Carbon markets were created to provide carbon offsets, credits or allowances, which are measured in metric tons of carbon dioxide or equivalent. One credit is equal to the reduction, sequestration or offset of one ton of carbon dioxide or equivalent of various greenhouse gases, which include:

• Carbon dioxide  (CO ₂ ) is a product of cellular respiration, you exhale it and plants absorb it.
• Methane  (CH ₄ ) is the main component of natural gas and cow burp.
• Nitrous oxide  (N ₂ O) is also known as laughing gas and is used as rocket propellant.
• Perfluorocarbons  (PFCs) are man-made compounds containing only carbon and fluorine that were historically a by-product of the electrolysis process in aluminum smelting.
• Fluorocarbons  (HFCs) are man-made compounds containing fluorine and hydrogen that are often used in air conditioning and refrigeration.
• Sulfur hexafluoride  (SF ₆ ) is naturally occurring but primarily manufactured as a madder and is used in the electrical industry as a gaseous dielectric medium, in semiconductor manufacturing, and in magnesium casting.(Lenore Elle Hawkins)