How quickly will Antarctica’s massive Thwaites Glacier melt, and what will that mean for global sea levels and coastal cities? Scientists spent several weeks aboard the research ship Nathaniel B Palmer, studying Thwaites as part of a five-year, international effort to try to answer those pressing questions. Our reporter Carolyn Beeler takes us onboard for a deep dive into the science and the stakes for our future.

(An iceberg in the Southern Ocean, is pictured here as the Nathaniel B. Palmer sailed by during its return trip from Antarctica in March 2019. Carolyn Beeler/The World)