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While climate models of atmospheric carbon dioxide concentrations and global temperatures have closely fit real world observations, the models have done less well in predicting sea levels. The following graph illustrates the disparity. The blue shaded region contains the upper and lower bounds of the IPCC climate model predictions. Sea level changes from satellite measurements (red line) and tidal gauges (orange line) since 1990 are consistently higher than predicted from those models.

 photo erl439749f2_online_zps007cd7b7.jpg

Since sea levels are a big deal for coastal populations and infrastructure, we cannot afford to guess wrong. So just how much water might we have to contend with in the 21st century and beyond?

A number of studies suggest that sea levels could rise between 1 to 2 meters by the end of the century. Taking thermal expansion and ice sheet melt into consideration, we would need to keep CO2 concentrations below 450 ppm to keep sea levels from rising more than a meter by the year 2100. Since a sea level rise of 3 feet or so would create quite an expensive mess, it would be wise to change our carbon polluting ways.

Far less comforting is data from studies looking at the geological record. It is all too clear that sea levels have been substantially higher than present day levels, perhaps as much as two hundred feet higher. That would be something of a game-changer. Sea levels have also been substantially lower than current levels during the peak of glacial periods.

A new study published in the Proceedings of the National Academy of Sciences (subscription required) examined the relationship between CO2 and sea levels in the geological record over a 40 million year time scale. Here is the abstract from the article.

On 103 to 106-year timescales, global sea level is determined largely by the volume of ice stored on land, which in turn largely reflects the thermal state of the Earth system. Here we use observations from five well-studied time slices covering the last 40 My to identify a well-defined and clearly sigmoidal relationship between atmospheric CO2 and sea level on geological (near-equilibrium) timescales. This strongly supports the dominant role of CO2 in determining Earth’s climate on these timescales and suggests that other variables that influence long-term global climate (e.g., topography, ocean circulation) play a secondary role. The relationship between CO2 and sea level we describe portrays the “likely” (68% probability) long-term sea-level response after Earth system adjustment over many centuries. Because it appears largely independent of other boundary condition changes, it also may provide useful long-range predictions of future sea level. For instance, with CO2 stabilized at 400–450 ppm (as required for the frequently quoted “acceptable warming” of 2 °C), or even at AD 2011 levels of 392 ppm, we infer a likely (68% confidence) long-term sea-level rise of more than 9 m above the present. Therefore, our results imply that to avoid significantly elevated sea level in the long term, atmospheric CO2 should be reduced to levels similar to those of preindustrial times.
Researchers Gavin L. Foster and Eelco J. Rohling looked at 2000 paired observations of CO2 concentrations and sea levels across time. CO2 concentrations were estimated using ice cores and chemical profiles from deep ocean sediments. Sea levels were based on chemical profiling of foraminifera, single-cell organisms, stratified in deep ocean sediments.

The reconstruction of the 550,000 years of the Pleistocene epoch prior to 1800 provides a fascinating look at the variability of CO2 concentrations and sea levels before the industrial age. CO2 levels ranged from 180 to 280 ppm, while sea levels ranged from 10 to 110 meters below current levels. CO2 concentrations and sea levels were highly correlated in this time series (r2=0.68).

What these data show is that CO2 concentrations in the past 50 years (currently around 394 ppm) are simply unprecedented as part of the normal fluctuations between glacial and interglacial periods during the past 500,000 years or so. We are tinkering with what has been a stable and predictable climate system. The longer we maintain CO2 levels above 280 ppm, the more sea levels are also likely to rise well above current levels. How fast and how much sea levels rise will depend on the dynamics of ice sheet melting in Greenland and Antarctica.

Combining all the proxies for CO2 and sea levels allows a reconstruction of the geologic record from the Pliocene epoch into the Eocene. Sea levels stabilize around 14 meters above current levels as CO2 concentrations fluctuate between 450 and 650 ppm. This plateau in sea levels may be the result of ice gain in East Antarctica compensating in part for the collapse of ice sheets in Greenland and West Antarctica. When CO2 concentrations increased from 650 to 1000 ppm, sea levels again rose rapidly to a maximum of 65 meters above current levels. The collapse of the East Antarctic ice sheet resulted in an ice-free planet with very high sea levels and very limited dry land.

