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On straw men and Greenland: Tad Pfeffer Responds

Filed under: — eric @ 18 September 2008

In a recent post about sea level rise, we highlighted a paper by the University of Colorado’s Tad Pfeffer and others in which they show that one can rule out more than 2 meters of sea level rise in the next century. While we liked the paper very much, we also complained that Pfeffer and colleagues had created a bit of a straw man, by implying that it had been seriously proposed that Greenland’s near term contribution to sea level rise could be much larger than that. In fact (we said), none of us in the climate science community ever took such ideas seriously, even if the popular press thought we did. Tad responds by pointing out that in fact there is published work attributing considerable likelihood to such extreme scenarios, and that there are numerous studies that at the very least strong imply it. He also reminded me that their paper actually rules out a contribution of more than about 50 cm from Greenland, significantly below some other recent published estimates. That makes their work even more important, since there are several publications that definitely consider upwards of one meter (from Greenland alone) by 2100 to be plausible. Pfeffer et al. conclude that that is simply not the case (at least in their informed view). Still, we remind readers that our chief complaint was that Pfeffer et al.’s work was taken by many in the media as a downward revision to sea level rise estimates, whereas in fact most informed estimates had put an upper limit well below that. See our earlier post on the IPCC Sea Level numbers.

In any case. Pfeffer et al’.s response to our post follows below. Fair enough.

A response to RealClimate’s post on our paper about sea level rise

W.T. Pfeffer, J.T. Harper, and S. O’Neel
15 September 2008

We have read with interest – and, we admit, surprise – the RealClimate post concerning our 5 September publication in Science entitled “Kinematic Constraints on 21st Century Sea Level Rise.” The source of our surprise, however, is probably not what the RealClimate authors imagine – we had fully expected a vigorous defense of very high rates of sea level rise (greater than 2 m/century), but not a denial that such rates had ever been hypothesized.

We do not state anywhere in our paper that 2m or more of SLR by 2100 has been published as a peer reviewed and “informed estimate”. We do state that this has been ‘inferred’ and ‘argued’ as a “viable 21st century scenario”. We believe there is value in constraining the upper limits to the role of ice dynamics in future SLR. And, from what we know about historical rates of SLR in conjunction with what ‘we know we don’t know’ about ice dynamics, we believe it is reasonable to ponder very high rates of SLR in the next century. However, we also believe that it is problematic to project such a ‘hypothesis’ as a supported theory without proper testing by the scientific method. The question raised by RC is whether or not this hypothesis has circulated within the scientific community.

In his 2007 paper (Environ. Res. Lett. 2(2007)) Hansen proposes a rate of sea level rise of “5 m this century.” This is hypothetical, but he is confident that it is a “far better estimate than a linear response”. This is accompanied by his statement that he finds it “almost inconceivable that BAU climate change would not yield a sea level change of the order of meters on the century timescale.” The provisional nature of his discussion is irrelevant; it is an explicit statement that 5 m of sea level rise in this century is a possibility he regards as viable, published in the scientific literature by the person who is arguably (and deservedly) the most visible and authoritative climate scientist in the world. No reader of this paper would assume that Hansen didn’t actually mean what he said. Hansen reinforced this idea in other publications and statements, including in his briefing to Congress on 23 June 2008 (“sea level rise of at least two meters is likely this century”). Our analysis specifically tested the likelihood of next-century sea level rise of more than 2 m, and Hansen explicitly hypothesized 5 m of sea level rise in this century.

Hansen has gone on record with specific numbers, but other published studies including the 2006 Overpeck and Otto-Bliesner Science papers left the upper limit open ended, and certainly implied it could be quite high. The fact that this idea was present in the scientific community was confirmed for us by 8 scientific presentations we gave on this topic in the past year (5 in the US, including the Fall 2007 AGU and 3 in Europe). At none of those talks did anyone in the audience question what high forecasts we were referring to. The comments we got back on our work were overwhelmingly positive, and were along the lines that what we had presented was a good next step – both to move past the IPCC’s low sea level forecasts, and as a response to the persistent hypotheses of very high rates of sea level rise that were circulating. Criticisms, where they were voiced, were largely that we were underestimating the power of dynamics and that rates of sea level rise well in excess of 2 m/century might occur in spite of our conclusions.

We agree that the media coverage of our paper (as well as others before it) has undesirable side effects. Wherever we had the opportunity we pressed media writers not to use terms like “exaggerated” or “high sea level forecasts debunked,” and we have consistently stressed that our results indicate a very significant sea level rise and are no justification for any kind of complacency. We have stressed that even our low end scenario of 0.8 m of SLR would have tremendous consequences. However, we stand by our statements that sea level rise at rates of substantially more than 2 m this century were in fact put forward as a likely possibility.

Earlier this summer Andy Revkin published a piece in the New York Times about what he has termed the “Whiplash Effect”: confusion created in the public mind by media coverage of rapidly evolving scientific ideas. There has certainly been some whiplash in this case. However it is others who cracked the whip. We have simply refused to let go of the other end.

126 Responses to “On straw men and Greenland: Tad Pfeffer Responds”

  1. 51
    RichardC says:

    39 David, one would expect temperatures to only rise at the margins and underside of the shelves, as that’s where warmer sea water exists. Old data (1999) but
    says that the Ross ice shelf’s grounding line is retreating ~120 metres per year. Anyone have current data?
    Dr Naish’s team drilled through the Ross and concluded that it has collapsed quickly in the past.

    As far as “providing” ice, lots of WAIS is on a reverse-slope marine bed.
    The further it retreats, the deeper the grounding line gets, and the more efficient the thermohaline pump where heavy warmer salt water dives to replace fresh meltwater at the grounding line. It’s a nasty positive feedback that is much enhanced by increases in ocean temperature.

