Example
Methane has a much larger value over twenty years than over one hundred years.
The catch
A GWP20 claim cannot be compared directly with a GWP100 inventory total.
Related terms
Global warming, Global warming potential, GWP100, Methane, Absolute emissions, Activity data
In more depth
GWP20, explained.
GWP20 is the metric for asking how much warming an emission causes in the 20 years after release. It applies the global warming potential calculation to that short window. Mass for mass, methane warms about 80 times as much as CO₂ over 20 years, compared with about 30 times over 100 years (IPCC AR6, UNEP). The gap exists because methane lasts only about 12 years in the atmosphere. A longer horizon spreads its strong early effect across decades when most of it is gone.
That makes GWP20 useful for questions about the rate of warming and near-term risk, and methane studies often report it next to GWP100. It also makes the metric easy to misuse. Converting a methane project's results with GWP20 makes its benefit look far larger than the same project under GWP100, and readers rarely notice which factor was applied.
Use it openly. State the horizon beside every converted figure and give the GWP100 result alongside it, so readers can compare like with like. Keep each total in one horizon from start to finish, and treat any headline that quotes only the larger number with care. Both horizons describe the same physics. They answer different questions about time.