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Climate Hustle

Past 150,000 Years of Sea Level History Suggests High Rates of Future Sea Level Rise

Posted on 7 December 2012 by Rob Painting

Key points
  • An accurately dated, near-continuous, history of sea level variations for the last 150,000 years has been compiled.
  • Comparison with ice core data reveals that major global ice volume loss, as implied by sea level rise,  has followed relatively quickly after polar warming. The Greenland ice sheet responding virtually straight away (0-100 years lag time), and a 400-700 lag for the Antarctic ice sheet.
  • These response times are much faster than was previously commonly suspected, and implies that once sufficient polar warming is underway, future ice sheet collapse may be unavoidable.
  • During all episodes of major global ice loss, sea level rise has reached rates of at least 1.2 metres per century (equivalent to 12 mm per year). This is 4 times the current rate of sea level rise.

Figure 1 - Sea level reconstruction from 150,000 years ago to the present. Relative sea level (RSL) in grey-shaded area, with RSL data in blue crosses. The downward-pointing red arrows indicates peaks in sea level rise exceeding 1.2 metres per century (12mm per year). The break in the record is due to the absence of foraminifera (upon which the reconstruction is based) as a result of excessively salty seawater during the last ice age. Adapted from Grant (2012).    

Relevant Sea Level Background

The last few million years of Earth's climate has been dominated by the ice age cycles. These consisted of long cool periods (glacials) where giant icesheets have grown on the continental land masses at, and near, the poles. With the water evaporated off the oceans being locked up as ice on land, this ice sheet build-up substantially lowered global sea level. During the shorter, warmer, intervals (interglacials) the ice sheets have disintegrated, and with their glacial meltwater draining back into the oceans, sea level has risen. From the coldest part of the last ice age (roughly 20,000 years ago) to present, global sea level has risen an astounding 120 metres.

Although all the details are not well understood, the driving force behind these glacial/interglacial cycles are slow variations in Earth's orbit as it circles the sun, which slightly decreased/increased the amount of sunlight reaching the planet's surface. For the current interglacial, the orbitally-driven warming eventually came to an end after the Holocene Climatic Optimum (HCO), and by 4-5000 years ago all the vulnerable land-based ice had disappeared. The volume of the global ocean was static until the arrival of the Industrial Revolution, and by the 19th Century global sea level had begun to rise again. Despite undergoing short-term accelerations, and decelerations, globally-averaged sea level has undergone long-term acceleration up to the present day (Church & White [2006]Merrifield [2009]).

Figure 2 - Global mean sea level from 1870 to 2006 with one standard deviation error estimates (Church 2008). 

With some 60-70 metres worth of global sea level equivalent locked up in the vast ice sheets of Greenland and Antarctica, and with global warming well underway, it raises the question of how much sea level rise we are likely to see this century (and beyond), and just how fast this might happen. Because the dynamics of ice sheet disintegration are only very crudely known, and ice sheet modelling is in its infancy, there is a large range of estimates of future sea level rise. Many now seem to converge on 1-2 metres of sea level rise by 2100 - much higher than current rates. But is this realistic? A recent paper, examining past ice sheet disintegrations, lends credence to these estimates.

Rapid Coupling Between Ice Volume and Polar Temperature  

A peer-reviewed paper, Grant (2012), outlines how the authors created a well- dated, and near-continuous, record of sea level over the last 150,000 years, a period which spans the last interglacial (the Eemian), and the last glacial maximum. Of particular interest is the finding that, during all periods of major global ice volume loss, rates of sea level rise reached at least 1.2 metres per century. An arguably more important finding that the more finely resolved dating uncovered, was that major ice sheet reductions (as implied by sea level rise) followed polar warming much quicker than had previously been suspected. 

The backbone of the sea level reconstruction are Foraminifera (forams), tiny shelled marine creatures which float in the water column (planktic), or live on the seafloor (benthic). Because they utilize minerals dissolved in the surrounding seawater to build their shells, forams incorporate elements into their shells which can provide information about the climate at the time in which they lived. Examination of oxygen-18 isotope ratios in the shells of forams, retrieved from Red Sea sediment cores, has revealed that they serve as a useful proxy for relative (i.e local) sea level in the Red Sea (see Siddall [2003]Siddall [2004]). Although a near-continuous record of relative sea level for the Red Sea has been constructed (Rohling [2009]), accurate, and independent, dating for comparison with ice-core data has proven problematic. Grant (2012), however, came up with a clever way around this roadblock.

Constructing a Well-Resolved Chronological Record of Sea Level

Much like the Red Sea, the Eastern Mediterranean Sea is a basin with only one narrow natural opening (The Strait of Gibraltar) which connects it to the rest of the oceans. This "basin effect" was exploited to build a sea level history in the Red Sea, because the extremely slow exchange of seawater within the basin means long local seawater residence times. The raising or lowering of sea level therefore acts to either shorten, or prolong the residence time of local seawater,  and also diminish or enhance the powerful rate of evaporation in the basin. In other words, changes in the oxygen-18 isotopes ratios, found in Red Sea foram fossils, are extremely sensitive to sea level variations. So the isotopes are, in effect, recorders of local sea level. 

