A colourless and odourless gas. The main sources of methane are agriculture and fossil fuel production, mainly natural gas. It is considered a GHG.

On a per-kilogram basis, methane, nitrous oxide and fluorinated gases all have higher climate change impact or global warming potential (GWP) compared to carbon dioxide.

For ease of understanding and consistency given these variations of GWP, scientists typically uses a unit measure called a ‘carbon dioxide equivalent’ or ‘CO₂ equivalent’, abbreviated as CO₂e to compare the emissions from various GHGs on the basis of their GWP by converting amounts of other gases to the equivalent amount of carbon dioxide.

Although these gases may have a higher GWP than carbon dioxide, carbon dioxide is the most abundant GHG emitted through human activities.