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I have been reading the discussion about pumping sea water into the desert for purposes of irrigation and changing the dry climate of that area, but what about to just purely offset the rising sea levels? Could pumping ocean water (with solar power) north of Malibu California into the dry areas help with coastline erosion and put water into the desert as a secondary but not primary benefit? I am a completely non-scientific person who just happens to have an interest in coastal erosion so I welcome all your educated thoughts on this. Ideally it would be done in all the deserts globally to have a coordinated effort. Think of the infrastructure jobs in places like Africa. It would require a “world bank” initiative to create the funds to do this but as a global coordinated effort it may be required as part of planet rehabilitation. Yes I said “create” the funds, ie “print money” which would have a slightly inflationary effect on world economies but would mostly “inflate” depressed economies through wealth redistribution since these economies would likely be the major supply of labor. Like we see in Canada when the people from poor fishing towns went to work on the pipelines and brought cash back home.

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    $\begingroup$ There's a related question about pumping water into the desert here: earthscience.stackexchange.com/questions/7553/… $\endgroup$ Jan 9 '20 at 17:39
  • $\begingroup$ Farmer John calculates that the Qattara depression in Egypt would hold 3mm of sea level. $\endgroup$ Jan 9 '20 at 23:13
  • $\begingroup$ "Can Huge Man-Made Lakes Fix Our Rising Sea Levels?" says 3cm of sea level for all land which is below sea level and dry. $\endgroup$ Jan 9 '20 at 23:23
  • $\begingroup$ Water is heavy so the result is less change in sea level relative to land than you might expect.Some of it will flow back to oceans.The flow causes erosion which is contrary to what you want.Adding to the water table makes the sea level will rise.Because we have coercive governments wealth can be redistributed without possibly wasteful infrastructure building.Thus infrastructure should be considered separately from the need to redistribute.If the infrastructure is a net beneficial public good then it is a good idea.An impermeable barrier around a desert is costly.Will cost exceed benefit? $\endgroup$
    – H2ONaCl
    May 10 at 2:28
  • $\begingroup$ Most of the water that do not flow to the oceans directly will evaporate and go to the oceans as rain. Some water may go in earth cavities (underground water). The existing underground water may become more salty. $\endgroup$ Jul 8 at 19:42
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This is no an answer per se, just a back-of-the-envelope calculation for fun.

Lifting 1 kg (one litre) of water up a height of 1 meter uses 9.8 (let's say 10) joules of energy.

Let's say you want to lower the sea level by 1 meter. You need to pump 3.6e17 litres (3.6e14 m2 of ocean area = 3.6e14 m3 to pump * 1000 for litre conversion).

Let's say you want to lift this water up a height of at least 10 meters, so it doesn't go right back into the ocean but rather stays behind some kind of dike. We're already at 3.6e18 J of energy. That's 1e15 Wh, or 1000 TWh. That's more than what the 20 largest power stations combined produce in a year.

This also assumes an ideal, 100 % efficient pump (no energy loss)...

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  • $\begingroup$ Ah, so there'd be a selective pressure towards quick infantile growth, and/or the development of fins, eh ... nature finds a way ... sorry, couldn't resist :-) $\endgroup$
    – user18607
    Jan 9 '20 at 20:43
  • $\begingroup$ @ebv: No, just a migration to the non-flat parts of California :-) But with California, there are ways that don't involve ongoing energy. Most of the rivers start in the Sierra Nevada. Just drill tunnels at about the 5000 ft level, send the water over to Nevada, and fill the Great Basin. (And further south, Independence Lake, which might drain into Death Valley...) Then build a dam at Carquinez Strait en.wikipedia.org/wiki/Carquinez_Strait and flood the Sacramento and San Joaquin valleys. $\endgroup$
    – jamesqf
    Jan 10 '20 at 5:31
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    $\begingroup$ @Fred How can lowering all the worlds oceans by 1 metre and dumping it into California possibly only flood it by 0.9 metre? That can't be right, you're missing some zeroes. The oceans cover 3.6e14m², California covers 4.24e11, so it would be covered by around 840 metre in my back-of-the-envelope calculation... $\endgroup$
    – gerrit
    Jan 10 '20 at 11:17
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    $\begingroup$ @gerrit - California, like the Tardis, is bigger on the inside. $\endgroup$ Jan 10 '20 at 11:23
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    $\begingroup$ @Will I don't think there's very much land below sea level, for obvious reasons. If the sea can be there, it already is. $\endgroup$
    – user253751
    Mar 3 '20 at 16:59
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Taking water out of the sea does require energy to lift it even if it's destination will eventually be below sea level. The dam idea of retaining rain water would require energy and resources for the production of the dam and require the loss of usable land. That is not the best dam way to approach this solution.

