Desalination seems perfectly capable of creating enough fresh water for agriculture. Desal requires plenty of electricity but with a big investment into new nuclear power plants these demands could be easily met. Switching to irrigation with desal water will come at a cost but I don't think it will be dramatic in the developed world.

Nuclear power has been ideologically poisoned, partly for good reasons, partly for bad (I'm not taking sides here). Whatever the reasons, the effect is that most politicos won't risk a voter stampede to the guy who didn't support reactor building, and as a result, not just in the US, nuclear energy is on its deathbed.

There's some irony in this, because one consequence is that a country's oldest (and hence least safe) reactors will be kept online for longer than planned.

Happily, desal can be powered by solar as well, and in fact this is one application that's OK to run just in the daytime, as the daytime's fresh water can be buffered overnight.

Is there ever talk about passive solutions? I.e. Just pumping vast quantities of sea water over open channels and letting evaporation take its course. It sounds infeasible but maybe there's a way to make an evaporative option viable.