
Why Our Intuition About Sea-Level Rise Is Wrong - dnetesn
http://nautil.us/issue/33/attraction/why-our-intuition-about-sea_level-rise-is-wrong
======
qewrffewqwfqew
Huh, yesterday's submission of the same thing got no attention at all:

[https://news.ycombinator.com/item?id=11125050](https://news.ycombinator.com/item?id=11125050)

Transcribing my comment from there:

I really want to see some papers, models or simulations to illustrate some of
these effects - starting with the gravitational influence of ice sheets on sea
level. This shouldn't be a difficult thing to illustrate numerically, but wow
it would have a big impact on how (at least I) perceive the ice sheets.

So far, I haven't been able to dig anything up - there's some prose at [1] but
nothing hard. A poster at [2]. Mitrovica's website [3] doesn't seem to have
anything. It's late, so I'll have to postpone the search for now, but here's
hoping other readers can help me :-).

[1]: [http://sealevelstudy.org/sea-change-science/whats-in-a-
numbe...](http://sealevelstudy.org/sea-change-science/whats-in-a-
number/attractive-ice-sheets)

[2]:
[http://geo.orst.edu/files/geo/Mitrovica-2009-Science.pdf](http://geo.orst.edu/files/geo/Mitrovica-2009-Science.pdf)

[3]: [http://environment.harvard.edu/about/faculty/jerry-x-
mitrovi...](http://environment.harvard.edu/about/faculty/jerry-x-mitrovica)

~~~
Clor1
If you still have some FORTRAN compiler installed you can run some simulations
yourself [1]. There are two difficulties in 'easily' solving this problem.
First of all the high level of feedback: changes in the sea level anywhere
influence all other sea levels (conserving mass!). So you cannot solve this
problem locally. Secondly, solving problems on spheres is difficult and
expensive, so most sea level models solve the problem in spherical harmonics
which is faster. (It's like the Fourier Transform, but instead of decomposing
1D signals into sines/cosines, you transform spherical shapes in more
fundamental 'blobs'. See the examples here: [2] , after the header 'Jouons un
peu avec les coeeficients harmoniques sphériques de la topography Terrestre'.
You can see the individual first 0-6 'blobs', which when added form the first
image reconstruction de l = 0 à 6. Which kind of resembles the Earth's
topography already.) Spherical harmonics have some desirable mathematical
properties and allow for quick simulations, but obviously formulating a
problem in a different domain masks the actual physics being modeled. So I
doubt you'll become wiser by studying these models...

Maybe you can be more convinced through [3] . Paolo Stocchi developed for the
SELEN FORTRAN program.

[1]
[http://www.fis.uniurb.it/spada/SELEN_minipage.html](http://www.fis.uniurb.it/spada/SELEN_minipage.html)
(nb. this requires GMT, nearly impossible to install on Windows, and needs to
be built from source in Linux. But OS X's homebrew has got it easily.)

[2] [http://www.geologie.ens.fr/~vigny/cours/chp-
gphy-2.html](http://www.geologie.ens.fr/~vigny/cours/chp-gphy-2.html)

[3] [http://www.tudelft.nl/en/current/latest-
news/article/detail/...](http://www.tudelft.nl/en/current/latest-
news/article/detail/sterke-regionale-zeespiegelstijging-tijdens-vorming-
ijskap-op-antarctica/)

------
jessaustin
Apparently the "Ice Age Effect", which has caused rotation to quicken by
making the planet more spherical, dominated over the last 20k yrs. More
recently, "polar ice sheet/glacier melting" has moved water mass from the
poles to the ocean, causing rotation to slow. It isn't clear from TFA how
these phenomena can be differentiated: in both cases ice is melting in polar
regions. However they seem to have opposite effects? I'm sure Mitrovica has a
way to tease out these opposite effects, and I'm sure they're not _exactly_
offsetting, but without those details TFA is just confusing.

~~~
sp332
The older effect is the earth getting less flat and more spherical. The newer
effect is water moving from the poles to the equator.

~~~
jessaustin
TFA:

 _What is the Ice Age Effect?

The Earth is growing more spherical because 20,000 years ago we had a lot more
ice at the poles. When ice sheets were at the poles they kind of squished the
Earth from both poles and the Earth flattened a little bit. When those ice
sheets melted, that flattening started to rebound and we’re becoming
spherical, so our spin rate should be increasing, like a ballerina or a figure
skater. The ice age correction is a speeding up of the rotation rate._

In both cases, polar ice is melting. Since it's claimed that this melting has
two opposite effects, it's unclear how to separate one effect from the other.

~~~
wiml
The timescale, I think. If the ice at the poles melts, the water immediately
(days?) distributes itself along the geoid, the earth's moment of rotational
inertia increases, it slows down. But, once the weight is taken off the poles,
the _crust_ rebounds over a period of thousands of years, making the earth
less oblate, its moment decreases, it speeds up.

~~~
jessaustin
_This_ is why I ask questions on HN. Thanks for this; I think you're probably
right. ISTM decent editing would have put this explanation in TFA.

------
peter303
Any competant geologist would tell you cant use local examples to illustrate
global effects. The Roman costaline could be under the influence of local
tectonic forces that far outweigh the global trend. That is why it takes a lot
of effort to construct accurate global trends which people constantly debate.

~~~
notahacker
And indeed there are well known "sunken cities" off the coast of Italy, which
is a pretty geologically active area...

[http://www.atlasobscura.com/places/the-sunken-city-of-
baia](http://www.atlasobscura.com/places/the-sunken-city-of-baia)

------
nabla9
In Finland the land is still rebounding from the last ice age. Land is rising
roughly 1-9 mm per year depending on where the ice melted last.

Rate of lithospheric uplift due to Postglacial Rebound:
[https://fi.wikipedia.org/wiki/Tiedosto:PGR_Paulson2007_Rate_...](https://fi.wikipedia.org/wiki/Tiedosto:PGR_Paulson2007_Rate_of_Lithospheric_Uplift_due_to_PGR.png)

------
tajen
Is he really saying that Greenland melting would lower the sea lever in the
near surroundings by 30-50m, or was there a conversion mistake?

~~~
Clor1
It's counterintuitive perhaps, but yes. The opposite also happened: during the
Antarctic glaciation (build up of ice caps), globally sea levels dropped by 60
m, but in the Antarctic region the sea level rose with 150 meters [1]. Simply
because of the huge gravitational pull towards the mass. Ice caps can be
several kilometers high...by g=Gm/r^2 and being on a sphere the effect is
quite local.

[1] [http://www.tudelft.nl/en/current/latest-
news/article/detail/...](http://www.tudelft.nl/en/current/latest-
news/article/detail/sterke-regionale-zeespiegelstijging-tijdens-vorming-
ijskap-op-antarctica/)

------
notahacker
Surprised the article had nothing to say about thermal expansion of the sea,
thought to contribute at least as much to global sea level rises as meltwater,
and something which would likely also affect local sea level dynamics.

------
netman21
Nice that he recognizes that land mass springs back after the ice sheet melts.
But it looks like he ignores the effect the weight of all that additional
water has on pushing the sea floor down. And would that increase the subsuming
of plates, thus speed up continental drift and geo activity?

