Generally, I agree with this statement but there is an however.As an FYI, here's some of the mechanisms with how the greenhouse effect works.. yea, it's complicated. And yea, I think watching species migrations are a pretty important indicator. Humans adapt, many species can't.
Creatures other than humans can adopt too, fairly easily even. The problem is the time frame that they have to do the adaptation in is now way to short. Normal climate change is an extremely slow process that takes thousands of years. Now we're doing it in 50-60. Most critters can't adapt that fast.