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Science Story: the Making of a Sea Level Study

Filed under: — group @ 6 April 2010

Guest commentary by Martin Vermeer

On December 7, 2009 the embargo expired, and my and Stefan’s joint paper ‘Global sea level linked to global temperature’ appeared in the Proceedings of the U.S. National Academy of Sciences. It had been a long time coming! But this post is not so much about the science as about the process, and about how a geodesist from Helsinki and an oceanographer from Potsdam, who to this day have never even met, came to write, to the surprise of both of us, a joint paper on sea level rise.

My own entry into climatology happened only a few years ago. A significant trigger was RealClimate, which I had learned to appreciate as one of the rare reliable Internet sources amidst the junk. Contributing to the oft-slandered science is my small ‘thank you’ and revenge as a scientist.

As I remember, it was the commenter calling himself Rod B. who enquired, sometime August 2008, what the story really was with Rahmstorf (2007). Trying to answer, I ended up reading the paper and getting interested. What seduced me was the simplicity of this, so-called semi-empirical approach: linear regression of sea level rise dH/dt against temperature T, yielding two unknown parameters: a regression coefficient a, and an intercept, or ‘equilibrium temperature’, T0. See our Ups and downs of sea level projections for a more detailed explanation.

The curve of temperature as a function of time over the 20th century has three parts: a steep rise in the beginning, a flat middle part commonly attributed to aerosols, and a very steep upswing at the end. Physically one would expect for the curve of the sea level rise rate dH/dt as a function of time to look rather similar, as indeed it does: this justifies the Rahmstorf (2007) approach of regressing the one against the other. Looking more carefully however one sees that the dH/dt curve has slightly more of an S-like shape, turning downward in the middle, before swinging up again at the end.

This suggested to me that, in addition to a proportionality to temperature T, sea level rise would also contain a term proportional to the time derivative of temperature, dT/dt. In other words, global sea level would be a good global thermometer, but with a ‘quirk’. I could even think of a physical mechanism for such behaviour.

I contacted Dr. Rahmstorf, proposing the idea: one would expect the ocean surface to warm up rapidly to completion, contrary to the deep ocean and the continental ice sheets. This would argue for a term, in addition to the secular a (TT0) term, of form b dT/dt. Stefan’s response was cautious; not surprising, as being something of a media figure in Germany surely means that he has to contend with his share of cranks. But he suggested I look myself into the idea, which I subsequently did: in for a penny, in for a pound.

I downloaded Stefan’s script, modified it, did the first computations with the same real tide gauge and temperature data Stefan had used — surprise: negative b. Hmmm, strange. That was for real data from the real Earth; what would happen if I applied the extended relationship to simulated data from the same general circulation model (actually, an Earth system model) for the period 1900-2100 that Stefan had used in his paper for testing his relationship? This model was in one essential way very much simpler than reality: it completely lacked the contribution of land ice melting to sea level.

Stefan helpfully sent me Matlab snippets and model output, and indeed I got it all working. What was more, the disagreement found by Stefan for the late 21st Century — between sea level rise as predicted directly by the model, and indirectly through the semi-empirical relationship between temperature and sea level rise — went almost completely away when using the new, extended relationship. With a positive value for b, just as expected from theory for an ocean surface water response.

Global sea level against time. Top, sea level rise, bottom, sea level itself. Red, sea level from observations; blue, with uncertainty band, the fit from global temperatures using our new relationship; black, the fit using Stefan’s original relationship. The thin red wiggly curve shows annual sea level values.

That was encouraging, but what again about the real data? Remember that this is real observational data from tide gauges, altimetric satellites and meteorological stations, warts and all, with a very imperfect spatial sampling both for the tide gauge data and for the surface temperature data. Nothing like the clean, formally perfect model output of truly global mean surface temperature and sea level.

At that point I was about to give up.

I remembered however Stefan mentioning a ‘reservoir correction’ and decided to see if that made a difference. It was not hard to find Chao et al. (2008), who had painstakingly compiled a list of all man-made reservoirs the world over, and the amount of water stored in them. I fitted a simple arctan function through their water storage curve and added that to Stefan’s already extended script. All that water, up to 30 mm sea level equivalent, that should have been in the ocean was progressively kept bottled up on land as dams were being built: a known correction that should be applied.

