The New Republic has a long article discussing the problems that Miami FL is already undergoing due to rising sea levels. The sea levels are rising from a combination of long-term trends, increased ocean temperatures, and melting ice caps. They are projected to rise in the future, although the rates at which the rise will occur varies quite a lot depending on what assumptions you make about future climate and human behavior.
As sea levels continue to rise, Miami and other coastal cities like Savannah, Charleston, and Mobile are going to have increasingly tough choices to make about how to protect their cities, their infrastructure and the people who live and work in those cities. Threats are coming from saltwater intrusion as well as flooding from high tides and heavy rain, not counting the occasional impact of a hurricane’s storm surge. Billions of dollars will ride on the states and local communities as they try to balance saving important property and infrastructure and abandoning it to the sea, affecting their priorities in spending in other areas, including agriculture.