When Al Gore received the 2007 Nobel Peace Prize for his efforts to raise awareness about man-made climate change, his acceptance speech featured a new word, or rather a new sense of an old word, that Oxford lexicographers have been watching closely: carbon, in the sense of “carbon dioxide or other gaseous carbon compounds released into the atmosphere.” As I wrote back in July, this extended sense of carbon can be found in all sorts of novel lexical compounds: carbon-neutral (2006 New Oxford American Dictionary Word of the Year), carbon footprint, carbon tax, carbon trading, and so forth. In his...