Wow. Introducing the b term had already improved the Pearson correlation r of fit from 90% for Stefan’s original relationship to 97%; nice, but hardly on its own compelling. Bringing in the Chao et al. man-made reservoir correction brought it up to 99.2%!

Slowly it dawned upon me that, hey, maybe I’m on to something real here, something based in physics: it seems the world ocean can be a remarkably good global thermometer, once you get to know its quirks.

The world ocean, a pretty good global thermometer (drawn using
GMT).

Stefan relates the moment when he realized that I had something worth publishing: January 16, when he saw the results of the ‘millennium run’ that I had done on the data he had sent me. All of the volcanic explosions over the last thousand years, which were translated first into top-of-atmosphere radiative forcing and then turned into sea water thermal contraction and a drop in modeled sea level, were faithfully reproduced in the sea levels obtained from the model temperatures by my new relationship! A beautiful performance on what are large, rapid and erratically occurring excursions in both global temperature and sea level. And that’s how Stefan came on board.

With the small number of independent data points we needed to make sure we were not ‘fitting an elephant‘, so I read up on statistics during winter 2008/2009, and in particular, information theoretical methods like the Akaike Information Criterion. The model intercomparison was useful for just that. I’m not the only one studying these ideas, and I learnt a lot from tamino and James Annan’s Empty Blog. Jaynes (2003) was also on my 2009 Christmas reading list; Hypothesis testing, null and alternative hypotheses, confidence bounds and all that, is a traditional approach to statistics that is easily misunderstood and often misused. Statistical refutations of “silly null” hypotheses abound — like the silly null of no relationship between temperature and sea level rise. If this sounds all cryptic to you, I don’t blame you. Pick up Jaynes (2003), it’s an eye-opener.

As part of his contribution, Stefan tightened up the draft paper to be suitable for submission to Nature. Nature gave us some very helpful reviews which we used to further improve our manuscript. The most useful reviewer remark had to do with the extraction of water from underground aquifers, a process potentially almost as important as the artificial reservoir storage that we did take into account — only, nowhere in the literature was there an equally painstaking accounting exercise to be found as what Ben Chao and colleagues did for the reservoirs. So, we settled for a sensitivity analysis, skillfully whipped up by Stefan.

Nature turned us down, like they do over 90% of manuscripts; had they accepted, the paper would have been out already in summer. We resubmitted to PNAS who obtained three further helpful reviews, the paper was improved yet again and finally published in December. As it happens, this landed it right on top of the Copenhagen meeting.

Stefan tells me that we have exchanged over a thousand emails in the run-up to this paper. I see some poetry in that number being close to that of the East Anglia stolen email selection. Easy, informal email plays a vital role in the work of climatologists, and the loss of trust in its confidentiality could be very disruptive for the science: if the internal discussions of an authoring team would have to be expressed with the same care as the finished product, not a lot of authoring would get done.

Would I have dared, or managed successfully, to submit to a top journal all on my own? Hardly. It is an illusion to think that you can just enter a field that’s not your own and become a productive researcher, whatever you might read or what denialists-of-service may pretend. There is a lot of domain knowledge involved, and precious little of it is simple. In this case, I did learn a lot (and I continue to do so), but this takes both a willingness to learn, and great teachers. RealClimate, and the community it represents, are an indispensable resource for that.

Still waiting for Al Gore’s cheque…

P.s. Over at Nature Stefan has a commentary on sea level today.

References

Martin Vermeer and Stefan Rahmstorf (2009): Global sea level linked to global temperature, Proceedings Nat. Acad. Sci. 2009 vol 106 no. 51 pp. 21527-21532, DOI: 10.1073/pnas.0907765106, open access link

Jonathan Overpeck and Jeremy L. Weiss (2009): Projections of future sea level becoming more dire, Proceedings Nat. Acad. Sci. 2009 vol. 106 no. 51, pp. 21461-21462, DOI: 10.1073/pnas.0912878107 link.

