Long known for their environmental activism and philanthropy, the members of Pearl Jam have taken a cue from bands like Dave Matthews and Coldplay and are now seeking to offset the carbon impact from their upcoming world tour, donating $210,000 to have trees planted in and around Puget Sound.The partnership with the Cascade Land Conservancy, announced last week, has gotten them a lot of positive press, with Times columnist Nicole Brodeur, among others, doling out the "atta-boys."Still, it's worth noting how long it will take for the estimated 5,474 tons of carbon that were already released into the atmosphere as a consequence of the band's 2009 world tour to be absorbed.Turns out it's going to be a while.According to Michael Totten, the climate expert who helped Pearl Jam calculate the carbon footprint of that tour—including the band's own emissions and those of its fans—it will take roughly 50 years for the 33 acres of new trees to absorb all that carbon from the atmosphere. That's roughly 8,577,010 spins of "Elderly Woman Behind the Counter in a Small Town."Of course, Eddie and company are going to be nonagenarians—or pushing up daisies—by the time that happens. They also will have gone on countless additional tours. Using the Rolling Stones as a model for how long a past-its-prime rock band will perform, Pearl Jam is obviously going to be in the tree-planting business for a very long time.