Wasn't really all that hard...
Methane, like carbon, is a greenhouse gas, but methane's global warming impact per molecule is 25 times greater than carbon's, according to the EPA.
I assume they mean carbon dioxide, right? Because if they're talking about pure carbon, I can't imagine it stays airborne for long enough to have much of an impact.
Maybe that's why it's so much less effective than methane.
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