Stefan Rahmstorf (2007): A Semi-Empirical Approach to Projecting Future Sea-Level Rise, Science 315, 368-370, DOI: 10.1126/science.1135456 link

B.F. Chao, Y.H. Wu and Y.S. Li (2008): Impact of Artificial Reservoir Water Impoundment on Global Sea Level, Science, 320, 212-214 link

Edwin Jaynes (2003): Probability theory: the logic of science. Cambridge University Press, ISBN 0-521-59271-2.


237 Responses to “Science Story: the Making of a Sea Level Study”

  1. 51

    Martin, congratulations on contributing to the field. I only hope I can follow in your footsteps. I have two papers at journals now, and I’m hoping like crazy that at least one survives peer review. Getting a paper published in a peer reviewed science journal is one of my life goals. I’ve been trying since I was 17. I’m now 49. Nice bit of deduction in connecting Chao’s reservoir work to yours, by the way.

    Edward (5), I agree about teaching kids statistics. I’d teach them formal logic, too.

    Jimbo (19), What, precisely, are you objecting to? The fact that Vermeer and Rahmstorf tried to analyze a relationship between global temperatures and global sea level? Why is that improper? What’s wrong with it?

  2. 52
    Bob says:

    Gotta Believe, #11 and #38:

    I’ll comment, except I’m nothing close to a “scientist” (except at heart).

    The Ogi study is a simple statistical correlation between a possible cause and a probable effect, specifically the impact of a particular, variable wind pattern on the rate/degree of ice melt, and the correlation they found is strong. That’s it, no more, no less.

    So… we have a study that is able to correlate certain wind patterns well with some degree of the ice melt. This has apparently contributed the unexpectedly high rate of decline in Arctic ice extent. It is what it is, no more, no less.

    In fact, the Ogi paper is probably a very good parallel with the topic of this post, the paper on sea level rise, in that it took a simple correlation (temperature -> ice extent vs. temperature -> sea level rise) and added the next “principle component” to the equation (a major influencing wind pattern for ice melt vs. a rate of change feedback factor for sea level rise) to help “fill out” the model.

    It’s all about incrementally expanding our understanding of how the earth works.

  3. 53
    Bob says:

    Quick correction to my last post… I frequently used the term “ice melt” which I think is misleadingly inaccurate… I should have said SEI (sea ice extent) as the Ogi paper does, and there is a clear difference between the two, SEI being defined as a specific, common measure (and therefore a proxy of) actual ice melt, but not exactly the same.

  4. 54
    Hank Roberts says:

    (Aside to Sou — when you get taken to the spam-filter page, try navigating “Back” — it should take you back to the Reply window and you can edit, copy, etc. and try again.)

  5. 55
    Bob says:

    Martin,

    You said:

    I could even think of a physical mechanism for such behaviour.

    May I ask you to share that thought? If it is already included in your post, I apologize, but I couldn’t find it.

  6. 56
    Completely Fed Up says:

    “I keep forgetting to copy my post before posting :( )”

    I use the “Back” button. Even if you are in a view that doesn’t show it, you can or should be able to right click and select “Back”.

  7. 57
    Completely Fed Up says:

    “Surely there must be a RANGE of opinions out there…”

    And we all know opinions are like arseholes. Everyone’s got one.

    If answered, what would you do with it? What would change? Nothing in both cases, really. Nothing you CAN do with it, nothing that would change.

    So questions go unanswered because they are like a broken pencil: pointless.

  8. 58
    Doug Bostrom says:

    Sou says: 7 April 2010 at 10:37 AM

    I keep forgetting to copy my post before posting

    If you use the posting facility provided in the main link to a thread as opposed to the pop-up feature, when you bump into the spam filter you can hit the “back” button on your browser and take as many stabs at cleaning up the post as you like.

  9. 59
    Bill says:

    Re;#51Sou & Hank #41 : After another 5 or 15 or whatever ….good scientific papers, will we still be having the same discussion on here? Your comments are great in theory but does the information really get across to the key policy makers in practice??

  10. 60
    Daniel J. Andrews says:

    I have what may be a very silly, perhaps stupid, question. Bear with me. I was impressed that freshwater reservoirs had the effect described. This leads me to wonder if the increasing levels of water vapour being held in a warmer atmosphere (rather than precipitating into the ocean) would also alter the sea level-temp relationship as well? Or will more water vapour just mean more precip and there won’t be any noticeable effect?

    btw, thanks for the Jaynes 2003 reference. I’ll check our library.

