to weigh in on:
    (1) Does the consensus of climate experts agree with Hansen et al.?
    (2) How does the consensus factor in the new results of Cox and Jones?
    (3) And ultimately, what should be the target atmospheric CO2?

    . . .

    Comment by Mark Singer — 14 Nov 2008 @ 5:10 PM

  145. Mark, I think most would agree that we cannot systematically continue to emit greenhouse gases and not expect changes in climate…and the faster the CO2 rises the more worries because rates of change matter as much as, if not more than, overall magnitudes.

    “450 ppm” seems to be a popular threshold number but you won’t get a large “consensus” on a single number like you would on other things which are well established, in part because “how much CO2 = dangerous” is in some sense a judgment call and subjective in nature. Also, given different responses from ecosystems, sea ice, mountain glaciers, etc you might get different responses from various fields of expertise. Dr. Ove Hoegh-Guldberg agrees with a 450 ppm limit for reasons of ocean acidification rather than just the warming.

    Hansen does not appear to be too off the mark with much, so if we hit 450 ppmv it’s probably not going to be a walk in the park in terms of impacts.

    Comment by Chris Colose — 14 Nov 2008 @ 5:53 PM

  146. Mark, if you’re the person who cited that study to the EPA, good work. It popped up with Google.

    It’s only a month-old paper
    http://www.scienceonline.org/cgi/content/summary/321/5896/1642

    so won’t have made it into the consensus, but the IPCC grinds slowly as you know. It will be interesting to hear from the climate scientists once they’re thought about it.

    This came out about simultaneously:
    http://bravenewclimate.com/2008/09/16/target-atmospheric-co2-levels-not-vague-emissions-reductions/

    Amateur readers like me here of course can opine without reading, but “some guy on a blog says” isn’t useful. Interesting paper tho’. I’ll note what I found where for others who may want to read what they can.

    Science is paywalled of course, but the supplementary data page is downloadable.

    This (see para. 2) might be the abstract of it, or a summary:
    http://www.ukcip.org.uk/index.php?option=com_content&task=view&id=573

    Climate change: Illuminating the modern dance of climate and CO2

    Climate and atmospheric CO2 concentrations are closely linked: the climate affects the stores of carbon on the land and in the oceans, and CO2 influences climate through the greenhouse effect. This coupled relationship between climate and CO2 will thus have a big impact on how the climate changes through the 21st Century. There is already evidence that the strength of ocean, and especially some land carbon sinks are weakening and becoming less efficient, and coupled climate-carbon models suggest that this relationship will persist into the future. The implication is that there will be more CO2 in the Earth’s atmosphere, leading to more global warming. Here, Cox and Jones ask the question “by how much, and how quickly will there be more CO2 in the atmosphere, as a result of increasing temperatures.” Using estimates from first-generation climate-carbon cycle models (C-CC models), and palaeo-climatic evidence from the Little Ice Age (the period 1500 to 1750), Cox and Jones show that the predictions from C-CC models may be too conservative and that CO2 in the atmosphere will probably increase more rapidly than the models suggest. This has implications for the development of policies that seek to stabilise atmospheric CO2 at a given level, and for the level of change which the world might experience and have to adapt to.

    Source: Cox, P. & Jones, C. (2008) Climate change: Illuminating the Modern Dance of Climate and CO2. Science, 321, 1642-1644.
    ————————-

    This looks like it may contain the same information– can you tell from what you know already?
    http://www.metoffice.gov.uk/research/hadleycentre/models/carbon_cycle/results_trans.html

    Comment by Hank Roberts — 14 Nov 2008 @ 6:20 PM

  147. The Cox and Jones article can be found here: http://www.secamlocal.ex.ac.uk/people/staff/pmc205/papers/2008/Cox&Jones_08.pdf

    Comment by Rick Brown — 14 Nov 2008 @ 8:41 PM

  148. PS, looking at related papers by the same authors is often useful; this one paper you mention is more interesting in the context of the previous work. It’s always useful to see if, and how often, a paper gets cited over time, and by whom.

    http://scholar.google.com/scholar?as_q=&num=50&btnG=Search+Scholar&as_epq=climate+sensitivity&as_oq=&as_eq=&as_occt=any&as_sauthors=Cox+Jones

    Clearly these authors are taken seriously, and their earlyer work has been much cited and quickly after publication. Because of that, I would expect given their earlier work that this is already being factored into the developing consensus. It’s not a sudden surprise from outside, it’s a contribution.

    So — one question for the modelers.

    What does it suggest that they are “Using estimates from first-generation climate-carbon cycle models (C-CC models)” — are these the ones policymakers have been hearing about, or is this somewhat correcting the historical record?

    That is — are there later generations of models of that sort already being considered, and are current estimates already incorporating this thinking?

    (That would be an answer to policy-wannabe folks who have contended publicly that the models from decades ago were wrong so today’s can’t be better. That’s alternate history — they were likely bidding for a policy job in an administration that didn’t happen — but still, it’ll be asked again.)

