- This is part two of a two-part post. Read part one here.
On the wall of Wally Broecker’s building at the Lamont-Doherty Earth Observatory hangs a 16-foot long terry-cloth snake, blue with pink spots, that he calls the ‘climate beast’. Left in his office as a surprise by his workmates, its name refers to one of Wally’s most powerful quotes about the climate: “If you’re living with an angry beast, you shouldn’t poke it with a sharp stick.”
Today, the sharp stick is the CO2 we’re emitting by burning fossil fuels, which Wally was warning about by 1975. By that time he had also helped confirm that throughout history, changes in Earth’s orbit have given the climate beast regular kicks, triggering rapid exits from ice ages. He became obsessed with the idea that climate had changed abruptly in the past, and the idea we could provoke the ‘angry beast’ into doing it again.
Among the many samples that Wally was carbon dating, from the late 1950s onwards he was getting treasure from the oceans. Pouring sulphuric acid into seawater, he could convert dissolved carbonate back into CO2 gas that he could then carbon date. And though nuclear weapon tests had previously messed with Wally’s results, they actually turned out to help improved our knowledge of the oceans. The H-bomb tests produced more of the radioactive carbon-14 his technique counts, and as that spike moved through the oceans, Wally could track how fast they absorbed that CO2.
In the 1970s, as Wally and a large team of other scientists sailed on RV Melville and RV Knorr tracking such chemicals across the planet’s oceans, a debate raged. Was cutting down forests releasing more CO2 than burning fossil fuels? Dave Keeling’s measurements showed the amount of CO2 being added to the air was about half the amount produced by fossil fuels. But plants and the oceans could be taking up huge amounts, scientists argued. Thanks to the H-bomb carbon, Wally’s team found the CO2 going into the oceans was just 1/3 of what fossil fuels had emitted. Faster-growing plants therefore seemed to be balancing out the impact of deforestation, and taking up the remaining 1/6 portion of the fossil fuel emissions.
Tracers in the sea
Carbon dating also told Wally how long water had been beneath the oceans, while the balance of oxygen and phosphate told him where it had come from. That let him map large-scale ocean flows, which generally arise from cold dense waters sinking and spreading out, before they rise again after being gradually warmed by the sun. However, seawater evaporates and falls as rain, and it doesn’t fall evenly. Our continents are shaped so that rainfall overall moves water from the Atlantic to the Pacific. That makes the Pacific slightly less salty, but the difference is kept to a minimum by ocean currents. They move cold salty deep water from the Atlantic to Pacific, and in the process bring back warmer water. Wally realised this has a huge effect on the climate, transferring almost 1/3 as much heat energy as that falling from the Sun onto the North Atlantic.
Around the same time, ice core records analysed by Willi Dansgaard and others suggested that there were rapid changes in air temperatures. That made Wally wonder: Could ocean currents rapidly change climate by switching on and off? Certainly, turning the conveyor off could dramatically cool the North Atlantic. Results from Lamont colleagues studying the Younger Dryas, a 1,300-year cold period starting 12,800 years ago that ended with a rapid warming, further inflamed his curiosity. Seabed mud and sediment cores showed species of tiny sea creatures called foraminifera as far south as Britain during the Younger Dryas that today only live in the Arctic. They decided this meant that polar waters had surged south, diverting the Gulf Stream.
Wally thought this could be the sign of a shutdown of the conveyor belt. It took cold, salty water sinking in the Atlantic to drive the conveyor, so perhaps a big flood of freshwater could jam it. At the end of the last ice age a giant ice sheet covered most of North America, with its meltwater flowing into the Gulf of Mexico. Scientists could track that because meltwater is relatively poor in one of the isotopes of water – oxygen-18. So foraminifera in sediment drilled from the seabed contained less oxygen-18 as long as the meltwater flowed south, which was until the start of the Younger Dryas. Then a giant meltwater lake burst its banks, flowing into the Atlantic and turning the conveyor off, quickly triggering thirteen frozen centuries. “Putting my finger on the fact that there were global abrupt climate changes that were triggered by the reorganisations of the ocean was entirely new,” Wally told me. “And of course it stood the test of time and became a huge topic of research.”
Wally was worried that modern warming might have a similar effect, and in the 1980s warned the public of that threat, through his ‘angry beast’ metaphor. But since then, studies suggest a similar halt of the conveyor is not our greatest concern today. “A lot of work was done on models, sure they could do it, but they had to have a hell of a lot of water,” he explained. “There just doesn’t seem to be that sort of water around. You’d need a sudden melting of a major part of Greenland, and that could stop the conveyor, but nobody’s saying that’s going to happen. So I wouldn’t cross it off, but I think that there are a lot of other things higher on the list to worry about.”
Around the same time, Wally wrote a book called How to Build a Habitable Planet. In its final chapter, he bleakly argued that as stopping burning fossil fuels was unlikely we should prepare ourselves for the climate changes ahead. He also ruled out taking CO2 out of the atmosphere. In fact, when he saw Klaus Lackner suggesting speeding up rock weathering that naturally removes the gas from air in 1998, he thought “This guy is nuts”.
But Wally and Klaus met again when Columbia University took over a three-acre greenhouse in the Arizona desert, known as Biosphere 2. Both sitting on its advisory board, Wally changed his opinion – far from being nuts, he decided that Klaus was brilliant. Wally lured him to Columbia, and was soon convinced that sucking CO2 out of the air – known as air capture – was technically and financially feasible. It could, in effect, take the CO2 stick out of the climate beast’s face.
Together they set up a company called Global Research Technologies, now Kilimanjaro Energy. The company continues slowly and steadily, with other scientists – most importantly those who control research funding – less convinced of its viability. By contrast, another project called CarbFix is ongoing in Iceland using Klaus’ original idea of speeding up natural weathering, with early data proving promising. ‘It’s actually looking much better, in things that you couldn’t know,’ Wally hinted mischievously.
Wally Broecker (2012). The Carbon Cycle and Climate Change: Memoirs of my 60 years in Science Geochemical Perspectives DOI: 10.7185/geochempersp.1.2
W. S. Broecker, T. Takahashi, H. J. Simpson, T.-H. Peng (1979). Fate of Fossil Fuel Carbon Dioxide and the Global Carbon Budget Science DOI: 10.1126/science.206.4417.409
Wallace S. Broecker, Dorothy M. Peteet & David Rind (1985). Does the ocean–atmosphere system have more than one stable mode of operation? Nature DOI: 10.1038/315021a0
Wallace S. Broecker (1991). The Great Ocean Conveyor Oceanography DOI: 10.5670/oceanog.1991.07
This year I’ve already written about the following pivotal climate scientists: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess,Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I
But 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.
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.