ABSTRACT
Between one-third and one-half of the land surface has been transformed by human action; the carbon dioxide concentration 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; about one-quarter of the bird species on Earth have been driven to extinction; and approximately two-thirds of major marine fisheries are fully exploited, overexploitedy or depleted.
