I think it's happening.
However, I think it's partially man man made.
Lastly, I think more data needs to be taken on how threatening it is.
As of right now, most of the damage incurred from Global Warming is ripple effect damage and not direct damage. Think about a single species of frog being displaced from the rain forest (ripple effect), as opposed to the sea level rising to such an extent that most of the most valuable property on the eastern seaboard is under water (direct damage).