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ANRV374-EA37-01 ARI ANNUAL REVIEWS 27 March 2009 14:52 Further Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. Click here for quick links to Annual Reviews content online, including: • Other articles in this volume • Top cited articles • Top downloaded articles • Our comprehensive search Where Are You From? Why Are You Here? An African Perspective on Global Warming S. George Philander Knox Taylor Professor of Geoscience, Department of Geoscience, Princeton University, Princeton, New Jersey 08540; Department of Oceanography, University of Cape Town, South Africa; email: [email protected] Annu. Rev. Earth Planet. Sci. 2009. 37:1–18 Key Words First published online as a Review in Advance on December 19, 2008 Africa, global warming, El Niño, Pliocene The Annual Review of Earth and Planetary Sciences is online at earth.annualreviews.org Abstract This article’s doi: 10.1146/annurev.earth.031208.100128 c 2009 by Annual Reviews. Copyright All rights reserved 0084-6597/09/0530-0001$20.00 Global warming, although usually associated with imminent environmental disasters, also presents splendid opportunities for research and education and for collaboration between the rich and the poor that will benefit both groups. Unfortunately, efforts to take advantage of these opportunities are handicapped by the misperception that scientific disputes concerning imminent global climate changes have been settled—that the science “is over”— in addition to a failure to appreciate that some people face problems more urgent than adaptation to and mitigation of the climate changes scientists predict. Changes over the past few decades in the way we conduct our affairs in the Earth sciences, specifically the atmospheric and oceanic sciences, contribute to these misunderstandings. This is a subjective, personal account of those changes. 1 ANRV374-EA37-01 ARI 27 March 2009 14:52 FULL DISCLOSURE As a former member of the editorial board of this series of books, I participated in the informative, enjoyable, annual, one-day meetings in Palo Alto, California to decide who should be invited to review specific topics. The first chapter, reserved for the reminiscences of a senior scientist, generated much discussion because identifying an author amounts to choosing a fruit that is perfectly ripe, not too mature, but no longer green. Shortly after I resigned from the editorial board because of commitments in South Africa, I learned that some people consider me ripe. Several colleagues encouraged me to write this chapter, explaining that my story— disadvantaged in South Africa, privileged in America—will interest readers. A story about exceptional good luck on innumerable occasions is boring. It can fortunately be summarized in a short poem: Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favor to men of skill; but time and chance happeneth to them all. Eccles. 9.11 Authorized (King James) Version The “time and chance” that have happened to me personally over the past few decades may interest a few young Africans, but they, unfortunately, are not avid readers of Annual Reviews. I have therefore written for the most likely readers, middle-aged, North American scientists, about science and also about social issues. I hope that even those who do not agree with my opinions on the science will be persuaded that, in our pursuit of social causes related to our science, we should pause to reflect on the disquieting dilemmas that arise when we mix science and politics. This essay also provides an African perspective on global warming. I hope that even those readers with no particular interest in Africa will agree that different perspectives on this complex, multifaceted problem can benefit everyone. My personal experiences over the past few decades reflect but a small part of much larger developments that influenced all of us in the Earth sciences and changed the way we conduct our scientific affairs. A development I consider particularly important is the transformation of informally organized “bottom-up” scientific activities into highly structured “top-down” programs—a transformation of “small science” into “big science.” This was an inevitable consequence of the enormous growth in our field and in the resources available to a larger number of scientists. This growth has been accompanied by global political changes, specifically the end of the Cold War, and a significant change in what governments expect of scientists. The result has been a shift in emphasis from the one main goal of science, an understanding of natural phenomena (or science for the sake of science), to the other main goal, the production of useful results. This is unfortunate because scientific progress is critically dependent on a balance between these two complementary goals. Another significant change since Sputnik is the growing involvement of scientists in political issues related to their research. During the Cold War, my friends and colleagues engaged in research that was divorced from their political concerns, the war in Vietnam, civil rights in the South, and apartheid in South Africa, for example. Today, many scientists who study global warming are convinced that their scientific results have vitally important political implications. This can create problems because the cold, uncompromising world of science is profoundly different from the world of human affairs, where compassion is a virtue, compromise a requisite. How do we reconcile the unanimity, as regards the science, that politicians request, with the commitment 2 Philander Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 ARI 27 March 2009 14:52 Figure 1 Sacred and Profane Love (Titian, circa 1514). Used with permission from Archivio Fotografico Soprintendenza Speciale per il Patrimonio Storico Artistico ed Etnoantropologico e per il Polo Museale della citta di Roma. to skepticism