Habitat destruction is the biggest reason for the loss of biodiversity to date. Most life on the planet lives in either the oceans or rain forest, both of which are over-exploited. The world's tropical forests are being cut at an alarming rate, with more than half of the primeval forests already destroyed. Nearly all ocean fisheries are fully exploited or over-exploited. Fresh water resources are over-harvested, leaving less for other species. To protect ocean biodiversity, fishing must be made sustainable and by-catch reduced. Forests must be preserved in adequate size to support the range of resident species. Fresh water must be conserved to preserve river, lake and wetlands habitats.
Pollution is a great destroyer of biodiversity, poisoning ecosystems and disrupting reproductive process throughout the world. In its worst manifestations, such as with the BP Gulf of Mexico oil spill in 2010, pollution can poison ecosystems of a large geographical area. Several common chemical pollutants are disruptive to animal reproduction, often acting as a form of synthetic estrogen. Reproduction problems can cause species populations to plummet, upsetting the delicate balance of ecosystems. To protect species and biodiversity, pollution must be strictly controlled and eliminated wherever possible.
Invasive species can be animals or plants that arrive from outside an ecosystem and then take over niches within the ecosystem, displacing other species and disrupting food chains and subsistence patterns. Stable ecosystems evolve internal control mechanisms, with each species serving a role. When invasive species arrive, often an ecosystem will have no natural control available, resulting in proliferation and dominance of the invasive species. When invasive species dominate, biodiversity suffers. To protect biodiversity, care must be taken to avoid introducing non-native species and to eliminate them whenever possible. Unfortunately, once an invasive species has established itself, it can be very difficult to dislodge.
Most mainstream scientists agree that the planet is warming because of human-caused greenhouse gas emissions, with some estimates forecasting rising temperatures of up to 10 degree Fahrenheit during the next century. Rising global temperatures will result in species loss throughout the world's ecosystems as individual species will be unable to tolerate higher temperatures and also will be unable to migrate quickly enough to adapt. Some ecosystems, such as coral reefs, are likely to be more sensitive to climate change than others. To protect biodiversity, greenhouse gas emissions must be brought down to sustainable levels. Given current economic and political trends, such reductions seem unlikely in the immediate future.