As I remember it, the effect of methane is not that clear-cut. It is a far more potent greenhouse gas than CO2, but it doesn't last very long in the atmosphere before getting oxidized or lost to space (years rather than centuries). So either as cow burps or ocean seeps, maybe no big deal.

Chlorinated and fluorinated hydrocarbons (i.e. refrigeration and air conditioning heat transfer fluids) are definitely serious - they are even more effective as greenhouse gases than methane and are only degraded very slowly. Domestic and automotive air conditioning should be banned worldwide and immediately (also because of their staggering energy demands).