    Eric, I’m guessing few folks here have access to such papers. Short excerpts accompanying each link would be appreciated. Thanks.

  2. 52
    Jess says:

    Question, (and I am sure there is link someplace here)

    — I realized that I needed a good way to explain average sea level rise. The reason is that when I look at the water here in NYC and I think, “well, here’s high tide. If the water was six feet higher, it doesn’t look so bad.”

    That’s probably really, really wrong, but I wanted to know if anyone has a way to explain what 6 feet (or two meters) of SLR would look like, that would help. I mean, in New York (Manhattan) when I check out the google maps widget it doesn’t look like much would happen. I realize it is very different out by Kennedy Airport in Queens. The thing is, SLR is usually discussed in terms of averages, and sometimes measured in millimeters.

    So when I see a study saying the SLR is in X millimeters, and do an “eyeballing” it seems small, and I guess that’s what I need some help visualizing. Like, when I see an NYT story that says sea level rose 8 mm per year (I am making that up) it seems pretty innocuous, and so I was looking for help in getting my head around what those measurements mean.

  3. 53
    Dave Andrews says:

    Speaking of sea level rises I need a little clarification.
    In his testimony to the UK court Hansen said that sea level was now rising at double the rate of the 20thC. But according to CSIRO it is rising at 50% more than the rate in the 20thC.

    Which is correct?


  4. 54
    RichardC says:

    45 – Barton, I don’t see it working. It takes decades for permafrost to warm up and centuries for the deep ocean. The difference between now and warming up from glacial is that we’re starting from a much higher baseline, giving the system a much bigger and faster kick, and using CO2 instead of orbital cycles. The remaining ice is closer to the poles, so that mitigates it a bit.

    If mankind were to stop spewing CO2 at 385ppm, do you think the ultimate peak would be fairly close to 385ppm?
    I agree we’d get a quick nudge down, but if we take the permafrost carbon inventory of perhaps double the atmosphere as a simplistic guess for future CH4/CO2 feedback in the pipeline (instead of trying to nitpick marine clathrates, etc etc), we’d peak at 1100ppm or so. Other opinions?

    47 – Brian, only if you live in/close to Greenland. For other areas, apparent local sea level rise will be a tad more since the oceans will increase in mass and drag the coasts down with them.

    49 – Hank, an excellent idea, but what about the Faux Gnus effect? Either you let the whole thing degrade into a “You’re wrong” “No, YOU’RE wrong” shouting match, or you end up with a counter-show. After all, there’s REALLYRealClimate… Have you noticed the tremendous increase in skeptical internet traffic at the grass roots level? Lots of sites to pick from nowadays – WattsUpWithThat? SolarCycle24. Barry Moore at just used Spencer Weart’s stuff to “prove” Gavin Schmidt is full of it. “In conclusion, I agree with Weart, there are no easy answers and the IPCC case is far from proven. ”

    I think it’s going to take an ice-free arctic to gain traction. “Fortunately” that’s just around the corner.

  5. 55
    Nick Gotts says:

    Timo Hämeranta @42,

    So why has the sea level consistently fallen during ice ages, and risen during inter-glacials?

  6. 56
    Hank Roberts says:

    Paulm above referred to the 2005 drill cores that found mangroves below the Great Barrier Reef and dated them to a 200-year range, suggesting a very fast sea level rise there; another press release here with a bit more info:

    I’m curious whether the scientists contributing to this thread knew about this and know of any followup — any chance that the Australian coastline sank suddenly rather than sea level rising that fast there?

  7. 57
    Steve Bloom says:

    Re #11 reply: Eric, what I wonder in particular about the new Howat et al paper is that they describe thinning extending quickly inland (quoting from the press release):


    Howat and his colleagues concentrated on the southeastern region of Greenland, an area covering about one-fifth of the island’s 656,373 square miles (1.7 million square kilometers). They found that while two of the largest glaciers in that area – Kangerdlugssuaq and Helheim – contribute more to the total ice loss than any other single glaciers, the 30 or so smaller glaciers there contributed 72 percent of the total ice lost.

    “We were able to see for the first time that there is widespread thinning at the margin of the Greenland ice sheet throughout this region.

    “We’re talking about the region that is within 62 miles (100 kilometers) from the ice edge. That whole area is thinning rapidly,” he said.

    Howat says that all of the glaciers are changing within just a few years and that the accelerated loss just spreads up deeper into the ice sheet.


    I find it hard to reconcile these results with the Pfeffer et al conclusion that gateways are constraining the melt (unless it’s the case that the constraining effect is predicted to not become obvious until the rate of melt is much greater than at present).

    Also, I had asked in the other thread about this recent Eos paper finding a large degree of frictional melting in a recent Greenland jokulhlaup. Was the extent of this effect previously understood, and is it consistent with the present understanding of how the melting of the ice sheet will proceed? Excerpting:

    “On the basis of the stage-discharge relationship, the maximum Watson River discharge during the jökulhlaup is calculated to have been approximately 540 cubic meters per second, and the total runoff during the event is estimated to have been 28.8 million cubic meters (Figure 2b). Outflow from the ice-dammed lake is estimated to have been 11.3 million cubic meters; the additional 17.5 million cubic meters is due to frictional melting of ice as the flood traveled in contact with the glacier, together with an input from base flow.”

  8. 58
    David B. Benson says:

    Guy (43) — Use 350 ppm. These folks


  9. 59
    David B. Benson says:

    Hank Roberts (56) — I suggest burial by landslide or mud from extreme rainfall event. Here is a link describing this sort of problem near Cairns, Queensland, a typical departure port for visiting part of the Great Barrier Reef:

    However, as a whole, Australia is extremely tectonically stable:

  10. 60
    Hank Roberts says:

    > 30 or so smaller glaciers there contributed 72 percent of the total

    Steve, have you checked the specific sources of the smaller glaciers?
    Why are they “smaller” glaciers?

