Methane is like CO2. It also is produced by natural processes.

Methane's processes are a little different, but, it is naturally produced. We are never going to run out of methane EVEN if we leave the stuff the petroleum industry drills IN THE GROUND.

Naturally occurring methane is mainly produced by the process of methanogenesis. This multistep process is used by microorganisms as an energy source. The net reaction is:

CO₂ + 8 H⁺ + 8 e⁻ → CH₄ + 2 H₂O

The final step in the process is catalysed by the enzyme methyl-coenzyme M reductase. Methanogenesis is a form of anaerobic respiration used by organisms that occupy landfill, ruminants (e.g., cattle), and the guts of termites.

It is uncertain if plants are a source of methane emissions.

So