# Ocean levels rising?

**URL:** <https://boards.straightdope.com/t/ocean-levels-rising/393618>\
**Category:** Factual Questions\
**Created:** [February 25, 2007, 5:14pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618 "2007-02-25T17:14:51Z")\
**Posts on this page:** 18\
**Page:** 1

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**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\
**Post date:** [February 25, 2007, 5:14pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/1 "2007-02-25T17:14:51Z")

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I just came back from Barbados (aka paradise). I saw a tidal chart for the entire year and no low tide was below mean sea level (the lowest was 0.1 m). The highest high tide was 1.1 m. Lot’s of times low tide was as high as 0.4 m and high tide as low as 0.8 m. Does this mean that the sea around Barbados has already risen by 0.6 m (over 2 feet)? What other explanation could there be?

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**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\
**Post date:** [February 25, 2007, 5:23pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/2 "2007-02-25T17:23:17Z")

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[QUOTE=Hari Seldon]  
I just came back from Barbados (aka paradise). I saw a tidal chart for the entire year and no low tide was below mean sea level (the lowest was 0.1 m). The highest high tide was 1.1 m. Lot’s of times low tide was as high as 0.4 m and high tide as low as 0.8 m. Does this mean that the sea around Barbados has already risen by 0.6 m (over 2 feet)? What other explanation could there be?  
[/QUOTE]

It’s sinking?

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [February 25, 2007, 5:50pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/3 "2007-02-25T17:50:03Z")

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Sea level isn’t so easy to define as you might think:

> [@](#):
>
> The geoid is essentially the figure of the Earth abstracted from its topographic features. It is an idealized equilibrium surface of sea water, the mean sea level surface in the absence of currents, air pressure variations etc. and continued under the continental masses. The geoid, unlike the ellipsoid, is irregular and too complicated to serve as the computational surface on which to solve geometrical problems like point positioning. The geometrical separation between it and the reference ellipsoid is called the geoidal undulation. It varies globally between ±110 m.

[Geodesy](http://en.wikipedia.org/wiki/Geodesy)

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**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\
**Post date:** [February 25, 2007, 5:54pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/4 "2007-02-25T17:54:36Z")

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[QUOTE=Hari Seldon]  
I just came back from Barbados (aka paradise). I saw a tidal chart for the entire year and no low tide was below mean sea level (the lowest was 0.1 m). The highest high tide was 1.1 m. Lot’s of times low tide was as high as 0.4 m and high tide as low as 0.8 m. Does this mean that the sea around Barbados has already risen by 0.6 m (over 2 feet)? What other explanation could there be?  
[/QUOTE]

No it doesn’t. There are three ways tides are measured on a daily basis by NOAA: Mean low water, mean high water, and high tide line. Some still measure the 1 year tidal flood but it is unusual. These three rates fluctuate yearly. I live on the coast of Connecticut, we have a dock, it was built in 1988. In 20 years the water has risen over the high tide line, through the planks roughly 20 times… or once a year. Otherwise, I can still see the mean high water mark I always see on the piling supporting our dock. The waters are not rising to such a degree that it is noticeable, we should know…living by the tides everyday for your life gives you a pretty good idea. I say this is no small terms, I do not make my living my the sea, but the town I live in does, and most natives know what the tides are doing almost like a sixth sense. And though it is not scientific…it’s a good base point for anecdotal info.

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**Author:** ![bonitahi](https://avatars.discourse-cdn.com/v4/letter/b/7993a0/32.png) [@bonitahi](https://boards.straightdope.com/u/bonitahi)\
**Post date:** [February 25, 2007, 7:58pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/5 "2007-02-25T19:58:52Z")

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For 25 years I lived on the bay side of an island off the west coast of FL, in Bonita Beach.  
The house was on two foot stilts abutting the bay (grandfathered). Never had a hurricane.

For the 1st 12 years the high tide never went above my docks. Then in two successive years the water rose above the docks twice a year at a high tide. Then 4-6 times a year for 4 years. Then water overrid the boards twice every month for two years. The last five years high tides monthly, and more, not only went over the docks but over the seawall too, tickling a few feet onto my property. The last two years the water went over the dock, over the sea wall, and 16-20 feet into the almost level slightly graded yard, twice a year, as well as over the docks 3 or more times per month.

I moved off the water two years ago.

