You don't need social media to learn that climate change is a thing. Just read Wikipedia. Look at the citations. And yet, a sizable portion of the US public believes it's a hoax.
Actually the problem with climate change deniers is that they doubt the source and cannot reason about the issue themselves. This is actually one example of needing a system to help people reason. Just telling someone something will not convince someone unless they trust the authority of the person telling them OR if they can reach the conclusion themselves. Thanks for this comment, it actually made me further realize how important such systems are.