Joe Hanson (via a retweet from Gavin Schmidt) tips us to an interesting video that gives some insight into the complexity of measuring sea level. A good use of 3 minutes follows. Watch.
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I have long been confused how anybody could measure such a thing. For the most part we haven’t a clue on what goes on under the waves. I first came to this confusion during the 2009 Samoa earthquake. I remember hearing that a huge swath of real estate went vertical x amount of feet. Doesn’t this sort of displacement effect the rise in sea level. of course it does. Does someone compensate for these types of tectonic movements. Haven’t a clue. I doubt I’m the first to think of it.
Interesting. In the 1950’s I was taught tilt gravimeters reported, by actual measurements, lesser gravity toward mountains and greater toward oceans, because the continental rock was less dense than the sub ocean and the mountain was floating above more dense material with a keel extending into it.
Does anyone know which is correct?
Then add in a bunch of inaccurate tidal gauges, add in pseudo scientific alarm, pull down the odd tree on a beach on a Pacific Atoll and before you know it, you too can have an alarmist sea-level scare with which to extort money from Western governments.
Wait!
Did they say in the video that the model correctly estimates sea level to “one meter”????
How on God’s green earth do we come up with increases or, for that matter, decreases of mm/year?
Sea level? I thought obama had that handled…
And they never mentioned the gravitational effect of ofter of other celestial bodies has on sea level. That really can confound things.
You are right! Not so easy to figure it out. But then some can measure it to a single millimeter. (uh huh).
“pull down the odd tree on a beach on a Pacific Atoll”
I think you are referring to the Maldives tree, which is in the Indian Ocean.
http://www.mitosyfraudes.org/Calen7/MornerEng.html
Or, you could get your fishing gear and enjoy sea level
http://www.downeasttour.com/sea_level/sealevel-wecome.htm
But also if you continually observe at a good benchmark over a 70 year period that king and highest astronomical tides in your tectonically stable neck of the woods actually fall then you can be pretty sure there is not much to worry about.
That reminds me of a stainless steel “marker” I saw last year at the Northern end of Bondi Beach in Sydney. It looked as if it had been damaged in some way, leaning at an angle, and totally unsuitable for giving any indication of sea-level as the minor chop surged up and down. But I’m sure it would produce useful data for the idiots who placed it there, at taxpayers expense, to justify their nonsensical claims for “rising sea levels”.
Given how quickly the magnetic poles are shifting, north shifted as much during 2000-2010 as it did 1900-2000, one would guess the gravity fields shift as well. Are they continuously updating their database?
http://www.ngdc.noaa.gov/geomag/GeomagneticPoles.shtml
Check out the map at the bottom of the page, a better graphic with more recent (2010) info.
I don’t know if i am the only one but to decide to measure sea level instead of sea volume makes the things even more messy?
quite hard to define a reference and an increase in sea level is only proportional to sea volume in first approximation.
Terrific little video.
Of course, this is a gross oversimplification in the context of the climate/sea level change debate. That usually centers on the difference between the (complex) sea level and the equally complex position and movement of adjacent land masses.
Check out the Sea Height image/animation on this very useful website:
http://www.stormsurf.com/
PS.- Thanks for all the interesting articles and comments.
As a Hydrographer I have always been interested in mean sea level and the rise an fall of the tide. I have always been blown away by statements saying the sea level has risen by 3mm blah, blah. I know in the real world I have never seen measurements that good even using real time kinematic gps to measure the z component, perhaps +/- 5cm.
Measuring sea level there are so many sources of error.
Millie-metric accuracy, they must be using some form of computer modelling?
I read somewhere (Daily Telegraph I think) last week that at any one time there are 100,000 ships at sea. With increasing trade and increasing sizes of ships I wonder what effect their displacement of water has had on sea levels. Any mathematicians out there willing to do a “back of the envelope” calculation?
I agree. Terrific little video. However, no matter how you measure (or try to measure) SLR, it occurs at a rate of somewhere between 1.5 and 3 mm/year into the recorded past. There is no statitistically admissible evidence of acceleration, and at 3 mm/year (the upper bound of what has been observed we’re talking just over an inch per decade. For the record, it has increased only some 7 to 9 inches since 1870.
Perhaps it will spike on up to the 1-5 METERS of SLR that form the more extreme predictions of Hansen et. al., just as perhaps the climate will suddenly heat up by 0.5C in two years and rejoin the high climate sensitivity models. However, there is little reason to think that it will given the instrumental records of either SLR or global average surface temperature, and the high climate sensitivity models (that naturally call for maximal SLR) are also maximally failing to have predicted the essentially neutral climate of the last 17+ years.
Given the DIFFICULTY of measuring SLR, there is probably a serious apples to oranges problem underway — SLR as measured from tide gauges in 1870 is not likely to be particular comparable to gravitation-corrected, GPS corrected, satellite measurements of SLR today, any more than sunspot numbers from the 1870s can be compared to sunspot numbers today without substantial correction.
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Interesting – Joe is my wife Frederika Haskell’s nephew
Great little video.
I did learn things I didn’t know.
But one thing I did know before I watched the video is that my head is above water.
(Give or take 860 feet or so.)
Since the video brings it up…
The roundness of the Earth is often said to be ellipsoidal or an oblate spheroid.
If shrunk to the size of a billiard ball, however, the Earth is within the same roundness tolerance range of a standard billiard ball. This is even allowing for the deepest ocean trenches and the highest mountains.
Even generic of Wikepedia admits this:
In other words, if the Earth were that small, it would roll as truly as a tournament quality cue ball. I base this on the following:
Billiard ball — .127mm tolerance/57.15mm diameter = 0.00222 = 0.222%
Earth — 21km nominal tolerance/12,735km (nominal diameter) = 0.00165 = 0.165%
So, nominally, the Earth is more truly round than a billiard ball.
Now, if we take into account high and lowest points, which points are they and how high are they?
and
So we end up with this:
Chimborazo at 6384 km height yields a 12,768 km diameter.
The 6353 km deepest Arctic Ocean height yields a 12,706 km diameter.
So, for Earth that would be 12,735km nominal diameter +33km / -29km. Let’s use a 31.0 km average of the two.
That comes to 31.0km / 12,735km = 0.00243 = 0.2434%.
So, even using the most extreme individual points on Earth, the roundness tolerance for the Earth is BARELY outside the standard tolerance for tournament billiard balls – 0.24% vs 0.22%. And I guarantee that many perfectly tested billiard balls have single microscopic POINTS outside that 0.22% range – especially on the negative side, which would not be easily measured; probe tips would not be small enough. (The Marianas Trench, for example, would not show up with standard measuring equipment.)
And, again, using the nominal polar and equatorial diameters of Earth, then the Earth is well within the tolerance range for billiard balls – 0.16% vs 0.22%.
So, the idea of the Earth being oblate is technically true, but in a real-world sense it is really still round.
Either that or we need to start calling pool balls oblate spheroids.
I don’t know how the SL is measured but as a surveyor we use the latest GPS equipment and the verticle accuracy is only 1 cm at best.
The more you learn about sea level, this and Dr. Soon’s video presentation, the more you realize the sea is rising as much as the sky is falling.
one would think…..if the Mississippi river can deposit enough silt to make New Orleans….
but then, I’m sure all of the sea level rise is because of CO2….and higher temps hiding in the deep ocean