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What makes sea-level rise?

Filed under: — stefan @ 1 June 2012

Last week the science community was shocked by the claim that 42% of the sea-level rise of the past decades is due to groundwater pumping for irrigation purposes. What could this mean for the future – and is it true?

The causes of global sea level rise can be roughly split into three categories: (1) thermal expansion of sea water as it warms up, (2) melting of land ice and (3) changes in the amount of water stored on land. There are independent estimates for these contributions, and obviously an important question is whether their sum is consistent with the total sea level rise actually observed.

foto (c) Stefan Rahmstorf 2012

In the last IPCC report (2007), the time period 1961-2003 was analysed in some detail, and a problem was found: the individual contributions summed up to less than the observed rise – albeit with rather large uncertainties in the estimates. In the years since then, much research effort has been devoted to better quantify all contributions. For the last decade there is also improved observation systems, e.g. the GRACE satellite mission and thousands of autonomous ARGO floats monitoring globally the warming ocean.

Last year Church et al. (2011) provided a new sea-level budget analysis (see Fig. 1). For the period 1972-2008 the budget is closed, with a total rise of about 7 cm. A bit over half of that is due to melting land ice, and a bit less than half due to thermal expansion. Land water storage makes a small negative contribution, because the water stored in artificial reservoirs (which lowers sea level) is estimated to be larger than the amount of fossil groundwater pumped up for irrigation (which mostly ends up in the sea). Also for the shorter recent period 1993-2008 (for which we have satellite measurements of global sea level rise, found to be about 3 mm per year) John Church and colleagues successfully closed the sea level budget. Granted, the uncertainties in the estimates are still significant so the issue cannot be considered completely resolved. Nevertheless, the Church et al. paper defines the current state of the art against which all further studies need to measure up.

Fig. 1. Sea level rise for 1961-2008. On the left the individual contributions are shown, on the right the sum of these contributions (red) is compared to the measured rise (black). Graph from Church et al. (2011)

The groundwater shock

On May 20, Nature Geoscience published a Japanese model simulation of global land water storage (Pokhrel et al. 2012), which surprised the expert community with the conclusion that 42% of sea level rise (about 3 out of 8 cm) over the period 1961-2003 is due to reduced land water storage. In contrast to earlier studies, reservoir storage was assumed to be smaller, but mainly groundwater pumping was calculated to be several times larger.

Are the new numbers realistic? I and many colleagues I spoke to have serious doubts. It is a model result which is in stark contradiction to data-based estimates. The simulation is based on a simple assumption: first the total water demand was estimated, second the availability of near-surface water, and then the shortfall was assumed to be completely supplied by unlimited use of fossil water. The realism of this assumption is debatable – to me it seems to run a risk of greatly overestimating the withdrawal of fossil water.

The uncertainties also need to be discussed: the fossil water withdrawal is estimated by subtracting two large, uncertain numbers. Yet there is no proper uncertainty analysis. Instead, a single number with three significant digits is presented (359 km3 per year for 1950-2000). That is almost five times the rate of 82 ± 22 km3 per year computed by Konikow (2011) for 1961-2008, based on data for groundwater usage and actual observations of water-level declines in aquifers being depleted. Leonard Konikow, a hydrologist with the US Geological Survey, says about the huge amount of groundwater depletion simulated by Pokhrel: “Groundwater hydrologists would have noticed if such a large volume of water were ‘missing'”.

A bit dubious is also the fact that for the largely overlapping period 1950-2000 Pokhrel et al. find that less than 20% of sea level rise is due to land water storage, not 42% as for 1961-2003. Yadu Pokhrel responded to my query that this is due to a large short-term increase in the landwater contribution to sea level between 2000 and 2003, combined with the fact that their rates are computed simply from the difference between the end points (2003 minus 1961). 2003 happened to be a drought year with little water stored on land. Church et al. compute their budgets based on linear trends, which is more robust by using all data points and not just the end points.

Pokhrel et al. don’t even mention the Church et al. paper (although that was published before their paper was submitted). They relate their discussion to the old IPCC finding of “missing sea level rise”, claiming to now have found the source of this missing water. The media largely followed this story line.

Impact on future projections

If the Pokhrel numbers were right, what would this mean for the future? There are two methods to estimate future sea level rise: complex process-based models, which try to compute all individual contributions (e.g. glacier melt) under changing climate conditions, and semi-empirical models, which exploit the observed relationship between global temperature and sea level and are calibrated with past data (see my article Modeling sea level rise at Nature Education). Both have their problems and limitations, and currently I don’t think anyone can seriously claim to know which will turn out to be closer to the truth.

