A bunch of stuff I'll bet you never knew about sea level

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.

Robert A. Taylor

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?

Ken Hall

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…

EW3

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).

AnonyMoose

“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

spangled drongo

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”.

Steve Keohane

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.

lemiere jacques

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.

Mike Smith

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.

mbur

Check out the Sea Height image/animation on this very useful website:
http://www.stormsurf.com/

mbur

PS.- Thanks for all the interesting articles and comments.

Julian Hancock

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?

Eric ah

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?

rgbatduke

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.
rgb

Pete Olson

Interesting – Joe is my wife Frederika Haskell’s nephew

Gunga Din

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:

Local topography deviates from this idealized spheroid, although on a global scale, these deviations are small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls.

WPA Tournament Table & Equipment Specifications (Effective November, 2001)
16. Balls and Ball Rack
All balls must be composed of cast phenolic resin plastic and measure 2 ¼ (+.005) inches [5.715 cm (+ .127 mm)] in diameter and weigh 5 ½ to 6 oz [156 to 170 gms]. [from http://www.wpa-pool.com/web/WPA_Tournament_Table_Equipment_Specifications%5D

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?

[from Wiki>Marianas Trench] The trench is not the part of the seafloor closest to the center of the Earth. This is because the Earth is not a perfect sphere: its radius is about 25 kilometres (16 mi) less at the poles than at the equator.[5] As a result, parts of the Arctic Ocean seabed are at least 13 kilometres (8.1 mi) closer to the Earth’s center than the Challenger Deep seafloor.

and

[from Wiki>Extreme points of Earth] The point closest to the Earth’s centre (~6,353 km (3,948 mi)) is probably at the bottom of the Arctic Ocean (greatest depth 5,450 m (17,881 ft)) near the Geographic North Pole (the bottom of the Mariana Trench is near 6,370 km (3,958 mi) from the centre of the Earth).

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.

DCA

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.

Psalmon

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.

Latitude

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

Steve Reddish

Steve Garcia says:
November 26, 2013 at 2:18 pm
“If shrunk to the size of a billiard ball, however, the Earth is within the same roundness tolerance range of a standard billiard ball.”
But the Earth is not the size of a billiard ball! The Marianas Trench does show up with our standard measuring equipment. If the Earth was shrunk to the size of a billiard ball, and we were shrunk with it, our measuring equipment would still be able to detect the Marianas Trench.
So, the point of your post escapes me??
SR

Duster

lemiere jacques says:
November 26, 2013 at 12:44 pm
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.

Sea level is at least relatively measureable. Ocean volume is far less exactly known. We don’t have anywhere near the necessary mapping precision of marine basin topography yet for one thing. Besides, even with that quality mapping, in order to estimate the volume, you would still need an estimate of sea level. Ocean basins are not graduated like measuring cups.

Pippen Kool

Eric ah “With increasing trade and increasing sizes of ships I wonder what effect their displacement of water has had on sea levels.”
2.15 billion cubic meters divided by the surface area of the oceans equals about 6 microns (0.006 mm).
http://what-if.xkcd.com/33/
But the article goes on: you don’t have to worry about that six-micron sea level drop. The oceans are currently rising at about 3.3 millimeters per year due to global warming (through both glacial melting and thermal expansion of seawater).

Alan Mackintosh

Re steve Garcia,
Is the emphasis of the spheroid not increased as the sea, being a fluid, will tend to be thrust out due to centrifugal force near the equator, and presumably drag some fluid from the poles to compensate?

Robert A. Taylor says:
November 26, 2013 at 12:09 pm
===========================================
You learned right. See: http://en.wikipedia.org/wiki/Gravity_anomaly
But that’s low resolution. At high resolution big marine volcanoes do attract the sea and raise sea level a little. –AGF

Jimbo

What I find absolutely astonishing about some Warmists is when they say stuff like:

“But the sea levels are rising!”

I then remind them that this has bee happening since the last de-glaciation. Then I tell them that the rate has flattened in the last few thousand years and there is no concrete evidence for acceleration. Sure, they show me references and I show them references to the contrary.

American Meteorological Society – Volume 26, Issue 13 (July 2013)
Abstract
Twentieth-Century Global-Mean Sea Level Rise: Is the Whole Greater than the Sum of the Parts?
………..The reconstructions account for the observation that the rate of GMSLR was not much larger during the last 50 years than during the twentieth century as a whole, despite the increasing anthropogenic forcing. Semiempirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of the authors’ closure of the budget is that such a relationship is weak or absent during the twentieth century.
http://dx.doi.org/10.1175/JCLI-D-12-00319.1
Journal of Coastal Research – 2011
It is essential that investigations continue to address why this worldwide-temperature increase has not produced acceleration of global sea level over the past 100 years, and indeed why global sea level has possibly decelerated for at least the last 80 years.
http://www.jcronline.org/doi/abs/10.2112/JCOASTRES-D-10-00157.1

Sea level rise is not an easy one to measure by any measure.

