I read this book when I was in high school, almost 50 years ago and it has stuck with me. It is the story of a French Canadian family that flees south on a fishing boat after a limited nuclear war obliterates the Panama Canal and changes the path of the the ocean currents. The world begins to grow colder and the isthmus of Panama must be rebuilt to restore order to the world's environment.
It is also the story of the human race and what comes after homo-sapiens.
I will re-read this book someday.