[microtonal]

So we do not need to store any amount under ground, we only need enough people to make irrigating deserts profitable.

In an ideal free market, perhaps, yes. In the real world, people will just move/flee from dry areas. As the global temperature rises and more regions of Africa and America become uninhabitable, people will just slowly migrate north (or perhaps partially south America). If you thought that we had a refugee crisis, just wait a couple of decades.

[chr1]

Fair enough, it won't happen automatically, but maybe instead of wasting money on subsidising biofuels, building non-effective renewable installations, funding additional border patrol or helping refugees, the rich countries can focus on helping the poor countries to build irrigation infrastructure and to become rich.

[bluGill]

irrigation isn't something they will build without reason. Thus biofuels encourage irrigation.

[chr1]

Sadly that's not what happens in practice, currently biofuels encourage cutting down forests and repurposing the land that could be used for normal food production.

[bluGill]

Not everybody flees from dry areas though. There are always a few people who love the area enough and stay behind trying to make a living. If they have the opportunity (mostly a combination of legal rights, knowledge, but there are a bunch of other factors not all of which I will claim to know) to make their part of the desert better, the total of all those small changes is a big thing.

My personal use of coal/oil (including indirect use in the products I buy) is insignificant to global warming. However across the population of the world...