For a long time, there existed no environmental problem. This was because there existed a proper balance among the natural and man-made elements. But as a result of the rapid growth of human population, spread of urbanisation, industrialisation, deforestation, extensive use of fossil fuels, shrinking of wetlands, etc., ecological equilibrium that existed among the four spheres of the earth got disturbed. This caused the emergence of many problems such as pollution, desertification, global warming, melting of snow, rise of sea level, etc. Since all these problems are linked to the environment, they are called environmental problems.