ENVIRONMENT-HUMAN INTERACTIONS

Over the long span of human evolution, the role of the environment in human activities and the role of human activities in the earth system have undergone many changes. Up until the beginnings of agriculture during the last stages of the pleistocene, some 12,000 years ago, it is difficult to imagine human activities having significant effects on the environment, beyond the local use of controlled

fire in hunting. With the onset of agriculture and its gradual spread from the Middle East during the early to mid-Holocene and later from centres in the Far East and Meso-America, the impact of human activities on the environment increased, first at a local then regional scale, and eventually becoming global. Since the onset of the industrial revolution some 300 years ago, the impacts have been ever more widespread, diverse and dramatic. This led to use of the term anthropocene for the period since the beginning of widespread industrialisation. During this period of rapid changes, the decades since the mid-twentieth century have seen the most dramatic acceleration in the significance and range of human impacts (the great acceleration) to the point where it is no longer sensible to see humans as the passive subjects of environmental influences. By now, the role of human activities in the Earth system has become so pervasive and, in some crucial respects, dominant, that a human-environment dichotomy is arguably no longer a useful paradigm. People themselves are now major players in the Earth system, and their activities are integral to its functioning.

A distinction has been made between human impacts that are systemic and those that are cumulative (see global environmental change). Though far from rigid or mutually exclusive, these categories form a useful starting point from which to explore the main ways in which human activities have become so important in the present-day Earth system. The most significant systemic impacts arise from those activities that have resulted in enrichment of the atmosphere by greenhouse gases, notably carbon dioxide, methane and to a lesser degree nitrogen oxides and tropospheric ozone. Cumulative impacts include the effects of deforestation and accelerated soil erosion.

[See alsoadaptive cycle, human evolution: climatic influences, socio-ecological/ environmental models]