From the inbox:
I aspire to become an environmental economist (specifically in your field) and I was sending this email in regards to advice on classes to take, and or organizations to join. I was also interested (of course at the expense of your time) in your approach to your current occupation; the classes you took or the routes you took in acquiring your current occupation. Thank you for your consideration.
Oh wow, I'm awful at giving advice.
I always tell undergrads not to worry so much about grades, etc and try to enjoy college as much as possible while learning as much general stuff as possible. This is why I don't like the "if you want to go to economics graduate school, then major in math" advice. It might be good advice for a potential grad student, but it seems to be a real turn off to someone interested in economics. How about this? Major in economics and try a math minor, that should get you enough calculus to survive the core theory courses in grad school. Also, find out if the college you choose offers an environmental economics course. If not, ask the chair if they plan to offer it. If not, don't change schools, one course shouldn't make or break this big decision.
On becoming an environmental economist? Here is a good answer from Tim (scroll down to the second question). My experience was similar, it was a bumble ... following my comparative advantage (econ came relatively easy to me, biology was relatively difficult), etc. I wasn't sure what to do after college, I had a friend at an MS program at UK, I applied, got assistantship money in econ (but not ag-econ), got a C+ in math econ over the summer and realized I might really need to study. It turns out I enjoyed economics, especially environmental, had a great advisor, and things have worked out OK since.