that science demands of its practitioners? The extremely polarized global warming debate between “believers” and “skeptics” seems to ignore that scientists are obliged to be skeptical. The most serious global warming dilemma, one which the rich and the poor view very differently, concerns the appropriate balance between our responsibilities toward future generations and our obligations toward those suffering today. On this matter, as on all ethical issues, science is mute. Scientists, however, have opinions that reflect their personal values. How do we prevent those values from influencing our assessments of uncertain scientific results? Dilemmas inevitably arise when we mix science and politics. Finding a balance between seemingly incompatible demands is a challenge with which many generations have struggled. Valuable guidance is available in Titian’s sixteenth century painting (Figure 1), which juxtaposes temporal love, in the form of a richly attired bride holding an urn of jewels, with its ideal counterpart, eternal love, as represented by the nude Venus who holds a flaming lamp, a symbol not only of divine love but also of universal truths. Late in the 18th century, the painting acquired the title “Sacred and Profane Love” and was moralistically interpreted as depicting the antithesis between Christian and Pagan values. The painting can also be interpreted in an entirely different manner because its original purpose was the celebration of a marriage. The woman in white, the bride, has Venus as an attendant. The painting glorifies both earthly and heavenly love; both are honorable and praiseworthy. This is attested to by the twin faces of the two figures. Cupid, who stirs the water in the fountain between the two women, establishes harmony between temporal values (the urn of jewels) and universal truths (the eternal flame). Scientists can offer additional interpretations of this painting. For example, the bride could represent experimentalists and observationalists who collect data (jewels) that describe natural phenomena. She could also represent the developers of complex climate models who try to include as many physical processes in their models as possible. Venus could represent reductionists (theoreticians) who explain natural phenomena by appealing to eternal truths. Whatever the preferred interpretation, the crucial role of Cupid has to be acknowledged. He encourages collaboration, cooperation, and new approaches. The following brief review of issues that happen to interest me is a story about attempts to integrate seemingly disconnected worlds, those of the observationalist and theoretician, of the www.annualreviews.org • An African Perspective on Global Warming 3 ANRV374-EA37-01 ARI 27 March 2009 14:52 oceanographer and meteorologist, of the different spheres of the Earth sciences, and of the rich and the poor. This story illustrates the importance of Cupid in connecting the bride and Venus in Figure 1 (for different versions of this story, see Philander 2004, 2006). A MARRIAGE OF MEASUREMENTS AND THEORY Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. “Why do our ideas about the ocean circulation have such a dream-like quality?” is the title of an article Henry Stommel (1995) circulated in 1954, a few years after his pioneering paper that explains how the torque that easterly and westerly winds exert on the oceans—a rapidly rotating spherical shell of fluid—generates intense jets such as the Gulf Stream and the Kuroshio Current (Stommel 1948). At the time, physical oceanography was being transformed from a mainly descriptive science into a branch of applied mathematics. That transformation accelerated after the former Soviet Union launched Sputnik, Earth’s first artificial satellite, in 1957. Concern that the communist countries may be scientifically more advanced than the countries of the West proved a bonanza to science in general and to oceanography in particular. One result was a significant increase in the number of young scientists—I was one—entering the latter field in the 1960s. Some of us produced mathematical refinements of Stommel’s original explanation for the Gulf Stream, but the results were untestable and decidedly “dream-like.” Unexpectedly, connections between measurements and theories concerning curious equatorially trapped waves emerged in the 1970s. Analyses of tide gauge data from the equatorial Pacific (Wunsch & Gill 1976) provided persuasive evidence for the waves previously postulated by Matsuno (1966) and Moore (1969). Theories indicated that similar waves play a central role in the response of the complex equatorial currents, undercurrents, and countercurrents to changes in the winds. These results prompted several international programs to explore the time dependence of oceanic conditions in various parts of the globe and to observe and explain the striking differences and similarities among the three tropical oceans. The winds that force the Atlantic and Pacific are similar, but those ocean basins respond differently because one is three times as wide as the other. The Atlantic and Indian oceans have similar dimensions, but smoothly varying trade winds prevail over one, whereas the other experiences monsoons with a sudden onset and with seasonal reversals of direction. To study the fascinating phenomena generated by the different wind patterns in the three tropical oceans, scientists built on the major contributions of Wyrtki (1973). They developed instruments for acquiring time series of the variations of the equatorial currents (Halpern 1987) and developed a hierarchy of models, from the simple and highly idealized (Cane & Sarachik 1976) to the complex General Circulation Models (GCM) that require supercomputers. The GCMs are capable of realistic simulations (Philander & Seigel 1984), but interpretation of their results requires a vocabulary and concepts, such as Kelvin and Rossby