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Friday round-up

Filed under: — group @ 28 January 2011

A few items of interest this week.

Paleoclimate:
1. A new study by Spielhagen and co-authors in Science reconstructs temperatures of North Atlantic source waters to the Arctic for the past two millennia, adding another very long-handled Hockey Stick to the ever-growing league.

2. From last week, an article in Science Express by Buntgen et al reconstructing European summer temperature for the past 2500 years, finding that recent warming is unprecedented over that time frame, and providing some historical insights into the societal challenges posed by climate instability (listen here for an interview with mike about the study on NPR’s All Things Considered).

3. The team of ice core researchers at WAIS Divide reaches its goal of 3300 meters of ice. [WAIS Divide, central West Antarctica, is a site of significant warming in Antarctica, over at least the last 50 years, a result recently confirmed by the study of O'Donnell et al. (2010); Stay tuned for more on the that soon].

Other Miscellaneous Items:
1. More in Nature on data sharing.

2. A great primer in Physics Today on planetary energy balance from our very own Ray Pierrehumbert (link to pdf available here).

3. Now shipping are David and Ray’s The Warming Papers and Ray’s Principles of Planetary Climate.


96 Responses to “Friday round-up”

  1. 1
    Pete Dunkelberg says:

    I got raypierre’s book recently. For some reason there was one available from Germany. It’s a beautiful book of pure physics. Now about that primer at Physics Today. pdf available where? $23?

    [Response: It's worth stating that the pricing model for Physics Today makes absolutely no sense whatsoever. PT gets delivered to everyone with an AGU membership ($20 a year), and so a charge of $23 for a single article is simply ridiculous. The marginal cost of allowing access to the article is close to zero and the actual income from these articles has to be trivial for the magazine as a whole. PT should either charge a trivially small amount per article or charge $20 and throw in a free subscription. I would encourage everyone to send an email protesting these ludicrously arbitrary charges. - gavin]

    [Response: I also think the Physics Today pricing model is ridiculous. In fact, it's so locked-down that people can't even get articles through the University of Chicago Library without a one year delay. You have to use your personal subscription for that. However, so far as I know, I am free to distribute reprints myself. Note that the pdf linked in the post is an a open-access version available from my reprint site. --raypierre]

  2. 2
    Stephen says:

    2nd attempt; sorry if this double-posts.

    Did you miss this week’s good news from Nature that Greenland glaciers appear to slow down in warmer temperatures:

    http://www.nature.com/nature/journal/v469/n7331/full/nature09740.html

    seemingly ruling out unexpected large additions to sea level rise from accelerated melting of Greenland glaciers?

  3. 3
    Hank Roberts says:

    Stephen, read that Nature article again and some of the linked papers. It’s saying not to expect the Greenland (continental) glaciers to rush to the sea in summertime in floods of water carrying chunks of solid ice.

    Not that they’re melting less, but that they’re melting so fast the meltwater cuts right through them and flows away during the summer, as happens with mountain glaciers. The paper isn’t about total meltwater volume but about the annual cycle observed so far.

    Here’s what I think they’re saying:

    The outburst floods seen so far
    http://www.google.com/search?q=greenland+outburst+flood
    aren’t expected to happen more often as melting increases.

    The sequence they describe as I read it would be something like this:

    Spring comes. The solid ice melts at the top; meltwater moves down through cracks to the base, builds up, lifts the ice and lubricates the contact with the rock; the glacier advances.
    Summer comes. Water melts ice out along the base and escapes downstream; the ice sinks back into firmer contact with the base rock as the lubricating water runs right through the glacier in the open channels.
    Fall comes. Less meltwater flows; it’s colder; the outflow channels freeze up; water builds up under the glacier and it advances again.
    Winter comes. The ice squeezes the channels shut and settles against the rock, closing the openings.

    A real scientist can do much better. As I recall only a few years ago it was just speculation that glaciers developed meltwater passages all the way through them annually.

  4. 4
    Robert says:

    Stephen @ 2
    “seemingly ruling out unexpected large additions to sea level rise from accelerated melting of greenland glacers”

    That is not a correct statement to be making. This study basically addresses the Zwally effect which is based on the theory that enhanced basal lubrication from meltwater reaching the bed would speed up glaciers. The study only shows that eventually the drainage becomes effective and the glaciers slow down after the initial pulse. The zwally effect is not considered to be the primary cause of accelerated ice losses from either ice sheet.