  11. 61
    Len Ornstein says:

    To further expand on my #3 and #23:

    The Figure (above) of Sea Level vs Time, (and the arguments within the Vermeer & Rahmstorf paper) suggests the first robust ‘explanation’ of the last decade ‘flat’ in GMST:

    It’s almost certainly been due to accidental ‘confluence’ of ‘heat-in-the-pipeline noise’!

  12. 62
    Oscar Mesa says:

    This quote from Stefan Rahmstorf commentary in most recent Nature’s issue has probably a typo that needs to be clarified asap:
    “Apart from this being just not so, the melting of all glaciers would add 60 centimetres to global sea level10, a lot more than in the worst-case scenario projected by semi-empirical models for 2050.”
    ojm

    [Response: What’s the typo?]

  13. 63
    David B. Benson says:

    Daniel J. Andrews (60) — Extra water vapor (due to warming) is about the same as the contents of Lake Superior.

    Len Ornstein (61) — Another reason to use decadal averages:
    http://www.realclimate.org/index.php/archives/2010/03/unforced-variations-3/comment-page-12/#comment-168530

  14. 64
    RonalLarson says:

    Agreed that the new second and third terms are wonderful additions to the global thermometer. Thanks for the personal tone and the many positive remarks about this important contribution for talking with deniers. My interest generally in RC topics is in the CDR (Carbon Dioxide Removal) topic- and specifically in Biochar. Were that (coupled with massive REDD+ and a few other CDR approaches) to be successful, dT/dt should be able to turn negative this century – maybe even mid-century. Question: should the 80-20 relationship between the second and first terms still hold and the magnitude of the multiplier b remain unchanged? I.e. – to hold sea level constant, would we need to achieve a negative temperature derivative about 1/4 th of today’s positive rate?

  15. 65
    Bob says:

    David, #63 —

    Puzzling… the web says the contents of Lake Superior amount to 12,000 km3 of water, and the surface area of water on the earth is 361,132,000 km2, so taking that water equally from that surface (an assumption)… 12,000 km3 / 361,132,000 km2 = 0.0000332288 km deep, which is 0.0332288 m, or a 33.2288 mm drop in sea level…

    That seems like too much (did I make a mistake in my math? I double checked…).

    Is that the actual increase in water vapor in the atmosphere to date, or on as ultimately expected by a 2C (or some other) warming, but not yet realized?

  16. 66
    Waqidi Falicoff says:

    I have a continuing debate with a colleague of mine on the climate change issue. He believes our planet is in a cooling phase as a consequence of it going into a Maunder minimum and other reasons. Nearly all the data and science I point him to on this subject is attacked. He claims the following analysis of the Vermeer and Rahmstorf paper is refuted at:

    http://climatesanity.wordpress.com/

    Perhaps you might comment on this supposed “refutation” of your work with Dr. Rahmstorf.

  17. 67
    David B. Benson says:

    Waqidi Falicoff (65) — Such solar variations are quite small forcings. HAve him look at 13 decades:
    http://www.realclimate.org/index.php/archives/2010/03/unforced-variations-3/comment-page-12/#comment-168530

  18. 68
    Oscar Mesa says:

    Fallowing 62
    I understand Glaciers as a general term, as in http://nsidc.org/glaciers/questions/types.html. In that case ” … the melting of all glaciers would add more than 60 meters to global sea level…”. Perhaps you are considering only mountain glaciers?

    [Response: With “glaciers” I meant glaciers and small ice caps, but not the big ice sheets in Greenland and Antarctica. Sorry the reference I gave for those 60 cm (Radic et al, ref. 10) is only in press – it uses the same definition and uses the latest global glacier inventory data to estimate their total volume is worth 60 cm of global sea level rise. -stefan]

  19. 69
    Hank Roberts says:

    > he believes … a Maunder minimum ….

