“The only problem here is that I have never taken an Environmental Science class (but I still enjoy the topic, just prioritized physics), …”
Guess what!
Many standout economists also were very interested in Physics. Modern economics is very mathematical. Even the life sciences have become a hotbed of numerical modeling… it was not always so.
I’m just an old man who enjoyed economics, math, physics and worked for a few years on environmental issues prior to the first earth day in 1970. Biochem was my nemesis as I never had a memory for Greek and Latin.
Check out subject discussions for undergraduate major ideas at WPI @ https://www.wpi.edu/search/google/environmental%20economics#gsc.tab=0&gsc.q=environmental%20economics&gsc.sort=
CMU would be a very good place to pursue these studies. See https://www.cmu.edu/
Have a good time!