    The primary cause of accelerated flow and accelerated losses is glacier acceleration due to grounding line retreat, removal of fringe ice shelves and removal of sea ice. These features provide backpressure on the glacier and when removed glaciers accelerate. Please consider consulting some reference textbooks or websites

    http://www.skepticalscience.com/Part-One-Why-do-glaciers-lose-ice.html

  5. 5
    Arthur Smith says:

    On Ray’s book – I dropped by my local Borders (the only place I go for paper books these days) and took a look at the “Science/Environment” section on the chance his book might have made its way there already. I was horrified! It was filled with “skeptic” books – yes it had 1 copy of “An Inconvenient Truth”, but there was a big display of “Cool It” from Lomborg, many copies of Roy Spencer’s books, Singer’s nutty “Unstoppable” book, etc. etc. I was not heartened to see Pielke’s “Climate Fix” also rather prominent. I didn’t look hard, but Al Gore and Donella Meadows seemed to be the only representatives of the truth about global warming, and their books were single entries spine-out, not front-facing piles like some of the others.

    Who makes these book placement decisions? Is somebody paying for all this? Can they really be selling that many of the “skeptic” books?

  6. 6
    Hank Roberts says:

    Mountain glaciers are showing more outburst flood events
    (hat tip to: http://www.desdemonadespair.net/2010/12/50-doomiest-graphs-of-2010.html )
    http://lh5.ggpht.com/_pQyvcBbJ0Fs/TP-16aj40VI/AAAAAAAADA8/vi6nmDsWTws/image_thumb%5B2%5D.png?imgmax=800
    http://www.grida.no/publications/high-mountain-glaciers/

    The Science paper, I think, says don’t expect Greenland to collapse as other giant ice caps did toward the end of the last ice age, like these:
    http://www.nature.com/nature/journal/v464/n7289/abs/nature08954.html

    Iceland: “…. The release of meltwater from glacial lakes can take place as a result of two different conduit initiation mechanisms and the subsequent drainage from the lake occurs by two different modes. Drainage can begin at pressures lower than the ice overburden in conduits that expand slowly over days or weeks due to melting of the ice walls by frictional and sensible heat in the water. Alternatively, the lake level may rise until the glacier is lifted along the flowpath to make space for the water and water discharges rise linearly, peaking in a time interval of several hours to 1-2 days. In this case, discharge rises faster than can be accommodated by melting of the conduits….” http://hal.archives-ouvertes.fr/hal-00480676/

  7. 7
    Ray Ladbury says:

    Arthur@5, Now you know the secret to publishing success–aim for the idiot market. Just think how much Singer could have made with a pop-up version of his screed.

  8. 8
    Dikran Marsupial says:

    I have also bought “Principles of Planetary Climate” and “The warming papers”, all I need now is the time to read them (have made a start on TWP). Many thanks!

  9. 9
    chris colose says:

    Ray’s Physics Today article is fully online through his webpage
    http://geosci.uchicago.edu/~rtp1/papers/PhysTodayRT2011.pdf

  10. 10
    JCH says:

    Hank, I think what Stephen is saying is nonlinear versus linear. If you can’t get large amounts of ice into the sea, does that support his statement that the possibility of nonlinear SLR is “ruled out?”

    It would seem at least some of it could be.

  11. 11
    Hank Roberts says:

    JCH, that’s not in the paper. The melt rate can continue to increase (more warm days, more meltwater into the ocean) without lifting the whole glacial mass and making it slide into the sea.
    It’s the difference between disastrous and catastrophic. The trend is not expected to be linear, in any recent work I’ve seen.

    Good: http://www.sciencefriday.com/program/archives/201101281
    (audio files usually go up fairly soon after the broadcast)

  12. 12
    Jim Groom says:

    Chris Colose #9
    Thank you for the link. What a great article. In particular I found the portion of ‘Spectroscopy of greenhouse gases’ most informative and useful. Again, thank you.

  13. 13
    Septic Matthew says:

    FWIW, Pierrehumbert’s book “Principles of Planetary Science” is a great bargain by contemporary book price standards. Not only is it 600+ pp of gorgeous text, mathematics and graphics for only $80 plus shipping, but the Python code for all the exercises is provided online and much else is available online besides. The author includes informative commentary on the references. I was surprised by the brief introduction to Lebesgue integration. I am sure that many more surprises are included.

