[Coral-List] sea level rise

Tue Mar 1 19:38:04 UTC 2022

I've just had a website recommended to me for sea level rise.   Anyone who
wants to see the trends in global sea level rise can go to the University
of Hawaii Sea Level Center website.  https://uhslc.soest.hawaii.edu/
This is an incredible website and data portal for anyone working on coral
reefs and sea levels.  They have great world maps showing SLR trends based
on individual decades (2002-2021, etc plus other time frames (1992 to
present) since satellite altimetry came into play. You can also see the
patterns with and without the global sea level trend. Without the globe
trend included, you can see the local drivers in action.
       At the home page, it presents a global map for sea level rise, based
on satellite and tide gauges.  Note the colors and consult the color bar
below the graph.  Notice that some places have actually had negative sea
level rise for the period of time covered!!!  This is not an error, it is
real.  Note in the text on the left that it says that sea levels are
influenced by winds.  Winds push the water in the direction that they
blow.  So, for instance, the "Walker Circulation" over the Pacific normally
blows westward along the equator, and that piles water up in the western
Pacific, which may be around 20 cm higher than in the eastern Pacific.
During El Nino, those winds die, and the water goes back to resting
position and the western Pacific can drop 20 cm.  Notice that this effect
is large compared to the differences in the map, which are on the order of
a few millimeters.  And that deviations from the average sea level rise
tend to be fairly short-lived, I'll bet.  If they didn't, there would be
places eventually that were meters or more above or below the mean, and the
winds can't produce that differences that large.  I'll just add here that I
saw in my notes that average world sea level rise is now about 4.9 mm a
year, I had said 4.5, my apologies.  Average.
       I recommend people look at the University of Hawaii website for
accurate and up to date sea level and tide information.  They have an
absolutely wonderful product called "station explorer" under their
"products" menu.  Station Explorer provides up to date (usually within a
day or two) of tide readouts from all the tide gauges in the Univ Hawaii
sea level center system, and tells you the residuals - how much the actual
differs from the predicted.  It is almost real time analysis of whether the
tides (and sea level) are higher or lower than average.  Plus they have
datum information and a lot more.  Coral reef scientists should know about
this.
       If you think about it, 5 mm is a difference you CANNOT see with your
eyes, because it is tiny compared to tides (not to mention you'd have to
wait a year to see the difference). The smallest tides are larger than the
largest local sea level rises, by a wide margin.  Add waves are always
larger than these sea level rises.  Pretty amazing that they can filter
those out to detect sea level rise.  In addition, the satellites can detect
undersea mountains (seamounts) by the gravity their mass exerts on the sea
surface, making the sea surface slightly higher over seamounts.  Seamounts
that were not known from sonar searches have been discovered that way, I
believe.   And a last point, and that is that the earth is not a perfectly
sphere, it is wider at the equator than at the poles.  This is due to the
rotation which produces centrifugal force, which partly balances gravity,
and so the oceans and even land and the sea floor all are higher near the
equator.  This effect is on the order of 1/300 of the earth radius, about
21 km, a tiny fraction of the world's diameter, but it is much larger than
these other effects.  The world's highest mountain is often said to be Mt.
Everest in Nepal, and indeed it reaches the highest point above sea level.
However, the world's TALLEST mountain is Mauna Kea in Hawaii.  And the
world's mountain that reaches the farthest from the center of the earth is
apparently in South America near the equator, due to this effect.  Lots
about this including an explanation of why earth deviates from a perfect
sphere on the Wikipedia page "Earth radius."
     By the way, one of my pet peves is flat maps of the world.  The world
is NOT flat (in spite of what the Flat Earthers say, Wikepedia has a page
explaining all the evidence demonstrating it is not flat.).  The world is
much better represented by a globe, and if you have to put it on a flat
surface, a series that looks like photos of the rotated globe is far closer
to reality.  Which you can see in the famous photo called "Earthrise" that
astronauts took from the moon, of the earth, which looks like a sphere
because it is very close to being a sphere.  We get ideas from flat maps
that are totally untrue.  Such as that if you fly east from the US east
coast you will have the shortest route to Europe.  Nope, shortest route is
up along the east coast of Canada, which points almost straight towards
Europe.  Fly from the west coast of the US to Asia by flying west?  No
airline flies that way without stopping, it is vastly shorter to take a
great circle route, the shortest route, which takes you north to the
southern shores of Alaska, and then down the east coast of Asia to your
destination.  A straight line on the surface of a globe but a wildly curved
one on a flat map, the globe is correct.  I can't get that into my head
because of seeing the misleading flat maps all my life, but look at a
globe, and you can see it clearly.
     We scientists need to be representing things accurately, not using
popular but highly distorted and misleading flat maps.  Flat maps work fine
for tiny areas, they are off by tiny amounts.  But not large maps.  No
airline in the world flies far based on flat maps, their flights would take
longer and use up more fuel, costing them money that takes money out of the
pockets of their owners, and they would lose customers by having longer
flights than their competitors and either have to charge higher prices or
lose money, and quickly be out of business.  Rather like Darwinian
evolution, there are no airlines left that do that (if there ever were
any), it is heavily selected against.

     Cheers, Doug

-- 
Douglas Fenner
Lynker Technologies, LLC, Contractor
NOAA Fisheries Service
Pacific Islands Regional Office
Honolulu
and:
Coral Reef Consulting
PO Box 997390
Pago Pago, American Samoa 96799-6298  USA

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now.
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