Remember the cooler, the ice rink.
Oh my gosh!
That's it!
The earth is getting warmer, and the return of the blobs are "proof!"
Exactly. Different entities can be detected visually within different temperature ranges — it's the thermal analog of the electromagnetic spectrum. If the temperature continues to rise, the dinosaurs will again become visible. If the temperature drops to minus 500°, for example, than humans will not be visible.