    There does not seem to be any actual definition of “climate”. Wikipedia says that it is the statistics of measured attributes such as temperature, pressure, wind speed, rainfall, etc. Would it not be better to call it the “distribution” of measurable attributes, including the spatio-temporal variation in the distribution. The statistics based on the measures can fluctuate with no change in the underlying distribution, and the distribution can change before there are confirmed changes in the statistics. Just curious.

    I am sure that no one here will regret buying the book.

  14. 14
    Deech56 says:

    This article has been making the rounds, especially because of this article:

    http://www.telegraph.co.uk/earth/environment/climatechange/8284223/Himalayan-glaciers-not-melting-because-of-climate-change-report-finds.html

    Interesting that the title of the Telegraph article does not reflect the content of the journal article abstract. Also interesting that the Telegraph devotes a lot of space to the “2035″ canard.

    Science Daily had a much better take, IMHO: http://www.sciencedaily.com/releases/2011/01/110124162708.htm

  15. 15
    Hank Roberts says:

    JCH, nope, what Stephen says is not in the paper.

    Stephen gives half the story: “Greenland glaciers appear to slow down in warmer temperatures.”

    The paper is about how, after warm weather first speeds up the glaciers, then if the meltwater opens big enough holes, those drain that lubricating layer off, and the ice slows down compared to its peak speed. They’re saying sometimes outburst floods won’t happen. But the evidence is they’re happening.

    “… you gotta know the territory ….” http://www.endresnet.com/mmsounds.html

    Take a look at doi:10.1016/j.epsl.2010.12.037 “Seasonal speedup of the Greenland Ice Sheet linked to routing of surface water”

  16. 16
    JCH says:

    13

    Hank, I perhaps misunderstand this. That would be nothing new, but water melting and flowing into the sea is linear melting and has been modeled by Vermeer and Rahmstorf and many others, and it arrives at a prediction of ~1 meter of SLR by 2100.

    Modeling nonlinear melting requires understanding how large amounts of ice, exceeding the background, will find their way into the sea ahead of “schedule”, which is what Hansen expects will happen during this century: closer to 5 meters than to ~1 meter.

    Your second link hints that their work can be a basis for that, which is exactly the sort of thing for which I have been looking.

  17. 17
    Jim Galasyn says:

    Just received Ray’s Principles of Planetary Climate from Amazon, and it looks beautiful. Now must order The Warming Papers.

  18. 18
    Hank Roberts says:

    Hm, that paper is being widely blogged. Pat Michaels at Cato claims ( http://www.cato-at-liberty.org/the-current-wisdom-3/ ) that paper proves sea levels won’t rise, because melting will stop when fossil fuels run out before the planet warms to equal 10,000 years ago.

  19. 19
    Hank Roberts says:

    JCH, are you thinking that paper rules out what Rahmstorf wrote not long ago?

    “The linear relationship … considers only surface mass balance, without taking account of the kind of rapid, nonlinear ice-flow changes that some glaciologists expect for the future” ( http://www.nature.com/climate/2010/1004/full/climate.2010.29.html )?

    I don’t see how. Make a hole under the ice one year, the ice flows down in to fill them during the winter, and then that melts out the next year; that’s a different kind of flow than horizontal. It happens in loose dirt too, look up “tunnel gully” — those might be an interestingly analogous process if drainage openings enlarge sufficiently for surfaces to collapse into them. I suppose someone’s watching for surface sag on the ice.

    It’s a lively area. I’ll await comments from someone who actually does science, I’m read out on this for a while.

  20. 20
    Hank Roberts says:

    > tunnel gully
    Interesting, these happen in permafrost too:
    http://onlinelibrary.wiley.com/doi/10.1002/ppp.595/abstract

  21. 21
    Nick Barnes says:

    The Sundal et al paper in Nature this week seems to be observational confirmation of Schoof’s modelling paper in Nature in November, which is reference 13 in Sundal et al. http://www.nature.com/nature/journal/v468/n7325/abs/nature09618.html

  22. 22
    Thomas says:

    The Nature paper seems to be saying that the enhanced basal slipage due to meltwater is a selflimiting process. We could still get increased overal flow, if the area of the icesheet which suffers significant enough annual melting to supply water to the base increases. It also says nothing about the trajectory of surface albedo with time in the melt zones. How much dirt accumulates from year to year, versus how much is flushed down the moulins? I think this is a crucual question concerning a potential acceleration in the rate of melting.

