I'm not worried about the soil, I'm worried about the water. The Ogallala Aquifer is shrinking. The more it shrinks, the more there will be compaction preventing it from refilling to previous states. We can always grow food in water but getting clean water will be an increasingly difficult task. Look how bad it already is in CA.
You should be worried about soil. Increasing the soil organic matter improves its water holding capacity, improves tilth and increases infiltration rate. In turn that decreases how much water is needed for crops in dry times and allows recharging of aquifers.
With the currently degraded soil, farmers worry about a couple inches of rain causing washouts or flash floods. Water runs over the top of the soil into surface waterways. Healthy soil can infiltrate many inches of rain an hour.
I'm not worried about the water, I'm worried about the phosphorus! Almost all of the fertilizer in the world is made from phosphorus that comes from Morocco and Western Sahara, and it appears that we're depleting it very quickly.
All the minerals needed for plant life are available in the sand, silt, and clay in soil. Soil life is the key to breaking down aggregate minerals into plant usable nutrients. In healthy soil fertilizing is not necessary.
It is hard to talk about soil life without sounding like a kook to most people. But, our practices of using synthetic fertilizers and spraying fungicides, herbicides, and pesticides are literally killing the soil's capacity to feed plants.
We can grow crops with far less water. Look at farms in Israel. The problem is that water prices don't account for externalities or sustainability, so in the short term farmers have little incentive to conserve.
Desalination is sufficiently cheap to not be a material problem for US consumers (or other developed countries). State-of-the-art desalination plants in Israel are fulfilling contracts at ~$0.40/m^3 [1] and the per-capita water usage in the US is ~1200 m^3/yr [2]. Even if we assumed that the current price of water is $0, this would only amount to a $480/yr increase in expenditure per American which would constitute a one-time 1.4% increase of yearly expenditure for the median American. Note that this accounts for all agricultural production in the US; if we consider just water for domestic use such as drinking, bathing, and watering the lawn the average person only uses ~100 m^3/yr [3] which is ~$40/yr which is within reach of every household. This also assumes that increased water prices will not result in changes to water usage which is very doable as the US uses ~3-4x as much water per capita as other peer countries such as France and Germany and 10x the water of Israel which already needed to adjust to a regime of desalination water prices.
All in all, considered merely in economic terms, desalination is a perfectly viable solution to the water crisis in developed countries and would incur at most a relatively minor economic impact by this analysis. Note that this does not necessarily apply to developing countries where a $40/yr expenditure increase could be catastrophic. I am also not making any statement about non-economic considerations such as possible effects on the environment that may occur as a result of the need for increased power generation for mass desalination.
Your analysis above is remarkably detailed, but it misses the point. When I used the term "sustainable" I was speaking of resource usage and environmental impact, not whether the practice was affordable.
The resource constraint that matters for desalination right now is not obviously seawater. It is the energy input for desalination, which in many areas still depends on hydrocarbons.
Why would desalination be unsustainable? The limiting factor is electricity. And renewables continue to deliver Moore's law like improvements in the price and quantity of electricity, without any environmental externalities.
I actually think that desalination and solar are a good pairing but
> without any environmental externalities
doesn't sound quite right to me. In particular I think there are reasonable concerns regarding lifetime energy and environmental costs of solar panels, mining of and disposal (or recycling) of the rare materials used in the panels, etc.
> Why would desalination be unsustainable? The limiting factor is electricity.
Disposal of the extracted salt is a serious issue. You can’t just inject brackish water back into he ocean as it screws up the ecology of the near shore environment (or wherever else you’re willing to squirt it.
Most desalination plants do just inject saline water back into the ocean. There's no where else to put it. In most cases the outflow pipe runs some distance offshore into deeper water to reduce the environmental impact.
> There is just so much land, we can't possibly deplete all of it.
Given that we are currently using 40% of the world's land area for agriculture, and that we are using ~0.0003% of the world's water, I don't think this is a fair criticism of my post. Only a fool would think that former isn't something to keep an eye on.
> I love this comment :) Messing a bit with drops in the ocean is how we got here in the first place.
No, we got here in the first place by messing with carbon and water and nutrient cycles that take tens of millions and hundreds of thousands of years to cycle through.
The atmospheric water cycle, on the other hand, operates on a scale of weeks. Seawater gets separated into brine and fresh water, fresh water irrigates crops, fresh water evaporates into clouds, clouds precipitate over the ocean. All of humanity's historic water consumption is quite literally a drop in the ocean. [1]
The volume of the oceans is 1.3 * 10^18 m^3. Humanity's annual consumption of fresh water is 4 * 10^12 m^3. Annual worldwide precipitation is ~5 * 10^14 m^3.
> Did you see how much air we have? Yeah burning dirty stuff pollutes it, but then the wind blows and it's clean again.
[1] Meanwhile, all of humanity's carbon emissions dwarf the ability of natural carbon sinks to absorb - because in hundreds of years, we have released carbon that took tens of millions of years to accumulate. The atmospheric water cycle operates on an entirely different scale. [2]
[2] The orders of magnitude between the unsustainability of <carbon use>, <land use>, <freshwater use>, and <seawater use> are each ~two orders of magnitude removed from eachother.
It's not the use of water that's the problem, it's the releasing of the brine. This will destroy the local ecosystem and historically we haven't been able to predict the consequences of that at all.
Why does desalination produce brackish water (this is a new term to me)? From context I expected "brackish water" to mean water that is saltier than seawater. But when I look it up, it's apparently water with salinity between fresh water and seawater.
> I'm not worried about the soil, I'm worried about the water.
Then quite frankly,m you only understand half of the problem; water will always be an issue even in times of abundance, the fact that when California goes from drought to deluge conditions nothing has been done to try and build infrastructure to replenish the aquifers that have been drained for decades.
The best we get, for all the taxes and myopic city planning is black ping pong balls, and then diverting the water into the Pacific Ocean. In my entire lifetime I will never understand how infinitely stupid this state has been about water despite Central Valley being such a vital to not just the US' food supply chain, but also for a lot out the rest of the World.
Desalination was always thought to be untenable until the preiumus could justify it, but the truth is I forsee some very affluent communities in SoCal (Carlsbad) will be the biggest benefactors of a near monopoly for reliable water sources.
Worth noting is that many Pharma megacoprs are in Carlsbad and the greater San Diego area who have learned from Nestle's business model to water rights in the developing world.
Do you have any papers on compaction induced reduction in water bearing capacity? This idea does not mesh with my understanding of the Ogallala as being generally coarse grained and thus not as at risk of what you’re suggesting. Compare to consolidation of fine grained soils which does have a hysteretical behavior relating to storage capacity.
It seems to me that aquifers aren't sustainable water sources to begin with--we shouldn't treat them as a primary water source, but rather as a reserve source for scarce years. On the other hand, topsoil could be sustainable (at least for very large time scales) provided it's properly managed.
