5 ms·

How much water is there on the Earth?

41 points by AliCollins 11y ago

cfontes 11y ago
Every time I see this it amazes me how little rivers represent of the whole fresh water available and how much Antarctica does.
- frandroid 11y ago
  Let's melt the whole thing!
- logfromblammo 11y ago
  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.
  - cjensen 11y ago
    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.
    - mturmon 11y ago
      In addition, the parent comment has omitted groundwater. Good current estimates for groundwater volume (in the OP, http://water.usgs.gov/edu/earthhowmuch.html http://water.usgs.gov/edu/earthhowmuch.html) are very close to icecap volume (24e6 km^3). And we are pumping this groundwater (~700 km3/yr as of 2000, and increasing [ * ]), which raises water levels and at the same time lowers land elevation as ground subsides. Depending on the Hollywood disaster scenario, that could play a role. Atmospheric water, on the other hand, is a rounding error in this context. [*]: See fig. 3 of http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full
    - logfromblammo 11y ago
      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 11y ago
exacube 11y ago
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?)
- mturmon 11y ago
  Groundwater is the resource we are depleting, because everything else runs in a circle. Here is a good worldwide groundwater study, based partly on gravity inversions from the GRACE twin satellites: http://www.jpl.nasa.gov/news/news.php?feature=4626 http://www.jpl.nasa.gov/news/news.php?feature=4626 The conclusion is: Probably the most at-risk aquifer (based on people affected and severity) is in the Gangetic plain in northern India. There are also critically threatened aquifers in the Arabian peninsula, southeast China, and our own Sacramento Valley. This conclusion is supported by other hydrological modeling groups as well (e.g., the very highly-cited, but older, http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full)
- hugh4 11y ago
  Depends what you mean by "sustainable". There's far more fresh water falling on the US than is being "used". Go look at any river. Gazillions of litres of fresh water per minute just flowing out to sea and getting salty. Then imagine the number of rivers doing that. Of course damming every river and diverting it to other uses is impractical and would have bad effects on various ecosystems, but there's a lot of spare fresh water just running out to sea. And then remember that the vast majority of the water that we "use" is not getting split into hydrogen and oxygen, it's staying molecular water and it's hanging around.
  - jofer 11y ago
    The problem is spatial distribution, not amounts. Saying we have far more than is being used is true, but misses the forest for the trees. Some areas have lots of water resources, some don't. Unfortunately our water usage is almost inversely correlated to water resource availability. Arid soils are _incredibly_ productive when irrigated, so we grow a lot of crops in the desert (or semi-desert). Also, people like to live in dry, sunny places. Dry, sunny places usually don't have abundant water resources.

41 points by AliCollins 11y ago

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

frandroid 11y ago
Let's melt the whole thing!
logfromblammo 11y ago
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.
- cjensen 11y ago
  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.
  - mturmon 11y ago
    In addition, the parent comment has omitted groundwater. Good current estimates for groundwater volume (in the OP, http://water.usgs.gov/edu/earthhowmuch.html http://water.usgs.gov/edu/earthhowmuch.html) are very close to icecap volume (24e6 km^3). And we are pumping this groundwater (~700 km3/yr as of 2000, and increasing [ * ]), which raises water levels and at the same time lowers land elevation as ground subsides. Depending on the Hollywood disaster scenario, that could play a role. Atmospheric water, on the other hand, is a rounding error in this context. [*]: See fig. 3 of http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full
  - logfromblammo 11y ago
    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 11y ago

exacube 11y ago

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?)

mturmon 11y ago
Groundwater is the resource we are depleting, because everything else runs in a circle. Here is a good worldwide groundwater study, based partly on gravity inversions from the GRACE twin satellites: http://www.jpl.nasa.gov/news/news.php?feature=4626 http://www.jpl.nasa.gov/news/news.php?feature=4626 The conclusion is: Probably the most at-risk aquifer (based on people affected and severity) is in the Gangetic plain in northern India. There are also critically threatened aquifers in the Arabian peninsula, southeast China, and our own Sacramento Valley. This conclusion is supported by other hydrological modeling groups as well (e.g., the very highly-cited, but older, http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full)
hugh4 11y ago
Depends what you mean by "sustainable". There's far more fresh water falling on the US than is being "used". Go look at any river. Gazillions of litres of fresh water per minute just flowing out to sea and getting salty. Then imagine the number of rivers doing that. Of course damming every river and diverting it to other uses is impractical and would have bad effects on various ecosystems, but there's a lot of spare fresh water just running out to sea. And then remember that the vast majority of the water that we "use" is not getting split into hydrogen and oxygen, it's staying molecular water and it's hanging around.
- jofer 11y ago
  The problem is spatial distribution, not amounts. Saying we have far more than is being used is true, but misses the forest for the trees. Some areas have lots of water resources, some don't. Unfortunately our water usage is almost inversely correlated to water resource availability. Arid soils are _incredibly_ productive when irrigated, so we grow a lot of crops in the desert (or semi-desert). Also, people like to live in dry, sunny places. Dry, sunny places usually don't have abundant water resources.