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The IPCC Fourth Assessment SPM

Filed under: — group @ 2 February 2007 - (Français) (Português) (Türkçe) (Español)

We’ve had a policy of (mostly) not commenting on the various drafts, misquotes and mistaken readings of the Fourth Assessment report (“AR4″ to those in the acronym loop) of the IPCC. Now that the summary for policy makers (or “SPM”) has actually been published though, we can discuss the substance of the report without having to worry that the details will change. This post will only be our first cut at talking about the whole report. We plan on going chapter by chapter, hopefully explaining the key issues and the remaining key uncertainties over the next few months. This report will be referenced repeatedly over the next few years, and so we can take the time to do a reasonable job explaining what’s in it and why.


First of all, given the science that has been done since the Third Assessment Report (“TAR”) of 2001 – much of which has been discussed here – no one should be surprised that AR4 comes to a stronger conclusion. In particular, the report concludes that human influences on climate are ‘very likely’ (> 90% chance) already detectable in observational record; increased from ‘likely’ (> 66% chance) in the TAR. Key results here include the simulations for the 20th Century by the latest state-of-the-art climate models which demonstrate that recent trends cannot be explained without including human-related increases in greenhouse gases, and consistent evidence for ocean heating, sea ice melting, glacier melting and ecosystem shifts. This makes the projections of larger continued changes ‘in the pipeline’ (particularly under “business as usual” scenarios) essentially indisputable.

Given all of the hoopla since the TAR, many of us were curious to see what the new report would have to say about paleoclimate reconstructions of the past 1000 years. Contrarians will no doubt be disappointed here. The conclusions have been significantly strengthened relative to what was in the TAR, something that of course should have been expected given the numerous additional studies that have since been done that all point in the same direction. The conclusion that large-scale recent warmth likely exceeds the range seen in past centuries has been extended from the past 1000 years in the TAR, to the past 1300 years in the current report, and the confidence in this conclusion has been upped from “likely” in the TAR to “very likely” in the current report for the past half millennium. This is just one of the many independent lines of evidence now pointing towards a clear anthropogenic influence on climate, but given all of the others, the paleoclimate reconstructions are now even less the central pillar of evidence for the human influence on climate than they have been incorrectly portrayed to be.

The uncertainties in the science mainly involve the precise nature of the changes to be expected, particularly with respect to sea level rise, El Niño changes and regional hydrological change – drought frequency and snow pack melt, mid-latitude storms, and of course, hurricanes. It can be fun parsing the discussions on these topics (and we expect there will be substantial press comment on them), but that shouldn’t distract from the main and far more solid conclusions above.

The process of finalising the SPM (which is well described here and here) is something that can seem a little odd. Government representatives from all participating nations take the draft summary (as written by the lead authors of the individual chapters) and discuss whether the text truly reflects the underlying science in the main report. The key here is to note that what the lead authors originally came up with is not necessarily the clearest or least ambiguous language, and so the governments (for whom the report is being written) are perfectly entitled to insist that the language be modified so that the conclusions are correctly understood by them and the scientists. It is also key to note that the scientists have to be happy that the final language that is agreed conforms with the underlying science in the technical chapters. The advantage of this process is that everyone involved is absolutely clear what is meant by each sentence. Recall after the National Academies report on surface temperature reconstructions there was much discussion about the definition of ‘plausible’. That kind of thing shouldn’t happen with AR4.

The SPM process also serves a very useful political purpose. Specifically, it allows the governments involved to feel as though they ‘own’ part of the report. This makes it very difficult to later turn around and dismiss it on the basis that it was all written by someone else. This gives the governments a vested interest in making this report as good as it can be (given the uncertainties). There are in fact plenty of safeguards (not least the scientists present) to ensure that the report is not slanted in any one preferred direction. However, the downside is that it can mistakenly appear as if the whole summary is simply up for negotiation. That would be a false conclusion – the negotiations, such as they are, are in fact heavily constrained by the underlying science.

Finally, a few people have asked why the SPM is being released now while the main report is not due to be published for a couple of months. There are a number of reasons – firstly, the Paris meeting has been such a public affair that holding back the SPM until the main report is ready is probably pointless. For the main report itself, it had not yet been proof-read, and there has not yet been enough time to include observational data up until the end of 2006. One final point is that improvements in the clarity of the language from the SPM should be propagated back to the individual chapters in order to remove any superficial ambiguity. The science content will not change.

Had it been up to us, we’d have tried to get everything together so that they could be released at the same time, but maybe that would have been impossible. We note that Arctic Climate Impact Assessment in 2004 also had a similar procedure – which lead to some confusion initially since statements in the summary were not referenced.

How good have previous IPCC reports been at projecting the future? Actually, over the last 16 years (since the first report in 1990), they’ve been remarkably good for CO2 changes, temperature changes but actually underpredicted sea level changes.

