We could really use a new Aral sea, but intuitively I’d expected that this would be a tiny dent in the depth of the oceans. So, to the maths:
Wikipedia claims that from 1960 to 1998 the volume of the Aral sea dropped from its 1960 amount of 1,100 km^3 by 80%.
I’m going to give that another 5% for more loss since then, as the South Aral Sea has now lost its eastern half enitrely.
This gives ~1100 * .85 = 935km^3 of water that we’re looking to replace.
The Earth is ~500m km^2 in surface area, approx. 70% of which is water = 350m km^2 in water.
935 km^3 over an area of 350m km^2 comes to a depth of 2.6 mm.
This is massively larger that I would have predicted, and it gets better. The current salinity of the Aral Sea is 100g/l which is way higher than that of seawater at 35g/l, so we could pretty much pump the water straight in still with net environmental gain. Infact this is a solution to the crisis that has been previously proposed, although it looks like most people would rather dilute the seawater first.
To acheive the desired result of 1 inch drop in sea level, we only need to find 9 equivalent projects around the world. Sadly, the only other one I know of is Lake Chad, which is significantly smaller than the Aral Sea. However, since the loss of the Aral Sea is due to over-intensive use of the water for farming, the gives us an idea of how much water can be contained onland in plants: I would expect that we might be able to get this amount again if we undertook a desalination/irrigation program in the Sahara.
Dead Sea and Salton Sea leap to mind as good projects.
Also could we store more water in the atmosphere? If we just poured water into a desert like the Sahara, most of it would evaporate before it flowed back to the sea. This would seem to raise the average moisture content of the atmosphere. Sure eventually it gets rained back down, but this would seem to be a feature more than a bug for a world that keeps looking for more fresh water. Indeed my mind is currently inventing interesting methods for moving the water around using purely the heat from the sun as an energy source.
However, since the loss of the Aral Sea is due to over-intensive use of the water for farming, the gives us an idea of how much water can be contained onland in plants
Isn’t it more of an indication of how much water can be contained in the Aral Sea basin? The plants don’t need to contain all of the missing Aral Sea water at once, they just need to be watered faster than the Sea is being refilled by rainfall. How much water does rainfall supply every year, as a percentage of the Sea’s total volume?
I recommend googling “geoengineering global warming” and reading some of the top hits. There are numerous proposals for reducing or reversing global warming which are astoundingly less expensive than reducing carbon dioxide emissions, and also much more likely to be effective.
To your direct question about storing more water on land, this would be a geoengineering project. Some straightforward approaches to doing it:
Use rainfall as your “pump” in order to save having to build massive energy using water pumps. Without any effort on our part, nature natually lifts water a km or more above sea level and then drops it, much of it dropped onto land. That water generally is funneled back to the ocean in rivers. With just the constructino of walls, some rivers might be prevented from draining into the ocean. Large areas would be flooded by the river, storing water other than in the ocean.
Use gravity as your pump. THere are many large locations on earth than are below sea level. Aquifers that took no net energy to do pumping could be built that would essentially gravity-feed ocean water into these areas. These areas can be hundreds of meters below sea level, so if even 1% of the earth’s surface is 100 m below sea level, then the ocean’s could be lowered by a bit more than 1 m by filling these depressions with ocean water.
Of course either one of these approaches will cause massive other changes, although probably in a positive direction as far as climate is concerned. More water surface on the planet should mean more evaporation of water which reates more clouds which reflects more energy from the sun, lowering the heating of the earth. But of course a non-trivial analysis might yield a rich detail of effects worth pondering.
In the past features like the Salton sea and the Dead sea have been filled by fresh-water rivers, essentially meaning that rain was used as the pump to fill them. The demand for fresh water has stopped these features from being filled. It seems to me that an aquifer to refill these features with salt water from the ocean would be relatively benign in impact, since in nature these features have been fuller of salt water in the past, and so the impact of that water might be blessed by humanity as “natural” instead of cursed by humanity as “man made.”
Where does the water go? Assuming you want to reduce sea level by a 1⁄2 inch using this mechanism, you have to do the equivalent of covering the entire ETA: land area of earth in a full inch of water (what’s worse, seawater; you’d want to desalinate it). Even assuming you can find room on land for all this water and the pump capacity to displace it all, what’s to stop it from washing right back out to sea? Some of it can be used to refill aquifers, but the capacity of those is trivial next to that of the oceans. Some of it can be stored as ice and snow, but global warming will reduce (actually, has already quite visibly reduced) land glaciation; even if you can somehow induce the water to freeze, that heat you extract from it will have to go somewhere and unless you can dump it out of the atmosphere entirely it will just contribute to the warming. The rest of the water will just flood the existing rivers in its mad rush to do what nearly all continental water is always doing anyhow: flowing to sea.
