Wednesday, November 27, 2013

Sea level for dummies - a video by MinutePhysics

Sou | 9:48 PM Go to the first of 4 comments. Add a comment

Update - I've added a longer sea level video below - from a Melbournite Melburnian :) - Jerry Mitrovica now at Harvard University . (h/t metzomagic)

This makes a change.  In recent months Anthony Watts has posted several articles claiming that over coming decades, seas cannot possibly rise any faster than they did last century.  This is despite the fact that Earth will continue to get hotter as we keep using our precious air as a garbage dump for waste greenhouse gases.  He thinks that ice doesn't melt as it heats.  He's a bit of a plonker is Anthony Watts.

Today Anthony has done something special.  He's posted a video explaining sea level.  Not rising sea level.  Just about sea level itself. (Archived here.)

Anthony got the video via Gavin Schmidt of NASA and realclimate.org, who retweeted it from Joe Hanson who saw it in a tweet from Henry Reich @minutephysics.  Isn't Twitter wonderful :)

I'll resist the temptation to make any snide remarks about cartoons being the best format for WUWT readers and just post the video.  (Oops - did I write that out loud?) It is very good.

Next time you come across someone who wonders how seas can be rising at different paces at different times in different places, this explains it rather nicely and more besides.


Courtesy of metzomagic in the comments - thanks! It's a longer video on sea level.  Jerry Mitrovica debunks some common denier myths.

From the WUWT comments

Eric ah may not have any conception of just how vast the ocean is compared to the size of a supertanker and says:
November 26, 2013 at 1:00 pm
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?

Pippen Kool responds and says:
November 26, 2013 at 2:49 pm
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).
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).

stuart L might not know about satellite measures and thinks three dipsticks might be enough to monitor changes in sea level.  He says:
November 26, 2013 at 4:39 pm
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.

Peter Miller doesn't know anything about how sea level change is worked out either. Or how by taking readings via satellite sweeps and making various comparisons and corrections with various checks and balances, the change can be measured with great precision.  And he's wrong with his 0.01 mm.  At the University of Colorado, the uncertainty in annual global mean sea level trend is +/- 0.4 mm.  The precision is to one decimal place not two.  (The trend is currently stated as being 3.2 mm +/- 0.4 mm / year.  He says:
November 26, 2013 at 11:49 pm
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!?!

Various other people comment about what is not covered by the video, sometimes with reasonable observations and sometimes with less reasonable (archived here).  No-one seems to be finding much fault with it though, which makes a nice change for WUWT.


  1. Anyone here who hasn't yet... really, REALLY wants to watch this lecture by sea level expert Jerry Mitrovica of Harvard. It fleshes out a lot of the concepts briefly touched upon in that cartoon short:

    The Fingerprints of Sea Level Change

    After you watch that, you'll definitely think differently about sea level than you did before. Fascinating.

    1. Wonderful. Thanks metzomagic. I've added it to the article.

    2. Melbournite? Melbournian, my Wangaratta Wahine...

    3. Oops - sorry about that, Anonymous. Spending too much time in Yacka-bloody-dandah :)


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