When it comes to specific discussions, the two that are going to be mostly in the news are the projections of sea level rise and hurricanes. These issues contain a number of “known unknowns” – things that we know we don’t know. For sea level rise the unknown is how large an effect dynamic shifts in the ice sheets will be. These dynamic changes have already been observed, but are outside the range of what the ice sheet models can deal with (see this previous discussion). That means that their contribution to sea level rise is rather uncertain, but with the uncertainty all on the side of making things worse (see this recent paper for an assessment (Rahmstorf , Science 2007)). The language in the SPM acknowledges that stating

“Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise. Understanding of these processes is limited and there is no consensus on their magnitude.”

Note that some media have been comparing apples with pears here: they claimed IPCC has reduced its upper sea level limit from 88 to 59 cm, but the former number from the TAR did include this ice dynamics uncertainty, while the latter from the AR4 does not, precisely because this issue is now considered more uncertain and possibly more serious than before.

On the hurricane/tropical strorm issue, the language is quite nuanced, as one might expect from a consensus document. The link between SST and tropical storm intensity is clearly acknowledged, but so is the gap between model projections and analyses of cyclone observations. “The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period.”

We will address some of these issues and how well we think they did in specific posts over the next few weeks. There’s a lot of stuff here, and even we need time to digest it!


364 Responses to “The IPCC Fourth Assessment SPM”

  1. 1
    cbone says:

    Where may I obtain a copy of the actual report, instead of just a summary?

    [Response: The full report won't be finalized until April. --eric]

  2. 2
    catman306 says:

    Just mentioning another possible environmental disaster linked to global warming and climate change: when the Greenland glaciers finally melt (either slowly or in a big whoosh) tectonic rebound will probably increase the frequency and magnitude of earthquakes around the world. The 30 foot rise in sea level will cause the Antarctic ice shelves to detach making it easier for the Antarctic glaciers to move more quickly into the ocean, causing still more sea level rise, tectonic rebound and earthquakes.

    Nice world we are leaving our grand children. And theirs.

    [Response: I am happy to be able to correct you that tectonic rebound from the Greenland ice sheet won't have impacts on earthquakes around the world. Big earthquakes are due to processes much deeper in the earth's crust, and much more localized. It is, on the other hand, rather likely that rising sea levels will help to destabilize the Antarctic ice sheet. On what timescale, however, remains quite uncertain. --eric]

  3. 3
    BCC says:

    Minor, minor observation:

    even we need time to digest it

    I know it wasn’t the intention, but that comes across as a little arrogant. I know that you are professional climatologists and wicked smart and all, but I would have gone with sometihing like “and we need time to digest it too.”

    Minor point, but tone matters.

    [Response: Fair enough! Of course what was really meant is that virtually all of the science being reported on is stuff that we are already very familiar with. "Digesting it" means making sure that what we think is in it (even before reading it) is actually in the final text, we most of us, like you, have just gotten a chance to start reading. -eric]

  4. 4
    Mitch Golden says:

    The direct link to the summary report (that is, what was published today) is here:

    http://www.ipcc.ch/SPM2feb07.pdf

    Keep an eye on http://www.ipcc.ch/ to see the other sections as they’re released.

  5. 5
    P. Lewis says:

    The immediate thing that stood out for me about the AR4 SPM is the willingness to talk (again) about “the globally averaged net effect of human activities since 1750″, whereas here and hereabouts, of recent times, there has been more of a “let’s keep it to the last ~50 years” kind of discussion (whether by accident or design).

    I find this encouraging, for the science.

  6. 6
    curving3 says:

    You can find the SPM report at: http://ipcc-wg1.ucar.edu/

  7. 7
    Anonymous says:

    “Scientists offered Cash to Dispute Climate Study”

    http://www.commondreams.org/headlines07/0202-05.htm

  8. 8
    Dave Cohen says:

    Note that some media have been comparing apples with pears here: they claimed IPCC has reduced its upper sea level limit from 88 to 59 cm, but the former number from the TAR did include this ice dynamics uncertainty, while the latter from the AR4 does not, precisely because this issue is now considered more uncertain and possibly more serious than before

    This is very confusing to the public. The 59 cm is the upper bound in the A1F1 scenario. I quote from AR4 –

    Models used to date do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in ice sheet flow, because a basis in published literature is lacking. The projections include a contribution due to increased ice flow from Greenland and Antarctica at the rates observed for 1993-2003, but these flow rates could increase or decrease in the future. For example, if this contribution were to grow linearly with global average temperature change, the upper ranges of sea level rise for SRES scenarios shown in Table SPM-2 would increase by 0.1 m to 0.2 m. Larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea level rise.

    Who among us expects a decreasing or linearly growing flow rate from the ice sheets until the year 2100? This would make recent trends anomalous. The public will see a lower number and not understand that the trend is “more serious than before” — and also not understand recent not-included studies that indicate accelerating flow rates in Greenland and W. Antarctica. Already there is considerable confusion in the media. This constitutes a disservice to mankind.