Grant (2012) likewise created a sea level history for the eastern Mediterranean Sea, with one distinct improvement; they were able to independently date the sea level variations by taking advantage of oxygen-18 isotopes stored in cave mineral deposits (speleothems) on land downwind of the eastern Mediterranean surface waters. With oxygen-18 isotopes in fossilized forams, and in the cave deposits (Soreq Cave), linked via the hydrological cycle, Uranium-Thorium dating of the cave deposits therefore gave an accurate date for both, and consequently the timing of sea level variations.

Because of the more complicated weather patterns in the Mediterranean however, the Mediterranean sea level history cannot be used to determine sea level variations with sufficient precision (Rohling 1999). To do that, the authors transferred their new Mediterranean chronology to the Red Sea sea level history.  The basin isolation effect of both sea level records, gave sufficient oxygen  isotope signal similarity for accurate transfer. The validity of this newly-dated sea level reconstruction was confirmed by comparison to other dated sea level benchmarks.

Figure 3a - Correlation of Soreq Cave (red line) and eastern Mediterranean (black line) oxygen-18 isotope signals. 3b - Eastern Mediterranean Sea oxygen-18 isotope record from another foram species (green line) and the highest probability sea level curve (blue line). The coloured dots and grey-shaded columns denote other paleodata used to validate and synchronize the reconstructions. From Grant (2012).  

Sea Level Rise Closely Follows Polar Warming

With an accurately dated sea level reconstruction now available, the authors were able to compare these sea level variations in time with that of polar temperature, as ascertained by ice cores extracted from the Greenland and Antarctic ice sheets. Within the sea level reconstruction there are 6 periods where sea level rose rapidly, reaching rates of at least 1.2 metres per century - around 4 times the current rate of sea level rise (see Figure 1).

Considering that humans have been warming the climate for several centuries, a more significant finding was the short time lag between warming at the poles (as shown in the ice cores), and the response of sea level rise - which implies the disintegration of the ice sheets. In the case of Antarctica, large ice reductions occur within 400-700 years, and for Greenland, ice reductions occur very quickly - within 100 years.

Learning From (Sea Level) History

Despite glacial periods having much more vulnerable ice at lower elevation, and closer to the equator than interglacials, the orbitally-driven warming which eventually disintegrated the ice sheets was a leisurely affair. Ice sheet collapse came quickly due to the greater proportion of vulnerable ice. By comparison; today there is far less vulnerable ice, but the warming has been virtually instantaneous, in geological terms. In fact, in the last 300 million years, the Earth has not experienced (as far as we know) such a rapid rise in atmospheric carbon dioxide (Hönisch [2012]).

The altered characteristics of the background climate state, from glacial to interglacial, makes a direct comparison for modern-day difficult. But current sea level rise estimates, and the rates of rise shown in the reconstruction, are in the same ballpark. With global warming having been underway for several centuries now, and with the Antarctic and Greenland ice sheets undergoing accelerated ice mass loss due to polar warming, the past 150,000 years of sea level history suggests we should expect much higher rates of sea level rise in the future.

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Comments 1 to 35:

  1. It is interesting to compare this new paper with this Milankovich-based model:

    "So, we can see that [in this model] the Earth often pops rather suddenly into a warm interglacial state and cools a bit more slowly into a glacial state."
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  2. Yes..

    Basically, when ice sheets grow, they appear to be limited by precipitation. Even if you have 2 meters of precipitation a year that all freezes, it would take 1000-2000 years to build a continental ice sheet.

    On the other hand, a back of the envelope calculation (direct sunlight, heavily absorbed) suggests that ice can melt at 10cm/day, or 36 meters per year.

    (36MJ/m2/day = 100kg ice/m2/day = 10cm)

    And ice dynamics/flow act to slow the growth of ice sheets and speed the melt.

    So a crude approximation suggests that meltdown should be much faster than freezeup..
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  3. Shorter Andrew: For ice sheets, gravity is a bee-otch.
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  4. So heres the twist...

    "Considering that humans have been warming the climate for several centuries, a more significant finding was the short time lag between warming at the poles (as shown in the ice cores), and the response of sea level rise - which implies the disintegration of the ice sheets. In the case of Antarctica, large ice reductions occur within 400-700 years, and for Greenland, ice reductions occur very quickly - within 100 years."

    sea level history suggests we should expect much higher rates of sea level rise in the future."

    That last sentence should read near future. ie next 10 - 50 yrs. ie the rate is around 1.5m per century, but we have be heating up relatively rapidly for the last 50yrs or so.

    So the majority of the 1.5m rise is going to happen in the trailing part of the 100yrs.

    So the rate is exponential as Jim Hansen has frequently pointed out and the data is indicating. ie a doubling every 7yrs at the moment.

