By Brian Palmer Special to the Washington Post — It's that time
of year when even environmentalists committed to saving trees
proudly display a massive tree carcass in the living room,
bejeweled and topped with a star. American cities are rarely
greener than during Christmastime, when every other street
corner can seem to be occupied by a tree peddler. Christmas
trees play into a wider debate among environmentalists: Are tree
farms better or worse at carbon sequestration than untouched
forests? The pro-tree-farm argument goes like this: When you
plant a tree, it goes from seedling to full-grown plant by
rapidly extracting carbon from the atmosphere, including carbon
that humans have emitted by burning fossil fuels and raising
cattle. (When a climatologist looks at a tree, he sees a leafy
pillar of solidified greenhouse gases.) Once the tree reaches
maturity, though, it slows its consumption of carbon. By way of
comparison, think of the appetites of a growing teenager and a
senior citizen. When you're done gro