ENVIRONMENTAL POLLUTION Efforts to improve the standard of living of humans - through the control of nature and the development of new products - have also led to pollution, or contamination, of the environment. Much of the world's air, water and land are now partially poisoned by chemical waste. Some places have become uninhabitable. This pollution exposes people around the world to new risks from disease. Many species of plants and animals are in danger of extinction or are now extinct. As a result of these developments, governments have passed laws to limit or reverse the threat of environmental pollution. Ecology and environmental deterioration The branch of science that deals with how living things, including humans, are related to their surroundings is called ecology. The Earth is home to approximately 5 million species of plants, animals and microorganisms. These interact and influence the surrounding environment, forming a vast network of interconnected environmental systems called ecosystems. The Arctic tundra is an ecosystem, as is the Brazilian rainforest. The Hawaiian Islands are a relatively isolated ecosystem. If left undisturbed, natural environmental systems tend to achieve balance or stability among various species of plants and animals. Complex ecosystems are able to compensate for changes caused by weather conditions or intrusions by migratory animals and are therefore generally considered more stable than simple ecosystems. A corn field has only one dominant species, the corn plant, and it is a very simple ecosystem. It is easily destroyed by drought, insects, disease or overuse. A forest can remain relatively unchanged by weather conditions that would destroy a nearby corn field, because the forest is characterized by a greater diversity of plants and animals. Its complexity gives it stability. Population Growth and Environmental Abuse The reduction of the Earth's resources has been closely linked to the increase in the human population. For many thousands of years people have lived in relative harmony with their surroundings. The population size was small and the life support tools were simple. Most of the energy needed for the work was provided by the worker and the animals. Since about 1650, however, the human population has increased dramatically. Overcrowding problems are multiplying as more and more people are added to the world's population every year. Air pollution Factories and transport depend on enormous amounts of fuel: billions of tonnes of coal and oil are consumed around the world every year. When these fuels burn, they introduce smoke and other less visible byproducts into the atmosphere.