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Comments 1 to 50 out of 69:

1. adrianco at 08:02 AM on 18 December, 2009
   I just finished reading James Hansen's new book (Storms of my Granchildren) where he talks a lot about sea level rise and references a bunch of papers. Could you do a review and summary of Hansen's position vs. the other researchers in this area? Thanks.
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2. timbo1235 at 08:33 AM on 18 December, 2009
   Problem with this, and this goes to most PR/comms with the public from science (and is a big failure in engagement with the public by science) is that these numbers have zero immediacy with the public. I'm far from being a skeptic (I bled concern at heresysnowboarding.com/blog) but I look at 2050 and see anything from 20-60cm and I think, so what. What science needs to do is make it clear in terms of lost land (i.e. X%) or number of people displaced, amount of arable land lost etc etc. Putting up values of 4cm, 10cm etc doesn't mean much to fat, lazy, ignorant, unconcerned Western consumer...
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3. HumanityRules at 12:13 PM on 18 December, 2009
   I guess that temperature could be replaced with energy in this article. The important issue being that with warming globe sea level rise will depend on where that energy is flowing (into sea/land ice, land, atmosphere, shallow or deep water etc). In your post "Understanding Trenberth's travesty" you reported on recent work to suggest that some of the energy is following into the deep ocean. My understanding is that old theories ignored deep oceans as an unimportant energy sink, being relatively stable. Energy into here, due to the higher pressures, has little affect on sea level. I was wondering whether is work is intergrated into estimates of sea-level rise. On a broader point Trenberth seemed unable to balance both the energy bugget and observed sea-level rise based on what we presently know. Suggesting there may be room for an unknown in the energy budget equation. I was wondering what impact that has on the work you present here. Trenberth's paper
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   Response: The issue of heat being sequestered into the deep ocean has no bearing on the semi-empirical method. I'm not sure to what degree it will affect the kinematic study but the general sense I get from both papers is that thermal expansion becomes less of a contributing factor as time goes on. The newly released paper on the last interglacial (Kopp 2009) backs this up, finding ice sheets are vulnerable to sustained warm temperatures.
   
   Pfeffer 2008 is freely available online (you can register on Science for a free account) so I leave this one as an exercise for the reader :-)
4. Riccardo at 19:23 PM on 18 December, 2009
   HumanituRules, the thermal expansion coefficient of sea water actually increases with pressure; hence, heat going into the deep ocean has a larger effect on sea level. The fact that current model do not include warming in the deep ocean is one more contribution to the underestimation of sea level rise.
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5. Riccardo at 20:28 PM on 18 December, 2009
   Those of you who have acces to Nature and are less inclined to the mathematical details of the anlysis should take a look at the published version of Kopp 2009 paper.
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6. neilperth at 23:23 PM on 18 December, 2009
   The IPCC tells us that warmer temperatures lead to higher sea levels. Fortunately, there is only one ocean. And while sea levels vary with tides over the year, averages are probably fairly reliable. The IPCC does present a chart of sea levels and its trend is more obvious than the temperature trend. It shows a steady rise of about 200 millimeters in the last 120 years. That's about eight inches. Is eight inches over 120 years significant or alarming? Better yet, scientists have produced a long-term graph of sea level changes, about 20,000 years worth. The data behind this graph are widely known and accepted. NASA, for example, accepts this data and the government of Canada publishes a similar graph. Firstly the graph ranges over about 120 meters (not millimeters), about 400 feet. On the graph by comparison, a change of 200 millimeters (or the change in the last 120 years as per the IPCC) would be would be about the width of your eyelash. When the seas were 400 feet lower, people could walk from Russia to Alaska and from France to England. Global warmists are taking their micrometer, literally, to the last 120 years on this chart, and from that, extrapolating that we are all about to die. If sea levels go along with global temperatures, as the warmists frequently remind us, then this chart makes blatantly obvious that •Man has just about nothing to do with global temperatures, •Any temperature changes in the last 100 years are insignificant compared to longer term changes, •And current trends are most likely just the final flattening out of temperatures after rising from the last ice age. How can you blame man for sea levels rising when about 99% of that rise since the last ice age occurred before man built the pyramids, much less SUVs? A rise in sea level over the last century should not be surprising; it's been rising for the last 20,000 years. If anything, looking at this chart would convince me that long term temperatures are cyclic and that we are coming near the end of the warming part of the cycle. In fact, it looks like we are near the peak of that warming and could be about to enter the cooling-down part of the cycle. Over the last 20,000 years, man did pretty well. His population grew from fewer than 10 million to almost 7 billion. He had an agricultural revolution, an industrial revolution and an information revolution. He started cities. He started writing. He started recording his own history. He walked on the moon. Over that time, the sea level rose about 120 meters. If the current trend continues, it will rise two meters in the next 1000 years. If man thrived like he did when the seas rose 120 meters, why would the world end if they rise another two?
