It's very real and very dangerous, at least eventually. As far as the portion caused by humans, I firmly believe people 100 years from now will look back at common actions regarding the environment today with confusion and anger. The irony here is that if climate change acted 50 times faster, people today would almost assuredly band together to abate it. Its slow creep, however, virtually guarantees the adverse effects won't really be felt until it's far too late.