WASHINGTON — Antarctica is melting more than six times faster than it did in the 1980s, a study shows. Scientists used aerial photographs, satellite measurements and computer models to track how fast the southern-most continent has been melting since 1979 in 176 individual basins. They found the ice loss to be accelerating dramatically — a key indicator of human-caused climate change. Since 2009, Antarctica has lost almost 278 billion tons of ice per year, the study found.