ABC: Coal: Can't live with it and can't live without it at least not yet. It is the biggest source of heat-trapping greenhouse gases that negotiators around the world hope to limit in an agreement to be thrashed out in Paris next month. Demand for coal is leveling off, but it will remain a key energy source for decades, no matter how many billions of dollars of investment go into cleaner energy like wind and solar. Too much of the world depends on it now for heating and power generation for us to...