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Yes, Virginia, There is Sea Level Rise

Posted on 22 July 2012 by greenman3610

In the newest video in the This is Not Cool” series at the Yale Forum on Climate Change & the Media (also posted at Climate Crocks), Peter Sinclair examines the impending sea level rise, including in the context of North Carolina lawmaker denial of the accelerating sea level rise, examined here at Skeptical Science by John Bruno and Rob Painting.  Sinclair does an excellent job as always - take a look:

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Comments 1 to 22:

  1. From the clip it appears that the century rate of sea level rise on the Virginia coast has been around 200 mm (8”), the same as globally, but compounded by an equivalent amount of land settlement. The global 20-year rate of sea level rise was 1.8 m/year in 1892, fell to 0.0 in 1934, rose to 3.2 in 1963, fell to 1.0 in 1978, rose to 3.6 in 2005 and is currently 3.2 mm/year and falling. The change in rate of rise follows a similar pattern to the AMO but lags it by a decade or so. The data suggest that the change in the rate of sea level rise is +0.014 mm/year². If the decline in the rate of sea level rise following the 2005 peak is similar to that following previous peaks, and taking into account the accelerating rate of rise, then the rate of rise might continue to fall to around 2 or 2.5 mm/year.

    I realise that a lot of this discussion is about whether to extrapolate from past data or rely on the projections AOGCMs. Whilst the data do show an underlying acceleration in the rate of sea level rise it is less that the models project.
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  2. In the near-term, the concern over future sea level rise is based upon the 65-70 metres of global sea level locked up in the giant polar ice sheets - Greenland and Antarctica, not thermal expansion of the ocean. Greenland & Antarctica are contributing to sea level rise at an accelerating rate.



    These ice sheets have been essentially stable for the last 7-8000 years and only began to melt/disintegrate in the late 20th century. Global sea level rise in the 20th century was anomalous within the context of the last 7-8000 years.

    Certainly there are other factors to consider in North Carolina - for one it is an area that was uplifted by the presence of the gigantic Laurentide ice sheet during the peak of the last ice age. The ice sheet is long gone, but the Earth is still responding to the change in loading - hence the subsidence going on along the North Carolina coast today.

    The trends in the global sea level satellite data (the last two decades) are consistent with the ocean heat content data (cooling between around 2004-2008), which is itself consistent with the solar dimming trend in the Southern Hemisphere, and the cooling phase of the 11-year solar cycle.

    The Earth has an energy imbalance, so it will continue to warm and sea level will continue to rise. Whether it will accelerate in the next few years remains to be seen, but unless reflective sulfate aerosols increase, it seems likely to.
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  3. #2 Rob Painting

    "Whether it will accelerate in the next few years remains to be seen"

    Yes, and in order to get to the prediction in the video, 6 Feet (1.8 meters) by 2100 it will have to average over 20 mm/yr for the next 88 years. That's well over six times the current rate. A very healthy acceleration will have to happen in order for that prediction to come true.
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  4. As Rob notes @2, an acceleration (which I would certainly not characterize as 'healthy' because of the unintended connotations of that word) is exactly what's going to happen.

    RonManley @1 - you are confusing short-term noise with long-term trend changes.
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  5. The best fit for the current trends in Greenland and Antarctica land ice (as per papers such as Velicogna 2009 which is linked to here) is an accelerating decline.

    If memory serves, the range of sea level rise considered most likely is between 0.75 and 1.9 metres by 2100, starting from the levels in 1990 (per Vermeer & Rahmstorf 2009).

    Even the 'best case' scenario is bad.
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  6. Rob Painting #2. Your graph actually suggests the rate has been more or less constant from 2001 to 2009 at about 1 mm/year. Since the era of satellite data the 5-year rate of rise peaked at 4.5 mm/year in May 2003. The current 5-year rate of rise up April 2012 is 2.3 mm/year. So, overall the rate of rise is falling.

    Dana #4. You suggested that changes in the 20-year rate of sea level rise were ‘short-term noise’ and then show a straight line fit. My point was the rate has fluctuated over periods of several decades and currently appears to be on a downward trend. I’m not sure showing the long-term trend is appropriate as the crux of this posting is to argue that the long-term trend is not a good indicator for the future. If a rise of 1 metre is to be attained by 2001 then the change in rate will be such that changes observed in the past pale into insignificance.
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  7. Ron @6 - my point is that "appears to be on a downward trend" is clearly not supported by the data.
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  8. Dana1981 #7. To avoid confusion, I am not saying that sea levels are falling, it is clear that they are continuing to rise. What I am saying, and what the data quoted in my previous posts support, is that over a 20, 10 or 5 year period the rate of rise is lessening.
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  9. Some "skeptics" posting here are focussing on very short periods again to try and obfuscate, whilst also not supporting their assertions with hard numbers or data. Church et al. (2008) demonstrate nicely how the long-term trend is not linear but accelerating.