  23. 23
    Chris Dudley says:

    raypierre,

    Now that your book is available again, could you please use it to explain what is wrong the the chapter on the Venus Syndrome in James Hansen’s book ‘Storms of my Grandchildren’? His book is available at your library. You seem to think that based on first principles, a water vapor runaway can’t happen but I’d like to know if his specific argument is countered by what is in your text. Thanks.

    [Response: I haven't gotten around to reading that section of Jim's book, but I have seen him present what appears to be similar claims at AGU. The answer to your question is: Yes, the fundamental physics which I go over in Chapter 4, as part of the discussion of the runaway greenhouse, absolutely rules out a water vapor runaway greenhouse on Earth, until the Solar luminosity increases sufficiently, which won't happen for a half billion to billion years. When you bring clouds into the picture (which I don't do in any detail in the runaway discussion in the book, because it's completely unresolved) it is harder to make absolute statements from any simple physical arguments, but clouds would have to do something so extreme that if the Earth were really subject to a cloud-induced runaway it is likely it would have happened during one of the high CO2 episodes sometime in the past. Basically, for clouds to induce a runaway you need near 100% cover of low albedo (large particle) clouds with high water content at very high altitudes. --raypierre]

  24. 24
    John Mason says:

    Ray P, thanks for making that PDF available. I concur with you & Gavin: paywalling material like this is ridiculous and it leaves interested people little option but to hassle authors for PDFs in order to keep up with their reading – few individuals like myself can afford to pay for several dozen papers a year in these austere times!

    Cheers – John

  25. 25
    Anders M says:

    An article from last week I hope to see some expert comments on is Kopp & Lean “A new, lower value of total solar irradiance: Evidence and climate significance”:
    http://www.agu.org/pubs/crossref/2011/2010GL045777.shtml
    What are the implications?

    [Response: Properly calibrating the solar irradiance measurements is important for getting better constraints on the variations in solar over the satellite era, but the actual mean value (or in this case the mean over the last three minima) doesn't actually matter that much for climate modelling. The impact of their suggested change is equivalent to rebalancing the energy balance at the top-of-the-atmosphere by a little less than a 1 W/m2 in climate model control runs. But this is such a small change that the climate sensitivity or climatology is not going to be noticeably affected. (Note that all climate models are tuned for radiation balance in their control set-up and small imbalances occur all the time as a function of changes in resolution, physics or parameterisations. This is a very different issue to how the models react to a transient change in TSI.) - gavin]

  26. 26
    Anders M says:

    Thanks for the guick and informative reply!
    Just one more question :)
    Does this in any way affect “Trenberth missing heat” ( http://www.sciencedaily.com/releases/2010/04/100415141121.htm )?

    [Response: No. It does slightly narrow the uncertainty on the albedo (i.e the SW component) at the top of the atmosphere, but the errors there are too large for them to be a useful constraint on the real net radiative balance. - gavin]

  27. 27
  28. 28

    See the world heating up 1884-2010 in this new NASA animation. Pretty hard to deny this! http://bit.ly/NasAni

  29. 29
    Daniel J. Andrews says:

    Thanks for the pdf to the PT article (as a new member of the AGU I thought I would have access to it for free).

    [Response: In fact you should. All members of AGU get Physics Today,
    so far as I know. You just need to enter your data on the PT web page to get an account that gives you
    electronic access. --raypierre]

    Are there any plans to bring out The Warming Papers in an e-reader format (e.g Kindle?).

    [Response: It would be nice; probably wouldn't be any cheaper than the paperback version, since the cost was mainly due to copyright fees the publisher had to pay. I could see it on an iPad, but the large format pages probably would be hard to read on a Kindle, unless they have a new large-format version out. --raypierre]

  30. 30
    caerbannog says:

    Nice piece in C&E News, Gavin (http://pubs.acs.org/cen/books/89/8903books.html). And it’s good to see some “D” bombs being dropped in such a staid publication. It’s especially nice to see C&E News take it out from behind the paywall and make it available to the general public. Good and gutsy move on the part of the C&E News folks.

  31. 31
    John Mashey says:

    1) Rudy Baum, Ed-in-Chief of C&EN is a savvy guy regarding this topic.