    I wonder — perhaps they don’t flow through ‘gateways’ and the large ones do? My hunch is the few large glaciers draw from the central ice mass through ‘gateways’ and the many smaller glaciers instead form mostly from snowfall on the outside of the ring of mountains around the icecap. Just speculating on this, I don’t have sources but perhaps someone can say whether there’s a different origin for the “smaller” glaciers.

  11. 61
    John Mashey says:

    re: #52 Jess is a useful tool for getting rough ideas. Zoom in on the map, and set the SLR in meters, and it grays out anything below sea levels (which of course, does *not* mean underwater). Do *not* use for real planning purposes, just to get a feel, since SLR varies, elevations aren’t necessarily great, etc, etc. The specific link is for +2m centered on NYC.

    As an exercise, pick an area you know well, simulate a town planner, and raise the SLR from 0 to +1m to +2m …. and guess at dates, and figure out what strategies you take.

    a) Do you build dikes?

    b) If so, where? Do you protect everything that’s already there, and keep raising the dikes, or do you draw the line further inland. If so, what do you tell the people outside the line?

    c) In considering the NYC area, the 3 major airports are near sea-level. Do you protect them all?

    d) Resources required for protection vary by the geography. For example, convex land isn’t too bad, because as the water goes up, the perimeter needing to protection shrinks, so you might be tempted to do the first dike further uphill.

    Concave shore is just the reverse, because the perimeter lengthens with SLR. Of course, with a concave shore that has a relatively short mouth, you might just close that off, and then have much less shoreline to protect directly. In some sense, that’s what the Dutch did with the ZuiderZee Works, although of course that wasn’t to protect against rising SLR.

    Of course, cities built around major river mouths have their own extra issues, i.e., that’s a particular kind of concave that has water flowing through it, and hence a long perimeter, and you can’t easily close it off without a lot of pumping. For example, one can imagine closing off the Southern end of the SF Bay, as not much water flows in from the South. It’s hard to imagine closing off the GoldenGate Bridge area.

    One always needs to make sure there will be enough energy to run pumps as needed, since area behind dikes will need pumping some of the time, i.e., see how New Orleans works.

  12. 62
    Hank Roberts says:

    David, did you find any source for info on that 2005 paper?

    Looking at the topography, the reef’s offshore a ways; the paper would suggest it was a barrier island covered with mangroves that was submerged. No cliffs nearby, no river deltas shown. But that’s only inference from looking on the map. Perhaps someone here’s from Australia or familiar with the research and can give us some facts on it.

  13. 63
    Mark in SF says:

    Serious question from a skeptic:

    If C02 is such a profound green house gas, and it has risen from 280ppm to 380ppm over the last century or so (?), why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already? As far as I know, the climate in California is much like it was in the 1850’s, and are things really much different?? Why should I worry about 450-500ppm?

    THIS IS A SERIOUS QUESTION, NOT RHETORICAL. If this is a true problem I want to do something about it. I understand this is probably not the appropriate place to post, but I’ve searched for an answer to this (I think) obvious question without result. I figure many knowledgeable people read this site, and can easily answer. Will check back in a day or so.

  14. 64
    Steve Bloom says:

    Re #60: I don’t really know, Hank, other than to point out that Howat stated that the small glaciers are draining the interior.

  15. 65
    Guy says:

    #58 – is a good site and one I want to embrace wholeheartedly, but their target seems to be based around Hansen alone. Also I’m surprised that their major NGO supporters seem thin on the ground – I assume because many are stll working to other targets thinking them sound. Are they sound?! These are precisely the reasons I’m desperately trying to get a specific 350ppm CO2 conentration RC response – still not forthcoming (10 attempts in 12 days and counting…) Remember, I’m not asking the impossible for an absolute definitive safe figure, but a reasonable target that stands a good probability of being safe, given all that we currently know, but is open to revision. RC’s Target CO2 posting seems to cautiously welcome the underlying science, but critically falls short of commenting on that vital conclusion.

    I’ve called it the elephant in the room in the entire debate, and that still stands as far as I can tell. With (seemingly) only James Hansen giving a figure for policymakers, there is little chance of real action being taken by the people that matter because they will simply point out his isolation. I’m nervous about the figure as I am antipating flack in the form of contradictiory statements from the scientific community. (as usual, existing links to other recent papers that I have missed or recent public statements by other senior climatologists referencing a target figure will be very welcome!)

    Incidentally, I found another recent story related to this by Tom Flannery – a study by Roger Pielke (doesn’t say which one), Tom Wigley and Christopher Green saying that the action needed to get emssions down will be much greater than forecast by the IPCC (report here – – if 350 is an appropriate target, it suggests it will be an even more phenomenally tough one than we already knew. Phew.

    PS – I appreciate that strictly speaking this off topic, but since it is a) essentially it is pertient to the outcomes of pretty much ever single thread on here and b) so important, I feel I must keep trying… thanks for everyone’s patience!

  16. 66
    Timo Hämeranta says:

    Re 42 Gavin, it seem we have to wait a bit more to see polar ice sheets growing for more heat when yr models have continuously overestimated polar amplification, please see:

    “Contrary to recent assessments based on theoretical models [IPCC, 2007] the anthropogenic warming estimated directly from the historical observations is more pronounced between 45 S and 50 N than at higher latitudes…. Climate models may therefore lack – or incorrectly parameterize – fundamental processes by which surface temperatures respond to radiative forcings…In contrast with climate model simulations, the zonal surface temperature changes…do not increase rapidly from mid to high latitudes.”

