“I’ve been in the department for 15 years, and I knew this was going on but didn’t pay too much attention,” says Serita Frey, a soil microbiologist and a professor at the university.“It didn’t have anything to do with climate change at first. Everyone just knew that the ginkgo tree dumps its leaves in one day.”

Why the single-day drop? In the autumn, deciduous trees form a scar between their leaves and stems to protect themselves from diseases and winter’s coming chill. Most flowering trees, like oaks and maples, form the scar at different rates, in different parts of the tree, over the course of weeks. Their leaves then fall off individually. But ginkgoes form the scar across all their stems at once. The first hard frost finishes severing every leaf, and they rain to the ground in unison.

A few years ago, Frey became curious about whether there was data documenting the ginkgo-dump day over the years. According to the National Climatic Data Center, fall temperatures in New Hampshire are now more than 2 degrees Fahrenheit warmer than they were in the late 1970s. Did that affect the flagship ginkgo tree? Had someone even kept records about the contest that far back?

For the first few days of her search, she couldn’t locate the record. “And then I found a piece of paper with handwriting on it that some secretary back in 1977 started, and that someone from the department had been adding to every year,” she said. “I put all that information in a spreadsheet, and I’ve been updating that graph every year since.”

The graph revealed that the ginkgo-dump day had been sliding forward over the ensuing decades. Every decade, the ginkgo tree loses its leaves an average of three days later than it had 10 years prior. When the James Hall ginkgo dumped its leaves this Thursday, November 9, it was the second-latest that the tree had ever hit the autumn milestone.

When Did the James Hall Ginkgo Lose Its Leaves?

“It’s our poster tree—our local example of climate change,” she told me. Frey uses the slide in her classes about global warming.

The James Hall ginkgo is not, of course, the only organism subject to the creeping relocation of the seasons. In 2016, the U.S. National Park Service examined when the first leaf or first bloom of spring arrived in 276 of its parks. In three-quarters of parks, spring was arriving earlier than it had in the past; in half of the parks, spring now arrives earlier than it did in 95 percent of the years since 1901.

Nor is the story of the James Hall ginkgo data trove unique. About two decades ago, climate scientists realized that springtime bloom records were some of the longest-running observations of the climate system available. By examining and digitizing old records, they have found: