Spiegel: While nations bicker about who should cut greenhouse gas emissions and by how much, scientists are dreaming up their own solutions to global warming. A German professor has created a filter which extracts more than a thousand times more carbon dioxide from the air than a tree. The situation may not be nearly as grim as it looks. For Klaus Lackner, at least, human-induced global warming is a problem that can be controlled, perhaps even solved — even if humankind doesn’t manage to …