waves, that come from idealized models. Today, large teams of scientists design complex climate models, coupled oceanatmosphere GCMs, for the purpose of realistic simulations, but efforts to explain, by means of simpler models, the phenomena being simulated are inadequate. The various phenomena observed in the tropical oceans provided stringent tests for theories and models, leading to rapid progress. Within a few years of the intense and destructive El Niño of 1982–1983, scientists could explain and simulate all aspects of that unusual event. They could accurately reproduce the timing and the magnitude of the dramatic changes in the various equatorial currents, thus convincingly eliminating the “dream-like quality” of earlier theories. This was the splendid achievement of a small community of scientists who took full advantage of the excellent opportunities for “science for the sake of science” in the post-Sputnik era. Some of the considerable resources that the government made available to oceanographers undoubtedly 4 Philander Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 ARI 27 March 2009 14:52 were for practical, military purposes, but the groups with whom I associated had remarkable freedom to decide on the questions they wished to address and to plan and implement research programs themselves. It was my extraordinary good fortune to have mentors who fully supported my participation in these bottom-up programs—Allan Robinson at Harvard University, Jule Charney at MIT, and Joe Smagorinsky and Kirk Bryan at GFDL in Princeton, where I started a very fruitful, ongoing collaboration with the incomparable Ron Pacanowski. Even more fortuitous was the opportunity to interact with and to befriend the exceptional scientists responsible for those programs, which provided some of the most rewarding personal and professional experiences of my career. Today, trips to cities as far apart as Boston, Bologna, Bangalore, Kiel, Paris, and Tokyo are still for the purpose of attending scientific meetings, but what I most enjoy are the opportunities to visit dear friends and their families. The documentation and simulation of El Niño of 1982–1983 demonstrated the success of oceanographers in marrying measurements to theory, but the achievement was flawed by a failure to alert the public in a timely manner that the devastating El Niño would occur. The focus had been on science for the sake of science while the equally important complementary goal of useful science had been neglected. The advances made during the 1970s were quickly translated into a capability to inform the public of an imminent El Niño. Hayes et al. (1991) initiated the deployment of an array of instruments to monitor conditions in the equatorial Pacific. Leetmaa & Ji (1989), by means of an oceanographic GCM, converted the measurements, transmitted to land via satellite, into maps of conditions in the tropical Pacific. These operational products made it possible to monitor the development of El Niño of 1997 from an early stage and to alert Californians six months in advance that they would experience an exceptionally harsh winter. El NIÑO Y LA NIÑA For more than a century, the Southern Oscillation and El Niño were studied as separate, unrelated atmospheric and oceanic phenomena, respectively. That the two are intimately related first occurred to Bjerknes (1969), when he studied El Niño of 1957, capitalizing on the plentiful measurements made during the International Geophysical Year. He realized that, from the perspective of oceanographers, El Niño is a consequence of changes in the winds over the equatorial Pacific but that those changes, from the perspective of meteorologists, are induced by the oceanic changes, especially those in sea surface temperature patterns. Bjerknes (1969) inferred that this circular argument implies that interactions between the ocean and atmosphere are unstable and thus amount to a positive feedback. The trade winds that prevail over the equatorial Pacific drive the warm surface waters westward, exposing cold water to the surface in the east. A perturbation in the form of a modest relaxation of the winds allows some of the warm water to return eastward. The decrease in the east-west temperature gradient reinforces the relaxation of the winds, and, in due course, El Niño conditions are established. What brings El Niño to an end? At first, scientists ignored this question and focused on indentifying the perturbations (triggers) that initiate the ocean-atmosphere interactions and that cause a departure from “normal” conditions. However, from a glance at a record of sea surface temperature variations, at the Galapagos Islands for example, it is evident that normal conditions seldom prevail because the tropical Pacific experiences a continual, irregular oscillation (the Southern Oscillation) between two complementary states. One is El Niño. An apposite name for the other is therefore La Niña (Philander 1985). The oscillations between these two states present us with an eigen-value, not an initial value problem. The interannual fluctuations between El Niño and La Niña correspond to a natural mode of oscillation of the coupled ocean-atmosphere. What are the factors that determine its period? Is it www.annualreviews.org • An African Perspective on Global Warming 5 ARI 27 March 2009 14:52 highly unstable or strongly damped? How predictable is it? These questions prompted the development of coupled ocean-atmosphere models, which simulate air-sea interactions. A particularly powerful and versatile tool is the idealized model developed by Zebiak & Cane (1987) in which the time-averaged background states, including the intensity of the trade winds and thermal structure of the ocean, are specified. The results from that and other similar models reveal the existence of several different types of modes, each covering a broad spectrum of space and timescales. Of