A Novel Way to Test the Impact of Rising Sea Levels

Eric Worrall’s recent essay on the Prime Minister of Tuvalu and his reticence to providing some evidence that his island nation is being inundated by rising sea level inspired me to devise a simple test to see if an island is sinking, vanishing or being washed away:

Planimeter a recent map of the island and compare it to an older map of the island.


Since the USGS has a large historical inventory of topographic maps, this should be relatively easy for any islands in these United States.

For my test case, I chose Key Biscayne, Florida.  It’s just south of the perennially sinking Island of Miami, has a maximum elevation of about 5′, is relatively small and the USGS had several vintages of 7.5 minute quadrangles available.


Figure 1: Key Biscayne, 1962 (USGS)

And Now…


Figure 2: Key Biscayne, 2012 (USGS)

I planimetered the coast lines of each map and found no significant changes over the 51 years from 1962-2012…


Figure 3: 1962 vs. 2012.  Roughly a 1% difference in area.  The apparent slight increase in well within the margin of error of the planimetering tool.

I guess I’m going to have to deny climate change or at least doubt the climate, because I can’t see any effect of sea level rise on this puny, flat, little island. (/sarc).


7 Responses to “A Novel Way to Test the Impact of Rising Sea Levels”

  1. Cliff Stiles Says:


    Apologies for using your website for this question, but if anyone can address this I’m sure it is you. For five days now I have been unable to access the ACG website from any computer or server system within my sphere of influence, including the local library and the College system. I can’t find anything online to account for this. Is the website down or closed? Are you having this trouble?

    Please advise, and thanks. Happy Holidays.

    Cliff (Martok)

  2. David Middleton Says:


    The site’s been down for at least a couple of days. There has been some discussion on the ACG Facebook page. No one seems to know when or if it will be back up.

  3. Cliff Stiles Says:

    Thanks. I found a bit of information about it. Hopefully the problem will be corrected.

    Merry Christmas.

  4. Martok Says:

    I guess you have seen this:

    COP21 climate change summit reaches deal in Paris


  5. josaphatbarlaam Says:

    Sorry, just saw this, but Key Biscayne is a very developed, extremely wealthy island, that has undergone significant construction and development between ’62 and ’12, with landmass being brought in to support construction and development efforts.

    This seems like a poor example to compare to a relatively poor nation. Not sure how you think this is scientifically valid.

    FWIW, I lived on Key Biscayne for several years.

    • David Middleton Says:

      It’s not specifically relevant to Tuvalu. I never said it was. It’s a method of quantifying the effects of sea level rise in places where sufficient historical topographic maps are available.

      • Barlaam Says:

        To be a valid premise, particularly a valid scientific premise, you would have to assume that there were no other external factors involved, such as dump trucks of soil carted onto the island to replace/reclaim areas/raise the height of land for construction, no sand put out to make the beaches longer and whiter, and to replace erosion, or anything else similar.

        All of this occurred (lot of money, so they could afford it).

        Hurricane Andrew had significant impact.

        The Key has effectively been terra-formed over the past several decades. None of this has anything to do with climate change proof or criticism, just that your premise ignores the cornucopia of external factors that you did not consider/account for.

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