After a series of negotiations between the United Nations, the U.S. Government, the State of Illinois, the City of Chicago and various ward aldermen and their constituents, sovereignties over several neighborhoods on the South and West sides were transfered to Pacific island nations whose territories had been made inhabitable by rising sea level. Generously compensated, residents of those neighborhoods relocated to the North side.
The new residents, also generously compensated by carbon-intensive nations in perpetuity or until global warming subsides, then set about colonizing their new homeland: an archipelago of extraterritorial enclaves carved out of the city. Some razed everything to the ground, then unearthed and discarded everything that was underground; they tilled the earth anew. Others adapted to and modified what was there, resulting in a patois of Midwestern and Pacific cultural traditions.
Still another nation-in-exile housed their entire neighborhood-state in vast greenhouse complexes: a City of Glass simulating a tropical memory, luminous at night, gleaming during the day.