Sea Level Rise

Determining the amount of sea level rise in the past, and predicting it for the future is a tricky proposition at best, and may possibly be something that’s not currently possible to do.

The media touts recent studies as proof of global warming and of disastrous sea level rise in the future.

Examining the basic components of sea level rise can provide a better perspective on the issue. They are:

  • The amount of glacier melt or growth
  • Increase or decreases in ocean temperatures
  • Subsidence
  • Rebound from past glacier activity
  • Geologic and topographic features along shorelines

It may well be that satellite measurements of sea levels are the most accurate, but these have only been available for the past twenty-five years, since approximately 1992.

These measurements show an average sea level rise of approximately 3.2 mm/year, or about 12 inches per 100 years. IPCC data show that sea level rise from 1930 to 1950 was equal to or greater than the rise shown by satellites from 1992 to the present. This would indicate there hasn’t been a recent acceleration in sea level rise.

Sea Level Rise from IPCC AR5 Satellite altimetry readings are shown with 90% confidence levels as an error bar.
Sea Level Rise from IPCC AR5
Satellite altimetry readings are shown with 90% confidence levels as an error bar.

Here are the variables involved in making estimates about past sea level rise, and predictions about future sea level rise:

  1. Sea levels have risen since the last ice age due to melting glaciers. What happens over the next 100 years depends on whether currently existing glaciers melt, or increase in size.
  2. Over the past 2,000 years global temperatures have increased and decreased. As a result, oceans levels have risen and fallen.
  3. Tidal gauges around the world have been used to measure sea level rise locally, and were the primary method for measuring sea level rise globally prior to the use of satellites. In modern times, tidal gauges have become very sophisticated, replacing gauges mounted on pilings etc. with electronic measuring devices. Tidal gauge measurements were inherently difficult to use for measuring global sea level rise because they were affected at different locations by:
  • Subsidence. Locally, the ground subsided so that the gauges indicated a rise in sea level that was actually a lowering of the ground level.
  • Rebound from the last ice age. Glaciers deformed the Earth where they stood during the last ice age. Areas where the glacier was thickest caused the Earth to sink, while at the edge of the glacier the Earth tended to rise. With the loss of glaciers the Earth rebounded where the glacier was heaviest, and the tidal gauges, such as around Sweden, would indicate a lowering of the sea level. Obversely, such as in Venice, the tidal gauges would indicate rising sea levels.

4. Geologic processes, such as described above, land use and coastal or river engineering and erosion can influence how sea level rise affects specific shorelines.

Sensational Cover Showing Statue Of Liberty Being Submerged by the Sea
Sensational Cover Showing Statue Of Liberty Being Submerged by the Sea

The recent dramatic National Geographic Magazine cover typifies how sea level rise is misunderstood and dramatized by the media. It so happens that the area around New York City has been sinking, by 1 to 2 mm per year, or at least 4 inches per century, which offsets the 11 inch rise claimed by the National Geographic article, bringing sea level rise close to what was considered normal over the past century, or approximately 7 – 8 inches.

Recent studies reach varying conclusions, but those cited recently by the media show sea level rise below that shown by satellites. More detailed information on recent studies can be found at http://bit.ly/1plW9y8

Media histrionics need to be kept in perspective, and understanding the basic variables and what satellite data has shown thus far, would indicate no dramatic disasters are awaiting us from sea level rise caused by global warming.

 

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Nothing to Fear explains why CO2 isn’t to be feared, why politicians are harming Americans by pushing the CO2 agenda, and that mankind has benefited from using fossil fuels and can continue to do so, perhaps for 1,000 years.

Nothing to Fear is available from Amazon and some independent book sellers.

Link to Amazon: http://amzn.to/1miBhXy

Book Cover, Nothing to Fear
Book Cover, Nothing to Fear

 

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0 thoughts on “Sea Level Rise

  1. Hi Donn,

    Always good to see people with common sense injecting some much needed realism into the mix.
    I hope my long-winded comment is constructive.

    I live in Holland and here there is a series on YouTube called ”Universiteit van Nederland” (University of the netherlands). Anyway, Prof. dr. Bert Vermeersen was speaking about sea level (an obvious topic in the Low Countries) and he spoke about research which said;

    – Glaciers are so large that they have their own gravity, such that when glaciers off the Alaskan coast melted the local sea level fell. Counter intuitive but he said it happenned and the loss of local gravity was what caused the sea to ”fall back” as it we’re.

    – He said that a full melt of Greenland’s Ice Sheet is unlikely and would take centuries but if it did melt, Holland would not see a -local- sea level rise. But if Antarctica melted Holland would be in trouble.

    //–// link to original video (Dutch)
    http://www.universiteitvannederland.nl/college/waarom-kan-de-zeespiegel-ook-dalen-wanneer-ijskappen-smelten/ (English translation: why can the sea level fall when Ice Caps melt)

    //–// some sea level info from same Professor (English)
    http://www.lr.tudelft.nl/en/organisation/chairholders/profile-of-a-prof/bert-vermeersen/
    What has been the highlight of your career?
    ‘In March 2010, I had the honour of sailing on the clipper Stad Amsterdam for a TV programme recreating Darwin’s voyage in the Beagle. We sailed from Perth to Mauritius, where I took GPS readings to determine the absolute height of sea level and the impact of gravity on it. It was an especially interesting mission, assisted remotely by colleagues in Delft. One of the most important conclusions was that with all the peaks and troughs on the Indian Ocean, the difference in sea level can be as much as 100 m. The footage was broadcast in episode 30, entitled Palm Trees on Antarctica.’

