Melting of Antarctica's massive Thwaites Glacier could add 60 centimetres to global sea level rise in the next 50 to 100 years, and unlock far more in the years beyond. A voyage by an icebreaker to the remote glacier's face laid the groundwork for a 5-year international research effort to try to answer urgent questions about Thwaites' future. Our reporter Carolyn Beeler takes us onboard the expedition, with deep dives into the science and the stakes for our future.

(The Nathaniel B. Palmer anchored off the Rothera research station near the Antarctic Peninsula. Nearing its destination offshore of the Thwaites Glacier in West Antarctica, the ship had to divert back north to the station for a medical emergency. Carolyn Beeler/The World)