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7. RSVP at 01:12 AM on 19 December, 2009
   to neilperth Obviously, you dont surf.
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8. RSVP at 01:40 AM on 19 December, 2009
   Referring to Figure 3. Even with a total Venus style greenhouse runaway scenario, on an expanded time scale, the curve would have to flatten out, as there is only a finite amount of ice in our polar caps. But for the short run of 100 years, as oceans grow, would'nt that volume of extra water dampen global warming? (since the heat capacity of water is twice that of ice)... in which case the curve would be a little flatter. Or does more ocean mean more water vapor and more global warming?
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9. Ned at 01:58 AM on 19 December, 2009
   neilperth: The IPCC AR4 predictions of future sea level rise were specifically designed to be conservative, by simply omitting processes that are difficult to predict but are known to contribute to sea level rise. In other words, they are a lower bound on SLR, and sure enough, as we see from the first figure in this post, actual SLR is nicely tracking the very uppermost range of the IPCC predictions. The Vermeer et al paper being discussed here makes a convincing argument for sea level rise of 7.5 to 19.0 mm/year over the next century. This is much faster than most pre-modern changes in sea level, and in fact is of the same order of magnitude as some of the extreme spikes that occurred during deglaciation. That's disturbing, because unlike the situation 14,000 years ago, there are now over 600 million people living within less than 10 m of sea level. Not to mention lots of nice stuff like cities, airports, shipping terminals, and other valuable infrastructure. None of that existed during past episodes of sea level rise. In wealthy countries, we can afford to move people inland (a 1 m rise in sea level might only cost the US something like $400 billion, though other estimates would put the price tag higher). In poor countries, this will mean vastly more hardship. Of course, in the worst-case scenario, if people fail to take action on climate now, and we keep burning more and more oil and coal, at some point we'll lose at least a large fraction of both the Greenland ice sheet and the West Antarctic ice sheet. Let's just hope they don't break up as fast as the portions of the Pleistocene ice sheets that were responsible for meltwater pulse 1A, when sea levels rose at rates of 50 mm/year for three centuries. Anything even close to that would be an immense disaster.
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10. Ned at 02:23 AM on 19 December, 2009
    RSVP writes: But for the short run of 100 years, as oceans grow, would'nt that volume of extra water dampen global warming? (since the heat capacity of water is twice that of ice) Don't take this personally, but are you seriously suggesting that the change in the thermal mass of the ocean as a result of melting ice would have a significant effect on the rate of increase in global surface temperature? A few seconds with Google suggests that the mass of the oceans is 1.4 x 10^21 kg. (e.g., http://hypertextbook.com/facts/1998/AvijeetDut.shtml). The area of the ocean is 3.6 x 10^14 square meters. One cubic meter of water masses 1000 kg, so raising sea level by one meter adds 3.6 x 10^17 kg to the ocean. That presumably would increase the ocean's thermal mass by 0.0026%. Working that out took one or two easy Google searches, plus a small amount of very simple calculations. John, our host on this blog, tries to keep everything polite and I want to respect that. But I'd like to gently suggest that you, RSVP, could probably have figured out the answer to your question first, rather than throwing it out here as an objection that others then have to address. Okay, end of sermon.
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11. chris at 06:17 AM on 19 December, 2009
    re #6 neilperth, your statement simply doesn't accord with the evidence:

    How can you blame man for sea levels rising when about 99% of that rise since the last ice age occurred before man built the pyramids, much less SUVs? A rise in sea level over the last century should not be surprising; it's been rising for the last 20,000 years.

