Hypothesis? Conjecture? Theory?

Worldwide climate change is an observed fact.
The extent to which human activity is a cause, or partial cause, is debatable. Correlation there may be, but this is not the same thing as causation. A sample size of one doesn't help.
Nevertheless it's undeniable that if we are a cause, and we can do anything to lessen our impact, we'd better get on with it PDQ. It might already be too late.