    So collapse of our society as we know it is inevitable and just around the corner, even from Only a SLR perspective!
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  5. Thanks Rob...

    This with the increase in the rate of rise just reported, the known uneveness of sea level, particularly affecting the Eastern USA, NASA's recent sea level rise report (expect 2m by 2100 globally, that is a little more New York of course), increased Hurricane storm surges, and it seems inevitable that New York does need relocating and Florida in the next 50-100years and with the rate warming accelerating and this being at the fastest ever noted in geological time along with the record impulse of CO2 and SO2 cooling about to be lost, and it does beg the question what on earth are we doing?

    Its not like there is a spaceship that can take us away anywhere sensible and if divine intervention is coming they are cutting it fine!

    Yet all that is discussed is reducing emissions slowly, and spending billions of extra tonnes of carbon to keep the lights on by putting up so called low carbon renewables and their infra-structures (also totally dismissing the other environemntal impacts associated with them in clinging onto the power green bullet), to provide fresh water security with de-salination plants, to build huge sea defences that will be futile in less than 50years, fighting senseless wars, to grow addictive cash and fuel crops, to pull down forests, to, to ,to, to, to, to charging billion of mobile phones toxic waste batteries.

    Where do you put Floridians and New Yorkers? West Scotland isn't that populated, Greenland? There will be new land here as well, that will emerge from the localised falling of sea levels there as the ice sheet shrinks.

    Well if we can put a man on the moon surely we work that out?

    Maybe the military arround would do a better service for their nations by working on these sorts of problems rather than killing people pointlessly???

    Like how to abruptly stop using fossil fuels??

    Isn't humankind mature enough yet to just stop fighting and realise than more is acheived by working together rather than in violent opposition to each other, well apart from progressing weapons development that is.

    How much carbon does the arms industry use? And how environmentally toxic is it?

    Anyway back to reality, worsening weather, middle east turmoil, rapid ice melt, CO2 emissions growing, more oil being mined, arms industry growth, economic fraility, biodiversity devastation, willingly making toxic materials, extreme inequalities, politicians happily gambling on 50:50 odds of an end of the world situation, highest emissions ever, permafrost tipped already, arctic amplification in severe feedback mode, and all with a dose of a total apparent lack of realisation of the actual scale of this problem.

    How many people in Bangladesh are needing to move?

    Mid / South USA dessert refugees?

    And so on and so forth.

    How much more carbon can be afforded?

    Peak CO2...

    450ppm, scarey!

    425ppm.....too worrying

    400ppm...still need to move New York and Florida.

    350ppm...the carbon debt, still give greater than 5% of 1.5C-2C, so New York and Florida still need to move.

    Therefore how much more carbon are people theoretically prepared risk?

    How tight is the carbon budget?

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  6. Paul Magnus@4 you said:
    So the rate is exponential as Jim Hansen has frequently pointed out and the data is indicating. ie a doubling every 7yrs at the moment

    Can you give the source of your claim (if Hansen, then full text is available in which I'm very interested).

    IMO, the dSLR acceleration cannot be that fast: we are already melting very fast: 35my-1, which is just 4-6 times slower than Heinrich events as seen on figure 1. So we've just 2 of those "doubling every 7yrs" before we reach a desintegration of Heinrich proportions.

    I'm not saying Heinrich on top of Holocene optimum won't happen but that it cannot happen so fast. Perhaps we will see a doubling of dSLR in this century, perhaps the second dubling later at the end of this century (most of us will not live up to this, only our children). IS response is a slow but sure process in today's state of climate. No one was able to quantify it to date let alone predict "doubling of dSLR every 7yrs"... The section title "Sea Level Rise Closely Follows Polar Warming" is very intriguing but left unquantified: did anyone heard "how closely"? 100y or 500y?
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    Moderator Response: [DB] This Hansen publication is likely the source. An accessible version containing the full submitted text is here.
  7. Chriskoz - see the text under that heading. A long time perhaps by human time scales, but a blink of an eye in a geological sense.
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  8. Thanks DB for the link to Hansen 2012. The claim therein, of exponential, 7y doubling, IS desintegration is from the curve fitting to GRACE data, as seen on its Figures 8a-d. With such curve fitting, it finds the SLR as high as 5m by 2100 possible.

    I find the practice of such curve fitting questionable. Especially, if it arives at the improbable conclusion of dSLR 50mky-1 (5mcentury-1), not seen in last 1500ky, far in excess of Heinrich events. On top of that, it must be remembered that strong negative feedbacks on melting rates do exists, like ice flow rates and cooling of the upper ocean. And there is simply not enough ice (far less than the emount of Laurentide IS than triggered Heinrich events) to sustain the exponential rate. So Rahmstorf 2007, being a conservative, semi-empirical linear model, concluding 1m SLR in 2100 is more realistic.
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  9. chriskoz @8, I think you are completely correct on this. A 5 meter sea level rise per century would be equivalent to melting a third of the combined West Antarctic Ice Sheet (WAIS) and the Greenland Ice Sheet (GIS) within a 100 years, which is IMO not credible. Hansens formula of 1 mm of sea level rise in 2005-2015, doubling every ten years results in the complete melting of all ice sheets by 2175, a 70+ meter sea level rise in under two centuries.