    2) Good review, but I offer a minor suggestion.
    I increasingly believe that it is worth distinguishing between pseudoscience and anti-science, because the former is often chaotic and even outright silly, whereas anti-science is often quite serious and lumping it with the former can trivialize it. Of course, in a short review, there may be insufficient space.

    From CCC, p.7:

    “Anti-science especially seeks to bypass science with regard to public policy, using many tactics created for the tobacco wars, and employed widely since then against other areas of science.”

    “Pseudoscience
    When ideas are repeatedly examined, often explicitly refuted, but originators persist in the face of a strong
    imbalance of evidence, at some point it becomes pseudoscience, an attempt to convince scientists to adopt ideas for which the balance of evidence is strongly adverse. In some fields, its primary use is sales.”

    “Anti-science
    Agnotology was coined by Stanford‘s Robert N. Proctor [PRO2008] to describe the deliberate production
    of ignorance and doubt. When applied to scientific topics, it might be called anti-science, employed
    especially when research results threaten strong economic or ideological interests. It is rarely intended to convince field professionals, but to confuse the public and especially decision-makers in government and business.”

    P.8 has a chart. I’d claim that typical pseudoscience starts with some idea desired to be accepted by science, whereas anti-science doesn’t care about the specific ideas as much as obscuring science.

    For example, when one sees N different contradictory ideas offered at Heartland conferences, each idea may be pseudoscience, and each promoter may believe their idea, but the overarching goal is to promote doubt and confusion. For example, Scafetta’s slides, see #62, where Rhodes Fairbridge is invoked on wobbles of Sun from Jupiter, etc feel like pseudoscience to me. GMI+Singer engaged in a long-term anti-science campaign, a bit different.

  32. 32
    lucien p. locke says:

    very slightly off topic sort of….
    I thought it would be a good thing to list all of the internet articles based on denial and put into a archive for future review of false information and misinformation propagation….for instance, from American Thinker, Jan.29,1011,…..http://www.americanthinker.com/2011/01/greenland_is_going_to_be_ok.html
    I am keeping these bogus articles in a folder for now…but am hoping someone thinks it would be a good idea to put this and others like this into a public domain to which others maybe able to add to.
    respectfully,
    lucien

  33. 33
    Daniel J. Andrews says:

    In fact you should. All members of AGU get Physics Today,
    so far as I know. You just need to enter your data on the PT web page to get an account that gives you
    electronic access. –raypierre]

    Ah. Indeed I now do. I hadn’t realized I needed to set-up an account–the original email link that should have set me up just led to a “too many redirect” loop. They just sent me a new link and that works. Thank you.

    I could see it [Warming Papers] on an iPad, but the large format pages probably would be hard to read on a Kindle, unless they have a new large-format version out. –raypierre]

    If it was too difficult to read on my Kindle, I could view it on the downloadable Kindle for PC. That is how I read my Climate Change Biology e-book when I want a better look at some of the pictures, or want to see more of the page.

    I wasn’t too worried about the cost of The Warming Papers either–it is a matter of convenience in that I like being able to carry numerous books/papers with me when I’m away. The Kindle 3 seems to have worked out the pdf viewing bugs that plagued Kindle 2, so I’ve loaded a number of pdfs too.

  34. 34
    J Bowers says:

    For thoes with access to the BBC, Storyville follows Monckton on tour in ‘Meet the Climate Scpetics’, BBC Four, 10pm, Monday 31st January.
    http://www.bbc.co.uk/programmes/b00y5j3v

  35. 35
    CM says:

    Re: Kindle
    I just read raypierre’s radiative transfer primer on one. Took a fair bit of panning and zooming to get all of figure 2, and of course the excellent fit between modeled and observed spectra in fig 3a was all but invisible in graytones. Otherwise it was great; the column width fits the screen width at 200% magnification for large, legible letters. It’s becoming my favorite platform for keeping up with comments here, and though I won’t often be typing a comment this long on it, it is now capable of getting past recaptcha.

    Great primer — I’ve absorbed some understanding of the subject from this blog, but this reading broadened the tails considerably. Saturation is still a long way off, though…
    :)

  36. 36
    Jacob Mack says:

    Thank you Raypierre, always fair and balanced commentary, projection analysis and sound physics from your posts.

  37. 37
    calyptorhynchus says:

    1. The reporting of the Greenland glaciers Nature paper that I saw was sadly along the lines of #2, not #3, sigh!

    2. Whenever I visit a book shop I check the climate science shelves and if there are any denialist books I move them to the fiction section.

