Artificial trees might look like the more environmental choice since it's reusable and you're not killing a tree. But they’re usually made of PVC! Do you know how many toxic chemicals are released into the air during production? Let's see . . . mercury, chlorine, oh and the most toxic chemical known to science, Dioxin. Compare that to a tree growing in a field which is producing oxygen. Also when they wear out, and they will wear out, where do they go? that's right the good ole landfill. Artificial tress can't be recycled.
The majority of live Christmas trees are from a farm and grown specifically for that purpose. When they're are harvested, another tree is planted to take their place. It takes from 10 - 12 years for a tree to grow to the standard Christmas tree size. With a growth rate that slow, you can rest assured that most farmers, if not all, are running their farms in a sustainable fashion.
It's true that many farms do use pesticides and other chemicals in their quest for the perfect tree shape, so you should always check them out before buying. Our local Christmas tree farm has birdhouses throughout the fields. Also try to buy local, if you're tree had to travel 300 miles it's caused quiet a bit of pollution on the way.
Artificial trees are crammed back in their boxes after Christmas or taken to the landfill. What do you do with a real tree after the holidays? Many cities have a recycling program just for the trees, they chip them and use them around the town for mulch or give away them away as free mulch (check around and see if you're town has such a program). If you live near a lake or pond, a tree can be sunk to provide habitat for fish and aquatic animals, yet another reason to make sure it's pesticide free. If you have a lot of land you can put it outside to slowly rot back into the earth. Don't forget to remove all your ornaments.
If you're still concerned. Try a rosemary topiary. They're often shaved into a Christmas tree like shape and you can use the herb in your cooking and crafts around the house. Or don't have a tree at all. Santa can leave those presents piled on the couch, under the kitchen table, or on top of the book shelves.
Really, he's flexible.