
How much water is there on the Earth? - AliCollins
http://water.usgs.gov/edu/earthhowmuch.html
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exacube
Can someone make a comment on the sustainability of our current water
consumption, in terms of the US, other parts of the world, and the world
itself?

If we are not living sustainably, should we expect more investment across the
world on things like desalination plants (I understand that desalination is
really energy-expensive currently, but will that change by much?)

~~~
Retric
The best example is the Ogallala Aquifer. "At places, the water table was
measured to drop more than five feet (1.5 m) per year at the time of maximum
extraction."
[https://en.wikipedia.org/wiki/Ogallala_Aquifer](https://en.wikipedia.org/wiki/Ogallala_Aquifer)
So it's a huge resource of fresh water that's being drained much faster than
it's replacement rate. But, building deeper wells is cheap and there is little
value in untapped water so it's reasonable for now.

However, long term it's a finite resource. At the same time a lot of fresh
water ends up in the ocean so desalination needs to compete with simply moving
water around.

Locally when transport is more expensive than desalination it may be useful,
but long term it's a balancing act between moving water a thousand miles+,
desalinating locally, or increasing efficiency.

PS: In theory these Aquifers could be used as a cheap form of transport, but
when any well get's to tap the water for 'free' who pays for it becomes a
major issue.

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jofer
>In theory these Aquifers could be used as a cheap form of transport...

For what it's worth, an aquifer isn't an underground river... It's solid rock.
What would you be transporting?

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Retric
Water, it's fine if it takes 10 years to move water from point A to point B as
long as you don't need to build and maintain a pipe. Also, they are not solid
rock or water, it's more like gravel with water in-between but the flow rate
can get fairly high due to size even if the flow speed is very low. 1 mile per
day is slow but * 365 days * 10 years that's a long way.

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cfontes
Every time I see this it amazes me how little rivers represent of the whole
fresh water available and how much Antarctica does.

~~~
logfromblammo
But on the other hand, even if every non-floating glacier and snowpack melted
and flowed into the ocean, that would only increase its mass by 2%. Combine
that with the maximum thermal expansion from -4 C to 50 C, which would
increase volume by 1.5% (and kill us all), and the highest the ocean could
possibly rise above its current level is about 10m.

The highest storm surge ever recorded was about 15m. The tsunami waves from
the destruction of Krakatoa ran up to 50m tall.

So now you are armed with the knowledge you need to scoff haughtily at
scientifically inaccurate Hollywood movies. For further reference, 1 WTC is
541m tall, Empire State Building is 443m at the top of the antenna, BoA tower
is 366m, Chrysler and Times are both 319m. NYC has more than 200 buildings
over 150m. The Statue of Liberty is about 93m.

So when you see that scene in A.I. (2001) where the arm and torch of Liberty
barely protrudes above the surface of the ocean, you can say, "Ha! The planet
doesn't have that much water on it! Even on an ice-free Earth, and NYC in the
heart of a hurricane storm surge the same size as the worst in recorded
history, the water wouldn't even reach her big toe!" Waterworld (1995) is
right out--the premise is scientifically impossible. You would have to
systematically throw comets into Earth capture trajectories with a total mass
of about 3x10^21 kg, adding double the current mass of all water on Earth, or
about 1/2000 the current mass of the Earth. That's about the same amount as
all the water on Europa.

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cjensen
The math: (1) the linked article says there is 24e6 km3 of water in ice caps,
glaciers, and permanent snow. (2) Area of Oceans from Wikipedia is 360e6 km2.
(3) The statue of liberty is about 93m, (Base is 46m, Statue is 47m)

Division gives 0.066km of sea level rise if all of item #1 melts into the
oceans, which is 66 meters. (In a more complex model, warmer atmosphere would
adsorb some of it as increased absolute humidity.)

For the Statue of Liberty, that's enough to cover the entire base plus ~40% of
the statue. The movie AI is wrong, but it's a lot closer to correct than the
"10m" you quote.

~~~
logfromblammo
Rise in ocean level increases the surface area of the ocean, because most
coastlines are not vertical cliffs. What is the average slope of dry land
between 0m and 10m above sea level?

Reviewing the math, I concede that I may have been off by a factor of 4. But
not 6.6!

The estimate for the amount of water needed to cover all land but the summit
of Everest is easier, since the upper limit is an ellipsoidal shell 8848m
thick. That's about 4.5x10^9 km^3, which is 3.4 times the current ocean
volume. Then it's just a matter of estimating how much of that volume is
already full of solid matter, and reducing the amount of water needed by the
rock that is already there.

~~~
cjensen
Indeed the model I used was simplistic.

I doubt Ocean area would change much with sea level rise on a percentage
basis.

A more realistic model would have to try to make a better guess at the amount
of permanent ice. The South Polar ice cap isn't going away completely because
(1) with a six-month darkness, it will remain cold enough to hold ice (2)
enormous storms in the Southern Ocean will generate plenty of precipitation
over the pole.