If there is a silver lining in this story, it is that continental ice sheet losses that produce sea level rise above thermal expansion tend to take centuries. Even though other climate catastrophes (e.g., droughts, floods, wildfires, and deadly cyclones) are likely in the near future, we may have centuries to curb carbon pollution before sea levels rise to unmanageable levels. However, the data indicate that stabilizing CO2 concentrations at 450 ppm will eventually result in sea levels 9 to 14 meters above current levels. The authors summarize the situation as follows:

Clearly our relationship has limited relevance to short-term sea-level projections for the next century. However, accurately determining the long-term response of sea level to CO2 forcing has significant implications for the long-term stabilization of greenhouse gas emissions (by natural processes or human activity) and for decisions about the “acceptable” long-term level of CO2/warming. For instance, our results imply that acceptance of a long-term 2 °C warming [CO2 between 400 and 450 ppm (46)] would mean acceptance of likely (68% confidence) long-term sea-level rise by more than 9 m above the present. Future studies may improve this estimate, notably by better populating the interval between CO2 concentrations of 500–280 ppm (i.e., the Pliocene/middle Miocene). Regardless, the current relationship is sufficiently refined to imply that CO2 would need to be reduced significantly toward 280 ppm before any lost ice volume might be regrown (similarly over many centuries).
We are engaged in a very stupid experiment as we allow fossil fuels industries to play with the CO2 climate control knob to maximize paper profits. And we are kidding ourselves if we think the consequences will be trivial. Given the lack of political will and public pressure, the chances of CO2 stabilizing under 450 ppm are remote and under 300 ppm virtually impossible. Hell and high water are coming.

Originally posted to DWG on Sun Jan 27, 2013 at 05:58 AM PST.

Also republished by Climate Hawks, DK GreenRoots, and Community Spotlight.

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Comment Preferences

  •  I read very recently that Greenland's ice (3+ / 0-)

    sheet has been relatively stable in past high co2/temp epochs. How does this jibe with the info you present?

    Even if I knew that tomorrow the world would go to pieces, I would still plant my apple tree. -Martin Luther

    by the fan man on Sun Jan 27, 2013 at 06:28:05 AM PST

  •  Perhaps fossil fuel was never a viable resource (19+ / 0-)

    Life on Planet Earth sequestered carbon over millions of years to give us the current climate and ecosystem. By releasing this carbon we are changing one of the basic parameters of the ecosystem. We currently have no viable technology to sequester the carbon that we have released. We could recombine the carbon with hydrogen to form hydrocarbons, gaseous, liquid and solid depending on molecular weight and then bury these materials in the earth. However, it would take as much energy as we released over history. From that perspective, the fossil fuel energy used was just a loan.

    Fossil fuel extraction was certainly necessary to create the industrial age and we may be forgiven for not understanding the consequences. This is not true anymore. Fossil fuels are not viable sources of energy. Our imperative now is to develop a sustainable civilization as fast as possible, and we may have to sequester much of the excess atmospheric carbon that we have released. This is bigger than any project that we have ever attempted and requires a commitment not possible in today's political climate. Fixing that will be part of the solution. I think that we are at a unique alignment and this may be possible, but will require clear purpose.

  •  Unfortunately we know enough.. (4+ / 0-)

    And all the reputable well done science tells us that we are in deep trouble.
    We can continue to burn fossil fuels and wait for the catastrophes to occur..... coastal city flooding to make Sandy look like a minor problem.
    Or... we can do something

    Please sign the petition
    Barry Allen

    •  Hopefully (5+ / 0-)

      we're doing more than signing online petitions.  Though I'll happily sign.

      On some level, we have to go full Gandhi on this and become the change we wish to see.  We can't expect top-down political initiatives to save us in spite of ourselves; we need to begin creating the culture we need to become.  Like, you.  Now.

