Environment & Energy

Methane's impact (and that of all GHGs) is measured in CO2E - that is, Carbon Dioxide Equivalent - and the implied question is how many pounds of CO2 does a pound of another GHG equal in terms of its warming potential, or GWP.

If you use the EPA's online calculator (as long as it's still online, of course) and feed in a ton of methane, you'll get 28 tons of CO2E.

https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator#results

There's some variability in how methane impact is estimated - as high as 34 tons of CO2 for animal methane (livestock) and 36 tons for fossil methane. An important point, though is that most of a ton of methane breaks down in about 10-12 years and in doing so, loses that big mutiplier effect. The problem is that it breaks down into CO2, and CO2 persists for thousands of years.

Just for shits and giggles, here are the other designated GHGs and their CO2E values per ton:

Nitrous Oxide (largely from wet paddy agriculture) - 256 metric tons CO2E
Hydroflourocarbons (HFCs) averaged across the class of chemicals - 1,810 metric tons CO2E
Perflourocarbons (PFCs) averaged across the class of chemicals - 6,630 metric tons CO2E
Isoflurane - anaesthetic gases - 7,121 metric tons CO2E
Sulfur Hexaflouride - Insulating gas in electric transformers, and in some brands of athletic shoes - 22,500 metric tons CO2E