How Bad Of A Greenhouse Gas Is Methane?

You'll often hear that methane is a more potent greenhouse gas than carbon dioxide, but how bad is it really?
methane global warming potential

You will often see a number given for methane that is ~30 times as high as for carbon dioxide. E.g., the EPA uses 28-36 as the number. What's potentially unclear though is what that number represents. It's not that methane traps 28-36 times as much heat. It's that methane traps much more than that, but doesn't last in the atmosphere for as long as carbon dioxide does. For a detailed writeup on this, check out this link. If you don't care much about the writeup, just look at this image from it:

methane global warming potential

In case it isn't clear, the black line is the warming potential of methane (CH4) relative to carbon dioxide (CO2). Notice that it's extremely high early on and decays over time. This is because methane is shorter-lived in our atmosphere than carbon dioxide is. However, this means that the short-term warming is significantly worse than ~30x CO2.

Pulling the numbers from the plot, I get the following estimated values:

To convert the image of the plot into values, I used this tool. As you can see from this, simply stating that methane has ~30 times the global warming potential of carbon dioxide is incomplete. In the near-term, it is significantly higher. This is significant since positive feedbacks can amplify warming meaning that near-term warming can be quite impactful.


  1. What are GWP units of measure, please?

    1. 'Global Warming Potential' relative to carbon dioxide.

  2. But why short term AGWP for methane is so high, if IR absorption is much lower than CO2...or water?