    Ref: Lean, Judith L., and David H. Rind, 2008. How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006. Geophys. Res. Lett., 35, L18701, doi:10.1029/2008GL034864, September 16, 2008, online

    Well, I can’t surprise you when we both know nobody knows how climate will evolve in near or far future.

  17. 67
    GlenFergus says:

    John Mashey at #61:

    a) Do you build dikes?

    If the stuff is valuable, too right; ample precidents.

    b) If so, where? Do you protect everything that’s already there, and keep raising the dikes, or do you draw the line further inland.

    This is not a new question. It applies to every city or town building or raising its flood levee. Politics aside (OK, I know…), you build it in the location which maximises the benifit : cost ratio (or some similar metric).

    If so, what do you tell the people outside the line?

    As per the town leeve, one says “Bad luck – move, or take ya chances.”

    c) In considering the NYC area, the 3 major airports are near sea-level. Do you protect them all?

    Yep. For expensive infrastructure like this it is definitely going to be worth building the levee for 2m SLR. 10m SLR, maybe not…

    d) Resources required for protection vary by the geography. For example, convex land isn’t too bad, because as the water goes up, the perimeter needing to protection shrinks…

    Huh? The 2-D slope shape does not affect the wetted perimeter. Guess you mean bowl-shaped vs mound-shaped. I.e. valley vs hill (peninsular)?

    For example, one can imagine closing off the Southern end of the SF Bay, as not much water flows in from the South. It’s hard to imagine closing off the Golden Gate Bridge area.

    The value of the infrastructure potentially protected by a Golden Gate barrage is gigantic. So the very large cost of a closure may well be justifiable – and it is certainly do-able. Yes, the pumping issue is huge, but while the SLR remains of the same order as the tide range (as here, at 2m SLR?) a tidal closure (a la Thames) will be feasible, and will reduce (not eliminate) pumping.

  18. 68
    Nigel Williams says:

    Dykes! Around the coast OF THE ENTIRE CIVILISED WORLD!!! You must be kidding! Will you have helicopters to drop sand bags for you? Nope. Will you have fuel for the scrapers and diggers to shift the dirt? Nope. Will you have spare energy to run the pumps? Nope. Will you have surplus cement or steel for the gates and weirs? Nope.

    Once our governments publicly acknowledge that we have to recognise sea level rise, then we will see decisions being made around where we can afford to spend remaining resources. Society will rapidly be driven to the logical conclusion that we cannot afford to rebuild our social infrastructure again and again for every increment in sea level rise. We can only rebuild once, and that has to be at or above the 100 metre line to be clear of the eventual 80 metreS sea level rise.

  19. 69
    Patrick Henry says:

    According to Aviso, current sea level rise rates are 24cm/century, and the second derivative of the six year trend is negative – suggesting that 24cm number will get smaller in the near future.

  20. 70
    Mitch Lyle says:

    Having read both the article and press release, the press release for the Pfeffer article was irresponsible ( This press release was under his control, so it is not a journalism error. It seems clear that he was upset by estimates of an extremely large Greenland contribution to sea level rise. However, it should also have been clear that the AR4 IPCC may have strongly underestimated the Greenland contribution (in Ch 10, the maximum Greenland contribution estimate by 2100 was 12 cm). A responsible press release would have discussed both–that the Pfeffer et al. minimum estimate for a Greenland sea level contribution was 25% above the IPCC maximum estimate. The paper discussed this–why didn’t the press release???

  21. 71
    Figen Mekik says:

    Mark (#63),
    It is blindingly obvious. What more do you need?

  22. 72
    Ray Ladbury says:

    Mark in SF, Good Lord man, where are you getting your info that climate hasn’t changed? Talk to a vintner and see where they are opening new vineyards. Read some actual data. The Start Here section on the front page has some good pointers. Second, since when is California the whole world? Have you looked at the melting glaciers and polar ice in the Northern hemisphere–and at the edges of Antarctica? You can look this stuff up as my good buddy Hank is fond of saying.

  23. 73

    Can we find adequate enough ways to escape “whiplash effects” and warn each other in the human community of impending danger before we “reap the whirlwind”?

    We in the family of humanity are going to be forced to do better in our efforts to communicate in a more reality-oriented way about ominously looming threats of an human-driven, global calamity of some kind. If we keep doing precisely what our leaders are saying and doing now, the future for our children looks bleak. We can surely do more and do it better. After all, human beings are remarkably intelligent, ingenious and adaptive.

    Before we can determine what new and different to do, perhaps a brief analysis of our current, distinctly human-induced, global predicament is in order. Consider for a moment some of the ways in which my generation of leaders has gone so terribly wrong.

    First, the leaders in my generation of elders wish to live without having to accept limits to growth of seemingly endless economic globalization, of increasing per capita consumption and skyrocketing human population numbers; our desires are evidently insatiable. We choose to believe anything that is politically convenient, economically expedient and socially agreeable; our way of life is not negotiable. We dare anyone to question our values or behaviors.

    We religiously promote our widely shared and consensually-validated fantasies of `real’ endless economic growth and soon to become unsustainable overconsumption, overproduction and overpopulation activities, and in so doing deny that Earth has limited resources and frangible ecosystems upon which the survival of life as we know it depends.

    Second, my not-so-great generation appears to be doing a disservice to everything and everyone but ourselves. We are the “what’s in it for me generation.” We demonstrate precious little regard for the maintenance of the integrity of Earth; shallow willingness to actually protect the environment from crippling degradation; lack of serious consideration for the preservation of biodiversity, wilderness, and a good enough future for our children and coming generations; and no appreciation of the vital understanding that humans are no more or less than magnificent living beings with “feet of clay.”

