Wednesday, November 04, 2009

Critical Transitions in Nature and Society by Marten Scheffer

Nice review from American Scientist.

Runaway Change

John R. McNeill

Critical Transitions in Nature and Society. Marten Scheffer. xiv + 384 pp. Princeton University Press, 2009. $99.50 cloth, $45 paper.

Like many before him, Marten Scheffer is impressed with parallels between social systems and natural systems. Moreover, he is convinced that problems confronting the human race require something more integrated than the fragmentary knowledge of the various academic disciplines. In short, he seeks to span the famous “two cultures” and to take a long stride toward consilience. Coming from a background in limnology and aquatic ecology, Scheffer is inevitably more at home in some arenas of knowledge than others, and his new book, Critical Transitions in Nature and Society, is mainly about the critical transitions in nature that are of interest to society. An example with which he begins the book is typical: the transformation of the Western Sahara into desert about 5,500 years ago as a result of initially small climate change that built on itself because the drier climate reduced vegetation, thereby heightening albedo.

central valley of ChileClick to Enlarge ImagePart of Scheffer’s aim is to contribute to the study of how well the theory of system dynamics corresponds to real life, in the behavior both of nature and of society. “If we are able to pin down the mechanisms at work,” he says, “this may eventually open up the possibility of predicting, preventing, or catalyzing big shifts in nature and society.” To be able to do so is a long-standing human ambition, which has been given fullest rein in political regimes that have seen utopia just over the horizon and have aimed to get there as soon as possible. In the abstract, such ambition seems laudable. In practice, it has led to many regrettable “big shifts” in nature and society, such as those undertaken in the headiest days of the Soviet Union or Mao Zedong’s rule in China. To date, those most keen on provoking “big shifts” have known far too little, and perhaps cared too little as well, about the possible outcomes of their actions. When results did not conform closely enough to their hopes, they used their powers to try to force society and nature into preferred channels, which led to gulags and environmental disasters. When trying to catalyze big shifts in nature and society, one must really know what one is doing—and that is very, very hard to do.

Scheffer would like to contribute to making it easier. He wants humankind to achieve a proper understanding of what he calls the “Social-Eco-Earth-System,” so that the predictability possible in petri dishes or lake ecosystems may be achieved on larger scales. This would allow, if not perfectibility of the human condition, then at least reliable improvement. Scheffer doesn’t say so, but a good argument for that goal, at least as far as big shifts in the “Eco-Earth” parts of the puzzle are concerned, is that humankind in recent decades, perhaps recent centuries, has acquired the technological power to effect “big shifts” without meaning to. For example, between 1930 and 1990 we dramatically thinned the stratospheric ozone layer without intending to do so, and until the 1980s we did this without realizing we were doing so. Given such powers, it is advisable either to try to avoid causing such shifts altogether, or to make them happen on purpose and carefully, rather than by happenstance as we have typically done. This would require far better knowledge than anyone currently has. So Scheffer’s ambition, at least as regards nature, is justifiable.

Whether or not this applies to big shifts in society as well seems less clear. Political conservatives are reflexively skeptical of efforts to reform society and the state that seem to smack of utopianism. They decry the excesses of the French, Russian and Chinese revolutions and argue that all such attempts necessarily run afoul of the basic fact of human imperfectibility. Their opponents think this cautious approach throws the baby out with the bathwater. They think calculated efforts can yield great improvements—big shifts—in society that are worth struggling to achieve. Over the past 12,000 years, since the first transition to agriculture, our species has repeatedly shown itself capable of big shifts in society, mainly unintended. Whether or not purposive shifts have a better record than accidental ones is impossible to say. We lack criteria for measurement. And unforeseen consequences have always been a large component of any purposive shift.

Part 1 of this book (the first 105 pages) consists of a primer on system dynamics. The presentation is mainly abstract, with occasional brief examples, a bit like a compressed version of a textbook. Graphs abound, but all differential equations and probability functions have been banished to an appendix. Readers learn about equilibrium, resilience, attractors, basins of attraction, strange attractors, hysteresis, homoclinic bifurcation and so forth—there is a helpful glossary of terms at the end of the book. The glossary defines a regime shift as “a relatively sharp change from one regime to a contrasting one, where a regime is a dynamic ‘state’ of a system with its characteristic stochastic fluctuations and/or cycles.”

The main point of the discussion in part 1 is to persuade readers to accept the existence of a subset of regime shifts that Scheffer calls “critical transitions.” These he defines as “sharp shifts in systems driven by runaway change toward a contrasting alternative state once a threshold is exceeded.” These are often hard to foresee and usually extremely difficult to reverse once under way. Scheffer gives the simple example of a loaded canoe. One may lean out to one side a fair bit with no significant consequences, but if one leans out too far the consequences are sudden and difficult to reverse. And it is hard to know in advance just where the tipping point lies. Scheffer invites those who are already versed in the concepts of dynamic systems to skip this section and begin with the environmental case studies in part 2. Readers who have digested the journalist Malcolm Gladwell’s best seller The Tipping Point will have already absorbed the basic concepts Scheffer discusses in part 1, albeit with respect to human behavior more than natural systems, and without the care and rigor that Scheffer brings to the subject.

The case studies are intended to explore the degree to which natural systems correspond to the theory of dynamic systems. Scheffer begins with lakes, one of his areas of expertise. Lakes, especially small and shallow ones, can tip from one fairly stable state to another easily enough. But the more closely one looks, the less the behavior of lakes matches theory, because the theory is too simple. There are more than two possible states; indeed, there are infinite gradations. Moreover, as Scheffer notes, the notion of stability is fraught.

Scheffer turns next to climate systems. In contrast to lakes, the opportunities for controlled experiments on climate systems are nil, and our knowledge of critical shifts, positive feedback and runaway trends is all inferred from slim evidence. Here Scheffer provides an orthodox discussion of matters familiar to all interested in climate history: the oxidation of 2.4 billion years ago, “snowball Earth” episodes more than 600 million years ago, glaciation and Milankovitch cycles, the Younger Dryas and shifts in the thermohaline circulation, and oscillations on shorter time scales, such as the El NiƱo Southern Oscillation. Climate history (as currently understood) presents many examples of critical shifts on various timescales.

Next comes a discussion of biological evolution, with possible explanations for shifts such as the Cambrian explosion, the five major mass extinctions and subsequent surges of speciation. Scheffer argues that some of these may have resulted from big environmental perturbations (such as an asteroid impact), but others perhaps were critical transitions arising from small perturbations that grew into big shifts as a result of positive feedback loops.

A chapter on oceans shortens the timescale, discussing regime shifts in Pacific and Atlantic waters and focusing on sardine-anchovy cycles, the famous cod collapse of the North Atlantic, and, in coastal ecosystems, on coral reefs, kelp forests and estuarine oyster beds. These matters remain comparatively mysterious, and the role of human actions in them is uncertain, but the pattern of sudden dramatic shifts from one state to another is unmistakable. Scheffer follows with a chapter on terrestrial ecosystems that includes several more examples of transitions between alternative stable states on geographic scales ranging from the Sahara desert to peat bogs. Here he emphasizes that critical transitions are rare, which is true in other contexts as well, but which he does not emphasize elsewhere in the book.

In chapter 12 Scheffer makes his own transition away from ecology to the volatile realm of the human sciences.
Read the rest of the review.

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