There is a natural “carbon cycle”, in which billions of tons of CO2 are exchanged back and forth between the atmosphere and the surface of the Earth. C02 is removed from the atmosphere by the oceans and growing plants (also known as “sinks”). At the same time, CO2 is released back into the atmosphere through natural processes such as the decay of dead plants, also referred to as ‘sources.’ When the carbon cycle is in balance, the total global CO2 releases and removals are roughly equal.

Natural sources of CO2 include:

• Plant respiration (just as plants “inhale” (or remove) CO2 from the atmosphere during the process of photosynthesis, they “exhale” CO2 when they convert oxygen and nutrients into energy;
• Ocean-atmosphere exchange; and
• Volcanic eruptions, which release carbon from deep within the Earth.

Carbon dioxide formula

Since the advent of the Industrial Revolution in the 1700’s, however, human activities such as the burning of fossil fuels, deforestation and other changes in land-use have greatly increased the amount of CO2 in the atmosphere. In 2005, for example, global CO2 levels were 35% higher than they were before the Industrial Revolution.