Clearly, the solution is to build a space elevator and ship water into orbit. We lower the sea levels, the water is there if we need it later, and in the meantime we get to enjoy the pretty rings.
Now I’m curious how much energy it would take to set up a stable ring orbit made of ice crystals for Earth, or if that would be impossible without stationkeeping corrections.
I think it would depend on the orbit? Obviously it would need to be in an orbit that does not collide with our artificial satellites, and it would need to be high enough to make atmospheric drag negligible, but that leave a lot of potential orbits. I don’t think of any reason ice would go away with any particular haste from any of them, but I’m not an expert in this area.
Orbital decay aside, why might ice (once placed into an at-the-time stable orbit) not survive?
I would think it would lose heat to space fast enough, but maybe not. I know heat dissipation is a major concern for spacecraft, but those are usually generating their own heat rather than just trying to dump what they pick up from the sun. What would happen to the ice / water? It’s not like it can just evaporate into the atmosphere...
It’s not like it can just evaporate into the atmosphere...
Vapour doesn’t need an atmosphere to take it up. Empty space does just as well.
So, how long would a snowball in high orbit last? Sounds like a question for xkcd. A brief attempt at a lower bound that is probably a substantial underestimate:
How much energy has to be pumped in per kilogram to turn ice at whatever the “temperature” is in orbit into water vapour? Call that E. Let S be the solar insolation of 1.3 kW/m^2. Imagine the ice is a spherical cow, er, a rectangular block directly facing the sun. According to Wikipedia the albedo of sea ice is in the range 0.5 to 0.7. Take that as 0.6, so the fraction of energy retained is A = 0.4. The density of ice is D = 916.7 kg/m^3. Ignore radiative cooling, conduction to the cold side of the iceberg, and time spent in the Earth’s shadow, and assume that the water vapour instantly vanishes. Then the surface will ablate at a rate of SA/ED m/s. Equivalently, ED/86400SA days per metre.
For simplicity I’ll take the ice to be at freezing point. Then:
E = 334 kJ/kg to melt + 420 kJ/kg to reach boiling point + 2260 kJ/kg to boil = 3014 kJ/kg.
For a lower starting temperature, increase E accordingly.
3014 916.7 / (86400 1.3 * 0.4) = 61 days per metre. Not all that long, but meanwhile, you’ve created a hazard for space flight and for the skyhook.
I suspect that ignoring radiative cooling will be the largest source of error here, but this isn’t a black body, so I don’t know how closely the Stefan-Boltzmann law will apply, and I haven’t calculated the results if it did. (ETA: The black body temperature of the Moon is just under freezing.)
(ETA: fixed an error in the calculation of E, whereby I had 4200 instead of 420 kJ/kg to reach boiling point. Also, pasting in all the significant figures from the sources doesn’t mean this is claimed to be anything more than a rough estimate.)
This is vacuum—all liquid water will boil immediately, at zero Celsius. Besides I’m sure there will be some sublimation of ice directly to water vapor.
In fact, looking at water’s phase diagram, in high vacuum liquid water just doesn’t exist so I think ice will simply sublimate without the intermediate liquid stage.
Here is the proper math. This is expressed in terms of ice temperature, though, so we’ll need to figure out how much the solar flux would heat the outer layer of ice first.
One possibility would be to replace the ice caps by hand. Run a heated pipeline from the ocean to the icecaps, pump water there, and let it freeze on its own. I don’t know how well that would work, and I suspect you’re better off just letting sea levels rise. If you need the land that bad, just make floating platforms.
Edit: Replace “ice caps” with “Antartica”. Adding ice to the northern icecap, or even the southern one out where it’s floating, won’t alter the sea level since floating objects displace their mass in water.
Well, this is not pumping, but it might be much more efficient: As I understand, the polar ice caps are in an equilibrium between snowfall and runoff. If you could somehow wall in a large portion of polar ice, such that it cannot flow away, it might rise to a much higher level and sequester enough water to make a difference in sea levels. A super-large version of a hydroelectric dam, in effect, for ice.
It might also help to have a very high wall around the patch to keep air from circulating, keeping the cold polar air where it is and reduce evaporation/sublimation.
Would it be possible to slow down or stop the rise of sea level (due to global warming) by pumping water out of the oceans and onto the continents?
We could really use a new Aral sea, but intuitively I’d expected that this would be a tiny dent in the depth of the oceans. So, to the maths:
Wikipedia claims that from 1960 to 1998 the volume of the Aral sea dropped from its 1960 amount of 1,100 km^3 by 80%.