Fig. 2. Change in sea level in mm per year due to the contribution of groundwater pumping (black curves – estimated based on data by Konikow 2011 and Wada et al. 2010) and water storage in artificial reservoirs (blue – this contribution is negative, i.e. lowers sea level). From Rahmstorf et al. (2011).

For the process-based models, the high fossil water pumping rates according to Pokhrel would simply have to be added to the projections (artificial reservoirs are generally thought to not offset much of this in future, because reservoir construction is well past its peak and there is not much scope for a large expansion). Last year we published simple projections of the groundwater pumping contribution (Rahmstorf et al. 2011, see Fig. 2), based on the data by Konikow (2011) and an earlier study by Wada et al. (2010) together with the medium UN global population projection. In the upper of the two curves, groundwater pumping raises sea level by 10 cm by 2100. If, based on Pokhrel, we assume groundwater pumping rates that are roughly twice as high, this could add 20 cm to sea level. Very recently, a new study by Wada et al. (2012) gave a more detailed projection up to 2050 which lies in between our two curves. By 2050 they find 2-4 cm sea level rise due to groundwater pumping. If the rate did not increase any further after 2050, this would add up to 5-8 cm by 2100. Whether 5, 10 or 20 cm – it is clear that groundwater pumping is a factor that must be accounted for in future sea level projections.

The impact of groundwater pumping on semi-empirical projections is smaller, because here we have two partly compensating effects. On one hand there is the added water as just discussed, on the other hand the climate-related part of the projection gets smaller, since the climatic effect on past sea level rise is also smaller, which affects the calibration of the model. In our paper we found that accounting for groundwater depletion according to Wada (i.e. upper curve of Fig. 2) lowers the projections for a moderate global warming scenario (RCP4.5) by 6 cm. If we assume again that Pokhrel’s numbers are roughly twice as high as this, also for the future, then our best estimate for this scenario would come down to 91 cm sea level rise, as compared to 98 cm in our ‘default case’ (for which we used the lower curve of Fig. 2, based on the Konikow data).

Overall, accounting for the Pokhrel landwater estimates would thus tend to increase the process-based sea level projections and lower the semi-empirical projections, thereby reducing the discrepancy between the two – in my view a very welcome feature. But do I believe it?


PIK sea level pages (publications, data, graphs, animations and more)


Church, J.A. et al (2011) Revisiting the Earth’s sea-level and energy budgets from 1961 to 2008, Geophys Res Lett 38, L18601, doi:10.1029/2011GL048794

Konikow LF (2011) Contribution of global groundwater depletion since 1900 to sea-level rise. Geophys Res Lett 38:5. doi:10.1029/2011gl048604

Pokhrel, Y.A. et al (2012) Model estimates of sea-level change due to anthropogenic impacts on terrestrial water storage. Nature Geoscience, doi:10.1038/NGEO1476

Rahmstorf, S, Perrette, M & Vermeer, M (2011) Testing the robustness of semi-empirical sea level projections. Clim. Dynam. 97, 1-15,

Wada Y, van Beek LPH, van Kempen CM, Reckman J, Vasak S, Bierkens MFP (2010) Global depletion of groundwater resources. Geophys Res Lett 37:L20402. doi:10.1029/2010gl044571

Wada, Y et al (2012) Past and future contribution of global groundwater depletion to sea-level rise. Geophys Res Lett 39, L09402, doi:10.1029/2012GL051230

168 Responses to “What makes sea-level rise?”

  1. 101
    Steve Fish says:

    Re- Comment by Jim Baird — 5 Jun 2012 @ 7:30 AM, currently at #92:

    Addressing your points 1 and 3, I want to see the numbers. So, please tell us how much power would have to be generated in order to prevent 1 mm of ocean rise. I believe that this is so impractical as to be not worth talking about, but I am willing to be proved wrong.


  2. 102
    owl905 says:

    @Paul S 98 – thx for the correction.

    Additionally Bierkens et al.
    (600k pdf download)

    “We estimate the contribution of groundwater depletion to sea
    level rise to be 0.8 (±0.1) mm a−1, which is 25 (±3) % of the
    current rate of sea level rise of 3.1 mm a−1 reported in the last
    IPPC report [Bindoff et al., 2007] and of the same order of
    magnitude as the contribution from glaciers and ice caps
    (without Greenland andAntarctica).”