  9. 9
    Sean Davis says:

    #1, the report can be found here

  10. 10
    Zeke Hausfather says:

    Sorry to nitpick, but it would be nice if, when finalizing a report that is to be read by hundreds of millions of people, the authors could remove unfinished formating suggestions (e.g. [Numbers to be converted to mm per year] on page 5 and [To be changed: Change annotation from cnstant composition to year 2000 constant concentration. Colour central bar in grey bars and lettering to match A2, A1B, B1 curves as appropriate. Drop model numbers and move to caption] on page 21). It makes an otherwise well-crafted report appear unprofessional. Both of the copies report linked from the IPCC site have these formatting errors, at least at the time of posting:
    http://ipcc-wg1.ucar.edu/wg1/docs/WG1AR4_SPM_PlenaryApproved.pdf
    http://www.ipcc.ch/SPM2feb07.pdf

  11. 11
    Sean Davis says:

    I think I already found an error in the SPM! If you sum up the contributions to sea level rise from 1993-2003 in table SPM-O, you get 0.657, not 0.28. I think they screwed up the Greenland and Antarctic values, which they list as 0.21 (each). If you assume they are 0.021 instead, the sum total contribution is indeed 0.28.

    OOPS!

    [Response: Well spotted. I noticed this as well and alerted IPCC a few hours ago. -stefan]

  12. 12
    CobblyWorlds says:

    BBC News24 are announcing it as the end of “the debate” about the reality of climate change.

    So that means the real battle to get individuals to factor this into behaviour is now starting. It seems to me that our only attainable option is to aim to take the edge off the increases by energy efficiency etc. Drop the talk about “Stop Climate Chaos”, implications that we can just stop fall in the face of evidence and reason. Argue for the attainable; piecemeal reduction of emissions. Do what you can. Every little helps.

    But I think it would have been a stronger “coup de grace” had it been presented at the same time as the WG1 Scientific Basis report. Surely as it’s based on the results of WG1 they could have finalised the full Scientific Basis first?

    BCC.
    These are the sort of people who do stuff as cheeky as attempting to model something as complex as climate and pull it off! (e.g. http://rabett.blogspot.com/2006/09/well-lookee-that.html ) As an intellectual also-ran I request RealClimate leaves the ‘even’ in.

  13. 13
    Karan says:

    Neal Boortz attempted to criticize the report. Very interesting and ALL flawed. What’s worse is that he uses it to convince listeners, who have no knowledge of the science and believe him. http://boortz.com/nuze/index.html

  14. 14
    E. C. De Fabo says:

    It would be both very good and very useful to have a point by point rebuttal of the charges this fellow makes. Not being a climatologist’s but certainly someone with a great deal of interest in this subject (I am a research scientist in photobiology) who gets called on to comment occasionally on global climate change (stratospheric ozone depletion/UVB impacts) it would help to have some good strong arguments to counter the comments by this person. Good references would be most appreciative as well.

  15. 15

    A few errors I’ve noted in the media coverage.

    1. Most reports I’ve heard say that the IPCC says it’s 90% likely that etc. Actually their term “very likely” means 90-99% certain.

    2. Most reports talk about temperature rise etc. by 2100. Actually the summary gives the averages expected 2090-2099, a half-decade sooner. Not significant I suppose but annoying.

    3. Most reports I’ve heard mention a 1.5-4 degree C expected rise. These are actually the best estimated central values for different economic-technological scenarios. Fair enough, but the ranges of temperatures the IPCC considers “likely” go from 1.1-2.9 for the most benign emission scenario to 2.4-6.4 for the least benign one (that’s the one with the 4.0 “best estimate”), so the actual “likely-depending-on-what-we-do” range is 1.1-6.4

    [Response: Spencer, your second point is quite relevant for sea level, where leaving off the last 5.5 years (when it rises fastest) and other technicalities are the reason why the new sea level values look a bit lower than the previous model projections. In fact, all else being equal, for any given emission scenario the new (AR4) models give a slightly higher sea level projection than the old models used in the TAR, we were told in Paris. -stefan]

  16. 16
    Jake says:

    O.K., so if we assume there is a human coponent, how do we know what percentage of global warming is attributable to humans and, even if we were to stop any further increase from the human component, that would slow down or even reverse the process?

  17. 17
    Jake says:

    Also, Spencer: let’s say “very likely” means 99% certain that (human) greenhouse gases have caused most of the observed increase in globally averaged temperatures since the mid-20th century. What does “most” mean in regard to my pending questions? Does that include gases from non-human sources? Keep in mind that the Paris study, looking at all the science of global warming, will only project a “best estimate” that temperatures will rise by 3 Celsius (5.4 Fahrenheit) by 2100 over pre-industrial levels. I doubt that is bad enough for the entire world to stop in its tracks.