    In fact the sea level rise from melting of polar ice during the last glacial to (present) interglacial transition was preetty much complete by a few thousand years ago. The evidence indicates that there has been little change in eustatic sea level since Roman times 2000 years ago, and if anything sea levels dropped somewhat (a small number of centimeters) in the nearly 2000 years up to around the middle of the 19th century, after which they've started to rise, increasingly so during the last century and especially during the last several decades: Pirazzoli PA (2005) A review of possible eustatic, isostatic and tectonic contributions in eight late-Holocene relative sea-level histories from the Mediterranean area Quart. Sci. Rev. 24, 1989-2001 “Finally, several data from tectonic and non-tectonic areas are consistent with nearly stable global eustasy since 6000BP, thus challenging the assertion of significant additional melting of Antarctica after the complete melting of the former Northern Hemisphere ice caps “ Lambeck K (2005) Sea level in Roman time in the Central Mediterranean and implications for recent change Earth Planet. Sci. Lett. 224, 563-575 “Part of this change is the result of ongoing glacio-hydro isostatic adjustment of the crust subsequent to the last deglaciation. When corrected for this, using geologically constrained model predictions, the change in eustatic sea level since the Roman Period is -0.13 +/- 0.09 m. A comparison with tide-gauge records from nearby locations and with geologically constrained model predictions of the glacio-isostatic contributions establishes that the onset of modem sea-level rise occurred in recent time at similar to 100 +/- 53 years before present.” Church JA et al. (2008) Understanding global sea levels: past, present and future Sustainability Sci. 3, 9-22 “While sea levels have varied by over 120 m during glacial/interglacial cycles, there has been little net rise over the past several millennia until the 19th century and early 20th century, when geological and tide-gauge data indicate an increase in the rate of sea-level rise.” Milne GA (2009) Identifying the causes of sea-level change Nature Geosci. 2, 471-478 ”The observed fall in sea level following the end of major melting (~7,000 yr bp; Fig. 3b) is due to isostatic processes52. A growing number of high-resolution records (Fig. 3c) detect an acceleration in sea level around AD 1850–1900 (refs 43–45)” etc...
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12. jliungman at 06:23 AM on 19 December, 2009
    Hello, and thanks for an interesting post! In the original post you state: "There are limitations to this approach. The temperature record over the past 120 years doesn't include large, highly non-linear events such as the collapse of an ice sheet." Isn´t the problem even more serious? If we view sea level as some kind of funtion of temperature, derived by looking at the evicence of the very narrow range of temperatures we have observed since 1880, how can we make any claims about a different range of temperatures? I´m not a scientist, but it seems to me that with so many variables involved, linearity would be the last thing to expect. The method seems interesting, but needs to be calibrated using more information about other temperatures and sea levels historically. And I don´t know if this information exists? Or am I mistaken? Thanks, John
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13. Riccardo at 07:05 AM on 19 December, 2009
    jliungman, actually the model is not linear. Whatever it is, extrapolation is always a tricky business and you need solid physical basis to be confident with it. If, for example, you push it too far to a situation in which there is no more ice anywhere the extrapolation will for sure be unjustified. But if you consider that the contribution to sea level rise is mostly due to only two processes (sea water warming and ice sheet melting, both in the end driven by GHG forcing) we might be confident enough that no dramatic changes will show up in a century. The model has also been tested tested against a simulation along a time span of 1000 years (fig.2 in the paper).
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14. jliungman at 08:40 AM on 19 December, 2009
    Thank you for your reply, Riccardo. However, the original posting also stated: "This calving process is accelerated by warming but the dynamic processes are not strongly understood." We attempt a theoretical model including glacial dynamics (and a lot of other parameters) but we find that those dynamics are hard to predict. So we try the "semi-empirical" approach instead, making the assumption that "highly non-linear events such as the collapse of an ice sheet" don´t happen. Then have we really solved the problem of collapsing ice sheets? NB. I´m not claiming that anyone is wrong, just trying to get my spontaneous objections resolved.
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15. jliungman at 08:49 AM on 19 December, 2009
    Sorry, now that I actually read the paper I see that the authors do address my point: "In addition, highly nonlinear responses of ice flow may become increasingly important during the 21st century. These are likely to make our linear approach an underestimate."¨ As a non-physisist, I feel just a little bit proud for having seen that coming... ;-) John
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16. Riccardo at 10:01 AM on 19 December, 2009
    jliungman, i think it's a success of this site if people like you come asking questions, read the papers and solve by themselves.
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17. neilperth at 14:31 PM on 19 December, 2009
    It is a fact that sea levels can rise and fall over 100 metres due to NATURAL causes. This has happened in the past and no doubt will happen again in the future. If the sea level rises say only 5 metres over the next 1000 years, obviously this will cause problems for low-lying areas of the world. But the world was never designed to be optimal for human habitation. If you buy a house near the coast, you should be aware that over time there is the possibility that it will be flooded by the sea. If you buy a house in a city located on top of a Benioff Zone ( eg Seattle, Vanouver ), you should be aware that it may be destroyed by an earthquake. Of course people living in say Bangladesh have little option but to live in low-lying coasstal areas. But over time sea levels will rise and fall whether man-kind is on this planet or not.