    It suggests the Pokhrel study has taken the larger groundwater+aquafir, treated it all as zero-sum aquafir, and concluded that all the output added to sea-level rise. It doesn’t seem to allow for recharging, or measure the obviously increased wet surface regions, or factor the huge growth of urban storage. Indeed, if the study has made correct assumptions, then AGW takes one on the chin.

  3. 103
    Hank Roberts says:

    Side questions–did the last couple of bigger-than-imagined earthquakes make any detectable difference in sea level for any period? Not the tsunami waves, but any persistent change? I realize a year of tide data may well not suffice for testing for such a tiny effect, but wonder if anything would be detectable.

    Same for undersea volcanos, actually — do sea level and sea temperature over the next months or year or two show a blip, when one of those events happens?

    Haven’t found data sets, haven’t tried to do the math, just … wondering.
    How big an effect does it take, to make a detecta

  4. 104
    Jim Baird says:

    Steve re 101, let me come at it on the basis of the NOAA study in 2010,

    “The upper layer of the world’s ocean has warmed since 1993, indicating a strong climate change signal, according to a new study. The energy stored is enough to power nearly 500 100-watt light bulbs per each of the roughly 6.7 billion people on the planet continuously over the 16-year study period.”

    This is about 330 TW a year and this is the accumulation of heat that is driving thermal expansion. According to this article, a bit less than half of 7 cms from 1972-2008.

    According to Richard Smalley, “To give all 10 billion people on the planet the level of energy prosperity we in the developed world are used to, a couple of kilowatt-hours per person, we would need to generate 60 terawatts around the planet—the equivalent of 900 million barrels of oil per day.”

    If you had created this 60 TW with OTEC over the period 1972-2008, I would assume you would have reduced about 3Cm * 60/330 worth of sea level rise.

    If you had done this however you wouldn’t have accumulate this much heat in the ocean or thermal expansion because there would be substantially less carbon dioxide in the atmosphere.

    If you had converted this 60TW to hydrogen to get it to market you would have further reduced sea level rise by some amount. I could do a calculation but then so could you.

    Ultimately if you replace all carbon emitting energy with renewables the atmospheric carbon concentrations will decrease. – you could reverse the build up each year by greening the deserts see post number 4 even with current additions.

    Once heat is no longer building up in the ocean then you would start to shrink them by extracting heat.

    These are all ideals. None of the 3 techniques is going to be the single answer, much less an overnight fix. It is attempt though to look at the energy/water/environment problem holistically.

  5. 105
    Hank Roberts says:

    > If you had created this 60 TW with OTEC

    What efficiency are you assuming?

    This may help:

  6. 106
    Edward Greisch says:

    All those off topic comments are too hard to not answer:
    Ocean Thermal Energy Conversion OTEC: another renewable source of energy or power that doesn’t work that well in practice.

    “geological disposal of high level radioactive waste” is a bad idea because spent fuel is fuel for the next generation of reactor.

    Why don’t we leave those subjects for the engineers who work for the electric companies and reactor companies? They aren’t going to miss a dollar to be made by OTEC or whatever.

    Fukushima: 573 certified deaths were due to evacuation-related stress at Fukushima. Zero due to radiation. February 4, 2012
    In other words, people they evacuated from intensive care units, died. Fukushima’s natural background radiation plus the radiation from the reactor leak is still less than the natural background radiation here in Illinois. It would almost be humorous if…..

    Let’s stick to sea level rise, please. I would like to know what happens if the ice on Greenland weakens and collapses. Does it make a tsunami or only raise sea level 23 feet? Does anybody know for sure the ice won’t all slide into the ocean next year? Joe Romm said Greenland is having record hot weather.

    When we desalinate sea water to irrigate the whole US, will that make sea level drop a little?

    Will the sea level get high enough to flood the Jordan river valley in Israel or Death Valley? When the Mediterranean basin and the Black Sea basin flooded, sea level must have dropped.

    Can sea level rise cause earthquakes if the Jordan river valley in Israel floods? Aren’t below sea level dry places part of rift valleys and won’t the extra weight make more rifting happen?

    Are there any more places below sea level that could flood soon? Are any as big as the Black Sea? It seems that a little sea level rise in the past made some big changes in geography.

