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Comment by eimrine | Hacker News Reader

> Earth is a closed system, so we should expect to see water storage decline in some areas and flooding increase in some areas.

Of course, Earth is a closed system, but I am not sure it is that closed.

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I don't mean this to sound snarky. I'm genuinely curious where you think the water will go, if not to other places on earth.

We lose atmosphere to space everyday.

The mesosphere has very little water in it.

http://scienceline.ucsb.edu/getkey.php?key=2

https://www.sciencedirect.com/topics/earth-and-planetary-sci...

And we also gain water from space through meteorites every day.

I’m sorry my model didn’t account for your 8th order effects. You’re technically correct.

> where you think the water will go, if not to other places on earth

I afraid that a lot of fresh water is going to become an ocean water. Flooding theory creates the impression of transferring fresh water from one place to another where it will remain just as fresh. It is incredibly hard to create a fresh water from salty one.

> It is incredibly hard to create a fresh water from salty one.

Fresh water is created from the salty water by evaporation all the time.

Indeed, and it's interesting to note that this natural desalination process also incorporates long-term storage mechanisms. Historically, vast quantities of freshwater have been stored in the form of snow packs and glaciers. However, in our changing climate, this storage is not occurring at the same scale as it used to. This could potentially exacerbate future water scarcity issues, making man-made desalination techniques even more crucial. As challenging as creating freshwater from saltwater may be, it's a puzzle we need to solve with urgency.

on the other hand, global warming will pump much more water in the atmosphere, and we will have more precipitation. In fact, global warming would not be a problem at all if what I said above was not true. CO2 alone could only raise the temperature by 1C no matter how much we would put in the air (by year 2100). The water vapor creates a positive feedback loop that warms it far beyond what CO2 can do alone.

But that's not actually helpful. Occasional massive rains don't refill aquifers very well. There needs to be a buffer to allow water to slowly make it's way into the system in a manageable way. Currently that is mountain snow melting over the warm season.

I mean, sure, but never in enough volumes to be actually usable by us. It’s not like we can capture every single evaporated water droplet before it cools to form fresh water.

So while technically it happens all the time, practically it’s as if it isn’t happening at all when it comes to the concerns talked about here, specifically the quantity of available fresh water declining.

I think you are quite wrong about that. The evaporated ocean water becomes rain. Evaporated ocean water is the source of over 80% of all rain on earth.

And most of that rain is going to go into the ocean again. Or be distributed in a large area. Neither of which can really be captured in any sort of predictable and scalable manner.

You know, unless we build a massive “roof” of devices to capture all that rain. Literally covering the entire planet. At that point yeah it would dev a reasonable thing to bring up in the context of fresh water reserves falling.

So I very much stand by the point that while, sure, it happens all the time, that does nothing to actually help with the topic at hand.

The rain can be captured by farms.

> in any sort of predictable and scalable manner.

How?

Rain is not predictable at the scale of a crop season. Rain is not scalable, it’s extremely localized.

Rain happens, and when it does your crops get watered, but you can’t in any way shape or form rely on that.

About 80% of that rain happens back over the ocean, and then about 25% of the rain that happens over land actually gets captured as ground water. Even that isn’t the main point though, the issue is we’re currently using water faster than rain replenishes it in many places. At worst as I understand it, in some places they’ve collapsed their aquifers by over-pulling from them, and that means less of the rainfall in those areas will be recoverable in the future. At some point we have to enter a mode where we only pull water in a way that is sustainable or we’ll suddenly find that we do indeed need desalinization to keep up with our use.

This is where essentially all freshwater comes from.

That’s great and all but how does that help with the issue of that freshwater being depleted? Which is the topic at hand.

Into the ocean.

The ocean covers the majority of the Earth's surface. The ocean is full of salt.

Water which rains out over the oceans is unusable as drinking or irrigation water without expensive processing (desalination).

If historic rainfall patterns change, there is absolutely no requirement that the rain land anywhere useful for our existing infrastructure or human habitation.

Yes, the water won't disappear, but if the effect is rainfall hits the ocean, or say, flood-prone regions even harder then it normally does, it's still going to be coming down somewhere not useful to us.

The problem is not that we can't solve these problems, it's that is is staggeringly expensive to do so.

>>it's that is is staggeringly expensive to do so.

Necessity is the mother of all invention, and with Necessity also comes scale, and with scale comes less cost...