    I doubt he can still believe that after yesterday’s solar storm.
    Has he looked at what’s going on lately?
    http://www.msnbc.msn.com/id/36201214/ns/technology_and_science-space/
    http://www.swpc.noaa.gov/SolarCycle/sunspot.gif

  20. 70
    David B. Benson says:

    Bob (65) — I just happened to remember what someone else claimed for the increase in atmospheric water vapor to date; it seems well to check that as well as your math.

  21. 71
    Gilles says:

    Martin:”Not necessarily. If by 2100 greenhouse gas emissions have been brought to zero (by that time I expect mankind, or what’s left of it, to have learned its lesson),”

    actually, a fair part of mankind has never really emitted a lot of greenhouse gases, I don’t know which “lesson” you expect from them, but I think you could easily go and live among them, if you like. But it is another issue.

    [quote]
    the CO2 concentration in the atmosphere will start to go down by absorption into oceans and biosphere. As a result, also temperatures will start to go down, but with a delay. Sea level rise will continue as long as temps are above pre-industrial, but at an ever-diminishing rate.
    [/quote]
    could you give a quantitative estimate of the maximum level that you expect with reasonable numerical values, in the best hypothesis ? (CFU , THAT was the second question).

  22. 72
    Brian Brademeyer says:

    David (70), Bob (65), David(63):

    Wikipedia gives: “The mean mass of water vapor [in the atmosphere] is estimated as 1.27 × 10^16 kg”

    This would be 12,700 km^3, or about the volume of Lake Superior (from Bob(65)).

    This is the TOTAL water vapor content, not the EXCESS due to warming which Daivd presumed(63)..

  23. 73
    David B. Benson says:

    Brian Brademeyer (72) — Thank you for the correction! Excess water vapor is a few percent of that, but I don’t recall the value.

  24. 74

    Global economy, Gilles (#71.) Increasingly global blogosphere. Of course, the contribution to the CO2 problem has been assymetrical, but the consequences will be widely shared.

    So, yes. I think we’ll all learn our lesson–French, American, Thai, whatever.

    The gist of that lesson will be that our numbers and technology make us dangerous to the environment upon which we depend. Essentially, the lesson that adolescents have to learn in order to survive.

  25. 75
    Bob says:

    Brian, #72, David, #73:

    Okay… skepticalscience.com (as reliable as any) gives the % water vapor increase as 6% to 7.5% per degree warming. So…

    12,700 km3 * 0.060 = 762.0 km3
    12,700 km3 * 0.075 = 952.5 km3

    Spread over 361,132,000 km2 gives 2.11 mm to 2.64 mm sea level drop for every full degree of warming. If we’ve seen 0.6˚C of global warming so far, then that’s a 1.27 mm to 1.58 mm to date, or (per year for 30 years since 1980) less than 0.05 mm drop per year due to loss to water vapor.

  26. 76
    David B. Benson says:

    Bob (75) — Thanks.

  27. 77
    Sou says:

    @ #59 Bill
    It’s obvious that governments are getting the messages as evidenced by changes to planning legislation to account for projected sea level rises, attempts to pass legislation to curb GHG emissions etc.

    The problem is less the information getting to the policy makers (if nothing else, they have their IPCC report, which was commissioned by about 190 governments from around the world). The difficulty that policy makers have is getting legislative change quickly enough when there are so many competing interests. Legislators have to deal with short term priorities as well as longer term issues. They are also subject to ‘lobbying’ (aka extortion and bribery) regardless of the form of government.

    Governments often pass legislation after the event. Government as a large ‘enterprise’ has built in intertia, like huge corporations. Medium and small businesses are more nimble and quicker to adopt / adapt to change – look at all the technological developments – solar energy, geothermal, wind power etc – even a solar aeroplane.

  28. 78
    Sou says:

    @ Hank and Doug,
    Re the spam filter: I do use the main board (not the popup), but when I press the back button on my browser after getting the ‘spam’ message, the message box is blank and I can’t retrieve it. (Using IE8).

    I’ll just have to remember to copy before posting – at least until RC can update/amend the spam filter or provide a preview button? (In any case, sometimes I say too much and add little :D)

    Sorry for going OT.

  29. 79
    Edward Greisch says:

    So now that we know that the sea level rise is over 1 meter, what do we do with it?