  7. 107
    Jim Baird says:

    Hank Roberts, 105

    “With a slightly different design, using an ammonia heat pipe instead of a cold water pipe, proposed by Jim Baird and Dominic Michaelis (British Patent No. GB 2395754). . . The parasitic losses are cut in half. The costs for the cold water pipe are eliminated, along with the cold water return pipe and condenser pumps, the cleaning system for the condenser, and the overall plant efficiency approaches 85% of Carnot vs. about 70% with a cold water pipe.

    The parasitic losses could be reduced as much as 50% and the complexity, mass (and cost) of the system reduced by at least 30%. The vast reduction in operating costs and environmental impacts would be worth investigation alone.”–by-Paul-from-Potomac-101214-315.html

  8. 108
    Jim Baird says:

    Edward Greisch, 106 “I would like to know what happens if”

    Which begs the question, what would you do if you knew?

  9. 109
    Hank Roberts says:

    I give up on this one.

  10. 110
    Steve Fish says:

    Re- Comment by Jim Baird — 6 Jun 2012 @ 8:44 AM:

    Your unsupported sales pitch figures on OTEC efficiency are off topic for a thread on sea-level rise. Further, your response to me regarding justification for your claims that OTEC can have a realistic effect on sea-level rise are off topic because they support my assertion of insignificance. Do your homework.


  11. 111
    Jerry Toman says:

    Here are three additional reasons why wide-spread use of OTEC for power generation (e.g., “grazers”) will not be practical any time soon (except possibly for niche applications where cold bottom layers come close the surface (Hawaii?):

    1) “Fouling” of the vast heat transfer surfaces required.

    2) No allowance for error or upsets.

    3) There exists a vast amount of low-grade heat available at temperatures much greater than even local sea water “hot spots” which can be converted to power using ORCs (or ammonia) as working fluid–e.g., industrial heat, including effluent water from power plant condensers (including CSP), low-grade geothermal sources, buildings or Urban Heat (A/C condensers), etc.,–I’m sure there are many others.

    Warm surface water is simply not yet the “lowest hanging fruit” available as a source of heat for a power cycle. In a few cases, it could be used as a base feedstock that would be further heated in solar collectors, for example.

    When it comes to efficiency, “temperature matters” for your heat source (a lot!)

  12. 112
    Jim Baird says:

    Jerry, at the risk of offending Steve Fish, one last post on the issue.

    With a deep water condenser, biological fouling is a minimal issue because the working fluid circulates internally and condensation takes place beneath a depth of 500 meters were biological activity is greatly reduced.

    With the Lau design warm water heat exchanger would not severely affect performance. He is working on a paper on his proposal which hopefully will emerge shortly.

    With respect to error or upset, a massive release of ammonia would have consequences. The Lau design however uses CO2 as the working fluid so a release would have minimal impact. The design is also for a subsurface unit that would be removed from the wave and wind action that has lead to the demise of a lot of prior efforts.

    With efficiency temperatures matters, hurricanes however are one of the most powerful forces on the planet and operate off of the same delta T as OTEC.

  13. 113
    Hank Roberts says:

    How about a short list with magnitudes?

    The answer is — the increase being measured is about half due to warming of the deep water, and half due to meltwater.

    Hoping (oh, please) to avoid further digression, is it safe to say that warming a given amount of cold deep water causes more sea level rise than warming the same amount of warm surface water? Remember this isn’t linear.

  14. 114
    dbostrom says:

    Jerry: 1) “Fouling” of the vast heat transfer surfaces required.

    IIRC fouling was a fly in the ointment w/the Hawaii pipe. Some of the gear is still used to retrieve deep water for aquaculture.

    One possible additional use for this water could be improved efficiency for AC heat dump? But again, fouling…

    At the risk of feeding still further off-topic discussion (who can resist the siren call??) there an interesting update on the Hawaii facility here.

  15. 115
    Jim Baird says:

    Hank Roberts 113, wouldn’t the cold water expand less.

    A small calorie is the energy needed to increase the temperature of 1 gram of water by 1 °C

    At 4C it is 4.204 Joules

    At 20C it is 4.182 Joules (both from wikepedia

    If you transfer one calorie from the surface to the deep you wouldn’t raise the temperature 1C and therefore the gram of water at depth wouldn’t expand as much?

  16. 116
    Mel Tisdale says:

    Re De-salination

    If the desalinated water is used in areas with few or no river systems, then at any one time it will either be in the soil, the vegetation, an aquifer or the atmosphere. If it is in the atmosphere, it will act as a potent greenhouse gas. If it goes into an aquifer, that will come to a natural end when the aquifer fills up.

