If you can breeze past a few sermons about global warming and polar icecaps melting, this was a great book.  Mara’s town is a tiny shrinking island in the Atlantic.  As far as the people in her town know, their island is the only dry land left on earth.  But as the waters keep rising, they must find a new home.  Mara convinces the islanders to set off in search of a rumored refuge–sky cities built high above the wet earth.