The way common language defines "nature" doesn't map well to reality and we end up developing contorted thoughts rather than re-evaluating the tools we use to think.
I like to contrast wild/raw stuff to artificial stuff, both of which are part of nature. Many things that are commonly considered "natural" are actually far from wild. Fields in the countryside? Artificial. Vegetables and farm animals? Artificial, even before GMO. Etc...
That being said, the way we've shaped the planet these last 200 years is radical, and possibly too radical for our own survival. Fossil fuel gave us an immense power and we probably didn't use it wisely. We'll see.
I think most people picture a place without human activity at all when they imagine a fully "natural" environment, like an island thats never had people on it. In this interpretation, people living naturally would cause their environment to deviate minimally from how it would be in their absence.
We are currently the direct cause of an ongoing mass extinction. We have yanked the surface of the planet so far from equilibrium that it may never return to its previous state. We are from being a part of nature.
Thankfully, we also have a reasonable expectation in the use of words in that they map to something real. The broader the internal consistency of that word, the more 'authoritative' it should be - although, admittedly, this is just my opinion. (Politics will surely have some say about this.)
On defining nature, we have witnessed two definitions.
1. Not human.
2. All of the cosmos.
Those who appreciate the theory of evolution, I think, will have a harder time determining where the threshold between human and nature would be.
All human terms are subjective that way. The universe is relative and probabilistic. Ideas like "nature" can be useful, but that's not to say the universe has a boolean type called "Nature" that actually exists in any objective sense.
Yet we keep having these sorts of debates year after year. Nothing exists in the ways that most people think them to be. I could care less whether something is "natural" if the conclusion has no use.
The most useful meaning of this word is simply, "Not Human". But the human belongs to the natural.
You would consider a car, or a chainsaw natural? I wouldn't.
It is now just a way to say, "not human". Unfortunately, the embedded arrogance is still perpetuated.
We've got plenty of words whose referents aren't sound concepts.