ABSTRACT
Realization that climate has changed radically with time came only during the 1840s, when indisputable evidence of former ice ages was obtained, yet in many parts of the world the climate has altered sufficiently, even within the last few thousand years, to affect the possibilities for agriculture and settlement. Reliable weather records have been kept only during the last hundred years or so, but proxy indicators of past conditions from tree rings, pollen in bog and lake sediments, ice core records of physical and chemical parameters, and ocean foraminifera in sediments provide a wealth of paleoclimatic data. The discussion in this chapter focuses on climate forcings and observed changes, as well as future projections, but first it is worth while to consider the nature of climate variations.
