Industrial and agricultural pollution is prevalent throughout the world, with man-made chemicals found in virtually all environmental niches. In the United States, pollution from mining contaminates 40 percent of western rivers, poisoning aquatic life and bioaccumulating in the food chain. Many chemical pollutants, including pesticides and plastics, disrupt animal hormonal activity and reproduction, reducing biodiversity in water and on land. Organic nutrients from agricultural runoff result in aquatic algae blooms that deplete dissolved oxygen levels, creating dead zones in coastal areas near major rivers. In many areas of the world, human pollution has destroyed entire ecosystems, leaving land and water unable to support life.
Over-exploitation of the natural world takes many forms. Forests are destroyed for lumber, agriculture and ranching, resulting in considerable loss of biodiversity. Nearly all of the oceans of the world are fully exploited or over-exploited, with most fisheries expected to collapse within the next 40 years if fishing practices are not changed. The world's soils are also being depleted at a rapid rate, leading to desertification and loss of agricultural productivity. In any of its forms, over-exploitation leaves ecosystems impaired and less capable of supporting life.
Invasive plant and animal species disrupt ecosystems by taking over ecological niches within their adopted home, preying on or driving out native species and disrupting food chains and other interdependent systems. The common rat is a species that has invaded countless areas of the world since the age of exploration. Invasive species tend to have no natural predator in the new ecosystem, allowing them to reproduce prolifically. Invasive plant species, such as kudzu in the southern United States, can take over vast amounts of land, forcing out other plants and destroying the natural habitat and food sources of the local animal populations.
Global warming threatens ecosystems throughout the world. Human-caused greenhouse gas emissions cause increasing amounts of heat to be absorbed by the atmosphere, leading to rising global average temperatures. Climate models indicate possible average temperature increase of between 4 and 10 degrees Fahrenheit during the next century. As air and water warm, many species will be unable to tolerate the higher temperatures. Those that cannot migrate to a suitable climate will become extinct, degrading ecosystem integrity in all areas of the world.