One day, when David McGee was a young graduate student at Columbia University’s Lamont-Doherty Earth Observatory in the late 2000s, he found a note on his desk. Written in pencil and in a distinct cursive, it read: Hey David, want to measure chlorine-36 at Mono Lake? -Wally
Wallace Broecker, or “Wally” to those who knew him, was a professor and geoscientist at Columbia and one of McGee’s PhD advisors. At the time, Broecker was already one of the world's leading climate science authorities, having made several key discoveries on the fundamental behavior of the Earth’s oceans, atmosphere, ice, and more. Broecker was the first person to reveal the link between carbon dioxide and climate change and later how the oceans circulate heat and affect Earth’s climate, eventually coining the term the Ocean Conveyor Belt.
McGee, meanwhile, was a nascent paleoclimatologist studying how windblown desert dust varied through Earth’s climate history. Though his research did not yet include the Western United States, three months after finding the note, McGee was with Broecker in California collecting chlorine-36 samples from Mono Lake (one of the oldest lakes in the western hemisphere), with the hopes of better understanding how things like volcanic inputs contributed to the lake’s unique chemistry.
McGee remembers the trip as equal parts entertaining and educational. He recalls one particular instance in which Broecker got the rental car stuck in a sand dune, after which a tow truck had to pull them out.
“It was just great fun,” says McGee.
Today, McGee, an Associate Professor at MIT EAPS (Earth, Atmospheric and Planetary Sciences) and member of Program in Atmospheres, Oceans and Climate (PAOC), is one of the many former students of Broecker’s who went on to their own notable careers in paleoclimatology research. McGee remembers his former advisor as man of many multitudes: an incorrigible prankster and prescient scientist who was both blunt and opinionated but still unpresumptuous and approachable.
“He didn't talk to you any differently than he would have talked to a colleague who he had been working with for 30 years,” says McGee. “He was happy to have you jump in and join the conversation, and he really invited you to do that.”
Broecker’s scientific legacy is marked by his uncanny ability to derive broad, fundamental trends amid the noise of a chaotic and complex climate system. He is perhaps best known for his landmark 1975 paper, titled "Are we on the brink of a pronounced global warming?” which correctly predicted that, despite the then-present natural cycle of cooling, rising carbon dioxide levels in the atmosphere would lead to pronounced warming.
“He really had sort of an intuition for trying to investigate the system until the more fundamental behavior emerged,” says McGee.
Broecker also pioneered the use of radiocarbon and uranium thorium dating to map changesin Earth’s climate. In fact, he began his career as the director of the radiocarbon dating laboratory at Lamont, and his 1982 textbook, Tracers in the Sea, is still a standard reference among climate scientists. Broecker himself used these tools to investigate the speed in which water circulates in the ocean, how the ocean absorbs atmospheric carbon dioxide, and what warming temperatures mean for sea level rise. Over his lifetime, he authored more than 500 research papers and 17 books.
“It's hard to think of anything in paleoclimate or chemical oceanography that he didn't work on at some point,” says McGee.
To the public, Broecker was known for his early and grave warnings on the consequences of climate change. Throughout his career, he routinely cautioned that the climate system is volatile, sensitive, and susceptible to major shifts, and worked closely with policy leaders to reduce fossil fuel emissions. This advocacy work, along with his 1975 paper which entered the phrase “global warming” into scientific lexicon, earned Broecker the title “Godfather of global warming”—a moniker he very much disliked.
“That annoyed me to no end,” Broecker told an audience at Boston University in 2014.
In 2009, Broecker offered $200 to anyone who could locate an earlier reference to “global warming,” thus letting him off the hook. McGee, then a post-doc working with Broecker, won the bet, finding an obscure reference in the Hammond Times of Indiana.
“I was never quite happy with that reference, but it was nice because at the time I had a new baby at home,” says McGee.
Later in his life, Broecker did not rest on his many accolades, of which there were many: the Vetlesen Prize in 1987, the National Medal of Science in 1996, the Tyler Prize for Environmental Achievement in 2002. Instead, he remained an important voice in a diverse range of scientific conversations. A week before his death, Broecker addressed a geoengineering symposium via livestream to advocate for controversial stopgap measures to reduce carbon dioxide emissions in the atmosphere.
“If we are going to prevent the planet from warming up another couple of degrees, we are going to have to go to geoengineering,” he told attendees.
His advocacy of geoengineering was one example of Broecker’s hallmark willingness to support unpopular ideas. In an interview with NBC News, Michael Oppenheimer, a professor at Princeton University, called Broecker an “instigator in a good way,” which McGee says is an apt descriptor of his former advisor.
“He believed that science moved forward by people taking strong positions and defending them, but also remaining open to alternative interpretations,” says McGee. “Rather than just sitting in the middle and shrugging your shoulders, he wanted you to take a side and argue it, but keep listening to the other side because you might be wrong.”
On Monday, February 26, 2019, a week after his mentor’s passing, McGee returned to Lamont, his and Broecker’s alma mater, to give a talk on his current research at MIT, which now includes Western United States paleoclimate in addition to wind-blown desert dust. Lamont was Broecker’s academic home for nearly 67 years. He received his bachelor’s degree in physics and PhD in geology there before joining its faculty in 1959.
“It was good to be around people who were thinking about him,” said McGee.
Broecker’s passing leaves a void in the climate science community, says McGee, but he is grateful that Broecker’s own life had no gaps in conducting science.
“I think all of us who knew him knew that he would have been really sorry to spend any part of his life far away from the scientific conversation,” said McGee. “So the fact that he was clear headed to the end, contributing and calling up people to talk about science, is really how he would have wanted it.”
Per Broecker’s request, his ashes will be scattered in the ocean by a fellow Lamont scientist.
In Broecker’s memory, McGee plans to donate the money he won in the “global warming” bet to charity.