  18. 18
    lars says:

    #16 exactly…… if humans are the culprit…..

    Should you not be calling for reducing the human population on this planet then?

    Should you not be doing a Kyoto on China, India, and Muslims which each have approximately 1.3 billion and growing populations?

  19. 19
    Steven Leibo Ph.D. says:

    Just want to think RealClimate for its efforts to help non-scientists to understand the new report. I am part of Al Gore’s Climate Project and working very hard to improve my understanding of all this to complement the local presentations of his slide show I am doing. Realclimate makes that much easier!

  20. 20
    Sashka says:

    The SPM predicts 20% drop in precip in subtropics. Do we trust the models enough to beleive the projections for regional shifts in precip?

  21. 21
    Scott L. Montgomery says:

    Release of this new IPCC summary is a profound event and will be covered by every major newspaper in the world, as it should. Scientifically speaking, no other domain benefits from such a magnificent collaboration of investigators, whose task is to summarize the published literature into concise, universally usable reports – imagine if every field of science had the benefit of such review! What a boon to researchers and the public both. But climate-related science especially demands this level of attention – it is a political decision to do this, not merely an intellectual one, for it reflects the importance and urgency of the relevant information, not to mention the widespread lack of action that it suggests is needed.

    To my mind, as a sometime student and scholar of scientific expression past and present, the report is a well-tuned document. It’s authors have clearly learned a thing or two from the last go-around. It is crisp, data-rich, fairly well-organized, and confident in its points. It uses qualitative but explained probabilities (extremely likely, very likely, likely, etc.), discusses (in yellow-highlighted boxes) the significance of the knowledge domain covered by each section, and admits uncertainties. It is not a policy document, per se: it does not recommend or critique specific measures, ideological concepts, weigh risks and benefits, or the like. It has what might be termed a low intimidation factor, meaning that nearly all the scientific points are comprehensible to the educated layperson. There is a pictorial rhetoric, too, that is very effective. The graphics, though placed at the end instead of embedded in the narrative (as in most scientific documents) are improved from the TAR (2001 report). Going through them has a cumulative effect that even supersedes that of the text. Especially interesting and well-done, in visual terms, is the global map showing temperature trends since 1900 for the major continents. The final two pages of figures, a culmination of sorts, showing predicted temperatures and precipitation patterns for the remainder of the century, are visually striking, and thus daunting. There is calculated force here (on the eye and mind), to be sure, but one that is warranted by the results. To claim this as “propaganda” would be absurd and naive: all effective documents employ these sorts of persuasive tools, and have done so since manuals of rhetoric were written in Greek and Roman times (Galileo’s famous little book, Sidereus nuncius, with the first pictures of a rocky moon, is a superb example).

    But here’s another point. It is not just the content of this document that matters with regard to its place in our evolving discussion on climate change, but how it’s represented in the media. This may be obvious, but the reality is a complex affair. Compare, for example, this morning’s coverage by the International Herald Tribune and our favored NYTimes. The former discusses the importance of the report, it’s confirming aspects with regard to the phenomenon of global warming, and implications, with some spicing of comments by authors and reviewers, some rather silly ones (“This is real. This is real. This is real.”) Most important, though, the article emphasizes that the science is not complete but in progress, and that the new report represents a further step in this process. Yes, we all know this, but saying it in these terms is fairly rare in newspaper and tv reports. As for the NYTimes, they decided to beat the drum of controversy: “Even before its release, world climate report is criticized as too optimistic.” It is focused almost entirely on the discussion over predicted sea level rise – the decision of the IPCC not to include potential ice melt, which is largely (as I understand it) due to timing issues of the published material and also uncertainties related to modeling. Moreover, the article ends with a little melody from Fred Singer about the IPCC being the contrarians now. This is indeed poor stuff from our most valued daily paper, but not really surprising.

    The media are able to bring a critical faculty to bear on scientific subjects, but choose to do so on a haphazard and selective basis. Highlighting controversy, or manufacturing it, is not merely a way to attract attention; it is also a means of distinguishing your own reporting from that of other papers. The most basic aspect to climate science – that it is science-in-the-making, always advancing, always partial, always ready to jettison some things and improve others, and therefore any summary of it will be no more than a snapshot of what has already been surpassed – does not make for good news all the time. Reporters serve different masters than scientists, not necessarily kinder and gentler ones. The final truth is that the media are not necessarily well-qualified, on their own, to transmit technical knowledge to the public, but they are what we have. To understand these matters better, I’d recommend reading Dot Neklin’s book “Selling Science,” which remains the more clear-eyed treatment of the subject.

    In the meantime, we will have to grit our teeth, hope, and sometimes smile at the popular treatment of this new, epochal report. Given the momentum that is now building in the U.S., I expect that good things will come out of the IPCC’s work. As I say, we can certainly hope so.

