Ice once played a significant role in Princeton life.
A century ago, the town’s average winter temperatures hovered just below 32 degrees Fahrenheit, and the Princeton Ice Co. — which operated a mile northwest of campus, on what is now Mountain Lakes Nature Preserve — harvested hundreds of tons of ice each winter for year-round deliveries. Students, children, and families skated through the winter on Lake Carnegie and held communal bonfires along its banks.
“It was all skating, and everybody skated,” recalled one resident quoted in a 1985 Historical Society of Princeton newsletter article. One spring, two young miscreants surfed a thick slab of ice for two miles down Stony Brook, until an angry father intercepted them. “He had a switch cut and I got a pretty good tanning,” one of the boys recalled, “but it was quite an adventure.”
Yet Princeton’s average winter temperatures have warmed by about 3 degrees Fahrenheit since then, and Lake Carnegie has not frozen deeply enough to meet the municipality’s criteria for safe skating since the winter of 2014–15. That January, geosciences professor Gabriel Vecchi got his first — and, to date, only — taste of Princeton ice.
“It seemed like the whole community was out there,” recalled Vecchi, a skater and youth hockey coach. “There were people walking on the ice, playing pickup hockey games on the ice. Parents with children. Grandparents with grandchildren. For this brief moment, the lake became … of everybody. It was just magical.”
When the lake was unskateable the following winter, and the winter thereafter, Vecchi began to wonder: Was Lake Carnegie freezing as often as it used to?
In the summer of 2020, Grace Liu ’23 — then an intern at the High Meadows Environmental Institute — tackled the question. Advised by Vecchi; Nadir Jeevanjee, a research scientist at NOAA’s Geophysical Fluid Dynamics Laboratory; and Sirisha Kalidindi, a postdoctoral research associate in Vecchi’s research group, Liu began piecing together the history of Lake Carnegie’s ice.
No scientific record of the lake’s ice conditions existed, so Liu interviewed community members and searched the archives of local papers to determine which years Carnegie had and hadn’t been safe to skate on. Some stories directly mentioned skating, but other references were more oblique. In March 1941, for example, The Daily Princetonian reported that “the thawing waters of Lake Carnegie” had revealed the body of German chemist Erhard Fernholz, whose disappearance the previous December had prompted the FBI to investigate a possible Nazi assassination.
Liu’s resulting data showed that the probability of safe skating on Carnegie started to plummet in the middle of the last century.
“Within a matter of decades,” said Liu, “the probability of safe ice skating on Lake Carnegie has decreased from almost 1 to 0.2.”
In other words: While the lake was once safe for skating nearly every winter, it is now safe one out of five.
This change is partly attributable to stricter safety standards. In response to instances of skaters falling through the ice and drowning, the municipality has, over the past half-century, narrowed its definition of safe skating conditions, increasing the minimum required ice thickness from three, to four, to eventually five inches. Still, when Liu and her advisers compared their findings to data on similar lakes around the world, they found that their results matched a rapid global decline in lake freezing.
“The reduction in lake freeze is related to the warming winters,” explained Vecchi. “And the warming winters are related to the long-term warming of the planet, caused by increasing greenhouse gases.”
Vecchi, who also studies hurricanes and other extreme weather events, is quick to point out that Princeton’s disappearing ice ranks low on the global list of problems caused by anthropogenic climate change. Some residents welcome milder winters, and Princeton offers other places to skate: Baker Rink holds open hours, and in 2019, Palmer Square opened a small rink made of an artificial ice product called Glice.
But Vecchi said skating on the lake is a special experience.
“It’s not the same,” agreed Princeton local John Cook ’63, who first skated on Lake Carnegie during World War II and went on to set the Princeton men’s hockey team’s career goals record, which stood until 2019. “If you want a nice cold winter with outdoor skating, you’ve probably got to move north.”
Members of the past three graduating classes never skated on Lake Carnegie. Liu, a Florida resident, has never skated at all. Vecchi hopes she will get her chance in the coming weeks.
“I really hope Lake Carnegie freezes safely this winter,” said Vecchi. “Selfishly, of course, but I also want Grace to be able to go on Lake Carnegie. It would mean something to me for Grace to get to go out on the lake.”