Ian McEwan’s latest work can be read as a farce whose principal theme is Hamlet’s musing that “there is nothing either good or bad, but thinking makes it so.” Indeed, when introducing the novel’s protagonist – the physicist Michael Beard, who is a “bald, short, fat, clever” man in his fifties – we are told that he believes he is attractive to women “and thinking seemed to make it so”.

Despite his allure, when we meet him Beard’s fifth marriage is disintegrating. His wife, Patrice, who resembles Marilyn Monroe, is having a flagrant, punitive affair with Rodney Tarpin, a builder; Beard is frantic, filled with shame and longing for her. Not that he has valued her much previously, having had affairs with 11 women during the course of their five-year marriage, which appears to be Patrice’s principal reason for taking up with Tarpin.

Beard is an intensely unlikeable man. In his personal life he is slovenly, creating instant and overwhelming disorder wherever he goes and treating his own body with little regard. Over the course of the novel he progresses from being an overweight 50-year-old to a morbidly obese man in his sixties who fills himself with alcohol and American junk food and who allows a melanoma on his wrist to go untreated. He is also without purpose, having long outlived his momentary fame as the originator of the “Beard–Einstein Confiation”, for which he received a Nobel Prize. This repugnant being holds our attention throughout the book in large part because of the role he’s fated to play in trying to save the world from climate change.

Beard attempts to get Patrice back through the ridiculous ruse of pretending he has another woman in the house. As the melodrama of the relationship plays out, it’s almost as if Beard is playing a typically female role, while Patrice plays the male one. But nothing is quite as it seems in Solar. In time, Beard is handed a thick file left by a deceased physicist, which contains the key to creating artificial photosynthesis – a vital technology in the battle against climate change.

Solar contains a stereotype of almost every kind of person who is interested in climate change: artists wishing to protest against it, bureaucrats administering institutions devoted to it, scientists researching it. Compared with Beard, however, they remain mere sketches. Where McEwan excels is in his descriptions of all the tiny physical changes that accompany our reactions and emotions. From the pain involved in having one’s penis frozen to a zipper to the sensation of eating a salt-and-vinegar crisp, his descriptions are sublime.

It’s not exactly clear what the moral of this strange farce is, but surely the book’s epigram is misplaced. It comes from John Updike’s Rabbit is Rich: “It gives him great pleasure, makes Rabbit feel rich, to contemplate the world’s wasting, to know the earth is mortal too.” This, for all his obnoxiousness, is not what Beard does. Instead, the moral power of the book – what there is of it anyway – comes from the paradox of a man whose private life is in such ruins imagining he can save the world.