  22. 22
    Mike says:

    Jake at #16:

    If you look at the SPM, page 16, there is a nice table of the magnitudes of various factors, anthropogenic and natural. The anthropogenic factors total out to a forcing of 1.6 Watts/m^2, while the natural factors are 0.12. Clearly, the human factors are the biggie. The vast majority of the current warming is ‘our fault.’

    There was also discussion of the ‘% attribution’ question here at RealClimate back in October: http://www.realclimate.org/index.php/archives/2006/10/attribution-of-20th-century-climate-change-to-cosub2sub/

    As for how much we have to change our behaviors before we restore our climate to a pre-industrial state, I think it can’t happen. A certain amount of warming is going to be with us for centuries. What we have to do is stop accelerating the process, so that the total warming is smaller than what are are currently heading towards.

  23. 23
    Sashka says:

    Scientists and economists have been offered $10,000 each by a lobby group funded by one of the world’s largest oil companies to undermine a major climate change report due to be published today.
    Letters sent by the American Enterprise Institute (AEI), an ExxonMobil-funded thinktank with close links to the Bush administration, offered the payments for articles that emphasise the shortcomings of a report from the UN’s Intergovernmental Panel on Climate Change (IPCC).

    http://www.guardian.co.uk/frontpage/story/0,,2004399,00.html

  24. 24
    Hank Roberts says:

    Jake, see the name immediately above your question? click on it to read: http://www.aip.org/history/climate/

  25. 25
    juandos says:

    The comment taken from the leftist rag the Guardian, “Scientists and economists have been offered $10,000 each by a lobby group funded by one of the world’s largest oil companies to undermine a major climate change report due to be published today”…

    Hmmm, so what did the IPCC pay people who for the most part aren’t scientists to come up with this myth called global warming?

    [Response: Indeed an intellectually brilliant conspiracy theory... But in case anyone seriously wants to know: the 600+ scientists working on the IPCC reports do this for free in their spare time. That involves lots of hours wading through review comments (the report attracted over 30,000 such comments), and evenings and weekends away from the family. A voluntary effort I right now don't feel like ever doing again, once seems enough for a lifetime... -stefan]

  26. 26
    tom street says:

    I would like to see more discussion of the reasons for the increase in probability regarding man induced climate change and how one goes from a 60 percent probability to a ninety plus probability. It’s not like rolling dice, I presume, so how precise are these probability estimates. Are they similar to the kinds of probabilities we get from noaa when we look up the forecasted weather? Or what?

    The primary reason I bring this up is the fact that Lindzen seemed to make fun of the whole notion of probability the other night on CNN. Yes, I can understand that all this data and analysis makes us more certain, but is it really reasonable to put a number on it?

  27. 27
    Pat Neuman says:

    Re: 2

    Could tectonic rebound from ice loss on Greenland and Antarctic result in additional significant increases in sea level?

    For example, if something raised a portion of the bottom area of a lake, the displacement of the water would increase the surface level of the lake (assuming no lake outlets).

  28. 28
    Jason Burford says:

    Does anyone know of any literature summarizing positive feedback effects. In particular I am interested in boreal permafrost feedbacks such as thawing permafrost, burning boreal forests…do these feedbacks overtake man made emissions scales and were these considered in the report findings such as shrinking sea ice was (hopefully)?

  29. 29
    Jeremy Kenyon says:

    First, I totally agree with point 8 – why did they put in a 59cm upper bound that nobody seems to think is likely to be right – it is confusing, misleading and will be seized on by contrarians. At the very least they should have included an apples to apples comparison, as well as the one discounting the effect, especially in the summary, which is all that many folks will ever read.

    Second – Point 13, Neal Boortz discussion – even if he was right, which is unlikely, he still seems to be saying that global warming is happening. Also he says that the IPCC are saying it is futile as we can’t stop it. That does seem to be the impression I get as well.

    It seems to me that we need to start taking the whole issue of what to do about it a lot more seriously – emissions control is not going to be enough, even if it was incredibly aggressive, and the more optimistic models are right.

    We are most likely going to have a sea level rise over the next century that will cause problems, and the rise will continue in the century after that, and possibly for quite a bit longer.

    Either we need to really give up on places like Bangladesh and Venice and Northern Africa and so on, or we need to get some serious research going into putting the genie back in the bottle.

    I know this is not a popular sentiment amongst climate scientists right now but I really don’t see that we have a choice, do we? Either we accept widescale disruption in the next 100-300 years with phenomenal human cost, or get cracking on finding additional techniques as well as the current ‘reduce carbon emissions’.

    Any additional techniques, such as widescale stratospheric aerosols, or iron filings in the ocean or such like are going to take a decade or more to research, do tests with etc. During that time, the accuracy of models will continue to improve, as will our understanding of ice melt behaviour and the other uncertainties.

