Stop Trying to Save the Planet is an interesting op-ed by Erle Ellis Ph.D., the director of the Laboratory for Anthropogenic Landscape Ecology.
“[Nature] was gone before you were born, before your parents were born, before the pilgrims arrived, before the pyramids were built. You are living on a used planet…We now live in the Anthropocene–a geological epoch in which [Earth has been] shaped primarily by human forces.“
The thesis reminds me of one of E.O. Wilson’s statement that (paraphrasing) humans have tipped everything out of balance since they emigrated from a particular plain in Africa.
You can find Ellis’s op-ed is on Wired Science.
Nullius in Verba 
The Anthropocene Epoch should not be defined by vague and undemonstrated atmospheric theories. As a working geologist, however, I do envision a future Anthropocene interval (c. 5000 ya to ?) where the cultural effects of the exticnt Homo sapiens will be, as they are now for archaeology, the key guide fossils.
I agree with your point that definitions matter. Putting into words allows us to begin the process of making sense of our world and our place in it. Acquired knowledge then allows us to make decisions based on the knowledge and we move forward until something else forces a change in our collective worldview.
I can’t agree that we shouldn’t define this epoch that’s based on our imprint on the earth. Or perhaps I miss your point, my degree is in forestry, geology was studied to know where soil came from; my horizons move only about two centuries into the future. What I took from the op-ed was that we are intrinsically part of the process and have been for a very long time.
Thanks for stopping by.