Desalination has been expensive because it is not necessary, the second it becomes necessary I bet you will see the costs drop..

If nestle had to use Sea water to fill their bottles I bet they would have a cheap way to do it right quick

> If nestle had to use Sea water to fill their bottles I bet they would have a cheap way to do it right quick

Make it so.

I think many of us working in software can be overconfident about how easy it is to scale things, probably because of the peculiar progress in the improvement of integrated circuits and the commensurate increased availability of raw compute for not that much more energy. But many processes (including desalinization, as far as I understand it) are energy bound. It is really hard to make exponential progress when a process is bound by how much energy you can muster up to put into it. That is why rockets haven't had an exponential increase in the amount of weight they can get into orbit in the last 100 years. With gravity you must pay the piper.

I doubt scaling desalinization is as hard as hurling stuff into space, but it may not be easy to scale either. There are plenty of places on earth which are very dry, adjacent to salt water, and extremely rich and yet no great desalinization technologies have come from them.

You may have neatly (and politely) pinned down why we computer folks are so arrogant about how easy problems outside our direct field would be to solve, if only we were the ones “allowed” to solve them.

> If nestle had to use Sea water to fill their bottles I bet they would have a cheap way to do it right quick

Why? Nestle just passes the cost on to the consumer, because where else are they gonna go?

There’s the rules of physics to consider.

There are more than a few places where desalination is necessary, and we still haven’t come up with a way to make it cheap.

The current issue is that there is just no way that we know of to reliably desalinate that isn’t super energy intensive, so it comes down to trading energy for water. That’s why desalination is expensive.

It seems that solar energy has gotten real cheap in recent years, especially in places without clouds and rain (deserts).

So maybe that will work out in the end if the economics make water expensive enough to trade energy for water.

Not staggeringly expensive, about 38 cents per day per person, apparently:

https://en.m.wikipedia.org/wiki/Desalination#Costs

Although that doesn't include irrigation..

EDIT: can even be economical for irrigation in some circumstances: https://www.fluencecorp.com/desalination-and-agriculture-les...

Kind of leaving out the main point there. People don't use a lot of water. Industry and Farming do. We depend on both of those for...pretty much our entire society.

Water-intensive industrial processes can move to where the water is. Farming is more of a challenge but some crops need more water than others; there's a lot of scope for substitution.

Yeah maybe someday we can stop growing all our produce in the damn desert just because the weather was slightly more profitable.

Because all of that's going to be cheap right? In a nation which loses its mind even gas prices go up 20c?

People use water directly and indirectly. And water is "used" and "used" - it's not as simple as measuring a pipe, you need to know where it goes.

Something like 600 million people live below the poverty line, which with current inflation is at $2.15 per day; so for them a 38 cent per day rate means diverting almost 20% of their income just on water. For comparison, that's a much larger share than what USA residents spend on food (~13% of their income).

The figures assume a US citizen level of water consumption, someone on $2 a day would use much less than this.

It's easy to overlook the effects of transpiration, which is a result of photosynthesis, which is impacted by biodiversity loss. It short circuits water's path back to the ocean and puts it back into the air above land where it can precipitate into lakes a second time.

Without it, snowmelt-fed rivers dry out earlier.

As more ice melts there might be more liquid water available, but the ecosystems that would process that water into vapor are struggling. So you end up with a situation where the only source of water vapor in the air is the oceans.

As temperatures increase that'll again be a net increase in ocean-driven evaporation, but it'll be less evenly distributed than evaporation+transpiration was.

So the concern is that the only available water will be too salty to drink, or too destructive to capture.

Higher global average temperatures means higher global average specific humidity. As the air warms it can hold more water vapour, which means less condensation. I don’t know how much difference this makes, but I expect it’s not insignificant.

It also means a higher rate of evaporation from the oceans.

True, but oceans only evaporate from the surface while the air retains moisture by volume. There is considerably more low, warm air than there is ocean surface.

The earth as a whole is roughly a closed system, but "usable water" is not.

Most resource problems are not about the quantity of some thing changing as a percentage of earth's matter. Most resources are about density and composition.

If all of the (non-ice) freshwater on earth was suddenly dumped into the ocean, we'd have the same amount of overall water - but little to no drinkable water.

Likewise, we're not really creating new carbon by burning fossil fuels. We're moving and re-distributing it. Compared to being deep underground, the form we create by burning captures much more heat, causing many problems.

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