    My current project is investigating the current set of options we have for attempting to reduce the impact of global warming – there are about a dozen methods at the moment, varying from plausible to blue sky. We need to push research for this sort of work way up the agenda, instead of it being the poor cousin to analysing what is actually happening – they go together – understand how it works and then changing things to improve the situation.

    Please note – I completely believe the current approach of reducing carbon emissions is necessary, so that we can return to a relatively stable climate and avoid having an even bigger problem to face in the future. But while that happens, I think we have to have additional measures in place, or face a huge human cost.

    Contrarians talk about how we will eventually go into the next ice age, as the climate changes no matter what we do. That is very likely true, and when that starts to happen, we are also going to have to deal with it, or accept even more destructive changes to the planet (I don’t want to get into the philosophy here of that issue…). That is not a reason to ignore the current problems. We have built a world that depends on a very stable climate, and until the population drops dramatically or we can easily adjust, we are going to have to try to maintain that stability, against the current warming and a future cooling.

  30. 30
    Mattias Dahlstrom says:

    A question regarding sea water rise…
    If seawater would rise … say 10 m … would the seafloor compact a bit, resulting in less than 10 m effetive rise?

  31. 31
    David B. Benson says:

    Pat Neuman — Tectonic rebound takes many thousands of years. The rebounding area you suggest is but a tiny fraction of the surface area of the oceans.

  32. 32

    A few comments:

    RC writes:

    How good have previous IPCC reports been at projecting the future? Actually, over the last 16 years (since the first report in 1990), they’ve been remarkably good for CO2 changes, temperature changes but actually underpredicted sea level changes.

    The AR4 states:

    Since IPCC’s first report in 1990, assessed projections have suggested global averaged temperature increases between about 0.15 and 0.3ºC per decade for 1990 to 2005. The can now be compared with observed values of about 0.2ºC per decade, strengthening confidence in near-term projections.

    Indeed, the observed trend in global temperatures is about 0.2ºC per decade from 1990 to 2006 (or 2006 for that matter). What seems to be forgotten both by the IPCC and Rahmsdorf et al. (or at least swept far under the rug in Rahmsdorf et al.), is that a big volcano went off in 1992 and cooled global temperatures for 2-3 years afterwards (if not a bit longer). A big non-anthropogenic cooling near the beginning of the period of record being compared in one dataset (the observed data) and not in the other (the collection of IPCC model results) doesn’t lend itself to an appropriate comparison. Using a longer period of record, say 1977-2006, shows the observed global warming to be about 0.17ºC per decade, or, alternatively, removing the known volcano-influenced years, say 1992 and 1993, from the 1990-2005 period of record produces a warming rate of about 0.15ºC per decade. Take your pick. But, in either case, the observed warming rate is certainly in the low range of IPCC projections (from any IPCC report) for the period 1990-2005.

    Also, RC comments about sea level rise and the potential contribution from ice sheet dynamics, quoting the IPCC AR4 SPM:

    Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise. Understanding of these processes is limited and there is no consensus on their magnitude.

    I would like to add that also found in the IPCC AR4 SPM is the following concerning the role of dynamic ice processes on sea level rise:

    Models used to date do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in ice sheet flow, because a basis in published literature is lacking. The projections include a contribution due to increased ice flow from Greenland and Antarctica at the rates observed for 1993-2003, but these flow rates could increase or decrease in the future. For example, if this contribution were to grow linearly with global average temperature change, the upper ranges of sea level rise for SRES scenarios shown in Table SPM-2 would increase by 0.1 m to 0.2 m. Larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea level rise.

    Notice the phrase “but these flow rates could increase or decrease in the future” [emphasis mine]. While some commentors may choose to ignore this (e.g. RealClimate) and others may think that it is a “disservice to mankind” (e.g. comment #8), nevertheless, the IPCC authors felt that the current state of the science necessitated its inclusion.

    -Chip Knappenberger
    to some degree, funded by the fossil fuels industry since 1992

    [Response: First, my name is Rahmstorf. Second, I find your accusation that we sweep something under the rug bizarre, since we show all the data since 1973. I invite everyone to see for themselves; to those without subscription, our paper can be accessed through the link on my home page. -stefan]

  33. 33
    Andrew Sipocz says:

    Re: #28. Something else would sink as Greenland rose but the timing would vary and contribute to the natural sloshing around of global sea level. I post this because I’m amazed at our need to totally understand how the earth and everything works. Somewhere, sometime, some comedian needs to do a skit of how we torture ourselves over our need to know every little detail. It kills my wife. Much more to worry about right now, but as an example the U.S.’s Gulf of Mexico coastline is slowly sinking in response to the melting and subsequent rise of the lands once under the laurentide ice sheet (see Gonzales and Tornqvist in Eos, Vol. 87, No. 45, 7 November 2006).

