"PNAS Study: Population Growth Will be Constrained by the Limits of Trading Virtual Water (Food)"

One of the few Limits to Growth that actually is a limit rather than some sort of scarcity meme.
However even this should be beatable if some smart people can do the deep dive into the wonder and magic (okay, chemistry and physics) that is H2O.
We'll be hearing about virtual water with increasing frequency, right now there are only 298,000 hits in a Google search.

From Big Picture Agriculture:

A new study has been released by the Proceedings of the National Academy of Sciences (PNAS), which calls into question the unsustainable global food export system based upon unsustainable export volumes of virtual water.
The first sentence sums it up:

Population growth is in general constrained by food production, which in turn depends on the access to water resources. … Most of the water we use is to produce the food we eat. With the world’s population that has doubled every 40 years, there is a growing concern that water limitations will soon impede humanity to meet its food requirements.

The study refers to a global water unbalance and challenges the long-term sustainability of the food trade system as a whole, based upon current food export rates. It projects that growing demographic requirements of water-rich nations will result in less exports to water-poor regions.

Water-rich regions are likely to soon reduce the amount of virtual water they export, thus leaving import-dependent regions without enough water to sustain their populations.

The concern is that virtual water trade is allowing for some populations to exceed the limits imposed by their local water resources, and that by sustaining demographic growth above the regional carrying capacity, virtual water trade has mitigated the effects of drought and famine in many regions of the world.

Using the estimate that the carrying capacity of one-third of all nations today depends upon food availability, and thus water availability, the study estimates maximum sustainable populations. Because both water-rich and trade-dependent populations are growing to rely on the same pool of resources, in the long run the virtual water exports are unsustainable.

One of the study’s scenarios takes into account plausible crop expansions, increases in agricultural production efficiency, and changes in diet and consumption rates.

These are huge variables, each one of them, making this a difficult assessment.

The study concludes that water will eventually limit population growth. This analysis estimates that the decline in the trade-dependent population is expected to start around 2030, but possibly not until 2040 to 2060 given the right amount of international cooperation. Interestingly, they compared their conclusion as coming out similarly to Heinz von Foerster’s Doomsday prediction for human population growth to cease expansion on November 13, 2026....MORE

See "Heinz von Foerster, P. M. Mora and L. W. Amiot (November 1960). "Doomsday: Friday, 13 November, A.D. 2026. At this date human population will approach infinity if it grows as it has grown in the last two millenia". Science 132 (3436): 1291–1295"

Here at the Pick-a-year-any-year club we're going with sometime after "NASA says 'Solar Cycle 25 peaking around 2022 could be one of the weakest in centuries.'"

If the space guys are correct it could set up an analog to The Great Famine of 1315-1317 which made things tough on Europe and combined with his own ineptitude made the reign of England's Eddie-the-Deuce one of the worst in history.