Unseasonal greetings

The Sea Surface and Global Change - The Ocean Circulation Inverse Problem - El Niño and the Peruvian Anchovy Fishery - Currents of Change
October 31, 1997

Quite by chance, this eclectic selection of books illustrates nicely the breadth of information required to unravel the causes and effects of global change, whether it is natural or the result of human activities. The recent envelopment of large tracts of Indonesia and Malaysia in a choking haze has provided yet another demonstration of our capability to cause large-scale environmental damage. A cascade of apparently unconnected events suddenly gave rise to a phenomenon whose intensity and extent nobody had anticipated. These dramatic events may seem far removed from learned treatises on the "inverse problem" in physical oceanography or on the quantitative science of the exchange of material across the sea surface. However, in coming to terms with global environmental change we must learn how to make such athletic leaps of intellect so that we can appreciate the interconnectedness of our planetary environment. The inclusion of two books on El Nino in this omnibus review provides the link between the particular and the global, between scientific curiosity and human need.

The volume by Carl Wunsch, The Ocean Circulation Inverse Problem, is an advanced treatise on "the (inverse) problem of inferring the state of the ocean circulation, understanding it dynamically, and even perhaps forecasting it, through a quantitative combination of theory and observations". This book is for specialists and would-be practitioners in physical oceanography and it will have a limited, though highly appreciative audience among those who are "faced with the problem of extracting quantitatively useful results from their hard-won observations". Although written by an acknowledged master in the field it is virtually impenetrable to those without an advanced understanding of mathematics. Its subtleties are inaccessible to most of us and it is unlikely to be widely read, but it does contain some essential pointers to understanding wider environmental issues. It exemplifies the difficulty of drawing information and understanding out of detailed studies of the real world and hence underlines the problems encountered in trying to manage the exploitation of the marine environment.

The author poses the problem clearly: "Armed mainly with slow moving, expensive ships, and instruments that have to work in a corrosive, high-pressure environment, oceanographers have over the years built up in a somewhat painful fashion a picture of how the ocean operates. But the picture is badly distorted by the very limited observational base."

Satellite observations of ocean colour, temperature, sea surface topography, wind stress and current movements (via tracked drogues) have resulted in a wealth of data to be incorporated into our understanding. Wunsch emphasises the key importance of such observations in constraining and refining theoretical approaches to ocean dynamics, quoting T. H. Huxley: "What you get out depends on what you put in; and as the grandest mill in the world will not extract wheat-flour from (peapods), so pages of formulae will not get a definite result out of loose data."

Although the approach to understanding the dynamics of the global ocean has to be meticulous and detailed, requiring abstruse mathematics for its synthesis, the phenomena themselves are far from abstract, influencing our environment on a global scale.

In stark contrast to a treatise on whole ocean basins, The Sea Surface and Global Change, edited by Peter Liss and Robert Duce, focuses on the sea-surface microlayer, the top millimetre of the ocean, and its interaction with the atmospheric boundary layer, the first half millimetre of the air. This thin skin controls the interaction between the atmosphere and the oceans, an interface that covers 70 per cent of the earth's surface. A collection of individually authored essays on the transfer of material across the ocean surface is prefaced by three joint workshop reports structured by a scientific meeting held at the University of Rhode Island in 1994. The three joint reports (covering trace gas exchange, biological impacts and photochemistry) are accessible to the scientifically literate layperson and repay careful reading because of the range of important phenomena that they cover. Here, for example, you will find information on the role of the oceans in regulating atmospheric gas concentrations (including carbon dioxide and methane), and on the impact of UVB radiation and of accumulating chemicals on the many life forms that inhabit or depend upon the microlayer. The remaining chapters provide more specialised reviews for the advanced student or the practitioner covering gas exchange (five chapters), life in the surface microlayer (three chapters), photochemistry (two chapters) and methods of study (two chapters). As with all compilations of this kind the style, content and opacity are variable, but overall this book provides a valuable review of a specialised, but globally important field of work.

Oceanic processes that involve both ocean circulation and exchange across the air-sea interface drive the El Nino phenomenon, which underlies this year's persistent pall of smoke over Indonesia and Malaysia. The remaining two books address this phenomenon.

Nutrient-rich water upwelling from the deep ocean along the coast of Peru has given rise to a rich and heavily exploited anchovy fishery. Occasionally this rich upwelling is capped by warm water flowing from the west, causing a collapse in the anchovy fisheries - the phenomenon known as El Nino (the boy child) because of its appearance around Christmas time. The events off the coast of Peru are a symptom of instability in an oscillating series of weather systems, which stretches across the Pacific. The dynamics of these systems are poorly understood and the changes in their characteristics over the past two decades, coincident with global warming, have given great cause for concern. The onset of El Nino appears to be linked to a low atmospheric pressure in Tahiti relative to that in Darwin, Australia. The variation in this pressure gradient across the Pacific basin (the Southern Oscillation Index) is driven by changes in the patterns of heat exchange between the atmosphere and the ocean. The coupled phenomenon is known as an El Nino-Southern Oscillation (or Enso) event.

