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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/… $\endgroup$
    – jeffronicus
    Jan 9, 2020 at 17:39
  • $\begingroup$ Farmer John calculates that the Qattara depression in Egypt would hold 3mm of sea level. $\endgroup$
    – Keith McClary
    Jan 9, 2020 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. $\endgroup$
    – Keith McClary
    Jan 9, 2020 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, 2021 at 2:28
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    $\begingroup$ 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. $\endgroup$
    – Valentin Stoykov
    Jul 8, 2021 at 19:42

4 Answers 4

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No, this is not practicable.

Imagine making another Lake Superior, the 3rd most voluminous lake on Earth, which according to Wikipedia holds 10% of the world's fresh surface water (excluding the ice in Antarctica). It has a volume of 12,100 km3, and would cover about one-fifth of California (at the same depth of about 150 m).

The ocean has an area of 361 million km2, so removing another Lake Superior's worth of water would reduce its depth $d$ by:

$$\Delta d = \frac{12.1\times 10^3}{361 \times 10^6} = 33.5\times 10^{-6}\ \mathrm{km, or}\ 33.5\ \mathrm{mm} $$

... a bit over one inch. According to sealevelrise.org, this is about 10 years' worth of rise.

If you had 639 5400-horsepower Pentair Fairbanks Nijhuis pumps (the most powerful pump in the world, built for keeping the Netherlands dry), you could pump at 38 million litres per second and keep up with sea-level change (not accounting for evaporation or rainfall). At 4000 kW per pump, I think this would require the combined output from the six or seven largest solar farms in California, or a bit more than the output of the Diablo Canyon nuclear power plant.

Unfortunately, there are a lot of other factors controlling local sea-level; see this other answer for example. Not to mention the issue of figuring out where this saline lake will go...

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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, 2021 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, 2020 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, 2020 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, 2020 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, 2020 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, 2020 at 19:38
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It is my genuine opinion that YES

How much exactly?

See the example: https://en.wikipedia.org/wiki/Qattara_Depression_Project

The Qattara depression is a region that lies 60 m below sea level on average and is currently a vast, uninhabited desert. By connecting the region and the Mediterranean Sea with tunnels and/or canals, water could be let into the area. The inflowing water would then evaporate quickly because of the desert climate. This way a continuous flow of water could be created if inflow and evaporation were balanced out. With this continuously flowing water, hydroelectricity could be generated.

According to this answer: 3mm

(current annual sea rise is around 3-4mm per year)

enter image description here

According to my math: 3mm

Volume of Ocean 1,350,000,000   cubic kilometer
Volume of Qattara   1213    cubic kilometers
        
The ratio   0.0000008985185185  
Average depth of Ocean  3700    meters

0.0000008985185185 * 3700m = 0.003324518519m
        
0.3324518519cm
3.324518519mm

Evaporation, changing water table, changing weather patterns not included .
Too many 2nd and 3rd order effects to reliably predict.

Calculation above: pure math based on the volume.

Scientific papers about Quattara Depression Project

The transformation of Qattara Depression into isolated anthropogenic inland sea could provide some ocean level adjustment, as well as generate energy, induce rainfall over some of the adjacent desert, reduce hottest desert daytime and nighttime air temperatures, and permit new local-use fisheries (aquaculture) as well as international tourism resorts.

enter image description here

Despite nearly a century of studies and proposals, and despite high interest on the part of Egyptian authorities, all plans for development of the depression have come to naught. In the end, they foundered on the analysis of costs vs. benefits and risks. A lot has changed, though, in the four decades since the last feasibility study was commissioned — and ultimately rejected — by the Egyptian government of Anwar Sadat. Perhaps it’s time to revisit?

Technical feasibility and roadmap

This can be achieved with the technology that is available Today:

  • developed in stages
  • generating hydropower in the process
  • pumping water uphill when excess energy

TBD. TBC. This answer can be improved. Old papers didn't account for Elon Musk and Boring Company though when calculating the cost.

Financing

ROI of reducing sea levels might be better than relocating cities that go underwater, however it will require some transnational agreements (country A has a sinking city, country B has a depression, financing coming from X).

Availability of labour

There is another large space project - The Grand Africa Green Up - they mentioned availability of labour. Useful to know.

enter image description here

Ethical aspect of geoengineering

We are already doing geoengineering with greenhouse gases in the atmosphere 🤷‍♀️ to use some desert and create energy, create jobs, and reduce sea levels - benefits far outweigh any potential concerns.

Note about glaciers and $$$

Geoengineer polar glaciers to slow sea-level rise

If nothing is done, 0.5–5% of the world’s population will be flooded each year after 2100. For example, a 0.5-metre rise in Guangzhou, China, would displace more than 1 million people; a 2-metre rise would affect more than 2 million1. Without coastal protection, the global cost of damages could reach US$50 trillion a year. Sea walls and flood defences cost tens of billions of dollars a year to construct and maintain.

Related projects

Not affiliated in any way, just being aware of their existence, in the theme of using desert (not just flooding):

EDIT / UPDATE: I've updated this answer a few times to reflect the feedback in the comments - thank you 😇 If you can, if you feel like it - please reverse the downvotes so that this answer receives some attention and bubbles on top - math adds up and people are already actively working on it.

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    $\begingroup$ How much would this reduce sea level? Or do you mean indirectly, by helping with low-carbon energy sources (which I don't think is what the question is after)? $\endgroup$
    – gerrit ♦
    Aug 16, 2022 at 9:12
  • $\begingroup$ Despite providing a detailed calculation on how much (3mm, roughly the annual sea rise) and even linking to another answer that comes to the same result this post is currently -2... Thank you for the comments so far, I was able to improve the answer. $\endgroup$
    – Mars Robertson
    Aug 17, 2022 at 10:31
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    $\begingroup$ Wikipedia suggests a 10.1 cm sea level rise since 1992 and "2–3 metres (6.6–9.8 ft) if global warming is limited to 1.5 °C", so if your math is right, it's a fairly insignificant drop in the bucket? So your headline and excitement seem a bit out of place? $\endgroup$
    – JeopardyTempest
    Aug 18, 2022 at 5:59
  • $\begingroup$ Matter of optics and presenting data. Option 1: 10.1 cm since 1992 Option 2: 3mm per year. In this particular example - only 1 project in 1 area - not even pumping but letting it flow downhill to generate hydropower in the process. Then we can continue with the project and FLOOD the DESERT just like YC Combinator suggested in the "Request for Startups - Desert Flooding" $\endgroup$
    – Mars Robertson
    Aug 18, 2022 at 9:53
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    $\begingroup$ Evaporation is a significant factor for any open-water body in a climate like the arid interior of California: "The open water surface evaporation rate at the Salton Sea is estimated at approximately 69 inches per year and the average annual crop reference evapotranspiration rate at Brawley is reported to be approximately 71 inches per year (California Irrigation Management Information System [CIMIS] 2012)." That is, water moved out of the ocean to an inland reservoir will evaporate, fall as rain somewhere else, and then make its way back to the ocean. $\endgroup$
    – jeffronicus
    Aug 18, 2022 at 21:12

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