Human activities are at the root of virtually all extinction threats.  Destruction of fragile habitats, wetlands, coral reefs, tropical and temperate forests, rivers and grasslands has accelerated in recent years due to human population increases and commercial exploitation of forests, ocean fish and other wildlife, as well as the introduction of non-native species, either intentionally or accidentally.  The massive pollution and chemical contamination of air, water and soil--and even the atmosphere that surrounds the Earth--are altering the climate and bringing about unforeseen declines in wildlife and plants.