Methane is a very strong greenhouse gas. But the upside is that it doesn't stay in the atmosphere for long. The half life of it is something like 9 years.
Something like 90 or 95% of the greenhouse effect is from water vapor. The only reason we really care about atmospheric CO2 is because we think that it triggers more atmospheric water which is the real driver of global temperature change.
Depends on who you ask. Today it's tomato soup and epoxy, tomorrow it's C4 and a cell phone. It won't be long before we have conversations about nationalizing fossil fuel companies.
