I totally concur with you in that the Earth's climate has been evolving/changing ever since the formation of the planet. However, there are numerous examples of where people have indeed impacted things to where we can observe, or at least surmise, changes over time that are human influenced. Some of those we can see right here in ND. For example, we know that tilled soils have a much lower capacity for infiltration of water from rainfall and snowmelt. So if we look at a graphic showing the amount of water that has passed by Jamestown over the past century, we see a rise in total water discharged on an annual basis that cannot be attributed to simply more rain and snow.
Well, at least that's my theory on cause and effect for the James. The same can surely be said about the Red River as well since it's probably the most tilled watershed in the area, so no real surprise there either. Lots of other examples across the planet of humans altering the environment enough to cause surprising changes. I noticed recently that the Chinese paddlefish has officially been declared extinct. I am pretty sure that is due to all the pollution and dams on the rivers in China. That's a species that has been around for a hundred million years, and in the blink of an eye (geologically speaking) it no longer exists.
The real challenge in my view is how to tease out of the overall change, what would have occurred without human influence, and what can be attributed to human actions. 8 billion people is not something this planet has ever seen before.