The term “greenhouse gases” refers to gases which trap heat in the atmosphere, much like in a greenhouse. Different gases vary in how much heat they trap, as well as how long they persist in the atmosphere before being broken down or absorbed.

As the largest contributor to climate change, carbon dioxide (CO₂) is used as our measuring stick, so emissions are reported as “tons of CO₂ equivalents”, or at larger scale, MTCO2E, millions of tons. CO₂ persists in the atmosphere for centuries. Methane, the next largest factor, has 80 times the effect but is cleared in about 12 years. Natural gas is primarily composed of methane, so leaks can have a major effect, particularly in the short term.

Other greenhouse gases include nitrous oxide (N₂O), produced by combustion of fossil fuels, and chloro- and hydro-fluorocarbons (CFCs and HFCs), used in older refrigerators and air conditioners. All of these also destroy the ozone layer in the upper atmosphere, which protects us from harmful solar radiation. In addition, nitrogen oxides can have severe health impacts, particularly on children and those with asthma.