  38. 38
    David B. Benson says:

    calyptorhynchus @36 —

    :-) for part 2; right on!

  39. 39
    Michael says:

    An interesting thing I see on the Atlantic water hockey stick is that most of the warming appears to have occurred between 1800 and 1900. The two possibilities I can think of are that natural variability played a large part, or that there has been a very non-linear response to Co2 increases (or both). Perhaps a non-linear response could be due to albedo feedbacks, if during the 19th century a small warming due to small increases in Co2 (280ppm > 300ppm) melted quite a large amount of ice in the far north Atlantic. In comparison since 1980 the ice edge in summer has hardly moved on the Atlantic side, and mostly retreated in the Arctic basin on the Pacific side.

  40. 40
    Steve Bloom says:

    Re the Greenland ice sheet (I don’t have access to the paper), is there a discussion of why we would expect the channels to be able to handle large increaes in the volume of meltwater? Coming at it from another direction, what would an eventual bulk melting process look like? I wonder in particular about the handful of major discharge channels that run all the way inland. To the extent that these would act like river drainages, would we expect to see at some point enough water in them to destabilize the overlying glaciers, and if so how would things proceed?

  41. 41
    Lewis Peterson says:

    Too bad most of these articles are only available on payment of substantial amounts of money.

    [Response: Yes, that's a hindrance. Always do a search for any openly available copies that may be available, and if no luck, email the corresponding author directly and ask for a copy.--Jim]

  42. 42
    Adam R. says:

    calyptorhynchus says:

    2. Whenever I visit a book shop I check the climate science shelves and if there are any denialist books I move them to the fiction section.

    What a splendid notion. I shall follow your subversive example the next time I am at the bookstore.

    [Response: Tempting, but not a good idea.--Jim]

  43. 43
    john byatt says:

    # 42, worth checking your local library though to see where they are putting denialist science, years ago our library was placing creation science in with science, managed to convince librarian to put them into theology,

  44. 44
    CM says:

    Re: free copies of paywalled papers,

    These often lie around somewhere on the web pages of one of the authors. Browsing for them takes time, emailing an author to ask can be daunting. The following trick is sometimes a shortcut:

    Locate a characteristic phrase from the paper — a sequence of say 6-8 words that would not be likely to show up in a whole lot of other documents. Paste into your favorite search engine and surround with quotation marks to search for the exact phrase.

    To avoid wading through a lot of hits that don’t contain an actual offprint, it’s best to avoid using a phrase from the abstract, or from the main conclusion, as these tend to bring up too many hits. (You can get a phrase from the article body if someone quotes from it, or if the paywalled site displays the first page of the article. Of course, it’s easiest for those who can access the full text to begin with.) Using Advanced Search options to search only for PDFs may help narrow it down.

  45. 45
    Paul Guinnessy says:

    You may find the permanent link to the Physic sToday article more useful. http://dx.doi.org/10.1063/1.3541943

  46. 46
    Hank Roberts says:

    For Steve Bloom, I recalled where Mauri Pelto answered when I asked that question:

    “… Ice under pressure would deform and flow into this void. This happens to much of the seasonal hydrology system each winter. Without water flow to keep tunnels open, they close, then in spring maximum water pressures often occur befor the conduit system redevelops. Once opened the flowing meltwater can maintain these narrow conduits. However, the meltwater does not have enough heat to melt much…. I still see a persistent misconception about the ability of meltwater to melt glacier ice and riddle the glacier with holes. I work on glaciers with lots of melt and they are not weakened by all the meltwater drainage….”

    http://www.realclimate.org/?comments_popup=550#comment-85450

  47. 47
    Chris Dudley says:

    raypierre (#23),

    Thanks for your response. That is pretty much what I remembered from your draft.

    Interestingly, Hansen addresses your point that a runaway should have happened in the past first on pp 231-232:

    “At earlier times, when atmospheric carbon dioxide was more abundant, the sun was dimmer. For example, 250 million years ago the sun was 2% dimmer than now. A 2% change of solar irradiance is equivalent to doubling the amount of carbon dioxide in the atmosphere. So if the estimated amount of carbon dioxide in the atmosphere 250 million years ago was 2000 ppm, it would only take about 1000 ppm of carbon dioxide today to create a climate equally warm, assuming other factors are equal…. In other words, the fact that some scientists have estimated the carbon dioxide was much larger earlier in Earth’s history, perhaps even by a few thousand parts per million, does not mean that we could tollerate that much carbon dioxide now without hitting runaway conditions, becuase the sun is brighter now.”

