The Anthropocene

The start of the period of large-scale human effects on this planet (the Anthropocene) is debated. The industrial view holds that most significant impacts have occurred since the early industrial era (∼1850), whereas the early-anthropogenic view recognizes large impacts thousands of years earlier. This review focuses on three indices of global-scale human influence: forest clearance (and related land use), emissions of greenhouse gases (CO 2 and CH 4 ), and effects on global temperature. Because reliable, systematic land-use surveys are rare prior to 1950, most reconstructions for early-industrial centuries and prior millennia are hind casts that assume humans have used roughly the same amount of land per person for 7,000 years. But this assumption is incorrect. Historical data and new archeological databases reveal much greater per-capita land use in preindustrial than in recent centuries. This early forest clearance caused much greater preindustrial greenhouse-gas emissions and global temperature changes than those proposed within the industrial paradigm.