Newsweek: Like many people who are scrambling for ways to stave off climate disaster, Klaus Lackner is thinking trees. But not the kind with green leaves and roots, and certainly not the sweet little specimens that “carbon offset” purveyors hawk as a way to balance out the carbon dioxide emitted when you tool around town in a Hummer. Lackner, a professor of geophysics at Columbia University, is helping to design a synthetic tree. It would stand roughly 1,000 feet tall with a footprint a …