I’m going to give that another 5% for more loss since then, as the South Aral Sea has now lost its eastern half enitrely.
This gives ~1100 * .85 = 935km^3 of water that we’re looking to replace.
The Earth is ~500m km^2 in surface area, approx. 70% of which is water = 350m km^2 in water.
935 km^3 over an area of 350m km^2 comes to a depth of 2.6 mm.
This is massively larger that I would have predicted, and it gets better. The current salinity of the Aral Sea is 100g/l which is way higher than that of seawater at 35g/l, so we could pretty much pump the water straight in still with net environmental gain. Infact this is a solution to the crisis that has been previously proposed, although it looks like most people would rather dilute the seawater first.
To acheive the desired result of 1 inch drop in sea level, we only need to find 9 equivalent projects around the world. Sadly, the only other one I know of is Lake Chad, which is significantly smaller than the Aral Sea. However, since the loss of the Aral Sea is due to over-intensive use of the water for farming, the gives us an idea of how much water can be contained onland in plants: I would expect that we might be able to get this amount again if we undertook a desalination/irrigation program in the Sahara.
Dead Sea and Salton Sea leap to mind as good projects.
Also could we store more water in the atmosphere? If we just poured water into a desert like the Sahara, most of it would evaporate before it flowed back to the sea. This would seem to raise the average moisture content of the atmosphere. Sure eventually it gets rained back down, but this would seem to be a feature more than a bug for a world that keeps looking for more fresh water. Indeed my mind is currently inventing interesting methods for moving the water around using purely the heat from the sun as an energy source.
Isn’t it more of an indication of how much water can be contained in the Aral Sea basin? The plants don’t need to contain all of the missing Aral Sea water at once, they just need to be watered faster than the Sea is being refilled by rainfall. How much water does rainfall supply every year, as a percentage of the Sea’s total volume?
I recommend googling “geoengineering global warming” and reading some of the top hits. There are numerous proposals for reducing or reversing global warming which are astoundingly less expensive than reducing carbon dioxide emissions, and also much more likely to be effective.
To your direct question about storing more water on land, this would be a geoengineering project. Some straightforward approaches to doing it:
Use rainfall as your “pump” in order to save having to build massive energy using water pumps. Without any effort on our part, nature natually lifts water a km or more above sea level and then drops it, much of it dropped onto land. That water generally is funneled back to the ocean in rivers. With just the constructino of walls, some rivers might be prevented from draining into the ocean. Large areas would be flooded by the river, storing water other than in the ocean.
Use gravity as your pump. THere are many large locations on earth than are below sea level. Aquifers that took no net energy to do pumping could be built that would essentially gravity-feed ocean water into these areas. These areas can be hundreds of meters below sea level, so if even 1% of the earth’s surface is 100 m below sea level, then the ocean’s could be lowered by a bit more than 1 m by filling these depressions with ocean water.
Of course either one of these approaches will cause massive other changes, although probably in a positive direction as far as climate is concerned. More water surface on the planet should mean more evaporation of water which reates more clouds which reflects more energy from the sun, lowering the heating of the earth. But of course a non-trivial analysis might yield a rich detail of effects worth pondering.
In the past features like the Salton sea and the Dead sea have been filled by fresh-water rivers, essentially meaning that rain was used as the pump to fill them. The demand for fresh water has stopped these features from being filled. It seems to me that an aquifer to refill these features with salt water from the ocean would be relatively benign in impact, since in nature these features have been fuller of salt water in the past, and so the impact of that water might be blessed by humanity as “natural” instead of cursed by humanity as “man made.”
Where does the water go? Assuming you want to reduce sea level by a 1⁄2 inch using this mechanism, you have to do the equivalent of covering the entire ETA: land area of earth in a full inch of water (what’s worse, seawater; you’d want to desalinate it). Even assuming you can find room on land for all this water and the pump capacity to displace it all, what’s to stop it from washing right back out to sea? Some of it can be used to refill aquifers, but the capacity of those is trivial next to that of the oceans. Some of it can be stored as ice and snow, but global warming will reduce (actually, has already quite visibly reduced) land glaciation; even if you can somehow induce the water to freeze, that heat you extract from it will have to go somewhere and unless you can dump it out of the atmosphere entirely it will just contribute to the warming. The rest of the water will just flood the existing rivers in its mad rush to do what nearly all continental water is always doing anyhow: flowing to sea.
Clearly, the solution is to build a space elevator and ship water into orbit. We lower the sea levels, the water is there if we need it later, and in the meantime we get to enjoy the pretty rings.
