Comparative GHG Strength
You might see on some graphs that instead of listing each emission type, they are combined and listed as CO2e – or CO2 equivalent. Each gas behaves differently when interacting with both energy from the sun and the Earth, and will contribute more or less to trapping energy (known as their “radiative efficiency”)(SOURCE). Think of it like different thicknesses of the blankets we are adding to the atmosphere. To make these emissions comparable, they are converted to their equivalent mass in CO2, since that is the largest GHG by far. However, we must also take into account factors such as lifespan! While we may not think of gases as having a lifespan, each emission only lasts so long in the atmosphere before it either reacts with other gases or falls back to the earth (like through acid rain, Source). For example, methane has a global warming potential (GWP) around 27 (that is, 27x stronger than CO2). However, it only lasts in the atmosphere for around 10 years, compared to the thousands of years that CO2 can last (SOURCE).
It is because of these relative strengths that atmospheric scientists take great care to track as many gases as possible. For example, Nitrogen trifluoride is emitted a lot less than CO2, but is over 17000x stronger than CO2 at trapping energy! Each time the IPCC releases a new report, they update the GWP of each greenhouse gas, based on the latest research(SOURCE, Link to examples).
Full List of GHGs and strengths? (US EPA, 2016b)