Join green groups, read green blogs or enjoy an evening with green-minded friends. Keep track of which topics draw you in. Do your ears perk up at the mention of organic corn; does alternative energy spark your interest; do you have a desire to design?
When you meet someone whose green career you envy or admire, start asking questions: What do they love about their job? What do they hate? You may find your rosy picture dulled by reality. Or your interest may be further piqued. Even if you don't make it all the way to career change, you will have a lot of fun learning and make new friends.