    “To limit global sea-level rise to a maximum of 1 m in the long run (i.e., beyond 2100), as proposed recently as a policy goal (26), deep emissions reductions will be required. Likely they would have to be deeper than those needed to limit global warming to 2 °C, the policy goal now supported by many countries. Our analysis further suggests that emissions reductions need to come early in this century to be effective.”

    Yes. We have to cut CO2 emissions faster and sooner.
    What does somebody who lives in Denver and doesn’t care think? How do we get the senator from Colorado or a coal state to vote for the bill?

    Martin Vermeer and Stefan Rahmstorf have done the fun part. Now we have to do the hard part. Most of the people around me have what I would call smart-Alec answers. They do not take GW seriously, and they will not until some climatic event clobbers them. They probably will not take AGW seriously even then. If they do, they will blame the scientists for causing AGW. “After all, civilization couldn’t have burned all that fossil fuel if you scientists hadn’t invented technology.”

    Sounds crazy? Yes. Insanity is normal. The denialists at least speak English rather than “Word Salad.” Just try talking to some people from a small farming or factory town. You will see what I mean by “the hard part.” They are likely to threaten you for being a commie or an environmentalist.

    How do we proceed from here?

  30. 80
    Ricki (Australia) says:

    30 Gilles,

    you miss my point I think, even if the A1B is roughly accurate, it still does not take into account any positive feedbacks or indeed higher early emissions (as we are currently seeing with business as usual). The ramping up of China and India is going to kick emissions along very nicely and it doesn’t look like any effective international agreement is in the wings.

    As Edward Griesch, 79 says, how do we convince people action is necessary NOW and not in 20 or 30 years time! If we wait that long, it will realy be too late for the next 500 years (in my opinion, a collapse of human society into chaos is likely in such a scenario).

    I ask again where are the projections that look at any of the positive feedbacks? The IPCC should be able to do this. Saying that under A1B we get to SLR of 1.2m by 2100 only gives us the lower bound when you think of the potential of the feedbacks.

  31. 81
    Martin Vermeer says:

    #73 David B. Benson:

    Brian Brademeyer (72) — Thank you for the correction! Excess water vapor is a few percent of that, but I don’t recall the value.

    Actually around 6% for every degree warming from Clausius-Clapeyron, assuming fixed relative humidity. If the total of 33 mm by Bob #65 is right, this amounts to 2 mm/degree for sea level.

  32. 82
    Martin Vermeer says:

    Bob #55:

    > May I ask you to share that thought?

    Yes, it is not in the post… it is briefly mentioned in the article above Eq.(2):

    However, some components of sea level adjust quickly to a temperature change, e.g., the heat content of the oceanic surface mixed layer. Therefore, we here propose to extend the semiempirical method by a rapid-response term:

  33. 83
    Martin Vermeer says:

    Gilles #71:

    could you give a quantitative estimate of the maximum level that you expect with reasonable numerical values, in the best hypothesis ? (CFU , THAT was the second question).

    If I could, I would write a paper on it ;-)

    Actually this is very difficult. It includes guesswork on how mankind is going to behave (I ventured one such guess), and how technology is going to develop (over centuries!), in addition to the physical uncertainties which seem more manageable. In other words, you’re producing ‘scenarios’ or ‘projections’ that are as questionable as the assumptions underlying them. The same problem as we see with the IPCC projections, but worse.

  34. 84
    Gilles says:

    “So now that we know that the sea level rise is over 1 meter, what do we do with it?”

    No Edward : now we know that sea level rise is over several meters, because it can’t stop before several centuries.

    But as the rate of increase will be one meter /century, the answer is obvious : built absolutely nothing below an altitude of X meters where X is the average life expectancy of what you build. Of course some people will do it nevertheless, but you know, some large cities are also built at the feet of volcanoes or on seismic faults …

  35. 85
    Gilles says:

    ““To limit global sea-level rise to a maximum of 1 m in the long run (i.e., beyond 2100), as proposed recently as a policy goal (26), deep emissions reductions will be required. Likely they would have to be deeper than those needed to limit global warming to 2 °C, the policy goal now supported by many countries. Our analysis further suggests that emissions reductions need to come early in this century to be effective.”

