Its always the people who complain about the lack of a certain demographic in a field who choose not to go into it. I've heard far more people who have useless degrees complain than people who went out and got good ones.
Astrophysics hardly gives you any knowledge of climate change. Granted an astrophysicist might figure out how climate change would work on a foreign body near a star, maybe. But that would all be theoretical.
TLDR
Astrophysicists aren't trained Climatologists.
TLDR
Astrophysicists aren't trained Climatologists.