Jimbo

Pippen Kool says:
November 26, 2013 at 2:49 pm
…………………
But the article goes on: you don’t have to worry about that six-micron sea level drop. The oceans are currently rising at about 3.3 millimeters per year due to global warming (through both glacial melting and thermal expansion of seawater).

Pippen, have you wondered what else might cause sea levels to rise?

Global groundwater depletion leads to sea level rise
Large-scale abstraction of groundwater for irrigation of crops leads to a sea level rise of 0.8 mm per year, which is about one fourth of the current rate of sea level rise of 3.3 mm per year.
http://www.un-igrac.org/publications/422

Here is the study.

Abstract – 26 OCT 2010
Global depletion of groundwater resources
[1] In regions with frequent water stress and large aquifer systems groundwater is often used as an additional water source. If groundwater abstraction exceeds the natural groundwater recharge for extensive areas and long times, overexploitation or persistent groundwater depletion occurs. Here we provide a global overview of groundwater depletion (here defined as abstraction in excess of recharge) by assessing groundwater recharge with a global hydrological model and subtracting estimates of groundwater abstraction. Restricting our analysis to sub-humid to arid areas we estimate the total global groundwater depletion to have increased from 126 (±32) km3 a−1 in 1960 to 283 (±40) km3 a−1 in 2000. The latter equals 39 (±10)% of the global yearly groundwater abstraction, 2 (±0.6)% of the global yearly groundwater recharge, 0.8 (±0.1)% of the global yearly continental runoff and 0.4 (±0.06)% of the global yearly evaporation, contributing a considerable amount of 0.8 (±0.1) mm a−1 to current sea-level rise.
http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/abstract

It’s not as simple as you previously thought!

Jimbo

Will groundwater abstraction get worse if we don’t act now?

BBC – 20 April 2012
Scientists say the notoriously dry continent of Africa is sitting on a vast reservoir of groundwater.
They argue that the total volume of water in aquifers underground is 100 times the amount found on the surface.
http://www.bbc.co.uk/news/science-environment-17775211

The abstract of the paper is here.

Steve Reddish

Since tidal gauges all around the Baltic Sea have displayed isostatic rebound of the coastline, is it not safe to assume that entire basin is on the rise, displacing seawater out into the North Atlantic? Likewise, for most of northeastern Canada? These are just two examples of how rising or falling sea bottoms around the world would have a tremendous effect upon global sea level. How could any human caused SLR, if there is such a thing, even be determined?
Since coastlines likewise rise and fall, all that really matters now that continental ice sheets of North America and Eurasia are melted, is the rise or fall of local sea level. Global sea level rise is swamped by local sea level changes.
As those areas that are subsiding have been doing so since before industrialization and people have been able to cope with the local rise of the sea, this is an artificial crisis created to bolster that other artificial crisis – CAGW.
SR

David in Cal

Very nice video. Of course, from the standpoint of CAGW, the key isn’t sea level, but sea level change.

“Brian Cooper says: November 26, 2013 at 12:06 pm
… I doubt I’m the first to think of it.”

You just might be!

Mike Rossander

Robert A. Taylor at 12:09 pm above asks about tilt gravimeters showing lesser gravity toward mountains and the apparent contradiction with the video.
Both are true. The difference is in where you take the measurement. The experiments in the 1950s were made based upon measurements relative to the surface. Those measurements would correctly show that continental rock is less dense (and thus has less gravitic effect).
The video’s calculations assume an external orbit uniformly above both the mountains and oceans. From that perspective, the less-dense mountain sits in a depression in the denser crust. But the ocean also sits in a depression in the crust. The sum of mountain plus crust is greater than the sum of ocean plus crust, leading to the video’s “puddling” of gravity around mountains.

Hmm We want to know if the sea level is rising and how much, so why measure it all over different places, if we took just three measurements in places that were not affected by gravity, isostatic rebound etc, like one in the Atlantic, one in the Pacific and one in the Indian ocean. wouldn’t that be more representative of true sea level rise.

