Question

If human civilization had never developed on earth, would there be a greenhouse gas?

Answer 1

A very high 90% or so of greenhouse gas is due to human actions, coal burning etc. Livestock are responsible for about 5%.

Answer 2

Yes. This is because natural gases can also come from natural sources like volcanoes and cows. Cows produce tons and tons of methane each year and volcanoes release many greenhouse gasses when they erupt. 

Hope this helps!!!