The surprisingly rapid melting of the icecap of the Arctic Ocean has been widely reported. In this book, Wadhams, an oceanographer, describes in simple terms the basic physics of what has been happening and why and puts forward a brief history of the role of ice on earth. He goes on to conjecture about some of the consequences of the almost certain continuation of Arctic melting, including both some economic advantages (such as increased ocean navigability) and some disastrous outcomes: the release of methane hydrates trapped under Arctic ice, which would aggravate climate change, and the relative cooling of Europe that might result from a southward shift of the Gulf Stream. Wadhams also discusses Antarctica, where, in contrast to the Arctic, the sea ice seems to be growing. The book would have benefited from more material on the land-based ice in Greenland, which is distinct from the sea ice around Greenland and which influences sea levels.