For much of the 20th century, winter brought an annual ritual to Princeton, New Jersey. Lake Carnegie froze solid, and skaters flocked to its glossy surface. These days, the ice is rarely thick enough to support anybody wearing skates, since Princeton’s winters have warmed about 4 degrees Fahrenheit since 1970. It’s a lost tradition that Grace Liu linked to the warming climate as an undergrad at Princeton University in 2020, interviewing longtime residents and digging through newspaper archives to create a record of the lake’s ice conditions.

“People definitely noticed that they were able to get out onto the lake less,” said Liu, who’s now a Ph.D. student at Carnegie Mellon University. “However, they didn’t necessarily connect this trend to climate change.”