Water is among the most essential resources that sustain Earth’s ecosystems, but these systems are currently under threat due to land use and climate change. Assessing the impact of this global change on water security and ecosystem’s functions is not only the key concern of the United Nation’s Sustainable Development Goals, playing a key role in sustainable development of society, but also the most important research focus in “Future Earth” and Earth critical zone research.

This book is concerned with the role of the ocean in the climate system, with a focus on physical processes relevant to scientifically describing and understanding that role. The two chapters in this Part I offer a context for the discussion extending over the nearly 30 chapters that follow. We are introduced in this Part to notions of the huge space and time scales over which ocean phenomena play a role in climate. Such phenomena extend from the millimeter and seconds relevant for irreversibly mixing heat, carbon, and other tracers, to the global scales of sea level changes, water mass variations, and air–sea interactions that comprise natural and anthropogenic climate fluctuations. We also encounter evidence seen for rather large fluctuations in the paleo record, and consider future climate scenarios suggested through computer simulations. <...>

The bright midday sun glinted off the calm waters of the Inland Sea and silhouetted the long, sinuous form of a huge mosasaur lying motionless amid the floating tangle of yellow-green seaweed. At 20 years old, more than 30 feet in length, and weighing over a ton, the adult mosasaur was almost full grown and was much larger than any of the fishes or sharks that lived in the shallow seaway.