    Sorry to insist, but this statement is simply wrong if Stefan and Martin are right.

    The rise will continue at least throughout the shortest time scale between the damping of the 2°C rise in temperature and the relaxation time of sea level, which is – if they’re right – much larger than one century and could reach 1000 yrs. So the rise CANNOT be stopped in any case at 1 meter level whatever we’ll do, and could reach 10 meters. That is a very robust conclusion IF there is a long relaxation timescale of the order of many centuries. So actually stopping fossil fuels now isn’t the best thing to do- it won’t stop the rise and it would be much more difficult to face the sea without concrete and steel !! . The best thing is to plan mitigation adapted to the unavoidable sea level rise, we just have to choose where to build the future civilization !

  36. 86
    Martin Vermeer says:

    Re Gilles #85: yes, it is tough. If we allow temperature to go as high as 2 degrees, the game is probably lost. If we allow temp to stay at 2 degrees, it certainly is.

    BTW the “damping time of the 2 degree rise in temperature” is not a single number — there is a range in time scales, and initially the drop in CO2 will be fast. I don’t think your assertion is anywhere near robust.

    One should read this, page 50 onward, for the thinking behind the statement.

  37. 87
    Martin Vermeer says:

    Zeke #2, Barton #51,

    thank you for your kind words. I wish you well with your own efforts. It is important that outsiders not only are, but are seen to be, able to contribute on merit, that there is nothing like this mythical ‘priesthood’. This was also among my reasons for having our paper Open Access, and accompanied by the code — paywalls suck.

    Now I am only a semi-outsider, having done my dissertation on a geophysics related subject. It’s great to see this amateur and semi-amateur activity take off, with Tamino, Nick Barnes and others. We need this kind of network, or interface layer, between the professional community and society at large.

  38. 88
    Hank Roberts says:

    Gilles, please stop. You took over one thread already. Don’t go on in every topic, repeating whatever others bring up, then concluding as usual “So actually stopping fossil fuels now isn’t the best thing to do” — we know your conclusion, it’s always the same, no matter what the question. It’s boring.

    Addicts talk like this.

  39. 89
    Gilles says:

    Martin, as you can see here : http://www.realclimate.org/index.php/archives/2010/03/climate-change-commitments/#more-3070 , stopping abruptly any CO2 emission would only result in stabilizing the temperature to current level, so there is actually no hope of getting a sensible decrease of the temperature in the next centuries. As it is extremely unlikely that CO2 emission stops abruptly before at least all cheap conventional resources are exhausted, I think personally that is a waste of time to claim that we should do our possible to limit the sea level rise below 1 meter beyond 2100 since it is already too late. So after what you say, I see only two reasonable positions : either you are wrong and the long relaxation time leading to a quadratic rise doesn’t exist, and the sea level rise will probably be limited and manageable without strong changes. Or you are right and the long relaxation time is predominant, and it is already too late to avoid it, we’d rather manage it as we can.

  40. 90
    EFS_Junior says:

    #66 Waqidi Falicoff says:

    http://climatesanity.wordpress.com/

    1) Download “VR2009 test 4″

    2) Extend Hypothetical Temperature #1 thru #4 to 2100 AD

    3) Ask yourself if those values look reasnoable (Answer? NO!)

    4) Ask yourself why use a deterministic relationship that quickly goes exponential with ludicrous values for temperatures, sea level rates, and sea levels past 2000 AD (which are not shown BTW (I wonder why? NOT!)?

    5) Ask yourself if a deterministic (and unreasonable BTW) relationship is used why not solve the solution analytically in closed form (do the appropriate integrals mathematically versus numerical integration).

    6) Just look at the temperature curves that are shown (ending at 2000 AD) in the following image;

    http://climatesanity.files.wordpress.com/2010/04/test-4-temperature.png?w=449&h=321

    7) GIGO

  41. 91
    James Staples says:

    In the (Feb or Mar 12th, I think) Science, there was a very interesting Item about a Sea Level peak, of ~ 1 M above current levels, at around 82kya (MIS 5-ish), which was based on the study of Calcite Fomrations in Majorcan Caves.
    Because, based on Antarctic Ice Core data, this rise cannot be attributed to CO2 levels being as high as they are now; many would see this as an excuse to nay-say Anthro-forced Glbal Warming.
    I think it’s probably attributable to a concurence of the various Milankovic Cycles leading to increased insolation; and, perhaps, that the subsequent plunge back into Ice Age Conditions was caused by the Toba Eruption at ~ 78 kya.
    It would be nice to see Real Climate offer up an Opinion on this; maybe we could convert Burt Rutan!

