The impact of climatic change on human affairs has been demonstrated dramatically in past years. Climatic extremes have placed increasing pressure on world food supplies leading to a doubling, then trebling, of grain prices during the 1970s. Moreover, there is mounting concern that society itself may soon bring about an unparalleled climatic shift by atmospheric pollution and changing land use. In order to deal wisely with the Earth's limited natural resources and to assess society's potential to alter future climate, more information is needed about the course of past climatic change....