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18. Steve L at 16:12 PM on 19 December, 2009
    neilperth @17 -- what's your point? People can die of natural causes, species can go extinct from natural causes, terrible living conditions can result from natural causes.... Therefore? neilperth @6 -- when did humanity make the biggest strides? Was it during the big swings in global climate and sea level or was it during the period of relative stability?
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19. Craig Allen at 17:25 PM on 19 December, 2009
    neilperth: By your logic, given that people sometimes die in car accidents even when everyone is being responsible, it is therefore perfectly OK for drivers to get blind drunk and career around ignoring the speed limit. People will inevitable die either way right, so why be careful?
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20. neilperth at 18:28 PM on 19 December, 2009
    Steve L, Pico. My points in relation to sea level changes and, by inference temperature changes, were that : 1- These change markedly over time due to natural causes. 2. Over time sea levels and temperature will rise and fall whether man-kind is on this planet or not. So I ask : do you consider statement 1 true or false? do you consider statement 2 true or false?
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21. FrankT at 23:02 PM on 19 December, 2009
    "Meanwhile, we cannot detect climate change on the Dutch coast" is the heading (in Dutch) of a summary of a presentation given in March 2009 by one of Holland's main government advisors on sea-level (Douwe Dillingh), who works for Deltares (www.deltares.nl), the main Dutch research institute for everything related to water technologies. The graph on the link below shows an essential linear trend of appr. 15cm / century increase of sea-level from 1900 to today. The text asserts that this linear trend started earlier, and can be dated to at least 1800. In Dillingh's opinion the 30cm/century measured by sattelites is no reason to conclude that there is an increase in sea-level rise, since the measurement methods are too different (sattelite vs. tidal gauge locally). Bottomline: on the Dutch coast the sea level does rise, but exactly as it has been doing for the past 200 years. No sign yet of any increase due to CO2 based global warming. Of course, this is a local situation, and one can think up all sort of hypothesis why this is just a local peculiarity, if it is. The link is: http://www.waterforum.net/index.asp?url=/template_a1.asp&que=paginanr=6609 The website 'waterforum' is a news site for Dutch professionals involved in water management.
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22. Riccardo at 01:21 AM on 20 December, 2009
    The only long term record i know of in the Netherland is Amsterdam (untill 1932 when it was separated from the sea). It shows a very slow increase of about 1.5 cm/century up to the second half of '800. Then, using also other coastal tide gauges, it started rising at about 17 cm/century up to today. It is quite similar to the world average during the same period. This points to a sea level rise along the Dutch coast similar to the world average, even if the noisier local record still cannot detect it. Indeed, as far as i know the Dutch have taken really seriously the threat posed to their country by sea level rise.
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23. Steve L at 03:41 AM on 20 December, 2009
    neilperth @20 -- your points are not substantial, then. 1. Yup, sea level and temperature changed over time in the absence of anthropogenic forcing. 2. Yup, they will continue to change while humans are here and after humans are extinct. In the meantime, however, it's worth pointing out that temperatures and sea levels will rise (probably accelerating for the latter) into the foreseeable future because of anthropogenic CO2 (and human choices will influence the rate of that rise). All else being equal, if anthropogenic influences on climate were removed, these rises into the foreseeable future would not occur.
