That's a big question with a bigger response. I'll try to be as short as I can cause I know I'm long winded.
There have never been 8 billion large animals on Earth that burned things.....that has to impact the environment......to what extent I'm not sure I would bet the under instead of the over though from an emissions perspective alone.....I actually think we are doing more harm from a water aspect. On the 1-10 scale above I'm a touch lower than 4 but wouldn't fuss with that number. If you say 6 or more you can't do the math to really talk about it.
We need to be pursuing technologies that can actually work. Renewables have a couple of issues....the weather, physics, and the rotation of the Earth those are tough to avoid. We should have gone with the best way to produce the energy we need with the best overall outcome.....not just built for the sake of building because it doesn't use fire....so we need to stop throwing money at that immediately. There may be a carbonless future someday but we are going backwards now and it's because of the renewable boom. And I don't mean like "oh we missed 20 years to be really researching safe nukes or something new".....I'm saying today we have a less reliable grid and are building dirtier less efficient plants because we wasted years and billions on something anyone that knows the basics knew would never work in the name of being green. We have made carbon the enemy and simultaneously not done a whole lot about the amount we produce while also ignoring every other aspect of the environment. There hasn't really been a lot of real science involved in the path we have taken. We need to go nuke, combined cycle, simple cycle emergency/recovery generators.....less carbon, less footprint, most reliable. We need to put the billions of dollars we have wasted on renewables into something that has a real future.