(No, I’m not serious.)
Now I’m curious how much energy it would take to set up a stable ring orbit made of ice crystals for Earth, or if that would be impossible without stationkeeping corrections.
How long will ice survive in Earth’s orbit, anyway?
I think it would depend on the orbit? Obviously it would need to be in an orbit that does not collide with our artificial satellites, and it would need to be high enough to make atmospheric drag negligible, but that leave a lot of potential orbits. I don’t think of any reason ice would go away with any particular haste from any of them, but I’m not an expert in this area.
Orbital decay aside, why might ice (once placed into an at-the-time stable orbit) not survive?
Sun.
Solar radiation at 1 AU is about 1.3KW/sq.m. Ice that is not permanently in the shade will disappear rather rapidly, I would think.
I would think it would lose heat to space fast enough, but maybe not. I know heat dissipation is a major concern for spacecraft, but those are usually generating their own heat rather than just trying to dump what they pick up from the sun. What would happen to the ice / water? It’s not like it can just evaporate into the atmosphere...
Vapour doesn’t need an atmosphere to take it up. Empty space does just as well.
So, how long would a snowball in high orbit last? Sounds like a question for xkcd. A brief attempt at a lower bound that is probably a substantial underestimate:
How much energy has to be pumped in per kilogram to turn ice at whatever the “temperature” is in orbit into water vapour? Call that E. Let S be the solar insolation of 1.3 kW/m^2. Imagine the ice is a spherical cow, er, a rectangular block directly facing the sun. According to Wikipedia the albedo of sea ice is in the range 0.5 to 0.7. Take that as 0.6, so the fraction of energy retained is A = 0.4. The density of ice is D = 916.7 kg/m^3. Ignore radiative cooling, conduction to the cold side of the iceberg, and time spent in the Earth’s shadow, and assume that the water vapour instantly vanishes. Then the surface will ablate at a rate of SA/ED m/s. Equivalently, ED/86400SA days per metre.
For simplicity I’ll take the ice to be at freezing point. Then:
E = 334 kJ/kg to melt + 420 kJ/kg to reach boiling point + 2260 kJ/kg to boil = 3014 kJ/kg.
For a lower starting temperature, increase E accordingly.
3014 916.7 / (86400 1.3 * 0.4) = 61 days per metre. Not all that long, but meanwhile, you’ve created a hazard for space flight and for the skyhook.
I suspect that ignoring radiative cooling will be the largest source of error here, but this isn’t a black body, so I don’t know how closely the Stefan-Boltzmann law will apply, and I haven’t calculated the results if it did. (ETA: The black body temperature of the Moon is just under freezing.)
(ETA: fixed an error in the calculation of E, whereby I had 4200 instead of 420 kJ/kg to reach boiling point. Also, pasting in all the significant figures from the sources doesn’t mean this is claimed to be anything more than a rough estimate.)
This is vacuum—all liquid water will boil immediately, at zero Celsius. Besides I’m sure there will be some sublimation of ice directly to water vapor.
In fact, looking at water’s phase diagram, in high vacuum liquid water just doesn’t exist so I think ice will simply sublimate without the intermediate liquid stage.
Right, I forgot the effect of pressure. So E will be different, perhaps very different. What will it be?
Here is the proper math. This is expressed in terms of ice temperature, though, so we’ll need to figure out how much the solar flux would heat the outer layer of ice first.
One possibility would be to replace the ice caps by hand. Run a heated pipeline from the ocean to the icecaps, pump water there, and let it freeze on its own. I don’t know how well that would work, and I suspect you’re better off just letting sea levels rise. If you need the land that bad, just make floating platforms.
Edit: Replace “ice caps” with “Antartica”. Adding ice to the northern icecap, or even the southern one out where it’s floating, won’t alter the sea level since floating objects displace their mass in water.
Well, this is not pumping, but it might be much more efficient: As I understand, the polar ice caps are in an equilibrium between snowfall and runoff. If you could somehow wall in a large portion of polar ice, such that it cannot flow away, it might rise to a much higher level and sequester enough water to make a difference in sea levels. A super-large version of a hydroelectric dam, in effect, for ice.
It might also help to have a very high wall around the patch to keep air from circulating, keeping the cold polar air where it is and reduce evaporation/sublimation.
This should be a what if question. I’d like to see what Randall would do with it.
I don’t know what you mean. Who is Randal?
Randall Munroe Is the person who draws XKCD. He also has a blog where he give in depth answers to unusual questions.
Randal is Randall Munroe who makes xkcd and, notably, answers what-if questions.