Carbon dioxide is a colorless and odorless gas occurring naturally in small quantities in the Earth's atmosphere. Earth's oceans, soil, plants and animals emit CO2. The formula for carbon dioxide is CO2. The CO2 molecule contains 2 oxygen atoms which each share 2 electrons with a carbon atom to form 2 carbon-oxygen double bonds. The atoms are arranged like this (OHT). This is called a “linear molecule”. Carbon dioxide is usually found as a gas and is never a liquid. It sublimates into a solid known as “dry ice” which is used as a substitute for normal ice because it is much colder and does not melt. Humans and animals exhale carbon dioxide, often called a greenhouse gas, as a waste product. Plants absorb this CO2 and use it to make food. This is called photosynthesis. During this process, oxygen is released and then breathed by humans and animals. This procedure is repeated again and again and a natural balance is achieved. But this natural balance is disrupted by human activity. The planet's inhabitants release more than 5.5 billion tonnes of CO2 into the atmosphere each year. 75% of this pollution is due to the burning of fossil fuels. These fuels are constantly burned to run factories, power plants and vehicles. The main sources of CO2 emissions are electric utilities, residential buildings, industry and transportation. The remaining 25% is due to the destruction of the world's forests. The reason is that there are fewer trees and plants absorbing CO2, but there are just as many, if not more, humans and animals exhaling it. The amount of CO2 in a planet's atmosphere affects the planet's temperature. . As more and more CO2 builds up in the atmosphere, less heat can escape and the planet warms. CO2 traps solar radiation like a greenhouse. This is called global warming or the greenhouse effect. Global warming is becoming a serious problem and CO2 is the main cause. The Earth is now warmer than it has been in thousands of years. The amount of CO2 deposited in the Earth's atmosphere due to human activities is expected to double by 2050. It could even quadruple in the future, as developing countries like China are keen to improve their standard of living..