Quite on the contrary, CO2 is at present the primary greenhouse gas. CO2 is at 387 ppm, CH4 is at 1780 ppb. The CH4 is about 250 times less than the CO2. However, should the Artic methane release continue, and warm the oceans enough that the continental shelf clathrates would release a major portion of their CH4, then CH4 would be the primary driver of warming, and there would be a major extinction.

Carbon dioxide, methane levels rise sharply in 2007

Another point on CH4, it is far more than 25 times as potent a greenhouse gas as CO2, for when it oxidizes, it forms CO2 and H20. So the combined effect of CH4, CO2, and H2O is closer to 60 times the total heating of a molecule of CO2.