Human Domination of Earth’s Ecosystems

Human alteration of Earth is substantial and growing. Between one-third and one-half of the land surface has been transformed by human action; the carbon dioxide con-centration in the atmosphere has increased by nearly 30 percent since the beginning of the Industrial Revolution; more atmospheric nitrogen is fixed by humanity than by all natural terrestrial sources combined; more than half of all accessible surface fresh water is put to use by humanity; and about one-quarter of the bird species on Earth have been driven to extinction. By these and other standards, it is clear that we live on a human-dominated planet. All organisms modify their environment, and humans are no exception. As the hu-man population has grown and the power of technology has expanded, the scope and nature of this modification has changed drastically. Until recently, the term “hu-man-dominated ecosystems ” would hav