This is a big one. The biggest, actually. There’s a reason you hear about carbon dioxide emissions the most. The atmospheric residence time is a whopping 100 years. This means that the CO₂ emissions that are happening today will remain in the atmosphere for the next hundred years. Unfortunately, the residence time says that even if we greatly alter our activity to reduce our greenhouse gas emissions, we will still see global warming over the next 100 years, though it will be somewhat reduced. The global warming potential is somewhat less daunting, however it is still a formidable foe, considering the sheer amount of CO₂ already in the atmosphere.

So where is most of this CO₂ coming from? Answer: fossil fuel combustion, deforestation, and cement production.