    I’ll shut up now, having figured out that the real scientists here already know about Cox and Jones’s work, and await further education.

    Comment by Hank Roberts — 14 Nov 2008 @ 9:33 PM

  149. Yes, Hank (No. 146), I cited Cox and Jones to the EPA in the Clean Air Act rule making proceeding. I also cited it to the EPA at a public hearing in the CCS rule making proceeding. I hope this did some good.

    Thanks for the cites. No surprise that it was mentioned by the UK Climate Impacts Program, since they’re both at Exeter in the UK. I think the last cite was from work by Cox and others in 2000.

    Concerning Chris’s statement (No. 145) that,
    “. . . you won’t get a large “consensus” on a single number like you would on other things which are well established, in part because “how much CO2 = dangerous” is in some sense a judgment call and subjective in nature. ”

    Your observations about “judgment call” and “subjective in nature” are at once so true, and yet so very discouraging. But to leave this statement alone, just like that, the world could be seriously screwed. (Please pardon my blunt language.)

    With deference and all due respect, it is not that simple. The context of a discussion is critically important. Unfortunately, statements that are perfectly appropriate in one context can be quite misleading when taken out of context. Scientific discussions occur within a cultural context. Most scientists eschew value judgments and are loath to venture into the policymaking arena. But what might be impermissibly subjective in the context of a discussion of scientific research can, and often should, be considered as highly pertinent expert opinion in a policymaking discussion.

    It is really not an overstatement to say that some of the most urgent and critically important discussions in the history of humanity are now taking place concerning humanity’s response to global climate change.

    These discussions are taking place at various levels: among climate change experts (think of specialized websites, online journals, listservs and the like); among scientists who are not climate change experts but who are nevertheless involved in scientific discussions and influential publications (think of Science magazine, for example); among policy makers (they have journals and blogs; not sure what publication example to give); among ‘popular’ news media (pick your own example: Economist, NY Times, Time, etc.); and so on. The level of technical detail and scientific depth is usually inversely proportional to the breadth of the audience. Yet scientists must not ignore the importance of asserting leadership and influencing public opinion. Meanwhile, policymakers are like Harry Truman who said, “I’m tired of economists who say, ‘On the one hand … and then on the other hand.’ Send me a one-armed economist.” This is totally reasonable from the policymaker’s perspective. Policymakers can’t use and don’t want scientific exegesis. They need the expert’s best judgment. Period.

    When a message is communicated to a broader audience, the context changes. The rules of discourse change. What once was (appropriately) subjective in one context becomes (appropriately) expert opinion in another context. But, importantly, the urgent need for informed, unbiased and good faith scientific judgment now is even more critical.

    Because now you can add to this mixture the venal sowers of confusion and doubt at the behest of vested interests. Stir into the mixture politicians and lobbyists appointed to inappropriate governmental positions, who deny, deceive, delay and obstruct, gag scientists and rewrite reports to downplay risks and accentuate the limits of knowledge rather than what is known albeit inconvenient to their vested interests.

    How in the world can a system like this produce enlightened leadership and policymaking in the public interest? Well, for eight years it hasn’t, by any reasonable standard of judgment. And this is true despite the courageous example of dedicated scientists and public servants, including but not limited to James Hansen.

    Chris Colose probably didn’t expect or deserve this response and I suppose I owe him an apology. But I am earnestly pleading that climate scientists must do what they are by professional orientation loath to do.

    The President, members of Congress, policymakers within the EPA, opinion leaders in the Fourth Estate, business leaders, teachers at all levels, and, yes, the American public, urgently need to know climate scientists’ and other scientific experts’ considered best judgment about:

    — What should be humanity’s target atmospheric CO2?
    — What emissions restrictions are required, and in what timeframe, to achieve that target?
    — What are the consequences and costs of failing to take the steps required to achieve these emissions restrictions?

    These answers must be given in as clear, simple and understandable terms as the context and subject matter may allow. Be blunt.

    . . . .

    Providing current best scientific judgment is better than policy paralysis. Granted, it’s all tentative and subject to revision based on later evidence. The accumulation of evidence and scientific knowledge hopefully converges on answers with ever increasing accuracy. (Pace Thomas Kuhn: A paradigm shift is essentially a mental event that seldom adduces reduced numerical accuracy of previous scientific predictions.) This is likely to be true even for nonlinear dynamic systems because answers in a policy context are usually first order approximations that are not extrapolated so far into the future that the nonlinearities dominate the outcome. Besides, as Hansen et al point out, model uncertainties can cut both ways. But again, caveats and quibbles aside, current best scientific judgment is better than policy paralysis.

    I hope you will all heed this call to action.

    . . .

