Big lumps of sooty coal hardly seem like the future of energy, but that's exactly what the U.S. Department of Energy predicts. Consumption of the fossil fuel-the main source of greenhouse gas and a major contributor to acid rain, smog and mercury poisoning-will hit 10.6 billion tons a year by 2030, a near doubling of the 5.4 billion tons burned in 2003, according to the agency.