    [Source]

    It is this reality that some in Virginia wish to deny, and that is the subject of this post "Yes, Virginia, There is Sea Level Rise".
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  10. Ron @8,

    Please make up your mind, @1 you said [my bolding] " Whilst the data do show an underlying acceleration in the rate of sea level rise it is less that the models project. "

    But now @8 you claim that "over a 20, 10 or 5 year period the rate of rise is lessening."

    Please stop playing word/rhetorical games.

    The Senate in Virginia wishes to deny all the science (both empirical and theoretical) that indicates that, in the long-term, the rate of sea-level rise will continue to accelerate. Does it not trouble you in the least that they are a) of this opinion/belief, and b) the lengths they went to to try and enforce their denial on others?
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  11. #6 RonManley said, "If a rise of 1 metre is to be attained by 2001 [sic] then the change in rate will be such that changes observed in the past pale into insignificance."

    The video actually predicted six feet or about 1.8 meters of sea level rise by 2100.

    #9 Albatross put up a graphic of the Church and White data.

    That data is available on the Church and White Data Page as Church and White (2006) If you graph it out and extend the Y axis to include the 1.8 meter prediction and extrapolate the time line out to 2100 as the video said, it looks like this:



    It's merely a question of whether Sea Level rise will accelerate enough to make that prediction come true.
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  12. Steve @11,

    Can I please remind you about the topic of this post. You seem to be trying your best to obfuscate. I will also note that I cited Church and White (2008), not their 2006 paper. Regardless, nowhere in their paper do Church and White simply extrapolate the best fit line over the observed record as you appear to have done in your figure @11. Doing so is a no-no from both statistical and physical stand points.

    Readers might be interested to note what Church and White (2008) have to say about recent rates of sea level rise when referring to the figure below (their Fig. 6):



    Caption: "Projected sea-level rise for the 21st century. The projected range of global-averaged sea-level rise from the IPCC (2001) assessment report for the period 1990–2100 is shown by the lines and shading (the dark shading is the model average envelope for all SRES greenhouse gas scenarios, the light shading is the envelope for all models and all SRES scenarios, and the outer lines include an allowance for an additional land-ice uncertainty). The updated AR4 IPCC projections (90% confidence limits) made in 2007 are shown by the bars plotted at 2095, the magenta bar is the range of model projections and the red bar is the extended range to allow for the potential but poorly quantified additional contribution from a dynamic response of the Greenland and Antarctic ice sheets to global warming. Note that the IPCC AR4 states that ‘‘larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea-level rise.’’ The inset shows the 2001 projection compared with the observed rate estimated from tide gauges (blue) and satellite altimeters (orange) (based on Church et al. 2001; Meehl et al. 2007; Rahmstorf et al. 2007)"


    "The concern that the sea-level projections may be biassed low has been reinforced by a comparison of observed and projected sea-level rise from 1990 to the present. For this period, the observed sea level has been rising more rapidly than the central range of the IPCC (2001, 2007) model projections and is at the very upper end of the IPCC TAR projections (Fig. 6; Rahmstorf et al. 2007), indicating that one or more of the model contribu- tions to sea-level rise may be underestimated." [My highlighting]

    In my opinion, those who wish or choose to believe, that uncertainty is skewed towards the lower end of outcomes, are being incredibly naive.
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  13. Steve Case @11, first I'll note that the sea level rise projected in that graph is approximately equal to the expected rise from thermal expansion alone assuming the IPCC A2 scenario (270 mm). However, if we linearly extend the rate at which ice sheets are loosing mass, we can expect a further 360 mm of sea level rise on top of that (and ignoring glaciers). That represents a sea level rise of 630 mm above 1980-1999 levels by 2100. That represents an increase of at least 50% above the approx 400 mm increase your projection shows over the same period.



    The CSIRO estimate that not more than 30% of the sea level rise since the 1950s has come from polar ice sheets. Based on that, and using your projection, the sea level rise contribution from other sources can be expected to be 280 mm from 1990, leading to a combined expected increase of 640 mm. That estimate is not based on models, it is simple extrapolation of known data.

    That illustrates, in part, the folly of simple projection. Using two different projections methods, we arrive at inconsistent results which diverge by over 50%. It also shows how foolish it is to think you can assess future sea level rise without examining potential future changes in temperature, not to mention such wild cards as the potential instability of the West Antarctic Ice Sheet.
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  14. When I was around 9 (1991) we were shown a video at school about global warming.

