When I was a little they were pure theory and somewhat ridiculous cosmological objects, they were pure fantasy even when I grew older. They remained a theoretic consequence, not real, not really; Black Holes.
They did not exist when I was young. Then again background radiation and supersonic flight are novelties as well. They are all pretty real now.
And now climate change is what? In existence or simply imaginary (which is not the same thing as theoretic…)?
Ref.: nasa.gov