      I'm pretty sure most people could find ways to cut their carbon footprint in half more or less overnight.  A small contribution individually can add up to a hell of a lot in aggregate.

      (Also, please note that I said more than, not instead of.  Obviously we need to continue putting pressure on our elected officials, but right now we're hardly a noteworthy demographic.)

      "Forecast for tomorrow? A few sprinkles of genius with a chance of doom!" -Stewie Griffin

      by quillsinister on Sun Jan 27, 2013 at 11:06:22 AM PST

      [ Parent ]

  •  Mission impossible: (1+ / 0-)
    Recommended by:
    Therefore, our results imply that to avoid significantly elevated sea level in the long term, atmospheric CO2 should be reduced to levels similar to those of preindustrial times. [emphasis added]
    I don't know what to do with such a statement. I'm having as much trouble grasping its implications as when I heard the other day about scientists discovering a far-away galaxy cluster that is/was 450-billion light-years from edge to edge.  

    We share this planet with about 7 billion humans, a population that did not exist in "preindustrial" times.  Most of these 7 billion either live with or aspire to the material benefits of industrialized society.  Industry has sold most of us on the notion that only new technology can resolve the problems caused by old technology, so barring any plans to cull the global human population down to a preindustrial census, we had all better start imagining how we can collaboratively preserve acceptable standards of living within preindustrial levels of CO2 emissions.

    “The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.” — William Arthur Ward

    by vahana on Sun Jan 27, 2013 at 03:31:21 PM PST

  •  Sea level rise is the least (2+ / 0-)
    Recommended by:
    DWG, oldhippie

    important worry that Global Warming will give us in the next decade.

    Within a decade we will suffer the loss of the Arctic ice cap (during summer). That will be devastating to our crops and world food prices will go up above and beyond the ability of the world's poorest to afford.

    By the time that sea levels inundate our coastal cities those cities would have been depopulated.

    There is no solution within the context of this civilization. The whole thing is rotten to the core and needs to be brought down, not reformed. The only thing to hope for (and work for) is for a new civilization to rise from the ashes of this one.

    •  Don't be so cheerful about it. (2+ / 0-)
      Recommended by:
      DWG, artmanfromcanuckistan


      We're all pretty strange one way or another; some of us just hide it better. "Normal" is a dryer setting.

      by david78209 on Sun Jan 27, 2013 at 09:24:53 PM PST

      [ Parent ]

    •  You are much too optimistic (0+ / 0-)

      It won't take a decade to see an ice-free Arctic. In September 2002 Arctic sea ice volume was 10846 cubic kilometers. In September 2012 volume was down to 3371 cubic kilometers. The arithmetic is simple. Argue with me if you want, it is very hard to argue with arithmetic.  Even those who imagine a remnant of ice persisting off the north coast of Greenland and Ellesmere are giving up on the idea there might be 500km for as long as a decade.

      The alarmist view is the ice is will be gone in eight months.  The hair-on-fire view is it will be gone in seven months. The stone sober view is two to three years. Once the ice is gone for a day the ice free period will lengthen very quickly. That's just physics. It requires not only optimism but denial to imagine we shall not be ice free  six months of the year within a decade.

      You are very correct this will end the ability to crop with any predictability. It won't affect only the poor.

      •  Underestimating (1+ / 0-)
        Recommended by:

        Is something that I usually do.

        Yes, there is the possibility that the Arctic will be ice free in the summer within 3 years. However we can always have a La Nina  and or a volcanic eruption to cool things down temporarily.

        When it goes it will go fast due to the heat absorption of water and the melt ponds collecting on top of the thin ice acting like magnifying lenses.

  •  "tend to take centuries" (2+ / 0-)
    Recommended by:
    Calamity Jean, DWG

    This is the only thing i take issue with. I'd say it's a quibble, or a nit, but i feel that this goes to the heart of the problem we face in convincing people how serious this is. A 2C rise in global average temperature over a few dozen millennia is going to act on the ice in a different fashion than that same rise over the course of a century or so. It's not just that temperature is rising but the rate of the change that is happening. I don't think we're going to have the luxury of centuries.

