I decided recently to look into the possibility of having a tree planted for me. I figured I could celebrate my daughter's first birthday, offset some of my family's carbon footprint and make the world a little greener. And besides, trees are nice. Planting them seems like the kind of eco-friendly gesture that couldn't possibly have a down side. Turns out I was wrong about the last part. There are numerous ways to plant trees. They might or might not help global warming, and cost anywhere from $1 to $1,000, depending on how big a tree you have in mind and whether you want it planted down the block or across the globe. I hate to say it, but tree planting is an issue where you can trust die-hard environmentalists to pick the issue to pieces and take all the fun out of it. There is a vigorous discussion on Grist's message boards on the pros and cons of planting trees to combat global warming. Here's what I've learned. Planting new trees in equatorial climes, to either replace or add to rainforest environments does seem to help cool the Earth and moderate global warming. This is a good thing to do. And if you pay to have trees planted through the Nature Conservancy, a sensible environmental organization, this is where they'll be planted. Because the Nature Conservancy plants seedlings in warm environments where they grow quickly, it can do it very cheaply, at $1 a tree. For a mere $50, you can generate a lot of important tree canopy.