The amounts of several other greenhouse gases would increase substantially as well, e.g., methane, has more than doubled. Because most greenhouse gases remain in the atmosphere for a long period of time, even if emissions from human activities were to stop immediately, effects of accumulated past emissions would persist for centuries. Each greenhouse gas differs in its ability to absorb heat in the atmosphere. HFCs and PFCs are the most heat-absorbent. Methane traps over 21 times more heat per molecule than carbon dioxide, and nitrous oxide absorbs 270 times more heat per molecule than carbon dioxide.
Greenhouse gases are global in their effect upon the atmosphere.
The primary greenhouse gases, unlike many local air pollutants like carbon monoxide, oxides of nitrogen, and volatile organic compounds, are considered stock pollutants. A stock air pollutant is one that has a long lifetime in the atmosphere, and therefore can accumulate over time. Stock air pollutants are also generally well mixed in the atmosphere. As a consequence of this mixing, the impact a greenhouse gas has on the atmosphere is mostly independent of where it was emitted. Anthropogenic emissions of greenhouse gases occur in every country of the world.