And we can't change crops? Or change methods? I'm not buying that. Humans grow crops everywhere, from equatorial deserts to the arctic circle. And the changes that make a given crop totally unworkable (as opposed to not quite as efficient as before) are generation-scale, not the flip of a switch.

Water will still exist. Soil will still exist. Short of postulating worst-case scenarios (which are possible), this is all stuff we can handle with existing technology, much less the technology of a century from now.