The Little Ice Age, roughly from 1500 to 1850, was a predominantly cold period as compared to the industrial era (after 1850). Four different prescribed wind fields and three radiative forcings, namely volcanic activity, insolation and greenhouse gas concentration, are used in a numerical Earth System Climate Model to answer following questions: Was sea ice thicker and more extensive during the colder Little Ice Age? Could colder temperatures at the ocean surface penetrate to deeper levels? Was there a change in ocean salinity due to a different sea-ice cover? Could the changes in ocean temperature and salinity have changed substantially the buoyancy of the ocean? How important are radiative changes as compared to wind-driven changes on the ocean circulation? These are just a few questions addressed in this book which is intended for readers interested in the climate of the last millennium.