Climate has been changing since before the first hominid.
of course, even before the first life.
Exactly what have humans done to change the climate?
to paraphrase Svante Arrhenius one of the first Nobel prize winners for chemistry and one of the first to examine the green house effect , We have evaporated our coal beds
see my previous post about CO2 being opaque to IR in certain bands
many of the bands it affects are already blocked by water vapor so there is really no additional effect there
but it makes a large contribution in one of the few ranges of IR not affected by water vapor
we also clear and pave large swathes of the planet
& we breed large herds of ruminants (but methane is opaque almost entirely in bands already at least partially blocked by water vapor so it adds to that but i forget the percent off the top of my head)
you haven’t heard any of this before?
Arrhenius, a Swede, was generally all in favor of warming things up a bit. It does get cold in Sweden. but at his time less was known about some other possible interactions
When and how did human activity begin to impact climate?
obviously as long as there have been people we have affected our environment. that is no big mystery.
when did that become something that wasn’t lost in the background noise of natural variations? Some say the neolithic age with the development of agriculture most push it forward to the industrial age.
there are some skeptics who say never… but we don’t pay attention to them
IOW, when did climate change become anthropomorphic?
“become” Anthropomorphic? what do you mean become anthropomorphic? as in the human contribution is the main variable?
never
who do you think is claiming that?
but that doesn’t preclude human activity form being a contribution. and in an energy balance, every little bit counts