Welcome to the club! Being in high school, you still have lots of time to decide on the specifics. I recommend finding a college that has good programs for both environmental engineering and environmental sciences. Take classes in both and see which one you prefer more. Switching majors during college is common and the first couple years is mostly filled with general courses anyway. Note that career-wise, engineering tends to pay more than science. But environmental companies certainly hire from both. I went to school in, and now work in the northeast U.S. Note that there are many sub-disciplines within the general categories of environmental engineer/science. For example, under engineering, there is things like water/wastewater treatment, hazardous waste management, air pollution, etc. Try a few and you'll find a niche (your college may focus on a particular type anyway so keep that in mind as you check out college programs). There is certainly a wide variety of careers available too...municipal (e.g., town engineer), utilities (e.g., conducting environmental impact statements for power plants, etc.), consulting (what I do), remediation contractors (companies that actually do cleanups), federal or state regulatory agencies (the folks that enforce environmental laws), quality control/process engineering for manufacturing plants, etc...the list goes on.
As far as availability, I suppose it depends on the region's environmental laws...of which the US and Canada have plenty. (where there's industry and legal requirements to follow...there's work for us) In the US, there the overal federal law (EPA) and then state laws...the state laws vary...some are strict and there tends to be more work there.
As an engineer, I work in a consulting company alongside with scientists...and we do very similar work (although the scientists tend to be the ones who go out to cleanup sites and do the investigations whereas I tend to work in the office and figure out how to solve environmental problems).
