Wallace Broecker and GISS
Dr. Wallace “Wally” S. Broecker (November 29, 1931-February 18, 2019) was a long-time collaborator, mentor, and sometimes foil to many at the NASA Goddard Institute for Space Studies (GISS), as elsewhere. Wally had an especially profound impact on the science and careers of the authors of this piece. His fundamentally iterative approach focused on developing ideas from disparate sources of real data, testing them with models, and then rigorously examining those conclusions as more data became available and more modeling was done. Over the years, Wally co-authored more than a dozen papers with GISS authors, but influenced far more.
Over the decades, Wally's work in part covered much of the same terrain as GISS, though sometimes with a different slant. In 1975, Wally published the paper “Climatic Change: Are We on the Brink of a Pronounced Global Warming?” In this work, he deftly combined early GISS work on the climate impact of atmospheric aerosols (Rasool and Schneider, 1971) with CO2 calculations from the NOAA Geophysical Fluid Dynamics Laboratory (Manabe and Wetherald, 1967) and threw in an estimate for natural variability from an ice core (Dansgaard et al., 1971) to predict a 1.1°C warming in 2010 — startlingly close to the warming that actually occurred (see e.g., GISTEMP) although Wally himself said in 2017 that the agreement was "dumb luck".
Wally's paper was published six years before the landmark GISS publication of Hansen et al. (1981), which attempted to quantify more exactly what ongoing greenhouse gas increases meant in terms of global mean temperature. Comparing the two papers points to the main differences of style; Wally's ideas were often far-reaching and innovative, but slightly ad hoc. He was both a dreamer and experimental pragmatist for understanding mechanisms of climate change, and his strong background in geochemistry often led to insightful, zeroth-order “back of the envelope calculations” (such as the use of the Camp Century ice core “cycles” for the internal variability). This tactic was complementary to the approach at GISS, where the focus was to use computers to create a simulated climate model “laboratory” (with our knowledge of the rest of the climate system built-in) to quantify and test these same concepts.
Later, shortly after Jim Hansen's now famous 1988 Congressional testimony, Wally showed his support of the work done by Jim and others here at GISS. Richard Kerr, then a Science news reporter, described in a 1989 Science Research News piece multiple criticisms and community unease related to Jim's testimony from participants at a meeting in Amherst in May of that year. In characteristic form, Wally pushed back in a letter that “Hansen's group might be referred to as the Avis of climate modeling”, while the criticisms came from “Rent-A-Wreck”. Those choice words were distinctly Wally's style. Both his and Jim's foresight have been vindicated in subsequent decades.
Also in the early 1980s, Wally suggested that Dorothy Peteet and David Rind pursue the question of the tropical temperature changes during the Last Glacial Maximum with climate models. These issues related directly to the heart of much of GISS's efforts to constrain climate sensitivity. The prevailing view, from the CLIMAP (1976) reconstruction, was that tropical cooling was muted during the last Ice Age and that subtropical temperatures may even have been warmer than today. We (Dorothy and David) compiled terrestrial data (pollen and glacial records) around the globe that were in direct conflict with this view, indicating much colder temperatures. By incorporating the warm CLIMAP SST values into the GCM, we showed that the global mean cooling was only 3.7°C, and implied land temperatures that did not match the data in the tropics. In order to accommodate the temperature changes implied by the land evidence, one would have needed cooling of ∼5°C, implying a larger climate sensitivity (and larger tropical sensitivity) (Rind and Peteet, 1985). More recent reconstructions suggest far more cooling than the original CLIMAP numbers, though there is still some residual uncertainty. Indeed, Wally's last paper with GISS authors was still on the difficulty in deriving climate sensitivity estimates from paleo-records (Schmidt et al., 2017).
His foresight in climate research was also evident in GISS studies with him on the Younger Dryas (YD) cooling event, an abrupt climate shift discussed in Broecker et al. (1985) and Rind et al. (1986). Dorothy and David used the GISS model to explore whether the observed temperature changes around the globe associated with this climatic event could be reproduced by climate model simulations. To the extent they could, it provided quantitative support for the mechanism of N. Atlantic Ocean cooling forcing of the climate system during this time period of rapid climate change, and stimulated further research on its spatial extent (Broecker et al., 1988; Peteet et al., 1990; Peteet et al., 1993; Kneller and Peteet, 1993; Kneller and Peteet, 1999). Exceptions to the N. Atlantic influence emerged in discovery of the YD in western coastal Alaska (Peteet and Mann, 1994) which led to our subsequent modeling of cooling of the North Pacific (Peteet et al., 1997). Wally's ideas concerning ocean variability formed the basis of Allegra LeGrande's thesis work on abrupt climate change at GISS (LeGrande et al., 2006) (he served as her PhD supervisor). The same basic concepts are fundamental to a paper we published just last year (Rind et al., 2018).
Wally's involvement with the ice core community brought researchers to Columbia's Lamont-Doherty Earth Observatory (LDEO) and then GISS, among them Jean Jouzel, who introduced water isotopes in the GISS Climate model (Jouzel et al., 1987). This feature made the GISS climate model one of the first to be able to compare proxy measures of past climate (water isotopes in ice cores, caves and corals) directly with model output. The New York Times obituary noted that Wally pioneered techniques using isotopes and other trace elements to map the world's ocean currents, and this general approach can be seen in his collaboration tagging water vapor tracers (Koster et al., 1986) and using bomb-produced tritium (Koster et al., 1989). He was interested in the atmospheric transport of freshwater to ocean basins and collaborated with GISS to track the effect of fluxes on the thermohaline circulation (Zaucker and Broecker, 1992; Zaucker et al., 1994). Tagging of water vapor (Kelley, 2003) remains an integral part of many GISS research projects today (e.g., Lewis et al., 2014). Indeed, the extension of this methodology to coupled ocean-atmosphere models was one of the key drivers of the rewriting and updating of the GISS climate model code in the early 2000s (Schmidt et al., 2006; Schmidt et al., 2007).
On the educational front, Wally heavily influenced and improved the Columbia climate program. Wally suggested to Jim Hansen that David should teach the “Introduction to Atmospheric Science” course, replacing Robert Jastrow (the original head of GISS, who had not received great grades from the students). He also suggested to Jim that he should talk with David about stratospheric modeling at GISS, and that actually led to David's being hired. When David wanted to expand the curriculum with two new courses, “Atmospheric Dynamics” and “Dynamics of Climate”, Wally supported them.
Wally also asked Dorothy to co-teach his “Terrestrial Paleoclimate” course so that vegetational change (pollen and macrofossils) would be included with atmospheric (ice core) and marine records, and he supported her development of the “Wetlands and Climate Change” class which she has taught for twenty years. His vision for the Columbia Earth and Environmental Sciences (formerly Geology) department to incorporate climate/atmospheric studies has helped GISS to provide numerous graduate and undergraduate students with a cutting-edge education in climate related topics.
Wally helped to establish the LDEO/GISS Climate Center over 20 years ago with an endowment from the Vetlesen Foundation. The foundation continues to promote climate research at Columbia University's Lamont-Doherty Earth Observatory, where Wally was based, and at GISS by providing seed money for research projects geared to exploring various climate issues. This foundation has supported many GISS projects and inspired Climate Center visitors from around the globe. Our research today continues active collaborations between LDEO and GISS through many research scientists, post-docs, and students who interact physically between both places. In his desire to understand the climate system, and to promote education in climate for students at Columbia, his goals were closely entwined with those of GISS. We will be continuing to pursue these common goals in the future.
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