I tend to agree with Dirk. For the moment, let's leave the panama Canal open. Maybe alluding to a narrow band of land (of which there isn't a whole lot in our hemisphere) for production of food. In the 24th century, I would imagine that inroads have been made towards greenhouses and various other underground food production facilities. Belts may be getting tight, but staples are still being produced.
Funnily enough, I'm working on a rewrite of my novel that has an object hitting the sun and forcing it to cool down. I published the first 5 chapters here, and agreed with the critical reviews that it needed rewriting. There is no reason at all why this novel can't use somewhat the same thing. Or, if a significantly large asteroid hit somewhere like China or the Indian sub-continent, then a great deal of the 'hungry masses" would be out of the picture. Cruel, yes, but realistic as it would cause the natural equivalent of nuclear winter. But, something like that would hardly affect the oceans enough to make much of a difference. What is needed is the sun to stop outputting, or a thick cloud cover for a couple of years.
I reread the chapter again and agree again with Dirk. Let it end as Delana hang up the phone with the President's sense of urgency echoing in her head.
EDIT: I was writing this while Karen responded, so a new post is forthcoming.
~Tom