    Perhaps we live in unsustainable ways in our planetary home; but we are proud of it nonetheless. Certainly, we will “have our cake and eat it, too.” We will own fleets of cars, fly around in thousands of private jets, live in McMansions, exchange secret handshakes, frequent exclusive clubs and distant hideouts, and risk nothing of value to us. We will live long, large and free. Please do not bother us with the problems of the world. We choose not to hear, see or speak of them. We are the economic powerbrokers, their bought-and-paid-for politicians and the many minions in the mass media. We hold the much of the world’s wealth and the extraordinary power great wealth purchases. If left to our own devices, we will continue in the exercise of our `inalienable rights’ to outrageously consume Earth’s limited resources; to recklessly expand economic globalization unto every corner of our natural world and, guess what, beyond; and to carelessly consent to the unbridled global growth of human numbers so that where there are now 6+ billion people, by 2050 we will have 9+ billion members of the human community and, guess what, even more people, perhaps billions more in the distant future, if that is what we desire.

    We are the reigning, self-proclaimed masters of the universe….. the thousands of greedy little kings of capital concentration, big business potentates and governmental sinecurists. We enjoy freedom and living without limits. Of course, we adamantly eschew any talk of the personal responsibilities that come with the exercise of personal freedoms or discussions of the existence of biophysical limitations of any kind.

    We deny the existence of human limits and Earth’s limitations.

    Please understand that we do not want anyone presenting us with scientific evidence that we could be living unsustainably in an artificially designed, temporary world of our own making….a manmade world filling up with gigantic enterprises, virtual mountains of material possessions, and boundless amounts of filthy lucre.

    Third, most of our top rank experts appear not to have found adequate ways of communicating to the family of humanity what people somehow need to hear, see and understand: the rapacious dissipation of Earth’s limited resources, the relentless degradation of the planet’s environment, and the approaching destruction of the Earth as a fit place for human habitation by the human species, when taken together, appear to be proceeding at breakneck speed toward the precipitation of a catastrophic ecological wreckage of some sort unless, of course, the world’s colossal, ever expanding, artificially designed, manmade global political economy continues to speed headlong toward the monolithic `wall’ called “unsustainability” at which point the runaway economy crashes before Earth’s ecology is collapsed.

    Who knows, perhaps we can realistically and hopefully hold onto the expectation that behavioral changes in the direction of sustainable production, per human consumption, and propagation are in the offing…..changes that save both the economy and the Creation.

    Steven Earl Salmony
    AWAREness Campaign on The Human Population, established 2001

  24. 74

    If C02 is such a profound green house gas, and it has risen from 280ppm to 380ppm over the last century or so (?), why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already? As far as I know, the climate in California is much like it was in the 1850’s, and are things really much different?? Why should I worry about 450-500ppm?

    Thanks for a good question. What is tripping you up are the delay loops in the system. Currently, global temperature is 0.7C warmer due to the net effect of various greenhouse gases and aerosols. That may not sound like much. In continental locations, and at high latitudes, it will be more. But sure, in a single location it will be swamped by natural variability, or “weather”.

    Still, if you went to the countryside you’d likely find folk testifying that growth conditions have significantly changed. (Still I’m surprised at Californian longevity. Eye witnesses from 1850?)

    About those delay loops: firstly, we live on an ocean planet. Without the oceans we would already have 1.5C warming. It will catch up with us in a few decades, no matter what we do.

    And there are things we just cannot do, like turning the switch on all our coal fired power plants. Those are huge investments and written off over 30-50 years. Same for real estate with their space heating systems, and urban sprawl with its assumption of cheap personal transport.

    If we decide now to start replacing them by C-neutral plants, the process will end by mid-century. And then, the warming “committed to” (but not realized until again decades later) will be as much as 3C. Double that in continental or high latitude locations.

    I won’t mention China or India. I will mention Iceland. Was there last month, they told me that all of their glaciers will be gone in 150 years. Their landscape, the backdrop of their sagas… Serious? Debatable. Blindngly obvious? You bet.

    You see, climate degrees are a lot bigger than weather degrees. The last Ice Age was just -5C. We’re getting there.

  25. 75
    RichardC says:

    61 – John, say that as a prudent capitalist, you purchase land x metres above sea level, and after all the data is in, you are projected to soon own stable oceanfront property. Then the folks lower than you decide to reach in your pocket and build a dike which will prevent you from enjoying the fruits of your good choices. Doesn’t that smack of double theft?

    23 – Pete, no way. Take Hansen’s doubling exercise. He used 10 years. Say he’s off a bit and it’s 7 years or 15 years. For a 100 year period, aprox last year response (close enough): 7 –> 17,000 10 –> 1,000 15 –> 100. And then there’s the other logarithmic unknown of carbon feedbacks. Some say BAU is ~500. A small change in assumptions and it’s 5000 (CO2 equivalent – CH4 is multiplied by 23). How deep will water percolation get and so thaw permafrost? says that as long as the current spike isn’t worse than 120kya, deep permafrost should be OK. I think 120kya was mild compared to where we’re going. Will the thermohaline system change location/strength? Current marine hydrate deposits depend on the current configuration. Add it all up and the answer you seek will have error bars far larger than the data itself.

    35 Lynn, given that we won’t turn off the CO2 spout instantly, the answer is likely 80 metres. (others will disagree) We can inject sulphur and try to stop the meltdown, but GHGs affect polar areas the most and dimming work best in the tropics. Polar stratospheric injection of sulphur is probably the technique we’ll end up trying, but keeping your feet warm (tropics) and head cool (poles) while adding thick blankets (GHGs) over your whole body is a difficult task when the pesky atmosphere keeps scattering your AC units (sulphur)

    And like the dike issue above, if this all comes to pass, what happens when Russia (and maybe Canada) start defending themselves from the sulphur attack by destroying launch sites? After all, Russia and Canada would become massively dominant world powers as owners of most of the viable property left on the planet. What right do other countries have to take that away?

