Timescape by Gregory Benford

The year is 1998, the world is a growing nightmare of desperation, of uncontrollable pollution and increasing social unrest. In Cambridge, two scientists experiment with tachyons – subatomic particles that travel faster than the speed of light and, therefore, according to the Theory of Relativity, may move backwards in time. Their plan is to signal a warning to the previous generation. In 1962, a young Californian scientist, Gordon Bernstein, finds his experiments are being spoiled by unknown interference. As he begins to suspect something near the truth it becomes a race against time – the world is collapsing and will only be saved if Gordon can decipher the message in time