Global Gap Analysis: towards a representative network of protected areas

The 20th century witnessed an extraordinary growth of the world's human population - from 1,650 million to 6,000 million people, with almost 80 percent of that increase occurring since 1950 (UN 2001). We now live in a human-dominated planet (Figure 1.1). Our population density is more than 30 times that predicted for an omnivorous mammal of our size and one-third to one-half of the land surface has been transformed by human action. Humans use about 40 percent of the planet's gross terrestrial primary productivity and 8 percent of the primary production of the oceans, 35 percent in temperate continental shelf systems. Sixty-six percent of recognized marine fisheries are fully exploited, overexploited, or depleted. The carbon dioxide concentration in the atmosphere has increased by nearly 30 percent since the beginning of the industrial revolution and more atmospheric nitrogen is fixed by humans than by all natural terrestrial sources combined. Humans use more than half of the runoff water that is fresh and reasonably accessible, with 70 percent of this for agriculture (Vitousek et al. 1997, Woodruff 2001).