    Plainly the doubling time (if it exists at all) must terminate rather quickly, and is very likely to do so at, or less than, the Heinrich event rate.

    Being fair to Hansen, his point appears to be, not that sea levels will rise by five meters in this century, but that far more rapid rises than is allowed for by linear increases are possible, so that the likely rise is significantly above linear projections. He may be right in that. I would not exclude a two meter rise, although I believe the 1 to 1.2 meter range to be far more plausible.
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  10. I should note, with regard to Magnus claims (@4), even a 10 meter sea level rise would not, by itself, be enough to cause the collapse of our society, or even significantly impoverish us. In particular regions, sea level rise is likely to be devastating in terms of lives lost and financial costs, but primarily by worsening the impacts of storm surges. A very small percentage of the total land surface will be lost to inundation. Consequently, except in low lying deltas, the cost of adaption will be met simply by moving major cities about a kilometer inland - something certainly within our economic ability.
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  11. Further to Magnus and Tom, maybe as so often is the case "it depends," in this case on what we mean by "our society." If you live in Norway it's reasonable to suppose 10m would not effectively collapse society. For Bangladesh a different story; most of Bangladesh is below 10m, with the capital Dhaka at 4m. It's hard to imagine most of the ~150M population of Bangladesh making a move to the <20% of the country left dry by a 10m rise in sea level and in any case they'd be confronted with the problem of what to eat after virtually their entire inventory of arable land was lost. There are a number of other countries in the world that live in a similar "deltaic mode."
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  12. And there's also the small matter that a 10 metre sea level rise would not manifest in isolation from other, extremely serious impacts...

    Oh, and there's the other small matter that if it gets to the stage of a 10 metre increase in sea level, it's not likely going to be stopping there. And if we've pushed the system that far, the final equilibrium point described by those aforementioned other, extremely serious impacts isn't one in which there will exist on Earth anything resembling a Western-style human society. Indeed, if it reached that point there'd likely not exist any society where even printed words and reticulated water supplies were in use.
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  13. The poles are warming faster than the rest of the planet because of energy in the atmosphere that is carried to the poles through large weather systems. The consequence is we have the threat of methane releases from the permafrost and icecap melting.

    These systems are driven in the main by sea surface heat which can be sapped to produce energy with OTEC. The more energy produced the more the ocean surface is cooled.

    Part of this heat is converted to mechanical energy in the process but the bulk, 20 times the energy produce, is moved to the deep water heat sink that has a lower coefficient of expansion.

    Kevin Trenberth, points out in a paper, "An imperative for climate change: tracking Earth's global energy", "The warming required to produce 1 mm SLR if the heat is deposited in the top 700 m of the ocean can take from 50 to 75 1020 J, or 110  1020 J if deposited below 700 m depth.

    In other words you can move heat from the surface to the depths with OTEC to counter 50 percent of current sea level rise due to thermal expansion.

    By sapping the heat of hurricanes you also diminish the amount of heat that would be moved from the tropics towards the poles and thus forestall melting.

    This is the lesson of Hurricane Sandy, no one apparently cares to learn.

    Disclosure - patents pending
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  14. Jim, you'll want to compare the current volume of water being moved via routine overturning circulation w/the possibilities of OTEC.

    Down the road I suppose it's conceivable that overturning might become so sluggish as to need help but as it stands now the volume in play is quite astounding, about 575,000km3/year or ~1km3/minute for the Atlantic. Not sure if the Pacific is larger or smaller but let's assume bringing the Pacific into play doubles that number. A lot of infrastructure would be necessary to obtain a useful boost on those numbers.
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  15. Pete@1: That was indeed an interesting read. Thanks for posting it!
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  16. Doug, Paul Curto, former Chief Technologist with NASA, recently pointed out, OTEC's impact on reducing the surface water temperature over time would be on the order of one degree F per decade at a power level of 2.5 terawatts.

    Sea surface temperatures running at over 3C above normal along the Atlantic coast from Florida to Canada where the driver for hurricane Sandy. Global warming is estimated to have contributed about 20 percent of this heat which would not have been available had we been producing 2.5 terrawatts of OTEC power the past 10 years.

    Kevin Trenberth points out, "With every degree C, the water holding of the atmosphere goes up 7%, and the moisture provides fuel for tropical storms.

    Five terawatts of OTEC power each decade would negate this increase.

