In Los Angeles on September 1 1955, the day temperatures reached a new record of 43°C, Wally Broecker stood, sweating, giving the first scientific talk of his life. He could scarcely have guessed where the new method he was telling an audience of sleepy archaeologists about, called radiocarbon dating, would send him. But thanks in part to its messages from history he would help spawn the phrase ‘global warming’ and warn of its effects, which have today pushed temperatures even higher.
Wally grew up and started college on the outskirts of Chicago, Illinois, good at maths, but largely uninterested in science. But college-mate Paul Gast steered his career sciencewards by helping get him a summer job at the new Lamont Geological Observatory that Paul had recently started working at. On June 15, 1952 Wally and pregnant wife Grace drove 800 miles to the Palisades, New York mansion Columbia University had inherited, and set up the observatory in. There, in the basement, Wally worked in and soon practically ran Laurence Kulp’s radiocarbon lab. Rather than lose him at the end of the summer Laurence organised for Wally to transfer to Columbia and stay working at Lamont, where he has remained ever since.
Taking advantage of the slow decay of a rare, radioactive form of carbon – carbon-14 – radiocarbon dating was in its infancy. The balance between carbon-14 and the usual form, carbon-12, is quite steady in CO2 in the air, and also in living plants that take up the gas as they grow. But when plants die, the carbon-14 they contain slowly decays to nitrogen. Measuring the ratio between the two forms of carbon, scientists can tell when the plants had died. But in 1952, Laurence’s lab was getting inconsistent readings, with carbon-14 counts sometimes coming out too high, even after Wally had fixed a problem with the equipment. Then Wally realised the problem came from outside the lab. The extra counts were coming from nuclear tests that had recently started over Nevada.
‘Be a dynamic incompetent!’
Laurence and Wally turned to Hans Suess, another carbon dating and climate research pioneer, whose method solved this problem. And while teaching his approach, Hans warned Wally to avoid the fate that took many scientists away from the lab: becoming an administrator. “Be a dynamic incompetent!” Hans advised. “Do at least three outrageous things a year. Then no one will want you as an administrator.” With a proven track record as a practical joker – including locking a custodian into a bell-tower at college in Chicago among many other pranks – this suited Wally well. “I’ve done my share of outrageous things,” Wally admitted to me. He added that Hans’ advice always stuck in his mind, and that beyond a 2½ year stint as chair of his department, he has never had any administrative responsibility.
By his 1955 talk, Wally knew all about carbon dating, but one audience member, Phil Orr from the Santa Barbara Museum could see what his education lacked. “You don’t know a goddamned thing about the Earth,” Phil told him. He invited Wally to come through the Mojave Desert with him. They toured the glacial lake remnants of a gigantic lake, Lake Lahontan, from the last ice age now fought over as water supplies. They drove, scrambled and crawled around hillsides and lake terraces, collecting calcium carbonate ‘tufa’ rocks that had once formed underwater.
Over three weeks, faced by obviously huge changes wreaked by temperature changes of just a few degrees, Wally ‘discovered’ climate. When Wally dated the carbon in the tufa, he found Lake Lohontan last reached its high point around 11,500 years ago. Similar dates turned up again and again, in samples sent to him from far and wide. The implication was shocking: when the last ice age ended, it did so abruptly, in many places at the same time. In his PhD Wally even suggested that the world existed in two states: one warm, one cold, switching quickly from one to the other.
Wally’s path towards explaining what causes ice ages continued through the 1960s. In preparing to teach a course at Columbia, he learned about Milutin Milanković’s theory that they were driven by slight changes in the Earth’s orbit. Though at the time the idea was widely rejected, Wally now had a lab of his own to test it in. His student, David Thurber, had devised a new way to track past climate change through the balance between uranium and thorium in coral.
But they used to warn about an ice age
Uranium’s radioactive decay produces one form of the element thorium, called thorium-230. Uranium dissolves in the water corals take up, but thorium-230 doesn’t. That means there is no thorium-230 in corals when they first form, but the amount increases over time as uranium decays to form it. And uranium turns to thorium-230 much more slowly that carbon-14 to carbon-12, meaning the method can reach back further.
With some corals only growing near the sea surface, the method gave Wally’s team a chance to look at how sea levels rose and fell over the course of ice ages. Testing corals sent from Barbados, David saw ice ages 82,000, 105,000 and 124,000 years ago, matching the gaps Milutin’s theory predicts. “The often-discredited hypothesis of Milankovitch must be recognized as the number-one contender in the climatic sweepstakes,” Wally wrote in the journal Science.
Evidence grew quickly from ‘cores’, cylinders of ancient mud drilled from the sea bed, or ice from glaciers, confirming Milutin’s theory. Cores like the one collected at Camp Century in Greenland and analysed by Willi Dansgaard also backed Wally’s idea – still outrageous to many scientists – of rapid changes. Wally himself was quick to point out each ice age showed the same ‘sawtooth’ pattern: a spurt of rapid warming was followed by a gradual descent back to cold.
Finding this ice age timing prompted an obvious question: How long until the next one? The world was in the middle of a cooling period that seemingly belied earlier predictions from Guy Callendar about CO2-driven temperature rises. Though an ice age would be centuries or millennia away some scientists called it ‘an immediate concern’, writing in 1972 to then US president Richard Nixon to warn him.
But in 1975, as articles voicing this warning were appearing, Wally argued just the opposite. He wrote that warming produced by rising CO2 levels in the air documented by Dave Keeling could emerge in a ‘surprising’ and ‘dramatic’ way. “At that time the first Greenland ice core record came out, and Willi Dansgaard found that it had 80 and 180 year temperature cycles,” Wally told me. “I took his cycles and extrapolated them into the future, made the gigantic assumption that they were global and that a natural cooling was balancing out the warming. If that were true then the Dansgaard cycle would turn around and global warming would be enhanced by natural warming.” Though later data hasn’t supported the short-term cycles, the cooling trend did stop the same year. And looking back now, our adoption of a phrase originating from his Science paper’s title shows how timely it was. He called it: “Climatic Change: Are We on the Brink of a Pronounced Global Warming?”
- This is the first blog entry of two on Wally Broecker’s contributions to climate science. Now read the second part.
Spencer Weart’s book, ‘The Discovery of Global Warming’ has been the starting point for this series of blog posts on scientists who played leading roles in climate science.
Robert Kunzig and Wally Broecker’s book, ‘Fixing Climate’ does a much better job of explaining climate change through personal stories than this series of blog entries.
Wally Broecker (2012). The Carbon Cycle and Climate Change: Memoirs of my 60 years in Science Geochemical Perspectives DOI: 10.7185/geochempersp.1.2
Wallace S. Broecker (1965). Absolute Dating and the Astronomical Theory of Glaciation Science DOI: 10.1126/science.151.3708.299
Wallace S. Broecker, Jan van Donk (1970). Insolation changes, ice volumes, and the O18 record in deep-sea cores Reviews of Geophysics DOI: 10.1029/RG008i001p00169
Wallace S. Broecker (1975). Climatic Change: Are We on the Brink of a Pronounced Global Warming? Science DOI: 10.1126/science.189.4201.460
This year I’ve already written about the following pivotal climate scientists who came before Wally Broecker, or were around at the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II