Q & A with Carl Wunsch

Jeremy N. A. Matthews for Physics Today
Wednesday, January 20, 2016

The semiretired MIT geophysicist has written a text that he says addresses the drift of his specialty—physical oceanography—from its observational roots

Read this story at Physics Today

Before Modern Observational Physical Oceanography: Understanding the Global Ocean (Princeton University Press, 2015) was published, Carl Wunsch had already made “an immense contribution” to the field, writes Stuart Cunningham in his January 2016 review of the book for Physics Today. Cunningham counts more than 250 papers and “an astonishing list of master’s and PhD students whose own merits are widely recognized.”

Modern Observational Physical Oceanography is Wunsch’s fifth book. Cunningham writes that it will be “of value to anyone wishing to know more about how to observe the ocean, interpret the data, and gain insights on ocean behavior and on how oceanographers reach their understanding of it.”

Wunsch was the Cecil and Ida Green Professor of Physical Oceanography at MIT before his retirement in 2013; he is now a visiting professor at Harvard University. He received his PhD at MIT under the tutelage of renowned oceanographer Henry Stommel. Among other things, Wunsch has studied the effects of ocean circulation on climate.

Physics Today recently caught up with Wunsch to discuss Modern Observational Physical Oceanography and his views on climate change issues.

PT: What motivated you to take up this book after retiring from MIT?

WUNSCH: In talking to students and postdocs, and in teaching, it became clear that we are in an era increasingly dominated by modelers and theoreticians, for many of whom observations are something downloaded from the Web and then taken as a “truth.” The field of physical oceanography and its climate components has become ever more remote from its observational roots.

In the past 25 years physical oceanography developed a number of highly useful, up-to-date, but theoretically based textbooks. There was no book known to me to which one could direct a colleague or student that emphasized the interesting complexities of the very diverse data types oceanographers now have available. The beautiful theories emphasized by the existing textbooks can produce the misperception of a laminar, essentially steady, ocean and in the extreme case, one reduced to a “conveyor belt.”

PT: With all the advances in remote-sensing technology, what benefits and advantages remain for observations?

WUNSCH: Remote sensing does represent observations! And very important ones, too. But the physics of seawater means that only ocean surface properties are measurable from space, and in a fluid with an average depth near 4000 meters, most of it is invisible without direct in situ observations. Also, the ocean-surface boundary layers are the most complex part of the entire system; many measurable properties at the sea surface can and often do differ radically from their values even centimeters and meters below. (The only slightly pedantic exception would be the gravity satellites, which are sensitive to the total mass of the water column below the satellite orbit.)

So one needs measurements at depth—inaccessible from space.

PT: Do you see a comparison between observational oceanography and human space exploration?

WUNSCH: A good analogy does exist with human space exploration. Historically, the only way to measure the ocean away from its edges, the shoreline, was to go there with an expensive manned ship and physically deploy a sensor at a point or points within the water column. About 40 years ago, it became clear that this “manned oceanography” was hopelessly mismatched to sampling what was clearly a turbulent, ever-changing fluid. Ships are very slow, expensive, and strictly limited in their ability to obtain the vital time series spanning months, years, and decades. The need for “unmanned” ocean exploration gave rise to the various satellites we do now have, the remarkable Argo program [a global array of more than 3000 free-drifting buoys that measure ocean temperature and salinity], autonomous gliders, acoustic remote sensing (tomography), and other devices.

An important need still exists for sending people on ships to obtain first-hand knowledge of many small-scale physical processes, but in a complicated, ever-changing ocean they will never be a substitute for global unmanned observational systems. The more romantic connections to the seagoing explorers of old is, however, lost.

PT: In 2007 you were featured in a documentary called The Great Global Warming Swindle—you later claimed the producers twisted your words to support their agenda. What is your view of public discussion of climate change nearly 10 years later?

WUNSCH: An impressionistic view is that a wider public now has a greater appreciation that climate change is a very dangerous process for both humans and all flora and fauna. The spectacle of the Republican presidential speeches and debates, the continued dominance of people like Senator [James] Inhofe (R-OK), and foolish forums such as the Wall Street Journaleditorial pages, remain dispiriting. I have long thought that the much younger, emerging generations were the best hope for the future. The intense debates in universities over divesting institutional endowment investments in fossil fuel—whatever the merits of that actual course of action—are one of the most encouraging signs of the emerging movement.

Perhaps, like parts of science, sensible social progress emerges “one funeral at a time” (paraphrasing Max Planck).

PT: What is your reaction to the goals that were developed at the recent climate change conference in Paris, particularly in relation to the role of observational oceanography?

WUNSCH: Paris seems to represent real progress, at least in the moral sense, and we can all hope that countries will live up to their commitments with concrete actions to follow. Real efforts to begin dealing with climate change are urgent and Paris is, perhaps, a breakthrough. A worry is that in the push towards emission limitations, technological advancement in energy, and carbon extraction methods et cetera, that the still primitive nature of much of the science of climate will be lost sight of.

The science, particularly the observational part, is extremely cheap compared to efforts involving shifts in the energy economy. And with all of the reasons to focus on the technical aspects of renewable resources, extracting carbon dioxide et cetera, a great deal of fundamental climate science still remains to be confronted. Much of it isn't sexy. It involves difficult long-duration measurements and new models that take years to construct and understand, and it’s in danger in many places of being regarded as not very relevant.

Furthermore, the unwillingness of the world to confront the zero-order issue of human population growth as an underlying driver of global change generally is discouraging. Population modelers keep increasing their estimate of the maximum expected population of the world in the decades to come. Adding billions more people can lead to the failure of even the most effective technologies.

PT: What books are you currently reading?

WUNSCH: H Is for Hawk (Grove Press, 2015) by Helen Macdonald: A vividly written description of training an almost intractable goshawk as a metaphor for life. Acqua Alta(HarperCollins, 1996) by Donna Leon: A literary escape to Venice. The Great Paleolithic War(U. Chicago Press, 2015) by David Meltzer: The long-lasting controversy over peopling the Americas.

Story image: Carl Wunsch - image credit: Helen Hill

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Carl Wunsch is the Cecil and Ida Green Professor Emeritus of Physical Oceanography at MIT. His degrees are from MIT (mathematics and geophysics) and he spent his professional career at the Institute. Wunsch has worked on many aspects of physical oceanography and its climate implications, with emphasis on observations of all types, including the global-scale, using satellites and acoustic tomographic, and various conventional observation methods.

Modern Observational Physical Oceanography: Understanding the Global Ocean, Carl Wunsch, Princeton U. Press, 2015. $99.50 (493 pp.). ISBN 978-0-691-15882-2

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