Air pollution is caused by the release of particulates, biological molecules or harmful gases into the atmosphere, which causes death to humans and damage to living organisms like food crops. Water pollution occurs by the contamination of aquatic bodies like lakes, rivers, oceans. The combustion of fossil fuels like coal, petroleum and other factory combustibles is a significant cause of air pollution. The greenhouse effect is the cause of global warming, i.e. overall increase in the temperature of the Earth.