This book reports on abrupt climate change which is defined as a large scale change in the climate system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few decades, and causes substantial disruptions in human and natural systems. Abrupt climate change presents potential risks for society that are poorly understood. An improved ability to understand and model future abrupt climate change is essential to provide decision-makers with the information they need to plan for these potentially significant changes.