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24. FrankT at 09:43 AM on 20 December, 2009
    Riccardo@20 Sea level rise is certainly taken serious in Holland. My point was that so far there is no indication locally that there is any increase in the rising of sea levels due to CO2. The Royal Dutch Meteorological Institute (KNMI) published a brochure in 2009 with an update on their 2006 scenario's. On page 20 (blue frame) it is stated (in Dutch): "In the past century the sea level has risen by appr. 20 cm. and there has been no clear local acceleration in the past decennia. On a global level there are indications for an acceleration in the rise of sea levels". http://www.knmi.nl/klimaatscenarios/documents/brochure09.pdf
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25. Tony O at 10:07 AM on 20 December, 2009
    As evidenced by our near total inaction on global warming to date; mankind does not do preparatory adaptation well. Added to our psychological short comings is that we really do not know what the seal level rise will be, ignoring changes in dynamic factors or only considering limited factors means that the estimate is likely too low. Ignoring changes to the carbon cycle, it is likely that temperatures will increase 2 or 3 degrees. Paleontological evidence suggests a 6 meter rise over time, but what time? As more evidence is analyzed that time lime seems to be shortening. For example how long have we been looking at a new Sydney Airport? About 40 years. And how far have we gone? Nada. Is there any chance that Sydney Airport will be fully functional past mid century? Don't look at the average elevation look at the low points. Add to average mean sea level: high tide, storm surge waves and wave ramping. Some articles you may find interesting Responding to Changes in Sea Level, Engineering Implications. National Academy Press 1987. (Based on lower slr estimates considers levees a practical solution for airports) http://www.smh.com.au/environment/threats-looming-fast-for-vital-facilities-20091113-iepx.html (I know a newspaper not peer reviewed) The Adaption Myth; Robert Repetto http://environment.research.yale.edu/documents/downloads/v-z/WorkingPaper13.pdf http://www.climatesciencewatch.org/index.php/csw/details/markey-adaptation-hearing/ http://www.swissre.com/resources/387fd3804f928069929e92b3151d9332-ECA_Shaping_Climate_Resilent_Development.pdf (A bit in there spread through the paper) http://www.newscientist.com/article/mg20126965.200-prepare-for-a-climatechanged-world-say-engineers.html (Not so much on SLR) Increasing flood risk and wetland losses due to global sea-level rise: regional and global analyses (1999) And don't forget James Hansen's 5m by 2107 Bradley Opdyke from ANU has some rather pessimistic views on how quickly various parts of the WAIS could collapse
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26. Riccardo at 11:16 AM on 20 December, 2009
    FrankT, i did not doubt that no increase in the rate sea level rise is discernible in the Dutch coastal stations data. I said that it cannot be seen in any case due to noise and that the similarity of the Dutch trend with the global trend is an indication on what to expect. This is an important point because, as i'm sure you know, the local response might be different from the global average; it looks like it is not the case in The Netherland.
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27. neilperth at 12:22 PM on 20 December, 2009
    Steve @23..... Hey we are getting somewhere in our discussion! So you agree that sea level and temperature changed over time in the absence of anthropogenic forcing and that they will continue to change while humans are here and after humans are extinct. Do you also agree that it is likely that the cyclical ice-ages which have occurred on earth over the last 600 million years will continue to occur in the future ?
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    Response: These are fundamental and well established issues. Every climate scientist will agree that:
    
    1. Temperature has changed naturally in the past (before humans).
    2. As sea level is directly affected by sea level (as established in Vermeer 2009) then sea level has changed naturally in the past
    
    Do not fall into the logical fallacy that past natural climate change means humans can't influence climate now. On the contrary, past climate change shows us that climate is sensitive to radiative forcing - to energy imbalance. As we are currently imposing an energy imbalance through an enhanced greenhouse effect, past climate change is actually evidence for our climate's sensitivity to CO2.
    
    Is it likely that cyclical ice ages will occur in the future? In the short term (geologically speaking), the peer reviewed science says no. The radiative forcing from CO2 far outstrips the radiative forcing from orbital changes that initiate cyclical ice-ages. I touch on this tangentially on We're heading into a new Little Ice Age although that page is talking more about the forcing from falling solar levels, not orbital forcing. However, orbital forcing is even less than solar forcing so the argument stands (one of these days I'll do a post specifically focusing on Milankovitch cycles).
28. Steve L at 14:48 PM on 20 December, 2009
    neilperth @27: I don't know if we're getting anywhere; you aren't saying very much and you repeat a high proportion of what you have said. Regarding your last question, my answer is "Not necessarily -- it depends on future forcings." Read this: http://www.skepticalscience.com/High-CO2-in-the-past-Part-2.html
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29. FrankT at 00:05 AM on 21 December, 2009
    Riccardo@26 Quite correct. The open question for research is why there is no correspondence between the local and global trend. This is peculiar, since the obvious causes(in particular sinking/rising land) are all carefully measured, and do not explain the difference. A related issue which is important for the long term implications for Holland is the recently re-discovered effect of 'self-gravitaion'. This is not yet included in the KNMI 2006 scenario's, but will be in the 2013 version. Self-gravitation refers to the effect that large ice-sheets on land attract the sea through the force of gravity, leading to a substantial local increase of the sea-level. The surprising implication is that a complete melting of the Greenland ice-sheet would hardly lead to any sea-level increase on the shores of Greenland. The gravitational effect of the Greenland ice sheets is still very noticable in Holland. Model calculations from different researchers are not in agreement yet, but as a rough indication it would probably diminuish the impact on sea levels at the Dutch shore by a factor three. So instead of a rise by 6-7 meters after a complete melt of the Greenland ice-sheet, the increase of the sea level at the Dutch shores would only be 2 meters. On page 15 of the popular publication of the Delft Technical University 'Delft Outlook' 2009-02 (url below) you can find a bit more context about this, in an article primarily about the new GOCE sattelite. http://tinyurl.com/yht6tdj
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30. SNRatio at 00:32 AM on 21 December, 2009
    At first glance, I must say that I don't like fig 3a in the paper, your fig 2, because they dont follow the development up to 2009. (It seems to have been last revised in October). The last years, we have had a trend closer to 2.5 cm/decade, the longer term trend still being ca 3.4 cm/decade. Furthermore, I feel a bit unsure about the modeling in the light of observations from the last 10 years. We may in fact have an accelerating ice cap melting going on with little surface temperature changes.
