Drilling through 500 feet of floating ice into the Antarctic Ocean floor, climate scientists have retrieved a rare 23-million-year record of sediments that helps demonstrate why the planet’s southern ice shield could determine the fate of distant low-lying coastal areas.

The layers of rock, silt, and fossils are like pages in a book of geological time, revealing how West Antarctica’s vast ice sheets and floating shelves respond rapidly to modest warming, with significant shrinking and melting in climates similar to today’s.

Along with other new modeling studies and analyses of current ice retreat, the core sample of ocean sediments affirms that human-caused warming is triggering an irreversible long-term meltdown that could submerge the southern third of Florida and other low-elevation coastal areas within two to three centuries.

The lines of evidence from paleoclimatology, as well as from modeling and observations, also converge to suggest that the average global sea level rise in the more immediate future will accelerate, reaching 3 feet by the end of the century and up to 5 feet in equatorial island regions, potentially displacing millions of people worldwide.