Now for what doesn't work: Replacing other types of natural environments, like grassy plains or snow fields, with new forest in cooler latitudes is a bad idea, won't curb global warming and might actually make it worse, some say. So it's important, when looking at tree-planting organizations or buying carbon credits, that the organization focuses on rebuilding existing forests the way American Forests and the Conservation Fund do. American Forests also manages to do its work for $1 a tree. You can be another Johnny Appleseed for not a lot of money, if you don't mind doing your good work far from where you live. The Carbon Fund provides a calculator on its Web site that lets visitors estimate their carbon footprint and then plant trees to offset it. Apparently, it would take eight trees to offset the carbon spew into the air every year. And the fund will plant them for me for $93.48 or $11.69 a tree. It's nice to know there are some options out there that will allow me to make the world a little cooler and shadier -- and without having to get my hands dirty.