When the weather becomes extreme or even unseasonal, "El Nino" is usually the phrase we hear. Every three to seven years, El Nino disrupts weather all over the globe, second only to the change of seasons in its influence on the climate. But what is El Nino? El Nino is the name given to the unusual increase in ocean temperatures along the Peruvian and the Ecuadorian coasts that is part of a larger pattern of changes in wind and weather throughout the world. With El Nino come violent storms and upsets in global food chain that dramatically affect both humans and wildlife. Effects can be as gentle as a mild winter in northeastern United States or as violent as drought in Southeast Asia, brutal storms in South America, and wildfires in Australia. With the help of carefully selected photographs and clarifying charts and maps, Caroline Arnold makes clear how this remarkable weather pattern forms, how scientists track it, what its effects are, and why following its path is of such importance.