The novel is set in the future when the seas have risen and is about people having to adapt. By the end of the novel humans are living on raft colonies and can communicate with whales who travel with them and look after them.
It could be The Hydronauts, written in 1970 by Carl L. Biemiller.
There is a series of three books that fit your description:
- The Hydronauts
- Follow The Whales
- Escape From The Crater
From the Hydronauts book's jacket:
"The range was not the entire world. But it was more than 80% of it, and all water. The nuclear war had long since melted much of the polar ice caps. Whole sections of continents were long gone. Hive cities had been set up under the surface of the water.
Set in this world of the future, The Hydronauts tells of a team of marine wardens picked by the International Marine Counsel. There is Kim, the leader of the group; Toby, whose ancestors had come from the forgotten country once called Japan; Tuktu, who came from McKinley City in what once was Alaska; and Genright, who had been selected for warden training in the Hive City deep within a plateau of ancient Ethiopia.
Carl L. Biemiller tells of a future environment in which men live beneath the sea, can communicate with dolphins, and can preserve human beings in a state of suspended animation for centuries."
Best yet, the author's son, Eric Biemiller, made the books available online!
Apart from the communications with Whales which I don't remember, if the book you recall was from more recently, another possibility might be Stephen Baxter's 2008 novel Flood.
Does this sound familiar?
Published in 2008, Flood is the work of hard science fiction by English author Stephen Baxter. It describes a near future world where deep submarine seismic activity leads to seabed fragmentation, and the opening of deep subterranean reservoirs of water. Human civilization is almost destroyed by the rising inundation. Civilization is virtually dead at the novel's end. Survivors continue to exist only on the rafts and some decrepit surviving former navy vessels. The children of the rafts, raised on the water, start building their own aquatic culture.
Flood was nominated for the British Science Fiction Award in 2008.1
Could it be "Cachalot" by Alan Dean Foster?
It features a lot of the detail you've described; humans living in raft cities, intelligent whales who can communicate with humans, but it doesn't have the climate change subplot that you're looking for. Its possible that might be from a different story, or perhaps you've combined "Cachalot" with "Into the Deep" by Ken Grimwood.