    If it is in an area with a normal number of river systems, a large portion of it will end up in the oceans, thus further reducing their salinity, which is already being reduced by the run-off of melt-water from glaciers and icesheets.

    So, could we simply pump the brine back into the oceans in order to combat this reduction in their salinity? If this is correct, would it not make sense to have the desalination plants near the Arctic where most desalination is currently occuring and pump/transport the desalinated water to arid regions instead of them producing it locally? This, of course, neglects geo-political considerations.

  17. 117

    I think it might be possible to verify the hypothesis by comparing the data of “Satellite Grace” every year. Aquifers are concentrated and thick, removal of water can be determined gravimetrically.

  18. 118
    Hank Roberts says:

    > desalination plants near the Arctic

    That would be after the icecaps melt;
    until all that fresh water ice is gone,
    it’s free.

    Well, it’ll probably get expensive
    when there’s very little left.

  19. 119
    Jim Larsen says:

    65 dbostrom said, “Over 20 years ago I invented the Subductive Waste Disposal Method for the elimination of nuclear waste.


    Gee. An abstract dated “Copyright 2012”. Im not clear how that invalidates a claim from 20 years ago. perhaps a tad better documentation?

  20. 120
    Jim Larsen says:

    82 Harold P says, “How much of sea level rise is due to soil and silt being deposited into the oceans from rivers?

    How much of sea level rise is due to erosion of coasts by the action of wind and waves?

    How much of the apparent sea level rise is due to subsidence of the continents?

    How much of sea level rise is due dust being blown out deserts and falling into the oceans?”

    Well, these things have been going on for billions of years. Obviously, the average result is: “NONE”

    So, yep, there could be some deviation due to current circumstances, but basically, all of these issues are non-issues unless you provide some rationale as to why their effect is larger today than average.

  21. 121
    dbostrom says:

    Gee. An abstract dated “Copyright 2012″. Im not clear how that invalidates a claim from 20 years ago.

    Hard to know how to reply other than “care to try again?” How about a free clue? Proc. R. Soc. Lond. A 8 September 1971 vol. 324 no. 1558 353-367

    Personally I like the borehole disposal idea; the irony of using technology developed principally for petroleum extraction to get rid of nuclear waste is pleasingly twisted.

  22. 122
    Jim Baird says:

    Mel Tisdale, I like the way you think. OTEC only works within 30 degrees of the equator so the power isn’t available for desalination. Seems to me it would be easier to capture Greenland runoff without the need for desalination. Quebec and British Columbia have also looked into bulk water sales. Quebec found shipping costs too great and there is a lot of public resistant (irrational to my mind) in this province. No thought has been given to sea level rise, which will impact BC coastlines significantly, in this regard.

    There are a number of new designs for pumping using wave action that could move this water economically.

    Steve Fish, I can’t let your comment that an 18% conversion of accumulating ocean heat to power is insignificant go unchallenged.

  23. 123
    MARodger says:

    Jim Baird @122
    18%? This is getting entirely silly as well as off topic.
    Go back to your numbers @104. Do you not see the error?

    The NOAA present the annual rise in OHC in terms of 500 100-watt light bulbs burning continually for each of the 6.7 billion folk on the planet. (Perhaps a tad high as it calculates out to 11zJ pa.)
    So that is every man jack burning 50kWh every hour of every day. That would worry me. My house might melt with that sort of energy use.

    You then take a a figure touted by this Richard Smalley who talks of “a couple of kilowatt-hours per person” (over an undisclosed period) with the world population marginally higher and, hey presto, by using exclusively OTEC sea-level rise is reduced by 18%.
    Now tell me – does this reduction in sea-level rise account for all the melted houses & household products that will be flowing seawards?

    Get a grip. Your numbers are nonsensical.

  24. 124
    Jim Eager says:

    dbostrom, you didn’t actually expect him to read for comprhension, did you? ;^)

  25. 125
    Martin Vermeer says:

    Hank Roberts #113:

    is it safe to say that warming a given amount of cold deep water causes more sea level rise than warming the same amount of warm surface water?

    Hank, just the other way around. Though the difference is not so big if you also take the pressure increase with depth into account.

    Note to all: physics is one domain in which idle speculation can be fruitfully replaced by looking it up… but you knew that :-)

  26. 126
    Jim Baird says:

    Dr. Rodgers 123, In all honesty, I’m not sure with whom you are taking issue? I read the NOAA article again and that is what it says.

