"I do believe the climate may be changing, but in the course of millions of years, most of them being without humans, this is a normal occurrence."

That's the "climate is always changing" argument which is claimed to be evidence that humans can't possibly cause global warming. That logic is equivalent to:

"A causes C. Therefore B cannot cause C."

But the fact that A causes C says absolutely nothing about the relationship of B to C. The logic is equivalent to these statements:

"Forest fires have always occurred, therefore humans can't cause forest fires."

"Floods have always occurred, therefore humans cannot cause floods."

"Earthquakes have always occurred, therefore humans can't cause earthquakes."

The first example is obviously false. The second is false because changes to land by man can create conditions for flooding, for example, removing forest. The third is false because pumping waste water from fracking into the ground can cause earthquakes - see Oklahoma.