Introduction

Current archaeological evidence indicates that modern humans, Homo sapiens, appeared in Africa by 200,000 years ago (McDougall et al., 2005; Shea et al., 2004). Their arrival occurred just prior to a very cold interval known as marine isotope stage 6 (MIS6), when ice sheets expanded across much of Europe, northern North America, and parts of Asia and southern South America. H. sapiens' migration out of Africa occurred during the last glacial cycle (LGC), an oscillating climate interval that saw the Earth move from the warmth of interstadial environments to the extreme cold of the last ice age. The highly variable climate of the LGC was followed by the onset of the relatively warm and stable Holocene period, beginning 11,650 years ago (see Chapter 1, Figure 1.2). About 10,000 years ago, at a number of disparate locations around the world, humans began to ensure a more stable source of food through the development of agriculture and the domestication of animals. The appearance of agriculture and advances in its techniques usually coincided with major climatic changes (see Chapter 8). Since the onset of agriculture we have continued to increase our capacity to manipulate Earth's resources and as a consequence have spawned an exponential increase in global population and consumption. These changes have also begun to seriously impact Earth's climate.