    Dr. Smalley is a Noble Laureate and if you don’t like his numbers the Intergovernmental Panel on Climate Change report on emissions scenarios foresees a wide range of primary power demand of anywhere from 20 to 50 TW by 2050.

    How producing this much power from the conversion of ocean heat is not a benefit with respect to sea level rise truly does escape me. Particularly when nuclear or fusion, which are the only other constant base load sources of power that do not emit carbon would add an additional 40 to 100 TWh to the oceans in the IPCC scenario?

  27. 127
    Jim Baird says:

    dbostrom, 65, sorry I missed the link to the paper. My proposal was a little different because it would have incorporated similar technology to that being used on the Chunnel at the time. Still it was a good idea in 1971 and to this day. I remain disgusted with the way the spent fuel problem has been handled. I contacted Lord Oxburgh at one point and he said he too had considered subduction as a solution.

  28. 128
    Mark E says:

    For a guy who said he was making a last post on the subject Jim has a lot to say. If I understand right, Jim has a financial interest in OTEC. You do have a related patent, right?

    Then comes the buzzword-laden sales pitch (where Jim has a personal financial stake), where Jim talks of turning deserts into “natural” carbon sinks with massive man-made water inputs, and a “holistic” removal of vast quantities of ocean heat in a context where we have no clue how mixing surface heat into the cold depths will impact overall ocean currents, and therefore trivial little things like distribution and timing of precipitation over the agricultural regions of the entire globe. Such personal profiteering while glossing over science is what continues to put all the extra heat into the ocean in the first place.

    Jim, I can appreciate your desire to to attract venture capital to your OTEC efforts. I have created two businesses myself. In my opinion, you’ll fare better without the buzzwords of “natural” and “holistic”.

  29. 129
    SecularAnimist says:

    Jim Baird wrote: “nuclear or fusion, which are the only other constant base load sources of power that do not emit carbon”

    That is incorrect on two counts.

    First, fusion is not a “base load source of power” because the technology to generate base load electricity from nuclear fusion does not exist, and now knows whether or when it ever will.

    Second, concentrating solar thermal electricity generation with thermal storage (using molten salts) does exist, is already used in commercial power generation and has already demonstrated the ability to generate 24-hour base load power.

    And then there is a cutting-edge technology for generating zero-carbon base load electricity that you may have heard of … it’s called “hydro-electric dams”.

  30. 130
    Jim Baird says:

    Good luck with getting 10TW with your hydro-electric dams. Agree fusion is nowhere but that doesn’t arrest the bundles of money being funneled into it. Fail to see how solar thermal benefits sea levels.

    Mark E., promise this is it. It is obviously an exercise in futility. My mistake anyone might be interested in discussing solutions to the problem highlighted in the original article.

  31. 131
    Hank Roberts says:

    Well, the tangent can be bent back around to some relevance for sea level rise, at least for how people have to plan for future scenarios. Planning for earthquake and/or tsunami will overlap planning for sea level change.

    > similar technology to that being used on the Chunnel

    Subduction zones produce repeated earthquakes larger than anyone a few years ago thought possible.

    “… describe a possible megathrust quake in the Pacific Northwest in this way: “Rather than 17 seconds or 30 seconds we’re going to be dealing with ground motion running perhaps six minutes total for the rupture to occur, that starts on one end and goes to the other, and strong ground motion in our area of maybe three minutes.”
    Based on historical averages, researchers from Oregon State estimate in the next fifty years, the odds of a megathrust quake occurring off the coast of the Pacific Northwest is roughly thirty percent….”

    “… scenarios (M8.8-9.2 or a series of M8’s), given a 550 year average recurrence time and the time since the 1700 earthquake ….”

    I think most people worry about what may happen during short term emergencies during their lifetime.

    Anticipating climate change in planning for short term emergencies ought to be possible.
    A 10-meter tsunami barrier is one thing; a higher storm surge for centuries to come changes things in very different ways. For a tsunami, you want a backflow preventer in the sewage outfall. For higher high tides, you want a different way of managing sewage entirely.

  32. 132
    Jerry Toman says:

    One point needs to be perfectly clear in this discussion–

    The ONLY thing that really matters with regard to renewable energy technology is the extent to which it can produce electricity (work) while reducing (displacing) the emission rate of carbon dioxide to the atmosphere, now occurring via the burning of carbon-based fuels–the total “emergy” impact of construction, operation and maintenance must be considered.

    Everything else is merely a second or third order effect. This includes the miniscule reduction (if any) in the specific volume when warm sea water near the surface is mixed with cooler layers below, where the specific volume of water is near its minimum.

