Skepticism is a good attribute, but there appears to be an almost overwhelming stack of evidence supporting the existence of global warming that's primarily caused by anthropogenic forcing.

I am not a climatologist, a chemist, a physicist or even a biologist. To reach their level of understanding in their vocations I would need about a decade. That's time I do not have, so I must therefore defer to the experts.

And there's a lot of literature that the experts seem to have supporting their arguments. Given what I know of the pure sciences, their arguments are plausible (e.g.: no violating of the "laws" of thermodynamics) and the hypotheses reasonably follow. The alternative is that they are clueless (unlikely), they're on some kind of social bandwagon (unlikely), our observations and models on a broad range of pure sciences are completely off-mark yet nobody has noticed (risible) or there's some global conspiracy of scientists going on (risible).

The other side hasn't presented much. It appears to consist of internet kooks with hilarious graphs, the usual vacuous sound and fury of the media, or entities that have a vested interest in the status quo. So far as I know, there have been no peer-reviewed articles published in respectable journals that present any strong case agaist the conclusion drawn from all the other observations; feel free to enlighten otherwise.

I think the problem here is that while you have not seen nor sought evidence for anthropogenic forcing, you haven't done so for the opposite either. You simply don't know. Therefore the correct response to "Do you think that global warming is primarily caused by humans?" is "I don't know." not "I doubt it."