    Five terawatts requires a lot of infrastructure but then so did the Manhattan Project and war efforts in general. I prefer to think that we should be on a war footing where global warming is concerned and so did over 70 percent of other Canadians in a poll a while back.
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  17. Not to be a jerk but how does the energy moved around by OTEC get transferred into space, Jim? I see your point and fully agree about mobilization on a large scale but it seems as though the Manhattan Project of OTEC would end up simply changing the respective profiles of the bulges in surface and ocean temperature we're creating. All the TWH are conserved, on Earth after all.
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  18. Jim Baird - I'm a bit puzzled, here; how would bringing cold deep water up to the surface (to provide the temperature gradient needed for power generation) help with global warming?

    That would essentially bury warm water, reduce surface temperature and infrared radiation to space with surfaced cold water, and overall increase the radiative imbalance and the accumulation of energy in the climate. It would in fact increase the warming of the deep ocean while simultaneously increasing the rate of energy accumulation in the oceans as a whole.

    In other words, I suspect OTEC would (to a small amount - current energy use is 1% of the greenhouse imbalance) worsen global warming.
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  19. KR@18,

    OTEC would not necessarily worsen GW. You considered just the TOA energy imbalance. Let's consider carbon cycle feedbacks. Perhaps speeding the deep ocean circulation would increase the rate of CO2 intake, even speedup silicate rock weathering by 2 orders of magnitude to 100y timescale:)

    But I'm skeptical about OTEC feasibility. We know so little about the effects of such invasion into the ocean circulation, that we must learn alot before attempting such geo-engineering.
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  20. Doug it isn't likely we would ever be able to draw down the total 3C excess seen in the Atlantic this summer. Some of this heat will continue to radiate towards the poles and into space. OTEC would however convert a small portion of this heat to mechanical energy and would dump 20 times as much as we generate to the depths where it would be diluted in an environment where the coefficient of expansion is about half that of the surface. To the extent you draw down the surface heat you would diminish the strength of storms like Sandy that move heat into space and towards the poles, where it is melting the icecaps and the methane trapping permafrost. The TWHs not converted to mechanical energy are conserved but in a colder environment where they would do less damage in terms of sea level rise.

    KR, I advise using a heat pipe rather than a massive cold water pipe which moves cold water to the surface. Hurricanes use phase changes to move heat rapidly as does a heat pipe. The difference being the hurricane has the stratosphere as the heat sink as opposed to the abyss.

    As to radiative forcing the sea surface is subject to a diurnal heat cycle. It warms by day and cools by night.

    OTEC operates around the clock and removes heat from the surface by night as well as by day. Each morning therefore, IMHO, the surface would begin to warm from a lower base that without OTEC and since the same volume of water is being warmed by the same heat source, it seems to me, the diurnal high temperature should be less as well?

    Chriskoz, IMHO using a heat pipe rather than cold water pipe overcomes many of the environmental problems associated with OTEC and reduces the cost as well because for a 100MW plant you need a 1 meter diameter pipe rather than one of 14.5 meters. I have a patent pending for a system that uses a counter-current heat flow and metering system for the capture and governing of the return of the latent heat of condensation back to the surface both to limit the impact on the Thermohaline as well as maximize the amount of energy the ocean can generate. My thinking is in the long run it is best to convert as much ocean heat to work as possible, which requires the capture and return of the latent heat, but during hurricane seasons it is best to move as much surface heat to the depths as possible.

    OTEC can not be implemented on the scale I would like to see overnight. In the course of building it out we would have plenty of time to learn of the ramifications before doing any significant damage.

    I believe though it has potential for geo-engineering because it the process we would be producing all the carbon free energy we need.

    The input of those on this sight far more technically skilled than myself is appreciated.
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  21. Jim Baird - While a heat pipe avoids nutrient exchange, it's still a heat transfer in order to extract energy: cooling surface waters (increasing radiative imbalance) and warming deep waters (speeding deep ocean energy accumulation).

    As to the diurnal cycle, heat loss and gain are dependent on the gradient - more energy will be absorbed by a cooler ocean surface during the day, less emitted at night, and again an amplification of the radiative imbalance. OTEC may not be able to provide the warming mitigation you claim.

    This is, however, completely off topic for historic sea level rises. I would suggest a thread actually on geoengineering, such as this one.
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  22. I don't pretend to have any depth of knowledge around climate change, but I do know technology and human nature. For all of you who believe that civilization will collapse, let's walk through a worst case scenario. All of the ice in the world melts. Temperatures go up 10C. We will still have cities. Technology will still advance. It will not happen in a year or a decade. We will not need to move out of the coastal cities suddenly, we will just stop building in them or near the ocean. As older people die, young people will move inland. Yes it is bad, people will starve and be displaced, but it is not the end of civilization. There will still be a few billion well-fed educated people on the planet. We will make it through this with flying colors.

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  23. Bill,

    Your story is sadly oversimplified. 

    1. Econimic upheaval... many industries will be affected, either directly (sea level rise, shifting agricultural zones, etc.) or indirectly (changes in transportation methods, power sources, etc.).  When economies change, people and sometimes entire cities (e.g. Detroit) lose their place in the economy.