  42. 92
    Anonymous Coward says:

    Ed (#79),
    You don’t need to convince reactionaries or coal state senators. All you need is 50%+ in most states including some of the biggest. If a minority is dead set against you, you need to work around it by appealing to the majority. It’s pointless to try to convince everyone. How do you think Lincoln got his majority? He wasn’t even on the ballot in the South. Even in Maryland, he got only 2% of the vote. But he got over 50% in most northern states, including the biggest ones.
    Lincoln had righteousness on his side but he also promised people land. Now you can offer them “Fee & Dividend”: most people consume less fossil fuels than the average and would therefore benefit.

  43. 93
    Doug Bostrom says:

    Hank Roberts says: 8 April 2010 at 10:15 AM

    Gilles, please stop.

    Hank, it’s sort of the same deal as getting ExxonMobil to stop selling gasoline. We have to stop using it before they stop selling it. With Gilles, it’s “stop replying.”

  44. 94
    Daniel J. Andrews says:

    Thanks David, Bob, Brian. I’m less embarrassed about asking that question now but unfortunately am now more embarrassed at the failure of my Google skills. :-( –dan

  45. 95

    Martin,

    It seems fundamentally reasonable that the rate of heat going into the oceans would depend on surface temperature.

    However, it looks like you and Stefan do not take into account the process whereby the global temperature, at the surface, would be reduced by the fact of heat going into the oceans. Is that true?

    I continue to think that the global temperature increase will be moderated by heat going into the oceans. Deeper ocean tempertures will continue to rise at a rate needed to keep weather somewhat under control. And of course, this will drive sea levels ever higher.

  46. 96
    Gilles says:

    Hank and Doug : I just post comments about what seems to me interesting, and sometimes erroneous. Possibly the fact that the conclusion is often “ehmm, I’m not sure it’s a good idea to stop now the use of fossil fuels” may be simply due to a frequent occurence of the opposite statement “oh we should obviously stop using fossil fuels” which may not be sustained by a real logical argument and biased by some prejudice- but if my argument about the long timescale is incorrect, I think you have here the opportunity of explaining why.

  47. 97
    Hank Roberts says:

    Ocean pH rate of change, Gilles. Forgetting all else, that’s enough reason to stop burning carbon. You can look this stuff up.

  48. 98
    Doug Bostrom says:

    Gilles says: 8 April 2010 at 7:34 PM

    Find a mirror and argue away.

  49. 99
    Martin Vermeer says:

    Jim #95:

    However, it looks like you and Stefan do not take into account the process whereby the global temperature, at the surface, would be reduced by the fact of heat going into the oceans. Is that true?

    Jim, I don’t think so. GIStemp are air temperatures a couple m above the land surface, and something more complicated involving both air and surface temps over the oceans, see Hansen et al. 1996. Above the ocean, air temps closely track water surface temperatures. If T changes abruptly, a heat flux into the ocean is established that rapidly (few years, much shorter than the smoothing time scale of 15 years we use) brings the surface (mixed) layer temperature up to the new equilibrium value, following roughly an exponential decay; and the measured air temperatures will do the same. This rapid-response behaviour is approximated by the b dT/dt term.

    I remember I had a detailed description of this (though not quite this one) in an early draft, but it fell by the wayside.

    I continue to think that the global temperature increase will be moderated by heat going into the oceans.

    And you would continue to think right… this is incorporated in the “secular” a (T – T0) term. The coefficient we found for this deep-ocean part from model runs was around 0.08 cm/year/degree.

  50. 100
    Gilles says:

    97. Hank: well – that’s another topics, but that could be an argument indeed. But then you have to state explicitly the amount of carbon above which the acidification of oceans become a problem worse than stopping fossil fuels. It may exist – the problem is only to convince people it is reached.


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