  26. 76
    Hank Roberts says:

    > Greenland, small/large glaciers, drainage

    Looks like most of my questions will be answered to the extent there are answers by
    Eric Rignot’s Chapter 5, in this book:

    Sudden and Disruptive Climate Change
    Earthscan, 2008
    ISBN 1844074773, 9781844074778

    He there has an illustration showing the drainage basins for many of the glaciers. (Google books doesn’t show the color illo, unfortunately).

    I haven’t found a map yet showing which glaciers cross the mountains above vs. below sea level. Glenn above writes that Pfeffer says melt will be limited because

    > ice must discharge to the ocean through bedrock gateways

    I’d think a “bedrock gateway” could go both ways — if the bedrock is below sea level, sea water can enter; if above sea level, as Mauri has pointed out clearly and repeatedly, the ice will fill melt voids in the winter.

    This search gets a good bit of info. I’m done til I read more on this

  27. 77
    Karen Street says:

    Re #63

    I live across the bay from you and I’ve seen climate change. The easterly winds used to come in September or early October, and now come in November. Last year’s winds were weak, I never saw that before. Sunrise didn’t used to be an exceptional event, but it was more normal for the summer sun to emerge from the fog sometime between 2 and 4, well some days and some years it didn’t emerge. Now many think that sunrise is normal. I used to teach seniors, so pay attention to warm days after spring break, as they were considered official cut days (by the students). In 6 years, I saw 5 such days. As of 1997, I never see fewer than 5 warm days between spring break and semester end, and might see 20 or more. (Warm by Berkeley standards)

    You can also check IPCC Working Group 2, chapter 1. You may not have been paying attention to dramatic increases in forest fires, or what the spittle bug and kelp have been up to, but others have.

    Elsewhere people have been noticing critter and flora movement at Yosemite and elsewhere, regional extinction of butterflies. The Chronicle covers this–here’s one such article in the The Difference a Degree Make series.

  28. 78
    John Mashey says:

    re: #67 Glen
    You seem to have the opinion that this is no problem.

    Can you explain your relevant experience in dealing with such issues? Can you point at coastal planning sessions you’ve been involved with (websites?), so the rest of us can discover the cheap and easy solutions that the professionals around here don’t know and worry about?

  29. 79
    Hank Roberts says:

    > As far as I know, the climate in California is much
    > like it was in the 1850’s, and are things really much
    > different?? Why should I worry …

    You should worry because what you don’t know can hurt you.
    You should worry about learning how to look these things up.

    Just one example below — not the answer, just an example.
    You can find answers for yourself.

    For more, talk to your school’s librarian, or if you’re out of school go to the reference desk at your public library. Tell the librarian you want to become able to learn for yourself. They will help.

  30. 80
    Hank Roberts says:

    For that link above to work, you’ll have to copy it and paste it into your web browser’s navigation window — the parentheses break it as it appears here.

  31. 81

    I can’t surprise you when we both know nobody knows how climate will evolve in near or far future.

    Actually we can, and we have. It will get warmer.

    No surprises there.

  32. 82
    Ray Ladbury says:

    Patrick Henry says: “According to Aviso, current sea level rise rates are 24cm/century, and the second derivative of the six year trend is negative – suggesting that 24cm number will get smaller in the near future.”

    Six-year “trend”. Thanks Patrick. That’s funny.

  33. 83
    RichardC says:

    65 Guy, CO2 was 280ppm, and has never been over 300ppm in an era where our climate has existed. So pick 280 or 300. Anything higher is risky. Hansen said 350 only with the mitigating statement that it was an initial maximum target that could be moved downwards. Since we are at 385, the answer from a policy standpoint is, “As low as we can get it as fast as we can get there,” so 350 is the number you’re looking for today.

  34. 84
    Joseph O'Sullivan says:

    Its good to see RealClimate providing the story behind confusing news coverage. Thanks to Tad Pfeffer, J. Harper, and S. O’Neel for adding to the discussion and clarifying their position.

    Jess (#52) 6ft of sea rise in Manhattan is a big deal. I used to work in a building on the waterfront in the Wall Street area. Considering that the first floor is at maybe 8 feet above sea level any buffer in case of even a minor storm is gone. This is very expensive real estate in a very crowded area too.

    I also walk and jog on the path that runs along the shore of the southern half of Manhattan, and six feet of sea level rise would flood many areas, including the entire subway system.

  35. 85
    Steve Bloom says:

    Even if one wants to look at just California, plenty of climate change has been observed. Fortunately the state government is not in denial about the problem, so it’s easy to access the information. The main portal is here.

  36. 86
    James Staples says:

    I haven’t had time to read all of these postings – let alone Jim Hansens DIRE piece (though I DID just download it and I will do so; and Thank You, by the way, for telling the WHOLE SCARY Truth Dr. Hansen); but, out of what I did scan, I didn’t seem to notice any references having been made in regards to the possibility that the Fresh Meltwater comming off of the Greenland Ice Sheets – and them plunging striaght to the bottom of the North Atlantic Ocean – could shut down the so-called ‘Atlantic Conveyor’.
    As I understand it, this would not only plunge Europe into a New Ice Age – by shutting down the Gulf Streams Warm ‘Return Flow’ – it would also lead to a dramatic warming of the Southern Oceans Surface Waters, and a subsequently – and equally dramatic – increase in the rate at which the Antarctic Ice Sheets are themselves Melting.
    It seems to me that the ‘One-Two Punch’ of a New Northern Hemisphere Ice Age, combined with the kinds of unprecedented (read: MUCH more than 5m) SLR that would accompany it, would constitute the ‘worst of all possible cases scenario’.
    In fact; I seem to remember reading, in the article that dealt with this issue (in SciAm or NewSci, most likely), that the author(s) were hypothosizing that this very effect may have been responsible for the LIG!!!
    Any thoughts or new Info on this subject for me (US! The “Carbon Free”), Gang? Please send me a fresh E-mail alert if you have any thoughts to share – whether you start a new post or not; as I’m out to Terrify those ‘Drill, Drill, Drill’ Idiots (say it like ‘The Brain’ would to Pinky!) into sensible submission, one Blog Entry at a Time!!!
    ‘Build’ Me The Truth, and They Will Come (Around)!

