Yes, the world gets warmer and colder. It generally does this in a pattern. According to all recorded data, the world should be getting colder now - not warmer. This does not prove that global warming exists, as we do not have enough knowledge or enough recorded temperature data to say with 100% accuracy.
Then again, there is no evidence to suggest the warming is natural other than humans lack of information, so I\'d go with the more likely scenario.