Pollution reduces biodiversity in countless ways. The Earth's ecosystems are exposed to an enormous variety of human-caused pollution, with individual species reacting differently to each pollutant. Many pollutants create reproductive problems in animal species, leading to decreased fertility. Industrial chemicals, pesticides, plastics and other petroleum hydrocarbons can interfere with hormonal processes, often by acting as synthetic forms of estrogen. When these pollutants end up in waterways, fish, amphibians, insects and bird populations can be profoundly affected.
Another example of pollution's effect on biodiversity can be seen in the growing presence of dead zones where large rivers empty into oceans. Dead zones are a consequence of agricultural pollution, most often high levels of nitrogen and phosphorus. Under natural circumstances, the mouths of rivers are biologically rich, benefiting from deposits of river sediment and a diversity of small ecosystems in a small area. When river water contains excessive levels of chemical nutrients, algal blooms can occur, resulting in a significant decrease in the levels of dissolved oxygen in the water. The oxygen-poor water becomes unable to sustain marine life, creating a dead zone. Notable dead zones grow seasonally at the mouth of the Mississippi River in the Gulf of Mexico and at the mouth of the Columbia River off the coasts of Oregon and Washington.
Most mainstream climate scientists agree that the planet is undergoing rapid climate change as a result of a human-caused increase of greenhouse gases in the atmosphere. Greenhouse gases such as carbon dioxide, water vapor, methane, nitrous oxide, and chlorofluorocarbons absorb the sun's heat as it is reflected from the Earth. The natural greenhouse effect keeps the Earth at a suitable temperature for life. However, human pollution, mostly in the form of carbon dioxide emissions, has created an enhanced greenhouse effect. The consequence is commonly referred to as global warming.
Global climate change manifests in a wide variety of ways depending on location. Rising average global temperatures result in the melting of glaciers and ice caps, raising sea levels and affecting coastal ecosystems. Global warming alters habitats for plant and animal species, allowing the introduction of new species in some areas and making the same areas uninhabitable for others. Climate change upsets the delicate balance that ecosystems develop over long periods of time.