  34. 34
    SecularAnimist says:

    Would the moderators consider deleting the ignorant, sneering, hostile, insulting, content-free and completely worthless remarks from the flame troll identifying himself as “juandos”? Such drivel belongs on Free Republic or some other right-wing hangout, not here.

  35. 35
    Jim Redden says:

    Re 21 [SPM and the media]

    As Scott writes: The media are able to bring a critical faculty to bear on scientific subjects, but choose to do so on a haphazard and selective basis.

    Indeed. Several media venues have a different spin.

    Popular media behavior is shaped by market forces; hence, the need for a hooking headline and topic based on culling and maintaining readership. Akin to what you have said, I submit media choices are the best guess of an editor seeking to satisfy readership, advertisers, and stockholders.

    Meanwhile, I am going to keep my eyes out for the reaction of ecologists–who can try to make sense of what will happen in the oceans–as currents accommodate to new exchanges of energy, and the poles continue to warm so much faster than the rest of the globe.

    Frankly, my guess is one may very well be able to start watching the collapse of ocean food chains on the news eventuallyâ��partly due to pollution, and overexploitationâ��and now overtaxed by new ocean transport current relationships which are sure to emerge–perhaps without specific prediction. While the task of the IPCC does not stipulate exploring the reaction of ecosystems, the crux of our most vexing of problems will be how the Earth as a whole reacts on a granular level to the new phase composite of climate. Sea level rise may rank as the simplest tasks to deal with.

    So far, rather predictably, the reaction to the report seems to resolve around preconceived attitude and how one tends to lens the world. As others have implied in an earlier thread, pure unadulterated science transcends rhetoric. Move to science applied, and politics rears a head. (The Boortz fellows web site left me shaking my head.)

    As an aside, reading the many earlier threads as of late, on real climate, has been quite time consuming�yet worthwhile. To see such discourse, with some well founded scientific explanation and outlinks�I am thankful.

  36. 36
    Pat Neuman says:

    Thanks for your comment. I wanted reassurance, with the thaws happening much quicker now vs the thaws in Earth’s history and those which didn’t involve Greenland and Antarctica. I’ve seen photos of the mud flats near near Anchorage, apparently from rebound. I was surprised by the magnitude of the lifting in that area. Maybe there’s more at work near Anchorage than rebound – like the giant quake they had in the 1960s.

  37. 37
    LochDhu says:

    Typo police:

    Actually, over the last 16 years (since the first report in 1990), they’ve been remarkably good for CO2 changes, temperature changes but actually undepredicted sea level changes.

    I assume you meant to type underpredicted. Keep up the good work!

    [Response:Thanks! - gavin]

  38. 38
    Mark Zimmerman says:

    Does the IPCC address the recent paper by Lyman et al., documenting ocean cooling the past couple years? Or has this work been dated already by more recent data?

  39. 39
    garhane says:

    I do not know if anyone will ever work out the evidence, but this lay reader is assured the contributors of Real Science have been a strong support for the work of hundreds of scientists who have worked to make the report of or to the IPCC the best science can do. This is due to the steadfast centering function RC has performed. Unhappily it will now be needful to prepare for the attacks of a crowd of ideologues who are even worse than the gang that could not count, the economists. I guess someone will come forward, but they will have quite a job to measure up to the standard RC has set. Three cheers and a tiger.

  40. 40
    James Stample says:

    Climate change. Maybe man made maybe not! But what does it matter. We obviously will have to make some tough decisions!
    Let me pose a Question?
    Lets say there is a large asteroid discovered on a collision course with earth!
    At that time, we may have many ways of which to stop this catastrophe. But maybe just maybe this is our only oppotunity to reverse the global warming issue by allowing it to strike! Therebye starting a new iceage.
    Are we ready to assume all resposibility for mankind who seems to be more concerned about whats causing global warming then the ultimate effects of sustained ignorance will lead us.

    Some day we will have to decide!
    It may mean that we lose half of the earths population but mankind will endure.Or will we?

  41. 41
    Ark says:

    #11: data for Greenland and Antarctica are messed up for the 1961-2003 period as well (factor of 10 too high). I guess those data were in mm/year instead of m/century (cf. the editing note above the table that they forgot to remove). Probably American authors, for them mm are units from Mars, like Btu/ft2/h for us Europeans.

  42. 42
    Lynn Vincentnathan says:

    RE #12, yes, every little bit helps. So print these 21 pages on used paper, if possible, or doubled-sided on recycled paper. I get my used paper at the university library, mainly page separator sheets, and it’s high grade. First REDUCE, second REUSE, third RECYCLE.

    I forgot what the cut-off date was for the journal articles included in AR4. Was it June 2005 or 2006?

    I always take these reports as being on the conservative side of conservative, since they require great consensus, beyond the typical conservative (false-positive avoiding) single scientific studies. I think the cutting edge studies of dangerous predictions would indicate greater harms than what IPCC indicates (though the reports do include ranges, but may excluded the highest ends).

