Old-growth forests are much better at removing carbon dioxide from the air than plantations of new forests, concludes a new study published today in the journal Science. In negotiations over an international treaty on climate change, the U.S., along with Canada and Russia, is proposing to meet as much as half of its greenhouse gas reduction requirements by using carbon sinks like forest plantations to sequester CO2 from the air, instead of putting more limits on the burning of fossil fuels and thereby preventing CO2 from being released in the first place. But the study throws to the wind the assumption that old-growth forests are in a state of decay and release as much CO2 as they capture. The study authors say that the treaty needs to establish protections for old-growth forests or else some countries could be tempted to cut down old-growth forests and then plant new trees on the deforested land, getting credit for reducing CO2 when they would actually be making the situation worse.