    My takeaway from that video was that the ice sheets could collapse as early as 2022 and this would result in a 60m sea level rise. Some of the kids in the class were crying.

    Does anyone here have an idea on what that video might have been or where it came from?

    Thanks in advance.
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  15. Tom @13,

    Good points. Steve Chase is also wrong about what he claims is stated in the video about global sea level rise.

    The video starts of with reference being made to a press release from the Niels Bohr Institute, the heading for that press release is:

    "Studies agree on a 1 meter rise in [global] sea levels"

    Nowhere do they state 1.8 m as the best estimate for the increase in global sea level by 2100. Admiral Titley does note in the video that sea levels could rise between 0.9 m and 1.8 m by 2100 (~3-6 ft), and that range is entirely consistent with the GRL paper referenced below. So we have some "skeptics" here cherry picking values to misinform and to fit their narrative.

    That Niels Bohr press release in turn refers to a paper just published in GRL by Jevrejeva et al. (2012) who conclude that:

    "With six IPCC radiative forcing scenarios we estimate sea level rise of 0.6–1.6 m, with confidence limits of 0.59 m and 1.8 m."

    So as new information becomes available the best estimates of increases in sea level are being revised upwards.

    Now 2100 is rather arbitrary, because sea levels will continue to rise well beyond 2100 because of global warming.
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  16. Tristan @ 14 - never heard that one before, probably because it is nonsense. Certainly the paleodata indicate rates of sea level rise of well over a metre occurred in previous warm intervals (interglacials), but there's no evidence to support rates greater than that. They may have occurred, but the evidence is lacking.
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  17. Hmm. I wonder if my childmind misinterpreted 2200 as 2022. Possible.
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  18. Ron Manley - "Rob Painting #2. Your graph actually suggests the rate has been more or less constant from 2001 to 2009 at about 1 mm/year"

    Ron, I'm sure if one confines oneself to looking at any short interval you can find a short-term trend that affirms a preconceived notion. We call that cherry-picking. On the other hand understanding the physical mechanisms driving these trends is far more useful. For example, if a reasonably-sized El Nino develops this Southern Hemisphere summer I fully expect that sea level will rise abruptly - as the continental land masses, and particularly the tropical basins, dry out.

    Furthermore, as mentioned above, the loss of ice from Greenland & Antarctica is accelerating - this will manifest itself in greater sea level rise. The solar dimming of the Southern Hemisphere in the "noughties" has shielded the oceans from greater warming, but can much longer can that last? We've already seen that the slowdown in ocean heat content between 2004-2008 has been replaced by greater warming:

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  19. I should have posted a graph earlier to minimise the confusion. I calculated the rate of sea level rise based on the data of Church et al merged with the Jason-Topex data for recent years. The data start in 1870 so for every year from 1890 onward I calculated the rate of change of sea level in the preceding 20 years (very easy in Excel using LINEST).


    This plot shows that:
    1. There is an underlying increase in the rate of rise. It works out at about 1mm per year increase every 70 years.
    2. The rate of increase in sea levels is quasi-cyclical. Thus, depending on the phase of the cycle it is possible both to have an underlying acceleration and short term (c 30 years) drop in the rate of rise.

    Despite the implications I am not a climate change denier. I believe that the acceleration in the rate of increase is almost certainly due to global warming alone. I am also in favour of the decision relating to the citizens of Virginia being based on science. However since the rate of sea level rise is quasi-cyclical and since as far as I know (correct me if I am wrong) none of the model projections include this then the four year pause to get better science may be to their advantage.
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  20. Ron - The notion that the sea level simply rises all by its lonesome, as part of some mysterious natural quasi-cycle, is ridiculous. And yes, you are right climate models certainly don't allow for this physically impossible scenario.
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  21. Rob Painting # 20. I don't say that the sea level rises all by itself. What the data do show that is the rate of sea level rise fluctuates in a quasi-cyclic way. You can download the Excel file I used here and check it yourself.
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    Moderator Response: [DB] Fixed link.
  22. RonManley:

    From previous discussions on this site (and examining all the graphs posted in this thread) it is my understanding that the principal driver of fluctuations in sea level rise (but not the trend) is ENSO; with the many La Niña years recently causing an appreciable dip in sea level rise.

    This seems to correlate with ENSO being a driver of fluctuations in surface temperatures, again without really affecting the trend in that metric, either.

    That would seem to account for the fluctuations you have remarked upon.
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