I, personally, believe that it is caused (or at least has been bolstered) by humans, because that's what most scientists in the world believe, and I don't think I, or anyone, is in any way qualified to dispute the discoveries of our world's greatest minds. That being said, I know there are people who think that because there's some snow outside, climate change can't be real, or that it's just a natural process.
Here's the thing: who cares if it's caused by humans? The people who do not believe it's real are a bit out of our (well my) reach for the moment, because climate change isn't something that happens overnight (even though its effects are accelerating). We'll just have to wait it out for those people's communities to start being swallowed by rising sea levels before they care. Which sucks, but that's the way it's gonna be with certain people.
However, I think there's another group of people, who aren't 100% on board with the notion that climate change is the biggest issue affecting people today, but they realize that its effects could be an issue. These people however, will say that it's a natural process of the Earth, that we go through cooling and heating periods all the time. And they're not wrong, even though human actions have had an impact on these things and are accelerating climate change. The thing is, who cares if it's natural? A swarm of wasps is natural, but that doesn't mean it's good for us or that we should sit around not doing anything about it. I think there's a middle ground to be reached with these people. If we are only to convince them that climate change's effects could be detrimental, it won't matter whose fault it is. If something bad is happening, we should be doing something about it.
Ultimately this isn't a perfect argument. To reduce climate change we'll need to regulate industries and enact other reforms that people who believe it isn't caused by humans won't be on board with. But if we can convince people that action is necessary, that's a step in the right direction.