    The story of sliding ice starts dozens of miles inland. In summer, some of the ice there melts and forms lakes. Most of those lakes drain thorough mysterious passages called moulins, which carry the water to the bedrock below the ice. Once the water gets under the ice, it lubricates the ice sheet, and the whole sheet flows faster toward the sea.

    Greenland's Mysterious Holes Speed Ice Flow to Sea

    All things in the sky are pure to those who have no telescopes. – Charles Fort

    by subtropolis on Sun Jan 27, 2013 at 09:58:16 PM PST

    •  Good point (0+ / 0-)

      If you look at the geologic record, these massive shifts in our ecosystem take place over long periods of time. However, there is no precedent for the rate we are altering the atmosphere, much less destroying the carbon carrying capacity of the environment. And we do see sudden shifts that far exceed what models predict based on available climate data. You mention one of the best examples in the remarkable Greenland Ice Sheet melt in the July of 2012.

      Be radical in your compassion.

      by DWG on Mon Jan 28, 2013 at 05:55:05 AM PST

      [ Parent ]

    •  The authors stated their reasoning (0+ / 0-)
      However, it will take many centuries to get to these high levels. Given the typical mean rates of natural sea-level rises on multicentury timescales [1.0–1.5 cm·yr−1, with extremes during deglaciation of 5 cm·yr−1 (41–43)], our projection suggests an expected equilibration time of the Earth system to modern CO2 forcing of 5–25 centuries.
      Sea-level rise in recent years (3.2mm/y in a warming climate) has been well within the long-term mean.  But even if we were to assume deglaciation-style SLR, it will take a long time to get to 6m, 9m, or 24m (authors' long-term SLR corresponding to 2011 CO2 concentrations): 120y, 180y, and 480y, respectively (at 5cm/y).  At 1cm/y, those time estimates become 600y, 900y, and 2,400y.

      With regard to the point of the post, those estimates doesn't diminish the threat of SLR, but I think it's important to keep them in context.  1m SLR by 2100 is well within the realm of possibility.  Since infrastructure decisions are costly and expected to last for decades, planners should plan for a little more than 1m SLR in case projections are too conservative.  But there isn't any reason to talk about abandoning coastal cities based on these projections - at least not in the next 100 years.  Nobody is going to abandon trillions of dollars worth of infrastructure.

  •  "what has been a stable and predictable system" (1+ / 0-)

    The glacial/interglacial climate system has not been at all stable. Tipping back and forth quickly from glacial to interglacial is as close to a definition of instability as you could get. We are tinkering with a system which is inherently unstable. It does not take as much to tip over an unstable system as it does to tip a stable one.

  •  Not just CO2, also falling soot (0+ / 0-)

    Don't underestimate the impact of darkening ice and snow with contributions from burning coal and diesel fuel, and wood fire cooking and heating, and forest fires.  

  •  I need a 120 foot sea-level rise, how can I help? (0+ / 0-)

    ... I'd like some ocean front property, but I can't afford it at the moment. So I was thinking, maybe I could work hard at raising CO2 levels to help my cause?


  •  sea levels and such. . . (0+ / 0-)

    I do a lot of research on Antarctica, mainly because I have two manuscripts I would love to get publish some day, both having to do with this truly singular continent. The "canary in the coal mine" scenario is indeed down south and at the Arctic counterpart; and both are headed into the Younger Dryas phase, along with the rest of us. More diaries and research, like yours, needs to get published. Most people, however, either don't give a damn about what's happening, and in some cases are just too damn lazy to find out and figure out what the high ground scenario is. So far, nada on that score. Thanks for writing the diary and for the evidence cited.

    Treat the world (yourself, and others) as part of a living organism. Everyone and everything will benefit.

    by richholtzin on Mon Jan 28, 2013 at 09:47:26 AM PST

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