Scientists are warning that the collapse of Antarctica’s massive “doomsday glacier” could eventually redraw large parts of America’s coastline, threatening major cities from Florida to California with severe flooding and rising seas. Researchers say the Thwaites Glacier in West Antarctica is becoming increasingly unstable, raising fears that its eventual collapse could contribute to dramatic long-term sea level rise. While the glacier itself could add around 65 centimeters (roughly 2 feet) to global sea levels, some scientists worry it could destabilize much larger sections of the West Antarctic Ice Sheet—potentially contributing to sea level rise approaching 3 meters (nearly 10 feet)...