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31. Riccardo at 07:27 AM on 21 December, 2009
    FrankT, thank you for the link. On the long run and if really huge Greenland melting occurs there may well be the gravitational pull effect. Unfortunately (especially for the Dutch), the same applies to the melting in Antarctica. This branch of oceanography is in its infancy, though. I bit more clear, instead, are the effects of the prevailing winds, atmospheric pressure gradients, redistribution of water due to large currents and temperature changes. These better apply to the short term trends, at least untill massive ice sheet melting will take the lead.
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32. Riccardo at 08:13 AM on 21 December, 2009
    SNRatio, the data are strongly smoothed. The degree of smoothing is not quoted for fig. 2 here but in fig. 4 in the paper it is quoted to be 15 years. Whatever it is, it's strong and i would not expect much sensitivity on short term fluctuation. The same is true for ice melting itself, its slow response time "smooth" away temperature fluctuations.
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33. yocta at 11:44 AM on 21 December, 2009
    RE#6 Neilperth Sorry to sound rude but the way you rose concerns made me believe that these were your questions and your findings (but it looked too neat and I myself are skeptical of everything in lift) I just did some quick googling on the phrases you used. On this site here: http://www.americanthinker.com/2009/08/my_global_warming_epiphany.html "How can you blame man for sea levels rising when about 99% of that rise since the last ice age occurred before man built the pyramids, much less SUVs? A rise in sea level over the last century should not be surprising; it's been rising for the last 20,000 years." - Randall Hoven. August 26, 2009 You said: "How can you blame man for sea levels rising when about 99% of that rise since the last ice age occurred before man built the pyramids, much less SUVs? A rise in sea level over the last century should not be surprising; it's been rising for the last 20,000 years." Either you are Randall Hoven which I apologize for, or you copied the statement from him, or, both you and him copied this statement from someone else. I'm not so fussy about using other peoples arguments but since people spend a lot of time replying, I think it is good manners to at least inform where you got the information from so at the very least they can more directly reply to your arguments/concerns.
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34. Bern at 12:09 PM on 21 December, 2009
    SNRatio @30: ice cap melting with little surface temperature change is not that unexpected - after all, ice melting to water absorbs very large amounts of energy (334kJ/kg) with negligible temperature changes, compared to about 4.18kJ/kg for every degree you heat liquid water. In other words, to absorb the same amount of energy as it took to melt at a constant temperature, you'd have to heat liquid water from 0ºC to 80ºC. That's actually quite a substantial buffer effect on temperatures, when you think about it. Temps increase to the point where icecaps start to melt, then stay there while they do, after which you'd expect a substantial acceleration of temperature rise (unless changes to weather patterns decreased coupling between regional temperatures).
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35. Bern at 12:17 PM on 21 December, 2009
    Neilperth: I (and pretty much every climate scientist out there) would agree with your point that both temperature and sea level have fluctuated in the past. But, as John pointed out in his response to your post at #27, this was on geologic time-scales. On human time-scales, sea levels (and climate) have been more-or-less constant since before those pyramids you mentioned were built. Human civilisation hasn't seen the sort of climate variation you're talking about, and whether it would survive the encounter is debatable. Tony O'Brien's list of references at #25 looks like interesting reading in that respect. But consider this: if sea levels rise by 5-6 metres, whether by natural or anthropogenic means, how are you going to deal with 600 million refugees? That's a nasty problem, and the science is indicating that it's one that we're bringing on ourselves.
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    Response: Just wondering where you get your 600 million refugees figure? I've been looking at Dasgupta 2007 for data on the impact of sea level rise - was wondering if there would be something more recent.
36. neilperth at 14:02 PM on 21 December, 2009
    Yocta re #33 Yes. I am Randall Hoven, but you can call me Randy. Apologies accepted :)
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37. yocta at 15:50 PM on 21 December, 2009
    RE:#36 Neilperth I inferred from your nickname you were from Perth (as opposed to Illinois USA) as you don't often find 4WDs referred to as SUVs in Australia. What you wrote (RE:post#6) clearly is a copy paste job from that site but since you claim you are Randall Hoven and did write it on the original site then I guess i'll just have to take your word for it, but i remain skeptical... (but as a skeptic yourself wouldn't you think that is good thing?)
