One of the clearest consequences of global warming is the rise is sea level. For now this is being driven mainly by thermal expansion of warming oceans, but the melting of glaciers is contributing as well, and that's almost certainly going to worsen as the planet continues to warm. At this point at least some amount of continued warming is inevitable — we've waited too long to prevent it entirely — so we have to deal with the consequences.
Many farmers around the world live in coastal areas subject to increasing flooding with salt water, which is deadly for conventional crops. (For the record, though, it's very likely a myth that after the Romans defeated Carthage they salted its fields to prevent anything from growing, though this apparently was a symbolic practice in the ancient Middle East. See The Straight Dope and Wikipedia.)
Research is underway with a modest amount of funding to find "halophile" (salt-loving) crops that can grow in salty conditions. There are millions of subsistence farmers who would benefit from this. Their only likely alternative would be to relocate, and it's not at all clear where they could go.
An Associated Press article by Katy Daigle describes the problem in more detail and what's currently being done to try to find a solution.