    This is true whether or not the layers are actually mixed, or heat is just transferred between the layers (increasing global entropy in either case, of course).

  33. 133
    SecularAnimist says:

    Jim Baird wrote: “My mistake anyone might be interested in discussing solutions to the problem highlighted in the original article.”

    With all due respect, I think your mistake is in mistaking skepticism of your particular ideas for disinterest in solutions to the problem of sea level rise.

    Judging by the number of comments on this thread devoted to discussing your ideas, there has clearly been no lack of “interest” in them. It’s just that a lot of people don’t find them to be very credible, and have stated in some detail why that is so.

  34. 134
    David B. Benson says:

    The comments in this thread have gone way off topic. Seve3ral of the comments also contain incorrect content but to avoid further derailing this thread I’ll let those pass here.

  35. 135
    Edward Greisch says:

    NASA Discovers Unprecedented Blooms Of Ocean Plant Life

    A super-bloom of phytoplankton was found under thin Arctic ocean ice that has meltwater on top of it. I hope this makes up for some of the 40% phytoplankton loss we heard about earlier. Not that it solves GW or sea level rise. But more phytoplankton helps eat up some of the CO2 that is causing the GW. The water is really green where the bloom is. But is the ice required? Or is this just one more thing to make your math too complicated?

    “Ocean current data revealed that these blooms developed under the ice and had not drifted there from open water, where phytoplankton concentrations can be high.” So the Arctic ocean at least saves the phytoplankton. Tropical water is clear. I recall that somebody proposed adding iron to the ocean to stimulate phytoplankton growth, then gave that up. Getting sea level to fall still requires getting CO2 to fall. Phytoplankton can’t keep up with coal burning.

    I Agree with 134 David B. Benson on off topic [and impractical] energy ideas getting too thick. Try those ideas with your own money some place other than where I live.

    What would I do if I knew collapsing Greenland ice could cause a tsunami? Stay away from the East coast. The more consequences of GW we know more about, the better the argument we have to stop GW.

  36. 136
    MARodger says:

    Jim Baird @126

    You say of me “In all honesty, I’m not sure with whom you are taking issue?
    You are the one lobbing the numbers in here. Try and be responsible for them. Try and make some sense of them. The NOAA talk of OHC circa 2000 rising 440,000kWh pa per head of human population. You compared that figure to one taken from an incoherent quote (by I don’t care who) relating to 2050 which equates to 83,000kWh pa ph.. Thus, you contend @122, here is a scheme that is significant (18%) to reducing the rate of sea-level rise.
    If this analysis were on-topic I would likely give it a more detailed critique & shepherd you down to a more realistic level of significance (probably below 1%). As it is not, I will suggest the following as a useful consideration in this matter.
    Today’s mix of fossil fuels release energy equal to one year’s worth of the energy trapped by the CO2 added to the atmosphere by its burning. That ‘trapping’ will be multiplied some fifty times the initial annual value before equilibrium is reached. That ‘trapping’ will essentially be heating the oceans. Coicidentally, today’s emissions are some 2% of total emissions to date. Sourcing today’s primary energy from today’s oceans would thus reduce the rise in OHC by (50/100) 2%. As half of today’s sea-level rise is not due to dOHC, the significance of your scheme would today be a whopping 1%.

    The OTEC you propose may have merit but you are wrong about its significance to sea-level rise.

  37. 137
    Jim Baird says:

    Dr. Rodger, thank you for the clarification.

    A hurricane is Nature’s response to an over heating ocean. It seems to me we would be wise to follow the analogy to get the power we need.

    Subduction is also Nature’s recycling mechanism, ergo how spent fuel should be eliminated.

  38. 138
    Rod B says:

    A couple of sandbox101 questions: 1) is a changing sea level floor considered? 2) I assume that sea temperature rise is kept within a band of surface water. What is the accepted/reasonable depth of such a band? Is the expansion assumed to be all seen at the surface or is some pushed into the seawater below the band?

  39. 139
    Marcus says:

    3) has anyone considered holes, maybe bore, spontaneously emanating from the sea floor compensating for sea leve rise


  40. 140
  41. 141
  42. 142
    Martin Vermeer says:

    Rod B, long time no see.

    > 1) is a changing sea level floor considered?

    Actually it is. It is part of the GIA (glacial isostatic adjustment) after-effect of the last termination. The ocean floor is still subsiding at a rate of 0.3 mm/year as a plastic response to the increased ocean water load after deglaciation. This effect has been studied extensively by Richard Peltier of Toronto.

