I wonder if it is more a phrasing issue in American polls. I live in a small, rural, Southern town. I've had a few conversations, as well as watching American media. I think the term climate change or global warming means man-made warming in most people's head. Many people I've seen pressed on the issue, even by gentle conversation show this conflation. The deniers tend to be people saying, even through a veil, "I don't think man has everything to do with it".

Oddly, in the back of many people's head that I've spoken with is the Cambrian period. They have a vague remembrance that Earth was hotter and more swap like. Since there were no men then, it is possible for the planet to heat up on its own. They latch onto this thought and back their view that modern peoples can't be causing this much damage.