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**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\
**Post date:** [February 26, 2007, 12:19am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/6 "2007-02-26T00:19:37Z")

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[QUOTE=Hari Seldon]  
I just came back from Barbados (aka paradise). I saw a tidal chart for the entire year and no low tide was below mean sea level (the lowest was 0.1 m). The highest high tide was 1.1 m. Lot’s of times low tide was as high as 0.4 m and high tide as low as 0.8 m. Does this mean that the sea around Barbados has already risen by 0.6 m (over 2 feet)? What other explanation could there be?  
[/QUOTE]

Are you sure? Whenever I see tide heights measured, the zero level is the _lowest_ you expect to see on a spring (low) tide, not “mean sea level”. Sounds about right to me.

AFAIK sea levels are not rising perceptibly on a global basis. Despite all the gloom and doom regarding Pacific islands disappearing beneath the rising waves, the sea levels measured at most islands has actually been falling in recent years.

**bonitahi** - your experience sounds like subsidence, not rising sea levels.

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**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\
**Post date:** [February 26, 2007, 12:40am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/7 "2007-02-26T00:40:27Z")

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Ok, I didn’t tell the whole story. There is a tide calculator that I used to use when I went to Barbados until the gov’t (along with most of the British Commonwealth, not Canada) decided the tidal information was proprietary and wouldn’t release it free. That predictor, when I was able to use it, displayed its information graphically and there was a line on the graph very clearly labelled “mean sea level”. A few of the very low low tides dipped below that level, but nearly all were above it. I wondered at the time, but forgot it till this year I happened to see of printout of the whole year tide prediction.

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**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\
**Post date:** [February 26, 2007, 12:40am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/8 "2007-02-26T00:40:38Z")

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[QUOTE=Colophon]  
**bonitahi** - your experience sounds like subsidence, not rising sea levels.  
[/QUOTE]  
In what way would it sound different if it _was_ rising sea levels?

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [February 26, 2007, 12:53am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/9 "2007-02-26T00:53:43Z")

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[QUOTE=Askance]  
In what way would it sound different if it _was_ rising sea levels?  
[/QUOTE]  
[It’d be slower](http://news.bbc.co.uk/2/hi/science/nature/4651876.stm):

> [@](#):
>
> Over the entire period from 1870 the average rate of rise was 1.44mm per year.
> 
> Over the 20th Century it averaged 1.7mm per year; while the figure for the period since 1950 is 1.75mm per year.

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**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\
**Post date:** [February 26, 2007, 1:06am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/10 "2007-02-26T01:06:57Z")

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[QUOTE=Hari Seldon]  
Ok, I didn’t tell the whole story. There is a tide calculator that I used to use when I went to Barbados until the gov’t (along with most of the British Commonwealth, not Canada) decided the tidal information was proprietary and wouldn’t release it free. That predictor, when I was able to use it, displayed its information graphically and there was a line on the graph very clearly labelled “mean sea level”. A few of the very low low tides dipped below that level, but nearly all were above it. I wondered at the time, but forgot it till this year I happened to see of printout of the whole year tide prediction.  
[/QUOTE]

That’s odd. Maybe a mislabelled graph? AFAIK a 0.1m low tide is, well, a pretty low tide. I don’t know what the tidal range is in Barbados, not huge I imagine. My parents live on the Bristol Channel which has a huge tidal range (second only to a couple of places in Canada I believe) and the tide heights there for next weekend’s full moon are about 1.1m for the low tide, 8.9m for the high. [Link](http://www.pol.ac.uk/ntslf/tides/?port=0061).

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**Author:** ![bonitahi](https://avatars.discourse-cdn.com/v4/letter/b/7993a0/32.png) [@bonitahi](https://boards.straightdope.com/u/bonitahi)\
**Post date:** [February 26, 2007, 1:31am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/11 "2007-02-26T01:31:58Z")

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“Quote:  
Originally Posted by Colophon  
bonitahi - your experience sounds like subsidence, not rising sea levels.”

```auto

I guess that is an option. 

My neighbors for a length of 250 feet on each side (50' lots, many owners) were suffering/noticing the same thing (the old timers like me especially). I also noticed the waters rising onto their properties gradually as I lived there for 25 years; and I noticed in the past dozen years their properties got progressively worse (more flooding).

I had a friend on the island, a fisherman, on the bay side also, 1 1/2 mile away from me, that could not believe the change in height of the waters. He moved into his house 32 years ago- that's 32 yrs ago plus the 2 that I have been gone. So, the higher waters were not just 'immediately' local. 

My seawall was solid. If the cause was 'subsidence' then the wall must have sunk too, as per your theory. Never had any mini-sinkholes on my property to indicate any earth settlement. Nor did my neighbors.

With my information, can you speculate that the island, Bonita Beach, was sinking?

I figured the waters are rising.
```