    2. Refugees and warfare... dwindling/shifting resources always leads to upheaval and violence (see the Arab Spring, as the most recent of a long history of examples)

    3. Storm damage... climate change will come with greater dangers from storms, which will in turn have an economic and human cost.

    4. If all of the world's ice melts, and if temperatures go up 10C, we will not still have cities.  Sea levels would rise tens of meters.  2/3rds of human population or more would be displaced.  Agricultural impacts would be untenable.  Food shortages and the resulting, violent social upheaval would be a death knell.

    5. Of course, you presented a worst case scenario which need not come to pass.  The biggest danger from climate change right now is that we have to stop using fossil fuels at some point.  If we wait until the costs are too high, then we will need to abandon fossil fuels so quickly that the transition will be anything but painless.  My personal guess is that 3/5 of the world's population will simply be cut out of the energy pie, and forced to return to pre-industrial existence.  The remainder will have to learn a new life style using behavior changes, frugal energy use, and renewables -- and it will be absolutely nothing like the world we live in today.

    What shocks me is the way people think that an 80 year old period of technological stability means that it can never end.  Countless powerful human civilizations have fallen over the course of history, many of them as a result of climate change, and yet some people seem to think that imagining such a thing in our case is impossible -- and yet our current society is so precariously positioned that it is frightening.

    We are so specialized and interconnected that many people are utterly incapable of surviving in anything but our interconnected society.  Imagine what would happen just as the result of something like the outbreak of a Spanish flu, something that wipes out even a small percentage of the population.  We do not run a society with much in the way of wiggle room for major industries, jobs and tasks.

    Our society and civilization is very, very far from safely grounded.  Something as huge as climate change is guaranteed to knock the foundation out from underneath, if we wait too long to address the problem.

    I think it's really funny (in a sad way) that Dismissives deny climate change, shouting alarmingly, "Alarmist!  What you ask would destroy our economy!" when in fact acting now would incur a small price (10 years ago would have been way better), while delaying any further virtually guarantees the outcome that they use to scare people away from effective and reasonable action.

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  24. Bob,

       I am in no way a denialist or a dismissive. My position is that we should transition to energy and fuels that reduce the impact as quickly as possible. But the most likely reality is that we will not do it until it is economically advantageous to do so. Given the new oil supplies and natural gas coming on line from fracking, we will continue having an economical oil supply for decades to come. I hope that we can produce cleaner sources of energy sooner than that to quicken that transition time. Ultimately people will make decisions based on their pocket books and oil is here for a while. As a species we collectively do not worry about the future. That is reality.

       Your Spanish Flu comparison doesn't really hold water. I agree that if we had a pandemic situation that wiped out say 90% of the world, it would takes a few decades to get society back to the functional level where we are now. But we will not lose our technical knowledge. The difference here is that this is a slow moving danger. It is not a tsunami. We will have time to adapt. We will move our cities, our industries, our farms. So there is not NYC, SF, or LA? THe loss of all our coastal cities is a tragedy, but not the end of the world.  Of course there will be wars and famine. In my post I never said that we have nothing to worry about. I said that civilization will survive this and prosper.

       My position is not in conflict with working to achieve  sustainable energy capabilities. On the contrary, realizing that the solution has to be about economics more so than awareness should focus our efforts on where it will do the most good. When people post that in the future we will be living in a Stone Age, it detracts from the validity of the problem and how to solve it by alienating realistic and hopeful people.


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  25. Bill...  What's the old saying? "A little knowledge can be a dangerous thing."

    As Bob points out, you're missing the big picture. And Bob is only pointing out a few of the complicating factors. You also have to consider that human population is going to be approaching 10B right about the same time things start to get bad. We already see social unrest when grain prices rise and bread becomes unaffordable to those in poverty. Amplify that and you've got some serious global problems. It's horrendous to see people starving in parts of Africa. Imagine that but with numbers approaching a billion or more. This is not something that technology is going to solve.

    Sea level rise is also not just a matter of moving coastlines. The worse problem is the amplification of storm surges. We already see this with a small amount of sea level rise and larger storms. Make that a meter of SLR and storm surges are going to extend much further inland, also making habitation anywhere near a coastline influence by tropical storms impossible. Think, the entire US eastern seaboard. Think,  Hong Kong, Taipei, Shanghai... this is not in the least insignificant.

    When you say worst case of 10C, that's probably as close as one could get to a complete collapse of the world's current ecosystem. That would mean that a good portion of the lower latitudes would be unihabitable due to temperature extremes at various times during a year. With Arctic amplification, that would be much greater in the north. So, it's not just a matter of everyone migrating further north because you're going to have a large number of days during the summer that are also going to be unihabitable due to temperature extremes.

    Another element you're ignoring is that, at that level (10C) we'd possibly see the ocean surface go anoxic. Richard Alley explains it here at minute 20:00. 

    Would humans survive this? Maybe, probably, but nothing like we know today. Likely a tiny fraction of the current human population. And the worst part would be the utterly immense amount of human suffering that would occur in the process.