    His next argument is that climate sensitivity is an increasing function of temperature. He claims that recent work on the PETM tends to confirm the model based estimates shown in fig. 30 on p. 227.

    Finally he considers that burning all conventional fossil fuels is likely to destabilize methane hydrates and, I think, that additionally burning tar sands and shale oil makes that certain to happen. At that point he sees a runaway as inevitable.

    On p. 225 he describes the Venus runaway as a water vapor runaway so I think that is what he means when he talks about ‘a runaway greenhouse effect that would destroy all life on the planet [Earth]‘ p. 236

    On your point about low albedo high altitude clouds, it seems pretty clear that an atmosphere which is primarily water will have high altitude clouds. The droplet size will depend on the vertical stability of that layer. If it is playing a primary greenhouse role, I wonder of the three micron ice absorption feature would play any role in radiatively induced mixing by providing an opacity switch? Models of stellar pulsation sometimes rely on that kind of physics.

    In any case, an atmosphere with say twice as much water vapor as nitrogen will be trying to sustain a steeper lapse rate and should be pretty convective for that reason leading to large droplets at high altitude I think. With a physically larger atmosphere (90% water vapor), things might settle down some since the temperature gradient would not need to be so steep.

    [Response: Jim's insistence that a Venus-type runaway is a credible risk is an unfortunate distraction. The crux of the matter is that it is very hard to place any simple a priori bounds on how much
    clouds could warm the climate. In order for cloud feedbacks to trigger a Venus-type runaway, however, the clouds have to do something so extreme that a tiny proportional change in the cloud feedbacks would enable that to happen even without any CO2 increase and even despite a slightly fainter Sun. Jim's argument about the dimmer Sun is not the least convincing. With the usual albedo estimate, a 2% dimmer Sun just amounts to 4.78 W/m**2 averaged over Earth's surface, and if you are going to argue for something like 30 W/m**2 of extra net cloud forcing to trigger a runaway then the difference that dim-Sun effect makes doesn't look so impressive; a slight further fluctuation in clouds could make up for it, or for lower CO2. Besides that, CO2 was probably already high in the Paleocene, and at that time, the Sun was less than a half percent dimmer. Talking about extra CO2 or methane release from feedbacks doesn't change the argument, since the OLR is determined by water vapor and water clouds in the runaway state. I actually think clouds make the runaway harder. As I argue in Chapter 5, clouds fairly deep in the atmosphere still increase the albedo, but in a steam atmosphere they need to be at altitudes well above the 100mb level to even have a chance to affect the OLR; otherwise their infrared effect is blocked by water vapor opacity. I also point out, however, why this argument isn't completely watertight. But basically, there is absolutely no credible cloud physics to suggest that clouds could make up the large energy deficit required for a planet in Earth's orbit to go runaway. You could worry that we can't absolutely rule it out, but that requires such extreme cloud feedbacks that you might as well say climate is so fragile it could do anything at all, with or without us poking it.

    So maybe I've made you all feel a little better by saying there's a vanishingly small chance that increasing CO2 could evaporate away our oceans and turn the Earth into Venus. But that deafening sigh of relief I'm hearing
    may just be drowning out the much more serious and credible threat I'm trying to tell you about -- that neither cloud physics nor any paleoclimate proxy can at present rule out a climate sensitivity as high as 8C for a doubling, while we might well go considerably beyond quadrupling if all the coal is burned and there are land carbon or sedimentary clathrate releases. That world wouldn't be as lethal to all life as Venus, but it would certainly pose an existential threat to human society. I don't view it as an especially probably outcome, but it doesn't require clouds to do anything nearly as farfetched as they would have to do in order to trigger a runaway greenhouse --raypierre]

  48. 48
    JBL says:

    Re: reshelving books, all you do is create more work for bookshop employees.

  49. 49
    Martin Vermeer says:

    CM #44: for me what often works is paste the full title into the search box of Google Scholar. You get a list of all the copies, and if you’re lucky, one of them is a clickable PDF.

  50. 50
    Steve Jewson says:

    David Carlson’s article advocating free and open sharing of data would cost me $32 to read (so I won’t). Pretty ironic.


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