  37. 87
    Dill Weed says:

    Mark (63),

    James Hansen does a good job explaining Global Warming. Reading his PDFs will give you a comprehensive understanding of the argument for GW, explanation of forcings (particularly CO2, which you asked about) and of the difference between historical evidence vs computer models. Go to:
    select Files/Links and download all pdfs starting with 2004. After your done with that…

    Roll up your sleaves, enlarge the print on your monitor and read everything here. This is by far the best site to gain a comprehensive understanding of the science and its complexities. (They are not paying me to say this!) I’ve been lurking in the weeds for several years. I recommend starting with Hansen’s material first.

    Here the evidence get laid out and explained, areas of weakness are identified and explored, assumptions get identified, tested and challenged – civilly, too!

    This site is the place to go when your not satified with someone making unsupported claims or just attacking and denying. GRRR!!!

    Kudos, Gavin et al.

    Dill Weed

  38. 88
    Steve Bloom says:

    Also re California info, see this publications page.

  39. 89
    Steve Bloom says:

    Re #80: Or do it as an embedded link, Hank. Then there’s no problem with a line break no matter how long the url gets.

  40. 90
    David B. Benson says:

    Guy (65) — I think RichardC in comment #83 makaes the point quite well; we don’t know enough to be much more precise about an eventual target; we do know enough to know that we have now committed the earth to sea level rise (at some rate) for centuries to come.

    Hank Roberts (62) — If a barrier island the result could be obtained by a large sea surge overtopping the island and burying the mangroves, possibly moving those to the lnadward side of the island. In any case, a sudden local sea level rise via rapid subsidence is most unlikely and such a rapid change due to proglacial lake release (or whatnot) even less so.

  41. 91
    Dave Rado says:

    Re. #86, James Staples, that’s highly unlikely – and some highly respected oceanographers would go further and say it’s impossible. There are enough high or medium likelihood scenarios to worry about, there’s really no need to exaggerate the threat, which is very serious without exaggerating anything.

    The IPCC rates the possibility of Atlantic conveyor shut-down as extremely unlikely. Regarding the hypothesis that it has happened in the distant past, the oceanographer Carl Wunsch has emailed me in the past to say:

    That’s a very controversial, if widely popular, interpretation of very fragmentary data. There is almost no information at all on the *rates* at which the ocean circulation moved in the past. Much of the paleoclimate community has confused the correct inference that water properties changed (got fresher or warmer for example) with the conclusion that means that the flow rate had to change. Of course, it could have changed, and almost surely did under different climate conditions, but the story of “shutdown” is part of the over-dramatization that led Gore astray. It would be a breakthrough in paleoceanography to find a measure of water movement rates. It *is* true too, that one can make numerical models, that when overlain with a large layer of fresh water that they reduce the so-called meridional overturning circulation. Those models have been used to buttress the shutdown story. But they raise a long series of problems including the fact that major ice melt events do not seem to have occurred at the “right” times, that fresh water comes in at the edges mainly, not in the middle of the ocean, and that the models do not properly represent the physics of the upper ocean.


  42. 92
    David B. Benson says:

    Earlier (on the orginal thread on this topic), concern was raised (by at least me) regareding WAIS stability. The Wikipedia page has a moderate, even calming, stance (except at the very end):

    This paper, “Ice Sheet Stability and Sea-Level Rise”

    states, in part, “Thus, in the foreseeable future, sea-level rise should not threaten the ice sheet’s stability [for Whillans Ice Stream out to the Ross ice shelf].”

    Here is a 1998 review paper which states, in part, “Almost all sea-level rise would occur beyond the twenty-first century. However, these outcomes are predicated on changes in basal melt rates that could accompany global warming of only a few degrees, warming that could be determined by emissions that occur during the twenty-first century. Given the long residence time of atmospheric carbon dioxide, and thermal inertia in the oceans, decisions being considered now could irreversibly affect WAIS in the distant future.”

    [Since there is going to be a computer-based study of this question of WAIS stability, Captcha wisely states “it investment”.]

  43. 93
    Lawrence Brown says:

    Re: #63
    “why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already?”

    All of the effects of the increase in greenhouse gas emissions have not taken effect yet. Further warming from the present increases are still “in the pipeline” as they say. One of the reasons for the lag is the delayed reaction of the surface waters of the oceans to the absorption of heat and it’s ultimate contribution by releasing this heat back to the atmosphere.

  44. 94
    RichardC says:

    84 Joseph, you’re right. I’d add in that the geographic range of tropical storms will probably increase, so NYC, which currently has one Cat1 Hurricane every 15 years, might get more frequent visits and from stronger storms. There’s no need for increased numbers of hurricanes for that to happen, only that they survive the trip north as they are fed by warmer waters.

    85, speaking of Blooms, Steve, gardeners everywhere have noticed that they can get away with planting too soon according to the old charts, and their tomatoes last a couple weeks longer in fall. There’s a big debate in the green thumb world about whether to republish the old climate zone charts. Bird watchers are noticing the changes too as species dwindle and show up in the wrong place at the wrong time. Nature is getting confuzzled.

