Well, two things.

First, "global warming" isn't quite the same thing as climate change. This is kind of a distinction without a difference, perhaps, but I find in many communities (not LW) that the semantic distinction between these terms causes confusion.

Second, and more important to me: supposing that N% of climate variation over time is accounted for by human activity, the wording of the question allowed some ambiguity between (N > 50) and (N is non-negligible). I'm fairly confident that N is non-negligible, which seems like the important question for policy purposes. I'm not confident that N > 50.