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38. Bern at 19:13 PM on 21 December, 2009
    John: re the number affected - I think I pulled that number out of Ned's post #9, referring the number of people living within 10m of sea level. Sorry, I should have said where that came from. The 254 million affected by a 5m SLR in Dasgupta 2007 is still a pretty scary number! Thanks for that paper, I'm going to read through it tonight.
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39. RSVP at 20:25 PM on 21 December, 2009
    Couldnt continental plate tectonics also complicate sea level measurements over time? Land is continually moving up and down, which could affect reference elevations, but also to some extend perturb volume through displacement.
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40. neilperth at 21:33 PM on 21 December, 2009
    RSVP There are many phenomena which can affect relative sea levels. These include : 1. Ground movements in the general area of Benioff Zones ( eg West coast of North and South America). 2. General rising or falling of land due to the addition\removal of ice-sheets ( eg, Scandinava. UK, Canada.... ) 3. General subsidence/ rising of large areas of the Earth's crust ( eg Pacific ocean ) For example, coral atolls in the Pacific ocean have been drilled to depths of 400 to 1000 metres and the drill has remained in coral. Yet massive coral formations can only grow within about 50 metres of the sea surface. So how is this drilling result explained ? The answer is not that the sea-level rose, although this may have played some part. The main factor was general subsidence of the ocean floor. Another interesting aspect of this discovery is that even though the sea-floor subsided by hundreds of metres, the corals did not die, they just kept on growing as the relative sea level rose.
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41. Riccardo at 21:41 PM on 21 December, 2009
    RSVP, land subsidence and uplift as well as glacial isostatic adjustment (also called post-glacial rebound) are well known and measured. They are taken into account in slr data.
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42. neilperth at 22:05 PM on 21 December, 2009
    Bern @35 I am a bit stumped at your statement that: "On human time-scales, sea levels (and climate) have been more-or-less constant since before those pyramids you mentioned were built. Human civilisation hasn't seen the sort of climate variation you're talking about, and whether it would survive the encounter is debatable." In the last 20,000 years sea levels have risen around 120 metres. This time is well within the span of humans. Aboriginals have been in Australia for about 40,000 years for example. Over the last 20,000 years humans have done well even without our modern technology. Thus I am perplexed as to why you would argue that humans in the near future may not survive the relatively minor changes forecast for temperature, sea levels etc.
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43. RSVP at 23:11 PM on 21 December, 2009
    Ned writes: quoting me (RSVP) "But for the short run of 100 years, as oceans grow, would'nt that volume of extra water dampen global warming? (since the heat capacity of water is twice that of ice)" Don't take this personally, but are you seriously suggesting that the change in the thermal mass of the ocean as a result of melting ice would have a significant effect on the rate of increase in global surface temperature? A few seconds with Google suggests that the mass of the oceans is 1.4 x 10^21 kg. (e.g., http://hypertextbook.com/facts/1998/AvijeetDut.shtml). The area of the ocean is 3.6 x 10^14 square meters. One cubic meter of water masses 1000 kg, so raising sea level by one meter adds 3.6 x 10^17 kg to the ocean. That presumably would increase the ocean's thermal mass by 0.0026%. ------------------------ Maybe my suggestion was not worth while, but I dont think that is the correct comparison. One could do a similar calculation comparing the contribution of the incremental radiative energy of man-made CO2 to the total radiative power of the Sun on the Earth and come up with an even smaller number. The correct comparison is the difference between the net energy required to raise the temperature of all that ice, vs the energy to raise the temperature of all the water that comes out of that ice.
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44. batsvensson at 10:06 AM on 22 December, 2009
    @Ned in #10, "raising sea level by one meter adds 3.6 x 10^17 kg to the ocean. That presumably would increase the ocean's thermal mass by 0.0026%." Interesting calculation, but is it relevant? I dont think so unless one like to treat all the oceans of the world as one(1) single thermal transparent medium.
