@fabsh, you asked for exactly this in episode 100, so here you go:
Re trees not being a carbon neutral source of power: dude, you’re full of shit! Plants don’t source carbon from the soil (well, some do, but that’s a miniscule percentage). Plants, by virtue of photosynthesis, capture carbon dioxide (CO₂) from the air, separate the carbon atom (C) from it and release the resulting oxygen (O₂) back into the air. Other chemical elements they need plants usually do get from soil, but not carbon. So when you burn a tree, you’re returning what carbon it has captured from the athmosphere during its whole life back into the athmosphere, which is exactly why it is considered carbon neutral.