    Comment by Mark Singer — 14 Nov 2008 @ 11:14 PM

  150. think the the precautionary level is 280 ppm. What this preprint (and it is a preprint, not a paper) is arguing is that the sensitivity is larger than has been assumed up until now and so a “safe” temperature (a la Exeter) corresponds to a lower concentration (350 rather than 450). It does so so much that a scenario is developed to show how 350 ppm might be achieved (fig. 6). So, the preprint takes the risk quite seriously. We don’t know what it will be once it is a paper. Hansen has a habit of being right, but there may be some flaw in the analysis that a referee catches.

    Comment by makale — 25 Nov 2008 @ 12:03 PM

  151. http://iodeweb3.vliz.be/oanet/OAimages/Wolf-GladrowGraph.gif

    Ocean Acidification’s Effects on Marine Ecosystems and Biogeochemistry – EOS meeting report
    The U.S. Ocean Carbon and Biogeochemistry Program sponsored a scoping workshop on ocean acidification research from 9-11 October 2007. The workshop brought together 93 scientists to address present and future acidification impacts, and to reach consensus on research priorities.

    http://www.us-ocb.org/Eos_Trans_OCB_OA_2008EO150004.pdf

    _________________
    ReCaptcha: “WATER injured”

    Comment by Hank Roberts — 25 Nov 2008 @ 3:15 PM

  152. Chris #138:

    “there exists an unequivocal lead in CO2 concentrations over temperature increase (which we can contrast with the well-established paleoclimate temperature lead over CO2 levels)”

    But the paleoclimate record showing a temp lead over CO2 does not apply in this case. Mostly because Triceratops didn’t have an SUV. Tyrannosours didn’t dig oil wells. Humans do.

    “Death always follows heart failure”. That’s fine, but if you’re talking about someone whose head has been chopped off, I would say that citing this genuine fact doesn’t explain when death occurs IN THIS INSTANCE.

    Comment by Mark — 25 Nov 2008 @ 4:28 PM

  153. A fairly low cost route to removing carbon dioxide from the atmosphere is via enhanced mineral weathering (enhanced carbonate formation). Here are some links.

    Olivine weathering:

    ftp://ftp.geog.uu.nl/pub/posters/2008/Let_the_earth_help_us_to_save_the_earth-Schuiling_June2008.pdf
    http://www.ecn.nl/docs/library/report/2003/c03016.pdf

    See references 7, 8 and 9 in

    http://en.wikipedia.org/wiki/Olivine

    Peridotite weathering:

    http://www.sciencedaily.com/releases/2008/11/081105180813.htm

    Mine tailings:

    http://adsabs.harvard.edu/abs/2005AGUFM.B33A1014W

    My cost estimates always come up about the same, or less, than the most optimistic of the usual CCS proposals. These have a cost similar to deeply burying biochar. So olivine, etc., weathering appears to be the best currently available solution; it has the further advantage of releasing micro-nutrients into a biologically available form, being then a soil amendment.

    Comment by David B. Benson — 25 Nov 2008 @ 5:07 PM

  154. David I almost got involved in a project similar to what you are proposing for LKAB in Sweden… however it is on ice atm… As I can see from your links the problems seams to be the same as when LKAB thought about it, transport cost and kinetics… It would be interesting to go further on any how and they are still talking about it. Mainly about using the apatite rich mine tailings…

    Comment by Magnus Westerstrand — 25 Nov 2008 @ 6:15 PM

  155. > weathering

    So we need just one small asteroid hit, that imacts in exactly the right geological strata to throw up a lot of one of these materials ….

    Comment by Hank Roberts — 25 Nov 2008 @ 6:16 PM

  156. Here is the Tech R3eview article on peridotite weathering. If this works, carbon dioxide can be removed from the atmosphere for a very low cost per tonne:

    http://www.technologyreview.com/energy/21629/?a=f

    (Thanks to Micael Tobis for noticing this article.)

    Comment by David B. Benson — 25 Nov 2008 @ 6:43 PM

  157. Responding to makale (No. 150) regarding: “(it is a preprint, not a paper)” and “We don’t know what it will be once it is a paper. Hansen has a habit of being right, but there may be some flaw in the analysis that a referee catches.”

    The situation has changed. Originally, on 7 April 2008, when this forum was started, the Hansen et al. article was a preprint (version 1). But the article (version 3) was published in The Open Atmospheric Science Journal, 2008, Volume 2, pp. 217-231, URL http://www.bentham.org/open/toascj/openaccess2.htm.

    This journal states:
    “Aims & Scope
    “The Open Atmospheric Science Journal is an Open Access online journal, which publishes research articles, reviews, and letters in all areas of climate research and atmospheric science.

    “The Open Atmospheric Science Journal, a peer reviewed journal, aims to provide the most complete and reliable source of information on current developments in the field. The emphasis will be on publishing quality papers rapidly and freely available to researchers worldwide.” (See URL http://www.bentham.org/open/toascj/index.htm)

    The paper as published states (p. 231) that it was received May 22, 2008, revised August 19, 2008, and accepted September 23, 2008.

    . . .

    Comment by Mark Singer — 30 Nov 2008 @ 1:45 AM

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