Regarding CO₂/CO₂e...

Greenhouse gases are components of the atmosphere that contribute to the Greenhouse effect. Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities add to the levels of most of these naturally occurring gases.

Greenhouse gas emissions from industry, transportation and agriculture are very likely the main cause of recently observed global warming.

Carbon dioxide, methane, nitrous oxide and three groups of fluorinated gasses (sulfur hexafluoride, HFCs, and PFCs) are the major greenhouse gases and the subject of the Kyoto Protocol, which entered into force in 2005.

Carbon dioxide equivalent, or CO2e, is an internationally accepted measure that encapsulates all GHGs (greenhouse gases) that contribute to global warming (e.g. methane, perfluorocarbons, nitrous oxide, etc). As the mainstream media grasps "carbon" and "CO2" jargon, it should be noted that CO2e is a more correct/broad measure of total GHG contribution.

Therefore, CO2e is used to compare the emissions from various greenhouse gases, based upon the amount of carbon dioxide that would have the same global warming potential (GWP), measured over a specified timescale (generally, 100 years) for emissions or current GWP for existing GHG concentrations.