Jacoby was an early pioneer in the science of dendrochronology, the study of tree rings. In 1975, he co-founded the Tree-Ring Lab at Columbia’s Lamont-Doherty Earth Observatory, only the second lab of its kind in the United States.

Trekking into remote forests on every continent except Antarctica, he extended existing climate records by sampling trees near the top of the world, in northern Siberia, and near the bottom, in Tierra del Fuego, at the tip of South America. Jacoby led the first reconstruction of Northern Hemisphere temperatures going back hundreds of years, helping to show humans were at the root of rising heat over the last century. He was also a leader in using tree rings to shed light on prehistoric droughts, earthquakes, tsunamis and landslides.

During the 1980s Alice Haagensen asked Gordon’s help in dating several of the older houses of the community. He established the earliest date for the construction of the Big House - 1737 - from beams in the basement of the building.

In retirement, Jacoby settled into a 110-acre farm in Virginia’s Shenandoah Valley, where he raised red Bourbon turkeys and sheep. Jacoby was a nearly lifelong bachelor, but in 2009, struck up a relationship with Rusty Lotti, then director of Lamont’s deep-sea sediment laboratory. They were making plans to officially tie the knot when Jacoby suffered a fatal stroke