    And the even worse part (worse than worst) would be... it would have been entirely avoidable, at a cost today of 2% of global GDP.

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  26. Bill said... "We will have time to adapt."

    I beg to differ. If you look at the ice core record, the climate system can make very abrupt changes with far less purturbation than we're currently imposing on the system. Look at the Younger-Dryas. A climate shift equal about to moving from Atlanta to New York in a decade or so.

    The problem is, we don't know what causes those abrupt shifts and we don't know when they might occur.

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  27. At risk of dogpiling. Photosynthesis dramatically drops in efficiency at around 32C and basically shuts down at 37C. And then there is the problem of water see Dai 2010. (seriously, look at the map from Dai). Both add up to considerable less food available than today - triggers for previous collapse of civilizations. No amount of technology beats thermodynamics. I strongly doubt all civilizations everywhere would completely collapse but extremely bad things would happen needlessly if we let climate change too quickly.

    You say you know technology and human nature. How well do you know those civilizations that did collapse?  A lot of technology is concentrated in skills of very few - how much disruption would it take to fracture that skill base?

    What economic studies exist show that is economically advantageous to transition now. The costs of mitigation are less than costs of adaption but we dont do so. Why? Because voters will believe any sort of comfortable lie rather than accept the need (as Milton Friedman pushed) to pay for externalities. We are not paying the full cost of coal. We are leaving that to future generations to pay. We need pricing on coal so that it stays in the ground.

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  28. An ounce of prevention is worth a pound of cure."

    From the SkS Comments Policy:

    No dogpiling. In the interests of civility and to enable people to properly express their opinions, we discourage 'piling on'. If a comment already has a response, consider carefully whether you are adding anything interesting before also responding. If a participant appears to be being 'dog piled', the moderator may designate one or two people from each side of the debate as the primary disputants and require that no other people respond until further notified. On topic comments on other matters not being discussed by the primary disputants will still be welcome.

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  29. Bill, you missed my point.

    If you actually think the world can recover from the loss of 90% of the population, you need to re-evaluate things.  I don't think we could recover from the loss of 20%, maybe even 10%.

    Modern society is like a hive mind.  Very intricate knowledge is squirrelled away in various people, and passed on in a stuttering variation on an oral tradition.  Through schooling, apprenticing, trial and error, and experience, people get to understand one minute facet of how our society works, from international finance to aerospace engineering to oncology.

    If you remove too much of that at once, basic services, like power, food production, processing and transport, and other things will devolve, and people won't be able to handle it.  I think that far, far less than a 90% population loss will be needed to cripple civilization because of how very complex our society and its use of technology has become.

    But even if you don't agree with that... you are a dismissive, even if you don't think that you are.  If you have no sense of fear or urgency, because you beleive that we can overcome everything, simply because history shows that for the past 100 years we have done so, then... you are a dismissive.  You dismiss the problem, not because you don't believe it exists, but because you believe it isn't large enough to worry you.

    That is a serious problem that is facing us all, because there is a time limit, and there is a point after which it will be too late to take relevant action.  More importantly, every year's delay makes the action that we will ultimately have to take than much more painful.

    It just astounds me that dismissives are guaranteeing the one outcome that frightens them most, and are avoiding the path of rewarding (both economically and socially) growth that renewables and a say-no-to-fossil-fuels would bring.

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  30. Bob Lacatena @29, you are correct about the balkanization of knowledge which is characteristic of our age, and that it makes us more vulnerable to a breakdown in society.  I think you are incorrect in your estimate of the population loss that would be required to bring about that catastrophe.  Except in areas of cutting edge research, the knowledge base is duplicated across several major nations, or groups of nations.  Specifically, the US, Europe, Russia, Japan, and now China and India all now have sufficient knowledge to allow for the recovery of civilization without much loss of current knowledge if any of them survive largely intact.  What is more, as casualties from global warming will be predominantly in poor, underdeveloped nations, they are also the nations (or groups of nations) most likely to survive with few casualties.  If 10 or 20% of the world's population is lost, most of the losses will be in Africa with least in the most developed nations.  Further, the missing knowledge, if any, following a 10% populatin loss, will be highly specialized, and consequently have marginal impact on world economic production.

    The same cannot be said for a 90% loss, which of necissity must hit all nations very hard.  Therefore, a 90% loss - ignoring the other impacts - does have the potential to end our civilization.  Never-the-less I think sufficient knowledge would remain even then to survive as a civilization, if not at the advanced levels previously achieved, then at least at a technological level equivalent to that of the 1950s.

    I think the far greater threat actually comes from the risk of sustained economic decline; and the end of substantial trade.  Our civilization is critically dependent on complex trade networks.  If these collapse, so will also the high standard of living that allows so many of us to devote so much time to learning.  If all must grub for food in subsistence, or near subsistence farms, there will be no engineers or scientists to sustain the knowledge.  Any event, particularly an ongoing even such as OA, ocean anoxia, and sustained very high temperatures which can knock out >20% of the population is also likely to knock us into sustained (multidecadal) negative economic growth, and potentially knock out the majority of the trade network, forcing each region to sustain its own population.  The problem will not just be in the population loss, but in the ongoing conditions that caused that loss in the first place.  