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**Author:** ![bonitahi](https://avatars.discourse-cdn.com/v4/letter/b/7993a0/32.png) [@bonitahi](https://boards.straightdope.com/u/bonitahi)\
**Post date:** [February 26, 2007, 1:44am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/12 "2007-02-26T01:44:39Z")

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[QUOTE=Squink]  
[It’d be slower](http://news.bbc.co.uk/2/hi/science/nature/4651876.stm):  
[/QUOTE]

Your 1870 year was but the starting of the industrial revolution.  
What’s the figure for the past 25 years?  
I did not notice it till about '92-'93.  
Previous to that there was no noticeable rise where I was.

Do you have more recent cites?

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**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\
**Post date:** [February 26, 2007, 2:04am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/13 "2007-02-26T02:04:15Z")

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[QUOTE=bonitahi]  
Your 1870 year was but the starting of the industrial revolution.  
What’s the figure for the past 25 years?  
I did not notice it till about '92-'93.  
Previous to that there was no noticeable rise where I was.

Do you have more recent cites?  
[/QUOTE]

[Fort Myers](http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8725520) apparently shows a mean trend of 2.29mm per year rise.

These figures “combine data on ocean fluctuations and vertical motion of the land at the station” according to [this](http://tidesandcurrents.noaa.gov/sltrends/sltrends_states.shtml?region=fl). I would be surprised if all that 2.29mm per year (~9in per century) is due to sea level rise.

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<div class="post-metadata">

**Author:** ![bonitahi](https://avatars.discourse-cdn.com/v4/letter/b/7993a0/32.png) [@bonitahi](https://boards.straightdope.com/u/bonitahi)\
**Post date:** [February 26, 2007, 2:09am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/14 "2007-02-26T02:09:47Z")

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Yeah, Ft Myers is real close, thanks.

But either the island is sinking or the waters are rising. Based on my anedotal obsevations (along with other oldtimers on the island) of over 25 years of living in the same house on those waters.

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**Author:** ![bonitahi](https://avatars.discourse-cdn.com/v4/letter/b/7993a0/32.png) [@bonitahi](https://boards.straightdope.com/u/bonitahi)\
**Post date:** [February 26, 2007, 2:20am UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/15 "2007-02-26T02:20:56Z")

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Colophon

Your figures are based on monthly mean sea level data from 1965 to 1999. I know more recent figures are not readily available.

The pertinent point I was making was that between 1980 & 1992 I saw no rise in water. However, post '92 I saw a dramatic increase annually. As was the case for the properties around me on the bay.

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<div class="post-metadata">

**Author:** ![bonitahi](https://avatars.discourse-cdn.com/v4/letter/b/7993a0/32.png) [@bonitahi](https://boards.straightdope.com/u/bonitahi)\
**Post date:** [February 26, 2007, 5:04pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/16 "2007-02-26T17:04:42Z")

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Would my experience over 25 years, as mentioned, be empirical evidence that the waters are rising? At least in the area described?

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**Author:** ![slaphead](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slaphead](https://boards.straightdope.com/u/slaphead)\
**Post date:** [February 27, 2007, 3:05pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/17 "2007-02-27T15:05:35Z")

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Apropos of not very much, I thought I would share this article on [isostasy](http://gemini.oscs.montana.edu/~geol445/hyperglac/isostasy1/) (rises of 1cm per year in the northern baltic!) and to also suggest that changes to sandbars, currents and other seabed features may be allowing the tides to reach the shoreline more rapidly - the ocean can do all sorts of odd things for reasons which are far from obvious.

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**Author:** ![bonitahi](https://avatars.discourse-cdn.com/v4/letter/b/7993a0/32.png) [@bonitahi](https://boards.straightdope.com/u/bonitahi)\
**Post date:** [February 27, 2007, 5:29pm UTC](https://boards.straightdope.com/t/ocean-levels-rising/393618/18 "2007-02-27T17:29:25Z")

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Thanks, Slaphead. Interesting article!

My experience of seeing the water rise as much as it has in the time that it did surely baffles me.