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Long Term Sea Level Trends

September 17, 2014
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By Paul Homewood 

 

I’ve recently looked at sea level trends on the US eastern seaboard, and shown how the rate of sea level rise was higher than now around the middle of the 20thC.

We also get the same pattern across the Atlantic.

 

ScreenHunter_1053 Sep. 14 16.07 

ScreenHunter_1055 Sep. 14 16.08

image

http://tidesandcurrents.noaa.gov/sltrends/sltrends_global.shtml

 

But it is not only a regional phenomenon, but a global one as well. In 2011, John Church & Neil White produced their reconstruction of global sea levels from 1880 to 2009. From their data, we can show the 50-year trends, centred as above.

 

image

Figure 1

http://www.cmar.csiro.au/sealevel/sl_data_cmar.html

 

The rate of rise over the last 50 years has been 2.0mm/year, just below the 2.1mm recorded for 1932-1981. This indicates that we are observing a long term phenomenon that began in the late 19thC, as the Little Ice Age ended. This can be better seen in Figure 2, which plots the actual sea levels from the Church & White reconstruction.

 

image

Figure 2

http://www.cmar.csiro.au/sealevel/sl_data_cmar.html

 

What is also noteworthy is how sea level rise slowed down during the 1960’s & 70’s. This, of course, was the period when Arctic ice began expanding again as NH temperatures fell sharply.

10 Comments
  1. September 17, 2014 5:32 pm

    First of all, you have to be sure why the sea levels are rising. In a number of countries, like Sweden, it is because the the land is simply sliding downward, because of tectonic movement. I think this applies to Florida as well. .
    2nd my data sets
    http://blogs.24.com/henryp/files/2013/02/henryspooltableNEWc.pdf
    imply that it has been getting warmer, naturally, for at least the past 45 years. [with a correlation coefficient of one on the minima graph I think I am entitled to a little backward projection?],
    so yes, I would think that this would influence the water level somewhat.
    But it does not change the fact that [now] we are busy cooling and that it will only be a matter of time before the whole trend reverses again.
    In any case, I do not think that sea level is something to worry about. A book that I have on the [South-African] shoreline says that in the “inter-glacial periods temperatures were occasionally warmer than they are at present, resulting in the melting of the ice sheets and a sea level higher than that of today. During such times sea levels around the South African coast were up to 30 meters higher than present levels and the Cape Peninsula was transformed into a string of islands”.
    30 meters? Natural variation? how does that compare with 100-200 mm?

    • September 17, 2014 7:48 pm

      Even assigning all the rise to CAGW takes the teeth out of it. The rise is virtually immeasurable on anything less than a millennium scale.

  2. September 17, 2014 6:31 pm

    As I knew it all and how will you all feel when I need it so much and try a lot better for it when I am going to the hole thing I need to know about all of it

  3. September 17, 2014 10:24 pm

    Thanks, Paul.
    I have been looking at this too.
    According to the Sea Level Research Group, University of Colorado, there is a strong correlation between the Global Mean Sea Level (GMSL) and the Multivariate ENSO Index (MEI), with the GMSL often lagging changes in the MEI.
    See http://sealevel.colorado.edu/content/2014rel4-gmsl-and-multivariate-enso-index

    What do you think?

  4. David permalink
    September 18, 2014 4:01 am

    Re:

    “The rate of rise over the last 50 years has been 2.0mm/year, just below the 2.1mm recorded for 1932-1981.”
    ________________

    Which data set are you using Paul? From the link I used both the reconstructed annual and monthly data and found that (according to the ‘linest’ function on Excel) the linear trend between 1932-1981 is 1.8 mm/yr and for 1960-2009 it’s 1.9 mm/yr.

    Also, what does the data on your first chart actually show? It’s introduced as 50-year trends but labelled as 50-year averages. I can’t replicate the same shape using either running trends or averages.

    For 50-year running centred trends I get this using the annual reconstructed data as it comes on the Excel chart from the link: http://oi58.tinypic.com/vq5mh5.jpg

    Thanks.

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