    The end product may well be a fall back to a medieval level of technology, with a few advanced holdouts.  Whether that counts as the end of our civilization or not, I think, is academic.

    Further, I think that any event that can so stress the worlds nations is also a substantial risk of triggering major wars and potentially an all out nuclear exchange.  In that respect, economic stress without population decline presents a greater risk.  An all out nuclear exchange represents, of course, and a very high threat of extinction for our species.

    Finally, although I regard Bill's comments as panglossian, I do not think it is fair to characterize him as a dissmissive.  There are a range of rational views on climate change, from those that consider it a major problem but not a threat to our civilization or species, to those that consider it a threat to both.  The threats to the later are, given the present state of knowledge, risks - not certainties.   

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  31. At no point before Bill chimed in, did anyone suggest climate would end civilization. He begins by attacking a strawman argument. It is a bizarre position to suggest that we should only take action on climate change if it was a threat to civilization (which his scenario over say 100 years would be, but still...). We should take action because it is the rational thing to do from point of view of both cost and risk. It is also the appropriate moral action from the point that those most affected by change are not the ones who are causing it.

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  32. To take scaddenp's comment and elaborate it a bit, in no way do we need to view global warming as civilization-threatening to be motivated, even strongly motivated, to take action to mitigate it at a global level.

    All we need is to have the following convictions:

    1. That mitigating warming, and preventing future warming, by emissions reductions, etc., is less expensive than adaptation/coping with the consequences of warming. Personally speaking, based on the probable consequences between 2050 and 2100, as far as I am concerned we have surpassed that point. Thus, mitigation/prevention, even very rapid mitigation/prevention, is the preferable course of action.
    2. That, if we are willing to consider the interests of others (in securing the basic necessities of life in a stable manner, and in securing occasional or intermittent access to luxuries) as being equal to our own, we have a moral obligation to reduce emissions in order to reduce the severity of the consequences of warming, which the evidence so far quite clearly shows will fall most heavily upon those least able to adapt to them.

    I do not think either of these are in any way radical notions.

    (Not to say that global warming could not be civilization-threatening if left unchecked; it very well could. My point is that you don't have to see it that way in order to support taking action on a society-wide scale.)

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  33. One of the problems with "correlations" especially serial (time related) correlations is that they do not prove cause and effect. A large amount of effort goes into "proving" a causation using correlation, multiple regression, etc., but consider that when the rooster crows, the sun comes up, but that certainly does not mean that he rooster causes the sun to rise.

    Also, other factors are raising sea levels, including Plate Tectonics, the continental shift that is impacting the depth of the ocean floor where one plate moves under another. It causes earthquakes, it releases heat into the ocean that cause frozen methane to become gaseous and rise to the surface (a far more potent greenhouse gas than CO2), but most important, it raises the ocean floor.

    Imagine the same amount of water in the oceans, and the sea floor rising, it clearly would raise the level of the surface of the water.

    There is also Solar output, the orbital radius from the sun, the "tilt" of the axis that changes over thousands of years, all impact climate (the weather).

    Be very careful about assuming that scientists have "proven" anything if they rely on correlations of any kind, and ignore some clear and obvious geological issues that have a large impact on ocean levels, and the release of methane into the atmosphere.

    Dr. T — A scientist interested in factual analysis, not correlations that are not proof of cause and effect.

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    Moderator Response:

    [PS] You appear to be engaging in a straw man. Nowhere is correlation being used to imply a cause and effect. However, if your model predicts a correlation (and the physical models most certainly do make these predictions), then an important test of your model is see that such correlations do in fact exist. If they dont, this is evidence against a model. If they do exist, then it strengthens the model. In science, nothing is ever "proven" (you can only do that in maths) and noone has suggested it has. The other factors you mention are already part of standard climate theory, and taken into account in models. Eustatic changes in sealevel have been known and accounted for since the 1980s eg (

  34. "A large amount of effort goes into "proving" a causation using correlation, multiple regression, etc., but consider that when the rooster crows, the sun comes up, but that certainly does not mean that he rooster causes the sun to rise."

    Yes, I am certain that none of the authors have suggested that evaporation in either the Red or Mediterranean Sea caused global sea level to fall.

    Your comments don't make a great deal of sense. How could the ocean basins shallow and deepen in concert with Milankovitch forcing? And where did the water locked up as ice in the vast Laurentide and Fennoscandian ice sheets disappear to if not into the ocean?    

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    Moderator Response:

    [PS] Dr T comments suggest that he/she hasnt actually read the Grant (2012) paper.

  35. For perspective, 7 billion people standing in close formation would fit within the boundries of Los Angeles. A very, very small space compared with the occupiable land area on the earth.

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