Except natural gas is a fossil fuel. The name is somewhat misleading.

I'm not aware of any way to create synthetic propane using renewable energy sources, but that might be my ignorance speaking. A quick googling indicates it's not possible, but I'm happy to be proven wrong here if you want to provide a reference I didn't find.

Easier and cheaper doesn't really cut it for the climate. Petroleum is easy and cheap, and so is coal. Both are terrible ideas in the long run though