Removing water up stream, from say the Mississippi or Rio Grande, could be diverted to a lower elevation area via a pipeline or canal system. This too would require energy and resources to build, but the fresh water could at least be sent to areas that are currently unusable arid areas. This would result in a greening effect without the risk of contaminating water tables below. Another benifit would be the ability to increase the amount available farm land without the need of taking water from an already depleted ground water source. Also replenishment of water tables would occur, and your end goal of reducing the amount of water entering the ocean would be accomplished.

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    $\begingroup$ Josh. Mankind has been damming rivers and moving water around since the dawn of civilization. But it's in no way a panacea. To meaningfully move water around requires massive infrastructure, massive amounts of energy and a willingness to disrupt the ecology and economy of the areas downstream of your diversion. Rivers like the Rio Grande are already overexploited. $\endgroup$
    – Andy M
    May 7 at 16:08
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Yes, it could reduce sea level rise, but it would be no good for irrigation. Many deserts, like the Aral Sea and Death Valley, are below sea level. This means you would not need to use energy to pump the water, but could use the siphon principle. Some people say that even if you filled all these low-lying deserts with sea water, it would not do much to lower sea level. However, it would have many other beneficial effects, especially in the Aral Sea. It would greatly improve marine transport, create new fisheries, prevent the present salt desert being blown onto agricultural land, and quite likely change the climate so there would be more precipitation.

Another way to reduce sea level, though it would be only by a tiny amount, would be to build more dams. Deprived of the held-back rain water, the sea level would reduce a little if enough rainwater was prevented from reaching the sea. The dams would produce carbon neutral power, create fisheries and be used for irrigation. On the other hand, if the proposed dams on the Nile are anything to go by, they also have the potential to start wars unless they are sited with great care and good international diplomacy and cooperation.

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    $\begingroup$ Well, one would need a many hundreds if not 1000km long frictionless pipe and dam construction without greenhouse gas emission. Doesn't sound like a plan ... $\endgroup$
    – user18607
    Jan 9 '20 at 18:35
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    $\begingroup$ The energy needed to pump the water would be enormous. Check again sea levels. $\endgroup$
    – user18607
    Jan 9 '20 at 18:48
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    $\begingroup$ It is not personal. You're just violating the rules of citing. SE explicitly encourages to downvote unsupported posts. Caspian is below, Aral above msl, right ? To get water from C to A, we must pump it up, not let it pour down. Or have i misunderstood ? $\endgroup$
    – user18607
    Jan 9 '20 at 18:57
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    $\begingroup$ i doubt much more to create a lagoon on those basins wouls afect a lot sea level. Even a big surface, the new sea wouldn't bee very deep $\endgroup$
    – user18590
    Jan 9 '20 at 19:29
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    $\begingroup$ A few meters, yes. The Aral Sea is more of a pan than a pot. I am still hopeful that @MichaelWalsby actually researches an answer before posting. I'll be the first to upvote (if fast enough). $\endgroup$
    – user18607
    Jan 9 '20 at 19:38

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