Broecker Wallace 1931

WALLACE BRoEcKER IS an American oceanogra-pher, Newberry Professor of Geology at Columbia University, and scientist at the Lamont-Doherty Earth Observatory who made major contributions to chemical oceanography, especially oceanic mixing based on radioisotopic distribution. Broecker set the research agenda for the field of paleoclimatology, thanks to his ability to devise coherent pictures of how all the different elements of the Earth shape the planet's climate. In particular, Broecker focused on the influence of oceans in triggering abrupt climate changes. His research has made him one of the most often-quoted scientists in contemporary debates about global warming. A New York Times reporter described him as the "iconoclastic guru of the climate debate."

Broecker was born on November 29, 1931, in Chicago, Illinois, where his father ran a gas station. He grew up in a fundamentalist Christian family and attended Wheaton College, a fundamentalist institution, before transferring to Columbia University in 1952. Broecker soon rebelled against his religious fundamentalist background. The skepticism that informs much of his scientific interest in the exceptions to general rules may be the result of this rebellion against the stifling religiosity of his family.

Broecker stayed at Columbia for his entire academic career. He earned his doctorate in 1958 and, a year later, became assistant professor. In 1961, he became associate professor, and in 1964, he was appointed full professor. In 1977, Broecker was named the New-berry Professor of Geology and, two years later, he was elected to the National Academy of Sciences and named chair of the Geochemical Society.

Broecker is the author of more than 400 articles and seven books. He began his research in the 1950s, developing techniques to measure the radiocarbon content of ocean water. He used his data to trace ocean circulation patterns over time. His researches connecting climate change with radiocarbon dating of marine shells found in sediment deposits on the sea bottom helped to date the abrupt end of the most recent ice age, approximately 11,000 years ago.

In the 1970s, Broecker was among the leaders of the Geochemical Ocean Sections (GEOSECS) program, which gathered information from the world's oceans through radiocarbon dating. In the mid-1980s, Broecker devised his theory of global ocean circulation, which is often called Broecker's Conveyor Belt. He theorized the circulation of chemical elements in the sea, the thorough mixing of surface and deep waters of the ocean that takes place every 1,000-2,000 years, and the rate of gas exchange between the atmosphere and the ocean.

Broecker came to the conclusion that climate is extremely volatile. It can cool down, as well as warm up very quickly, and these alterations can produce global changes. The Earth's climate is subjected to the on and off action (thus the conveyor metaphor) of deep ocean currents that transport great amounts of heat around the planet. Broecker used radiocarbon dating of samples of ocean water to study the world's oceans. He was one of the first scientists to stress the importance of the carbon cycle and to be able to work out its chemical processes. His research also pointed out the ocean's influence on atmospheric carbon dioxide levels.

While researching changes in the Earth's climate in the past 200,000 years, Broecker discovered that major climate shifts actually occurred much more rapidly than was previously thought. Focusing on the Younger Dryas, an event dating back 11,000 years when temperatures in northern Europe suddenly plummeted and remained low for about 1,000 years, Broecker concluded that the transition periods from warm to cold and back again may have taken as little as 20 years. This cold spell, Broecker explains, was due to a temporary disturbance in the global circulation of the world's oceans. Because this global current is linked to the atmosphere, the emission of greenhouse gases through fossil fuel combustion could cause a major interference in today's climate.

Broecker likens climate to "an angry beast" that "we are poking with sticks." He has had no qualms in explicitly stating that if world temperature continues to rise, the conveyor belt could slow down or stop, causing disruptive events throughout the world. The most disruptive of these events would be what he calls brief, but large /'flickers" in global temperature as the climate readjusts itself in fits and starts. These flickers would be largely unpredictable and could produce drastic climate changes in periods as short as five years. This would lead to agricultural disasters.

Thanks to his investigation of oceanic cycles and the connection between the oceans and the atmosphere, as well as his research into chemical cycles such as the carbon cycle, Broecker has improved knowledge of how climate changes. He has also supplied fundamental information to devise possible strategies to deal with the problem of global warming.

SEE ALSO: Carbon Cycle; Carbon Sinks; Current; Global Warming; Oceanic Changes; Oceanography.

BIBLIOGRAPHY. W.S. Broecker, "Converging Paths Leading to the Role of the Oceans in Climate Change," Annual Review of Energy and the Environment (v.25, 2000); W.S. Broecker, The Glacial World According to Wally (Lamont-Doherty Earth Observatory, 1995); W.S. Broecker, "Was the Younger Dryas Triggered by a Flood?" Science (v.312, 2006); W.S. Broecker and Robert Kunzig, Fixing Climate: What Past Climate Changes Reveal About the Current Threat and How to Counter It (Hill and Wang, 2008); W.S. Broecker and T.H. Peng. Greenhouse Puzzles (Eldi-gio, 1998); W.K. Stevens, "Scientists at Work: Wallace S. Broecker; Iconoclastic Guru of the Climate Debate," New York Times (March 17, 1998).

LuCA PRONO University of Nottingham

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