    86, James, Dr Hansen’s work is tame. It assumes sanity and incredible luck. Folks get more insane as the luck runs out. Wars between nations, classes, religions, and social groups get ugly if, as Dr Lovelock predicts, 6.1 out of 6.6 billion people must die. Dr. Lovelock is the original Earth Systems (Gaia) scientist. It’s possible he’s wrong, but he’s no crackpot. As to your ice age prediction, I seriously doubt it. Killing the conveyor would only mitigate northern warming, not reverse it. The Arctic Ocean losing its ice is almost certainly involved in the initiation of northern thermohaline demise, so albedo change will compensate. Besides, the Gulf stream is only 1/2 driven by thermohaline. The 1/2 that is driven by coriolis can never die until the continents move or the Earth stops spinning. And IF a “northern ice age” tried to start up, it would IMMEDIATELY kickstart the northern thermohaline, and prevent the ice age! (Note: the real thermohaline is driven by Antarctica. The stuff in the North Atlantic doesn’t even make it to the ocean floor. We just focus on it because we’ve got a Eurocentric bias.)

  45. 95
    David B. Benson says:

    Somehow the link to the Wikipedia page didn’t make it into my previous post. Here it is:

    This 2002 abstract, “Risk Estimation of Collapse of the West Antarctic Ice Sheet”

    states in part “However, a refusal by scientists to estimate the risk leaves policy-makers with no sound scientific basis on which to respond to legitimate public concerns. Here we present a discussion of the likelihood of WAIS-collapse, drawing input from an interdisciplinary panel of experts. The results help to summarise the state of scientific knowledge and uncertainty. While the overall opinion of the panel was that WAIS most likely will not collapse in the next few centuries, their uncertainty retains a 5% probability of WAIS causing sea level rise at least 10 mm/year within 200 years.” That’s 1 meter/century.

  46. 96
    Steve Bloom says:

    Yet more California::

    Sacramento Bee “Sierra Warming” page (inc. a linked blog)

    A Change in the Wind” blog by SoCal journalist Kit Stolz (not all climate change)

    Between the two of them they don’t miss much of interest re CA climate.

    There’s also a new paper out in GRL that commenter Lazar quoted at length over at the Open Mind blog.

    California can afford a lot of infrastructure, but between sea level rise and the need for a year-round water supply it’ll be interesting to see if we can manage it.

  47. 97
    Jim Eager says:

    Re Mark in SF @63: “If C02 is such a profound green house gas, and it has risen from 280ppm to 380ppm over the last century or so (?), why is it not blindingly obvious that human-induced climate change is happening, and had a profound effect already?”

    Well, we are seeing profound effects already in the Arctic and in the Antarctic Peninsula and in mountain glaciers all around the world, but to answer your question, it is not blindingly obvious in more temperate climates because we have not yet seen all of the warming that an increase of 100ppm will produce. This is because so far much of the added warmth has been absorbed by the ocean, which warms very slowly due to its enormous mass. But even if CO2 were to stop increasing tomorrow, that extra 100ppm will remain there for many, perhaps hundreds of years, continuing to add warmth, and as the ocean slowly warms to equilibrium then more of the warming will be felt at the surface. This is what climate scientists mean when they say that there is warming “still in the pipeline.” But, of course, CO2 is not about to stop rising tomorrow or any time soon, so it’s not just the warming “in the pipeline” that we have to worry about.

    “Why should I worry about 450-500ppm?”

    Because the last time there was that much CO2 in the atmosphere Earth, including California, was a much warmer and very different place from what it is now, yet all of our infrastructure has been built to cope with the climate we have now.

    “As far as I know, the climate in California is much like it was in the 1850’s, and are things really much different?”

    Are you sure? You might want to check agricultural records showing a steady long-term trend in lengthening growing season for some crops in California, and northward creep of climate zones suitable for some crops. You might also want to check hydrological records showing decreasing trends in snowpack depth in the Sierra.

  48. 98
    Steve Bloom says:

    Re #93: This is somewhat a matter of perspective. Arguably for the more informed among us the time to have gone into a blind panic was twenty years ago when Jim Hansen announced the apparent detection of an anthropogenic signal in global climate. Of course that’s not how scientists prefer to go about things, but after twenty years some of them are beginning to show public signs of impatience. Hansen was first, but encouragingly others seem to be following.

  49. 99
    Timo Hämeranta says:

    Re 93. Lawrence, yes, the accumulation of heat in the oceans is the primary metric of global warming, but it’s distributed unevenly, and we don’t know how much of it will be diluted in cold waters and how much, when and where it will be released to the atmosphere.

    For the moment, both NAO and PDO will cool the atmosphere for the next 20 years or so.

    We have to wait to see the effects you, Jim Hansen et al are waiting.

    [Response: You are better when you simply misquote papers. The heat going into the ocean is not going to be ‘released to the atmosphere’ any time soon – it is instead part of what will be the higher OHC in a warmer world. NAO and PDO have little or no correlation to the global mean temperature, and your implication that you have 20 year predictability in either is laughable. And as for Hansen, he predicted decades ago that the OHC data would be rising – many years before the analysis was done. Your predictions don’t seem to have been quite as prescient. – gavin]

  50. 100
    GlenFergus says:

    #78 John Mashey:

    [edit] Perhaps you can quote where I said – or even implied – that “this is no problem”. Or that there are “cheap and easy solutions”; indeed I said the opposite (“the very large cost of a closure”). FWIW, I’m a professional engineer with 30 years experience in the design of major civil works, including levees and coastal protection. So I guess, on this subject, I’d be one of those “professionals around here”, no?