    What it means is that, if the total ocean volume were not to change at all, we would still see the ocean surface subside. Conversely, if we want to obtain a measure for the change in total ocean water volume (the climatologically interesting quantity, also in the context of this post!), we have to add 0.3 mm/year to the “raw” observed change in mean position of the sea surface obtained by, e.g., satellite altimetry. This reduction is nowadays routinely made.

    It has no relevance for any change in rate of sea-level rise however, as the effect has been constant for the last 4000 years at least.

  43. 143
    David B. Benson says:

    Martin Vermeer 142 — Thank you. That is certainly of interest.

  44. 144
    Hank Roberts says:

    > Subsiding
    Does that go all the way down through the plates, is the underlying plate being pushed down at all, or is it the softer sediment that’s subsiding?

    Are the sediments squeezed, closing pores, so becoming more compressed?

    I noticed this: GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L11310, 7 PP., 2012
    doi:10.1029/2012GL051854 on the earthquakes in that material:

    A self-consistent mechanism for slow dynamic deformation and large tsunami generation for earthquakes in the shallow subduction zone

    “… Dynamic pore pressure changes in the overriding wedge above a shallow-dipping plate interface significantly affect the rupture dynamics of shallow subduction zone earthquakes and their tsunamigenesis….”

  45. 145
    Yartrebo says:

    I’m not sure of the effect of OTEC on the carbon cycle, but the effect on sea level would be to increase sea levels. Pumping heat from the surface, where most of it is lost to evaporation in a matter of weeks, to the deep ocean, where it may reside for millenia, will serve to increase sea level rise due to thermal expansion. It’ll also make the Earth’s energy budget (energy received from the sun – energy lost to space) even more positive, by reducing heat losses from the upper ocean. Any reduction in temperature will be local or limited in duration.

  46. 146

    Stefan: I’d like to use that haunting photo in a class that I teach…would that be OK? Can you say more about the picture? Location, elevation of the photographer? ( I don’t see a different way to contact you, so trying here in comments).

  47. 147
    Jerry Toman says:

    Before signing off on this thread, since nobody responded to my assertion in my first comment (#51) with regard to where it is best to reject heat removed from the sea surface (after energy in the form of work is extracted), while rightfully insisting that those commenting be more quantitative, I’m including in this comment a link to paper where not only is the process described, but the “math” is also done.

    While the “theoretical” work in such an ideal process is calculated to exceed 30% even in a “marine air” environment from sea water with temperature at 26 C, the need to consume energy to accelerating air into the vortex, as well as to create surface area for mass transfer (spray +elevation required for “trickling” over packing) would reduce this by an estimated 50%.

    After considering other mechanical losses as well, I think it’s reasonable to assume that about a third of the “theoretical work” , or ~10% of the heat removed from the sea could be extracted from the device—more than double that obtainable from OTEC at a fraction of the investment cost..

    Only by building an experimental device can we know for sure what to expect.

    At the same time, the heat rejected from such a device would go to a location above the clouds where it could be more readily dissipated to outer space.

    No need to take 20 steps backward for every 21 steps taken forward on this journey, which is what is done by mixing it back into (any) ocean layer.

  48. 148
    Edward Greisch says:

    Answering my own question, there is a map of where higher sea level goes at:

    WOW! The Black sea and Caspean sea become one and grow. Etc.

  49. 149
    MARodger says:

    Edward Greisch @148
    That map of yours is a bit worrying. It appears to show that global warming in the tropics will be severe enough to melt entire islands. Look! Your map shows Papua New Guinea completely disappeared!

    A more up-to-date world map is used at this site to show the inundations from varying levels of sea-level rise. The maximum rise it provides for is 60m so it doesn’t show the full results for both Antarctica & Greenland melting to zero and raising sea level 70m+
    Its main failing however is how it deals with land below sea level (eg the Dead Sea, Caspian, etc.). The map fills them to the increased sea level even when they would remain unconnected to open sea.
    This one here does show the 70m contour & when basins like the Dead Sea or Caspian would flood but is less easy on the eye for accurately assessing the impact of any rise lower than 70m.

  50. 150
    Hank Roberts says:

    For Jerry Tolman, you posted a link to a “Pre-publication manuscript submitted for peer reviewed publication IEEE Power Energy System Magazine / sustainability Transaction in September 2011” — it’d be good to post the reviewers’ comments and whether a final version emerges that’s publishable.