    //–// another link on counter intuitive consequences of (very long term) Ice Cap melts.
    http://harvardmagazine.com/2010/05/gravity-of-glacial-melt

    //–// yet another link throwing cold water on the panic-PR about sea level rise.
    http://euanmearns.com/how-much-have-sea-levels-really-risen/

    Keep up the good work,

    Best regards,

    • Thanks. Great comments. My career has been varied, interesting and informative. I can’t point to a single highlight, since I was fortunate to have sailed to the Orient, South America and Europe before I was 20. My family and all that has meant are precious. Working in one of the world’s great companies, with outstanding engineers and managers was, in itself, an unparalleled experience. I have been extremely lucky, and continue to do what I find most interesting … trying to get people to think critically about global warming and the importance of real science.

    • I think you need to read my article more carefully. It’s clear that tidal gauges don’t accurately reflect global sea level rise. Satellite readings may be the most accurate, but using the IPCC’s own date it wouldn’t appear that there has been a rapid change in sea level rise.
      What’s important is to stop yelling wolf, until we know what’s really happeningIn addition, a 12 inch rise over a 100 years isn’t a disaster.

      • “The rate of sea level rise is faster now than at any time in the past 2,000 years, and that rate has doubled in the past two decades.” – NASA

        Why are you, IMO, trying to rationalize this point away?

      • John: Because what you say is not correct. The rate is at 3.2 mm per year, or 12″ in a century according to satellite measurements. Satellite measurements have only been in place for a few decades, and its results can’t be compared directly with tidal measurements. Tidal measurements are not reliable, and the idea that satellites are entirely reliable when the ocean wave height varies from a few feet to a hundred feet, and is constantly changing, seem unlikely.
        It’s important not to jump to conclusions.

  2. As Donn says, there is much variation in measurements of sea level for various reasons. One possible explanation for slightly higher levels measured by satellite may be that satellite orbits have degraded more than have been compensated for in the acquired data.
    Climate scientists and media (like the Natl. Geographic article) predict much higher future seas based on models of how much increased future melting will occur for Greenland’s and Antarctica’s glaciers and not on extrapolations of past and current sea level data trends. There are no data for this, or course, and some scientists and media don’t correct the (intentional??) misunderstanding that readers get about possible causes of future sea level rise.

  3. Donn,
    Excellent article.
    Some data on SLR below: Note that 0.3 mm/year has recently been added to the SLR readings to account for sea floor subsidence, but it does not actually raise the sea level relative to land. Why would they do that? “It’s an attempt to calculate what the rate of sea-level rise would be were it not for the hypothesized sinking of the ocean floor.” That reduces the impact of sea level rise but makes the figures more alarming.

    “No sign of any acceleration”

    “NOAA has done linear regression analysis on sea-level measurements (relative sea-level) from 225 long term tide gauges around the world, which have data spanning at least 50 years. (Note: the literature indicates that at least 50-60 years of data are required to determine a robust long term sea-level trend from a tide gauge record.) There’s no sign of any acceleration (increase in rate) in most of those tide-gauge records.

    More than 85% of stations show less rise than 3.3 mm/year

    The rate of measured sea-level rise (SLR) varies from -17.59 mm/yr at Skagway, Alaska, to +9.39 mm/yr at Kushiro, Japan. 197 of 225 stations (87.6%) have recorded less than 3.3 mm/yr sea-level rise. At 47 of 225 stations (20.9%) sea level is falling, rather than rising. Just 28 of 225 stations (12.4%) have recorded more than 3.3 mm/yr sea-level rise.”

    “NOAA says that the average is 1.7-1.8 mm/yr. Some of the difference between the calculated average and NOAA’s figure for MSL rise may be due to the addition of model-derived GIA adjustments to the measured rates when calculating the average to account for post glacial rebound (PGR). My guess is that they’re using Prof. Richard Peltier’s figures. Unfortunately, those figures are only very loosely correlated with what is actually happening at the tide-gauge locations.”

    “Prof. Peltier also estimates that melt-water load from the melting of the great ice sheets (~10k years ago) is causing the ocean floors to sink by enough to cause a 0.3 mm/yr fall in sea-level, absent other factors. That number (0.3 mm/yr) is usually added to calculated “global average” sea-level rise rates, inflating the reported average, even though the resulting sum is not truly sea-level, and is not useful for projecting sea-level for coastal planning. It’s an attempt to calculate what the rate of sea-level rise would be were it not for the hypothesized sinking of the ocean floor.”

    – See more at: http://notrickszone.com/2015/09/03/sea-level-analyst-not-possible-to-torture-coastal-tide-gauge-data-into-yielding-a-sea-level-rise-anywhere-near-3-3-mmyr/#sthash.pXcGFoUq.FrC7rFc5.dpuf

    Don Shaw

    • Thanks foe the additional information. The alarmists will do anything to scare people, including preposterous covers on magazines …such as the National Geographic.

  4. Pingback: Weekly Climate and Energy News Roundup #218 | Watts Up With That?

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