Gizmo, like a large proportion of deniers, simply believe there are much larger forces at work on the planet than mankind.
They dont know what it is, but they know, absolutely, it exists.
Its a kind of god thing. The religious element will come right out and call it "god". Those not so inclined sometimes clamor for vague concepts like "natural cycle", or "solar influences".
Maybe God only knows what exactly these are.

Because these things sound "scientific", they believe it gives them more credibility and distances themselves from their god-bothering bretheran.
The question is, at what point does mankinds population and technology start to impact on the climate of a planet the size of ours. Scientists are saying, "about now".
Deniers think it sometime off, or maybe never.