They've arrived. A team of nearly 40 global researchers have succeeded in a treacherous trek through sea ice to study the Thwaites Glacier. For a while, they weren't sure they'd make it at all, reports PBS News Hour science correspondent Miles O'Brien. Known as the "Doomsday Glacier," Thwaites is a vast expanse of ice roughly on Antarctica's Walgreen Coast. It's about the size of Florida. As temperatures rise, its melting is increasing and threatens to raise global sea levels. O'Brien and team h