There is also the tidal effect of extra-terrestrial bodies such as the moon and the sun (and the great planets when they are in alignment.
What about erosion. When I visited the ancient city of Troy, which was a port a few thousand years ago I found it is now 14 kilometers from the sea. Apparently this is because the river that was next to Troy has dumped so much sediment from the mountains in Turkey into the sea at that point. It makes you wonder how much sea level rise is due to sedimentary increases. This would be accelerating as mankind develops cities and towns. Another source is deliberate dumping of waste into the ocean. The OK Tedi mine in Papua New Guinea comes to mind as 80 million tons of waste was dumped each year into the local river which in turn would have taken most of that to the sea.

Curt

The video, while raising many valid points, is only scratching the surface (sorry if that sounds like a pun) of the problems in trying to measure sea level changes. Prevailing weather patterns of high and low pressure, plus general wind direction and magnitude, can lead to significant changes in sea level at various locations. For instance, California levels are quite a bit higher during El Nino periods.
Geological effects include isostatic rebound at high latitudes, seismic movement, and human induced pumping of groundwater and/or petroleum.
Satellite measurements bring in a host of other issues. Fundamentally, they measure distance from the satellite to the sea surface by measuring the speed-of-light delay in bouncing a laser off the surface. But the speed of light varies with atmospheric conditions such as temperature and humidity that are not that precisely known.
The fundamental resolution of the satellite measurements is far above the annual trend they claim to measure. I believe it is only recently that this base resolution has gone below 1 meter. It is only by averages of averages of averages that can claim the precision to measure the trends.
Also, the satellite altitude is not that precisely known either. All of the gravitational variations that the video mentions do affect the satellite’s trajectory at this level of precision, as well as density variations in the very tenuous, but still real, atmosphere, there. So the measurements must all be calibrated against ground measurements.
Many other issues as well…

Speaking as sailor, I’ve yet to see a change to the lowest or highest astronomical tide measurements on any nautical chart. Nor have I managed to find detail that any have ever changed as a result of climate change.
http://thenewaustralian.org/?p=10285
To misquote Joe Strummer; London ain’t drowning and I….. live by the river!

RoHa

There is no problem with finding sea level. Go down to the beach and find the sea. (Look for something big, wet, and moving slightly. No, not that. Bigger, and made of water.) Found it? Now look at the top of the sea. Sea level is where to top of the sea is.

mbur

@Brent Walker “What about erosion. When I visited the ancient city of Troy, which was a port a few thousand years ago I found it is now 14 kilometers from the sea. Apparently this is because the river that was next to Troy has dumped so much sediment from the mountains in Turkey into the sea at that point. It makes you wonder how much sea level rise is due to sedimentary increases. This would be accelerating as mankind develops cities and towns. Another source is deliberate dumping of waste into the ocean.”
Maybe that’s part of the Anthropogenic part of it.People are always changing (i.e. Port Building, Levees,Dredging,Canal Building) their environment .But,i think that natural forces dominate the system.My comment on another article:http://wattsupwiththat.com/2013/11/26/real-pollution-not-carbon-pollution-increases-storm-clouds/#comment-1484975 ,IMO,says that also.What i mean is that the high pressure(more dense) cold weather(air) system causes an inversion layer where it pushes down on the lower level emissions.Warming is not caused by the anthropogenic forcing because of the natural atmosphere phenomena.Well,that’s what i’m thinking,Who really knows?
Thanks for the interesting articles and comments.

Sea Level Trends – NOAA Tides & Currents, at http://tidesandcurrents.noaa.gov/sltrends/sltrends.html might be of interest.
[Very interesting NOAA reference page, Thank you. Mod]

lee

Sea level rise due to subsidence seems incongruous.

Peter Miller

And to top everything, we rely on sea level measurements, using the speed of light, from satellites in decaying ellipsoid orbits.
Then there are also these factors to consider: wave heights, currents, tides, winds, isostatic rebound, tectonic movements and seasonal changes in ocean temperature.
And we believe we can measure changes in sea levels to an accuracy of 0.01mm!?!

What about erosion. When I visited the ancient city of Troy, which was a port a few thousand years ago I found it is now 14 kilometers from the sea. Apparently this is because the river that was next to Troy has dumped so much sediment from the mountains in Turkey into the sea at that point.

eo

The video missed one important aspect of sea level which is the rotational speed of the earth. The earth moves from west to east. Land mass are fixed to the earth while the sea being liquid is mobile. Long land mass such as the north and south america practically slams the water in the Atlantic Ocean and in the process increases the sea level and in the process creates a slight vacuum on the Pacific Ocean side reducing the sea level. The separation could be very short as in the Panama canal, it could have the same gravitational force, same force of attraction from the land mass within this small area, but the sea level could be different on each side of land mass.

ColdinOz

Psalmon says: “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.”
And according to the IPCC (and no one else) that is very very fast.

bertief

I love Minute Physics.