Habitats are altered in many ways by human activities. Forests and other natural environments are cleared to make agricultural land or urban areas. Climate change due to rising emissions of greenhouse gases like carbon dioxide will influence some regions by, for example, increasing periods of drought. About half of the emissions of carbon dioxide has been absorbed by the oceans and this is changing the chemistry of sea water. Alteration and loss of habitats is a major problem facing the biosphere and some examples are described on this page.
Although they represent only 7 percent of the Earth's land surface, tropical forests are home to 60 percent of the species of animals and plants that are alive today. These forests are being cleared at an alarming rate in South America and southeast Asia, and loss of these environments will lead to significant extinction. One estimate made in 2004 suggests that three quarters of the forests of Southeast Asia could be gone by the end of the century. Such a loss of habitat could produce extinction of as much as 42 percent of species of animals and plants in the region.
Across parts of southeast Asia, including Indonesia and Malaysia, natural rainforest is being replaced with oil palm plantations. Palm oil is a major source of vegetable oil, which may be used for biofuels. The loss of rainforest habitats threatens many species, including the orangutan.
Palm oil is the most widely used vegetable oil, both for food products and to make biofuels. By 2008, more than 50,000 square miles of tropical habitat had already been converted to palm oil plantations, mostly in Indonesia and Malaysia. Estimates suggest that about three quarters of bird species and more than 80 percent of butterfly species found in Indonesian forests do not occur in the plantations. If forest habitats continue to be lost extinction is inevitable.
Rainforest declined dramatically on the Indonesian island of Sumatra due to logging and conversion into agricultural land (including oil palm plantations). Loss of rainforest continues today.
Climate change in the Arctic
Each summer, some of the sea ice floating in the Arctic Ocean melts and reforms over the winter. Satellite images show that the amount of summer melting has increased dramatically since 1979 (the first year that data from satellites became available). Some of the Arctic sea ice melts in spring and summer and reforms in winter.
The area of the Arctic Ocean covered by ice at the end of the summer is much lower than it was 30 years ago. This change is related to warming of the Arctic by increasing levels of greenhouse gases like carbon dioxide. The warming is magnified by other factors, including a change in albedo, or the reflectivity of the surface. Ice reflects most of the heat from the sun but seawater absorbs most of it. As open ocean replaces melting ice, the increased warming allows even more melting to happen.
The loss of sea ice is a problem for some Arctic animals. Polar bears build up fat reserves in the winter by feeding on seals on the ice. They also use the ice to travel through the region. If the trend towards reduced sea ice continues, polar bears could become endangered.