The lathe of heaven / Ursula K. Le Guin.

In a world beset by climate instability and overpopulation, George Orr discovers that his dreams have the power to alter reality. Upon waking, the world he knew has become a strange, barely recognizable place, where only George has the clear memory of how it was before. He seeks counseling from Dr. William Haber, a psychiatrist who immediately understands how powerful a weapon George wields. Soon, George is a pawn in Haber's dangerous game, where the fate of humanity grows more imperiled with every waking hour.