    Another point, each succeeding report not only reveals greater precision in the science, but also that global warming is more potentially dangerous than experts had earlier thought. I might be wrong, but that’s the sense I get.

  43. 43
    Sean Davis says:

    Ark, You’re right. They apparently screwed up the Antarctic contribution for 1961-2003 as well in Table SPM-0. Also, if you assume they meant 0.014, the numbers in the 1961-2003 column don’t add up (i.e. .042+.05+.05+.014 = .156, NOT .11 as they have in the table)

  44. 44

    [[Now that you are one of those who are either ignorant beyond all help or just a pathological liar, do you have any other excuses for being a fear monger?

    Just asking... ]]

    Stay off the sauce when you post. It improves the quality of your prose.

  45. 45

    Where is the discussion of natural variability in all this? There is of course the minor contribution of solar irradiance but the changes over the ENSO cycle, over decadal timescales and over longer period don’t rate a mention. The decadal variance in particular is dismissed at Wikapedia as climate noise and addressed on this site as a single paragraph and a blind link. How is this possible?

    The cyclical changes in global temperature and climate more generally over periods of decades – to 1946, 1947 to 1975 and 1975 to 1998 in the instrument record – and, from proxy data, occuring 11 times in the past 400 years with an average duration of 23 years.

    FAR predicts a 0.2 degree C/decade rise in temperature over the next couple of decades. The history of decadal variability suggests that temperatures will decline (since 1998) over the next couple of decades – well before which the entire science community is utterly discredited. Don’t believe me – this is very simple experiment and one that doesn’t require 5000 of the world’s leading scientists.

    Random fluctuation is not much of an explanation for such a persistent and influential phenomenon. I feel like being very rude but will of course refrain. Feel free to claim that the temperature decline since 1998 is random climate noise – pretty much as the CRU did on New Years Day 2007 when claiming, after 2006 came in at the sixth warmest year, that 2007 will surely see the upward trend return. I am not likely to be listening until I see the data.

  46. 46
    Ajit Singh says:

    Says RK Pachauri, DG, The Energy and Resources Institute & Chair IPCC: “A number of scientists say Siachen should be made a protected area, a heritage site of sorts, and that there should be no army presence on either side. For purely ecological reasons, this *might* be a good idea. But I *don’t* see why there would be melting as a result of military presence and activity.” The *s show a vagueness unworthy of an environment leader who ought to ask for withdrawal of all troops immediately’
    Please Cleck to see how indian and Pakistan Army melting Siachen glacier
    http://www.zeenews.com/articles.asp?rep=2&aid=345084&ssid=26&sid=ENV – 58k –
    http://www.wwfpak.org/15-01-07meltingofthesiachenglacier.php – 32k – Cached – Similar pages
    in.news.yahoo.com/061230/211/6apcs.html – 39k – Cached – Similar pages
    http://www.thenews.com.pk/daily_detail.asp?id=38553 – 21k – Cached – Similar pages

  47. 47
    Hans Vermeer says:

    While you can appreciate the representation of scientific knowledge, available late 2006, in this IPCC report, you might wonder how it will affect the political decision-chain. Here in the Netherlands, the rather conservative estimates on sea-level-rise already led to (secondline) features in the national television news show, in which the one-line statement “Holland will not be flooded…” sounded like a sense of relief. But even without accounting for possible dynamic changes in icecaps the consequences stated in the report make clear there is not much relief while reading carefully. My point is that it is not just a question of how much sea-level-rise will occur. Agricultural and land-use change, growing salinity of groundwater and estuaries, re-arranging drinking-water facilities, changing character of rivers etcetera. This will put an ever growing strain on our national budget. Not to mention the help we might want to offer in less fortunate regions in the coming world. It is time to be clever and to accept that it might cost us a considerable amount of our “business as usual” to cope. I just hope the full fourth assessment will contribute to that awareness!

  48. 48
    Lee Morrison says:

    Any significance to the fact that the report was released on Grounfhog Day? “If the groundhog sees his shadow, there’ll be another six weeks of winter.” (Probably as valid as some of the exquisitately accurate computer modelling with questionable input data.)

  49. 49
    David B. Benson says:

    Sea stand rise — On another thread, Nigel Williams asked for a 500 year prediction. I offered 7 m for the melting of the Greenland ice sheet and up to 20 m (conservatively high) for the melting of the West Antarctic ice sheet. So minor adjustments due to isostacy and tectonic rebound are just too insignificant to consider when faced with a long-range prediction of 22–27 m.

  50. 50
    David Price says:

    One query concerns precipitation. In a warmer world the oceans will warm, causing more evaporation. The warmer air will be able to hold more water. Therfore one would expect a greenhouse world to be a lot wetter. Yet the report forecasts droughts and reductions in rainfall most places.
    This is odd, especially in the tropics where there will be a lot of extra precpitation looking for somewhere to go. Where will it all end up?


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