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45. batsvensson at 10:36 AM on 22 December, 2009
    @RSVP in #8: "would'nt that volume of extra water dampen global warming?" "does more ocean mean more water vapor and more global warming?" I find these question interesting: If I follow your reasoning correct here; we know that melting ice absorbs heat, thus would not this dampen the warming. However, the whole point with global warming is that the heat is accumulated locally at earth and not beamed away again into space, so in that respect the answer would be ‘no’ to your first question. The second question on the other hand is a bit more tricky to analyze. Amount of evaporations is a function of surface area and temperature. With more ice melting the sea surface will increase, but the change in water evaporation due to a surface change will be insignificant compared to any change in water temperature. Melting ice will not increase the temperature of any local sea water but rather decrease the temperature (liquid water will transfer heat to the ice causing it to melt and as melted ice adds mass/volume to the water it will lose temperature), therefore melting ice will tend to decrease local water evaporation and since water vapor is a green house gas it will thus work as negative feedback on temperature change. However if ice melts at the cost of ice sheets areas then more darker areas - sea water - will be exposed which in turn will contribute to an increase of solar radiation absorption and thus contribute to heating the local water and therefore increase evaporation. What the net effect of these both effects would be is thou unknown to me,and I think your question deserves a proper answer.
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46. Bern at 10:48 AM on 22 December, 2009
    neilperth @42: I don't dispute that humans have been around for tens of thousands of years, and that humans as a species will (probably) survive any climatic upheavals we might trigger. My comment was in reference to human *civilisation* - prior to about 10000 years ago, humans were hunter/gatherers, as I understand it. Indeed, if I remember correctly, the substantially lower sea levels during the last ice age allowed humans to spread to many areas of the globe they previously didn't inhabit. But I stand by my point: if we see dramatic climate shifts, do you really think modern civilisation will come through unscathed? Even ignoring the issue of hundreds of millions of refugees from sea level rise, you've got issues with trade interruptions from drowned seaports, potential crop failures & famines, severe water shortages, and many other problems. I think human civilisation *could* adapt to the sorts of climate change being posited by the experts, but it would take a mighty effort, and it would probably be as disruptive as the 20th century was. And that's assuming no wars break out over land or resources...
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47. batsvensson at 11:23 AM on 22 December, 2009
    @Roccardo in #22. "Indeed, as far as i know the Dutch have taken really seriously the threat posed to their country by sea level rise." The reason the Dutch taking this very seriously is because they already had a break in the sea walls a fee decades ago due to an Atlantic storm with devastating consequences for the whole western country, and after that they decided "never again" and built a wall construction that now are able to with stand any storms the Atlantic can hurl at it. The western provinces, which are among the most densely populated regions in the world, is sunken like 5 meters below sea level and if the country would be flooded again it would lead to an economical impact of enormously scale not only because it is a densely populated region with important international trade exchange but it has also a highly efficient farming and agricultural landscape that would be destroyed. There is simply to much on stake for the Dutch to not be considered. But the concerns lies more with weather or not they need to reinforce the sea walls or not as the protection was built with a certain specification in mind, and if the specifications still holds true then there is no need to ask for extra tax money to reinforcing the present sea wall construction. So if anyone knows what is happening with the sea levels right now, ask the Ducth - they will know.
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48. Riccardo at 12:13 PM on 22 December, 2009
    batsvensson, yes, I asked. Or better, I read the Summury Report of the Delta Committee. They found two climate related effects that exacerbate the risk of flooding, increasing rate of sea level rise and increasing river discharge. I sggest you also read it before claiming that their concern is just weather.
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49. batsvensson at 17:41 PM on 22 December, 2009
    "I sggest you also read it before claiming that their concern is just weather." Did I claim that? No I did not.
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50. SNRatio at 21:25 PM on 22 December, 2009
    @Riccardo "the data are strongly smoothed. The degree of smoothing is not quoted for fig. 2 here but in fig. 4 in the paper it is quoted to be 15 years. Whatever it is, it's strong and i would not expect much sensitivity on short term fluctuation." ...Yes, but, then what about the "rapid" term in the expanded model presented, proportional to dT/dt? That's exactly what gives this new model the improved performance. It may all be explained there, but, skimming through, I could not find it. @Bern, 34: Sure we agree on the factual description, but the context here is the paper with its model. And the model looks very simple, with no apparent thresholding, catering for differential rates of rise corresponding to ice cap conditions. In the model, there can be no accelerating ice cap loss at constant temperature without a concomitant deep ocean cooling. So, if the model is right, the recent acceleration of ice loss at near constant temperature is just a transient phenomenon. Wish it were right. @batsvensson, 47. Sea level rise is not constant over the globe, and some places it may even be mostly canceled out by land rise. The Dutch themselves make the distinction between local trends - they have been approximately constant for a long time - and the global, which, on the same time scale, has accelerated. They have already been adapting to sea level rise for a long time, so if people elsewhere are to look to them, it can only be to set up a similar apparatus for managing the changes.
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