The El Nino student teaching package by Edward Laws, El Nino and the Peruvian Anchovy Fishery, provides a clear, step-by-step analysis of the impact of the Enso phenomenon on the management of the Peruvian anchovy fishery. The information is focused and accessible. The section on the El Nino itself is brief (five pages) but is supplemented by an appendix. The statement of the feedback mechanisms controlling the periodic appearance of El Nino is a model of clarity and simplicity. The concept of this teaching package is excellent since it provides direct insight into the importance of considering the variability of the natural populations and their environment when making management decisions. This is of key importance since the fecund species that we fish commercially have large and dynamic populations that, through their profligate breeding strategies, are able to survive periodic environmental catastrophes. In managing these stocks it is essential to ensure the level of exploitation leaves the population with sufficient resilience to cope with such disasters.

Annoyingly, the accompanying software is dull and inflexible and wastes a great opportunity to press home these vital lessons on resource management. There is no graphical output and the results of model runs are presented as tables of figures on catch, profit etc, listed to six significant figures (itself a travesty of the kind of data presented to managers). The data cannot be edited or exported to spread sheets for analysis. The "player" is therefore reduced to watching reams of figures scrolling down the screen. This gives no sense of hands-on management of a living resource. The only feedback provided is crass and uninformative: "Hey! What are you doing? The fish are dead, pal. I hope you're happy!!!" I certainly am not and I would recommend those who buy this book to reformat the disc supplied and put it to better use. An hour or so with the equations in the book and a good spreadsheet should produce a model that is more worthwhile to run. It would appear that the same programming approach that brought the winking paper clip to haunt Microsoft Office users has struck again to trivialise one of the key resource issues facing this generation.

Michael Glantz's El Nino: Currents of Change provides a non-specialist introduction to the complexities and global impacts of this climatic instability in the Pacific. He emphasises the startling lack of a coherent approach to studies of the economic and social aspects of the El Nino events. As a social scientist trying to unravel these mysteries for himself, his style is clear and didactic and spiced with a good selection of illustrations, detailed maps, and even a crossword puzzle. The structure of the book is less satisfactory. His approach is repetitive as he traces the growing interest in the El Nino phenomenon in section one, and then catalogues again the sequence of events to the present day in more detail in section two. His social history is more approachable than his explanation of the Enso phenomenon, which is fragmentary and not well organised. He would have benefited from the simple and direct approach of Laws. His account of the massive El Nino event in 1982-83 (the largest recorded in 400 years) is timely, given that in 1997 we seem to be on the verge of an even larger event. Up to 1982, a pattern could be discerned with three- to five-year occurrences of El Nino conditions following a fairly reproducible time course of development from month to month. This pattern was broken in 1982-83 and has not been re-established in the intervening years. The distinct nature of recent events underlines the difficulties in providing El Nino forecasts, and Glantz exploits these uncertainties to make a heartfelt plea for greater emphasis to be placed on an "objective accounting of the social and economic impacts and the consequences of these events".

Section two finishes with a discussion of teleconnections that Glantz defines as "linkages between distinct climatic anomalies". El Nino events also produce drought in Southeast Asia, Australasia, Africa, Brazil, India and Central America and heavy rainfall down the western coast of the Americas. He also points out that the term was originally used by Anders ngstrom to describe phenomena in the North Atlantic. There is indeed a North Atlantic Oscillation, parallel to the Southern Oscillation, with pressure centres in the south around the Azores and the Caribbean, and in the north around the Labrador and Barents Seas. This pressure system drives the transport of heat in surface waters northwards on the Gulf Stream drift, which is running at its highest recorded level. This system has proved fickle in the past and it is apparent that in a warming world the Gulf Stream itself can be switched off in a few decades - providing cold comfort for the UK. Section three, "Who cares about El Nino - and why" is anecdotal and fragmentary and, although there is much interesting material, here the book lacks a developmental thread. Overall, this is a very useful book because of the considerable range of topics covered, but it would not be my first port of call in order to come to grips with El Nino.

To understand and try to prevent such disasters, we must learn how the oceans and atmosphere are interconnected and put this knowledge quickly into the hands of those who manage. Only then can we hope to anticipate the unexpected and to learn from such sudden and catastrophic events. The uncontrolled burning of tropical rain forests in Indonesia gave rise to the Southeast Asian smoke haze, which was exacerbated by photochemical smog over tropical cities. These events coincided with an unseasonably dry period resulting from the onset of a large El Nino event, possibly aggravated by global warming. In normal times, the seasonal rains would have damped down the fires and rinsed the smoke particles and the smog out of the air - but these are not normal times.

Michael Whitfield is professor and director, Marine Biological Association of the United Kingdom.

The Sea Surface and Global Change

Editor - Peter S. Liss and Robert A. Duce
ISBN - 0 521 563 2
Publisher - Cambridge University Press
Price - £60.00
Pages - 519

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