I can't really say anything about enviro sci, but I believe psych 1xx3 will be dealing with the more biological aspect of psychology...such as:
- Evolution
- Development
- Brain
- Vision
- Colour Perception
- Form Perception
- Depth, Distance, & Motion
- Audition
- Music
- Chemical, Senses, & Touch
- Motivation (Hunger)
(taken from the Psych 1A03/1AA3 review)
So, if you feel like you'd excel in that kinda stuff, then I say take psych!