Friday, February 2, 2007

Real Climate Explains IPCC Conclusions on Sea Level Change

Real Climate Comments on The IPCC Fourth Assessment SPM: Sea Level Change Real Climate

When the IPCC started to release highlights to the press before today's launch of the IPCC Fourth Assessment, I was wondering why the IPCC had such low numbers for sea level change.  It turns out that the new numbers simply exclude the dynamic shifts of ice sheets because the magnitude of those shifts are not clear.  What is clear is that the increasing evidence on ice sheet dynamics all points in a single direction: ice sheet dynamics will substantially increase the sea level change expected from a given change in mean temperature.

From Real Climate: ...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.

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... 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.

....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 undepredicted 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.

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 undepredicted 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!

32 Comments »

 

  1. 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]

    Comment by cbone — 2 Feb 2007 @ 11:08 am

  2. 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

    Comment by catman306 — 2 Feb 2007 @ 11:25 am

  3. 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]

    Comment by BCC — 2 Feb 2007 @ 11:27 am

  4. 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.

    Comment by Mitch Golden — 2 Feb 2007 @ 11:29 am

  5. 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.

    Comment by P. Lewis — 2 Feb 2007 @ 11:32 am

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

    Comment by curving3 — 2 Feb 2007 @ 11:37 am

  7. "Scientists offered Cash to Dispute Climate Study"

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

    Comment by Anonymous — 2 Feb 2007 @ 11:59 am

  8. 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.

    Comment by Dave Cohen — 2 Feb 2007 @ 12:00 pm

  9. #1, the report can be found here

    Comment by Sean Davis — 2 Feb 2007 @ 12:07 pm

  10. 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

    Comment by Zeke Hausfather — 2 Feb 2007 @ 12:09 pm

  11. 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]

    Comment by Sean Davis — 2 Feb 2007 @ 12:11 pm

  12. 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.

    Comment by CobblyWorlds — 2 Feb 2007 @ 12:12 pm

  13. 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

    Comment by Karan — 2 Feb 2007 @ 12:13 pm

  14. 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.

    Comment by E. C. De Fabo — 2 Feb 2007 @ 12:44 pm

  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

    Comment by Spencer Weart — 2 Feb 2007 @ 12:48 pm

  16. 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?

    Comment by Jake — 2 Feb 2007 @ 12:53 pm

  17. 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.

    Comment by Jake — 2 Feb 2007 @ 1:19 pm

  18. #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?

    Comment by lars — 2 Feb 2007 @ 1:31 pm

  19. 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!

    Comment by Steven Leibo Ph.D. — 2 Feb 2007 @ 1:35 pm

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

    Comment by Sashka — 2 Feb 2007 @ 1:38 pm

  21. 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.

    Comment by Scott L. Montgomery — 2 Feb 2007 @ 1:41 pm

  22. 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.

    Comment by Mike — 2 Feb 2007 @ 1:44 pm

  23. 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

    Comment by Sashka — 2 Feb 2007 @ 1:50 pm

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

    Comment by Hank Roberts — 2 Feb 2007 @ 1:55 pm

  25. 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...

    Comment by juandos — 2 Feb 2007 @ 2:06 pm

  26. 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?

    Comment by juandos — 2 Feb 2007 @ 2:08 pm

  27. 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?

    Comment by tom street — 2 Feb 2007 @ 2:08 pm

  28. 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).

    Comment by Pat Neuman — 2 Feb 2007 @ 2:10 pm

  29. 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)?

    Comment by Jason Burford — 2 Feb 2007 @ 2:16 pm

  30. 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?

    Comment by Mattias Dahlstrom — 2 Feb 2007 @ 2:24 pm

  31. 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.

    Comment by David B. Benson — 2 Feb 2007 @ 2:26 pm

  32. 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.

    Comment by SecularAnimist — 2 Feb 2007 @ 2:57 pm

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Secular Animist,
Sounds like someone questioned your faith.
You should be more tolerant.

Posted by: Lee | Feb 4, 2007 12:52:18 PM

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