relevance to the observed Southern Oscillation is the delayed oscillator mode in which the atmosphere responds instantaneously to changes in sea surface temperature, but the more ponderous ocean responds in a delayed mode to the changes in the winds (Schopf & Suarez 1988). For this mode, the memory of the coupled ocean-atmosphere is in the oceans. To anticipate future developments, the ocean has to be monitored. This justified the deployment of the array of instruments in the equatorial Pacific mentioned earlier. Modes other than the delayed oscillator are involved in the intriguing asymmetries, relative to the equator, of sea surface temperature and rainfall patterns. (The warmest water and heaviest rainfall occur north of the equator.) Those modes also play an important role in the response of tropical oceans to seasonal variations in sunlight. (An annual harmonic characterizes seasonal variations in temperature and rainfall on the equator at the Galapagos Islands even though the sun crosses that location twice a year.) These insights contributed to rapid progress in explaining and simulating tropical phenomena involving ocean-atmosphere interactions. Measurements, which are of central importance in any science, present a special challenge in the Earth sciences because we deal mostly with phenomena that do not repeat themselves. For example, the weather pattern on any day (the global distribution of warm and cold fronts, cyclones, and anticyclones) is unique. Tests for theories and models of the weather, therefore, require measurements that cover many days. Those tests are needed to determine the validity of empirical parameterizations that allow computer models to cope with the numerous processes on spatial and temporal scales too small to be dealt with explicitly (e.g., turbulence and clouds). In the case of models for weather prediction, a new test is available each day. This has contributed to parameterizations that are valid over a wide range of conditions and has led to enormous progress in weather prediction, which was not long ago regarded as witchcraft, then became entertainment on television because it was so inaccurate, and now provides reliable, valuable, and important information. The prediction of El Niño is different from weather forecasts because El Niño is part of a quasiperiodic oscillation sustained by random fluctuations. On long timescales it may be possible to anticipate far in advance when El Niño is likely to occur, but on short timescales the random fluctuations complicate matters. In 1997, for example, El Niño had an unexpectedly large amplitude because the right perturbation appeared at the right time (Fedorov et al 2003). The capability to predict El Niño is improving, but is not yet as advanced as is weather forecasting because we have not had an opportunity to observe a sufficient number of realizations of that phenomenon. This is evident in the way each El Niño has thus far surprised us. Nobody anticipated the exceptional intensity of the event of 1997, for example. Over the next few decades, we will observe and simulate several more events and the forecasts will improve. Meanwhile, the array of instruments in the tropical Pacific alerts us of developments over the next few months. Advances in the study of El Niño, and more generally of ocean-atmosphere interactions, are the fruits from the improbable marriage of oceanography, which appeals to romantic, intrepid explorers who ask for a tall ship and a star to steer her by, and meteorology, whose practitioners produce reliable daily weather forecasts by being assiduous and diligent. This success also attests to the wisdom of Titian’s philosophy as expressed in Figure 1. Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 6 Philander ANRV374-EA37-01 ARI 27 March 2009 14:52 Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. THE PAST AND FUTURE CLIMATE CHANGES How will global warming affect the future of El Niño? Different models give different answers. To appreciate why, inspect Figure 2. The interannual oscillations between El Niño and La Niña, which are associated with adiabatic thermocline displacements of the type shown in Figure 2a, depend on a background state that is defined by the time and spatially averaged depth of the thermocline, and several other parameters. A change in this depth, as in Figure 2b, alters the properties of El Niño. Hence, to determine the impact of global warming on El Niño, it is necessary to determine how the mean depth of the thermocline (and other properties of the background state) will change. The different results from different models underline the need for tests for the models. Changes in the properties of El Niño over the past hundred years—it was energetic early and late in the 20th century, and weak for a few decades starting in the 1920s—provide possible tests, but unfortunately the available instrumental records are inadequate (Fedorov & Philander 2000). Part of the reason is the high sensitivity of surface conditions to changes in the depth of the thermocline in the eastern equatorial Pacific, where that depth is very small. The sensitivity decreases to the west as the depth of the thermocline increases; it is small at the dateline, where the depth of the thermocline is approximately 100 m. This suggests that a relatively modest change in the mean depth of the thermocline, a change of the type shown in Figure 2b, could have a huge impact on the properties of El Niño. Why is the thermocline currently so shallow? Under what conditions will it deepen as in Figure 2b? To check the available answers to these important questions, we are obliged to turn to descriptions of paleoclimates. My experience with the use of instrumental records to test models of the ocean did not prepare me for the challenge of using paleoclimate information to test climate models. Explaining and simulating well-documented oceanic changes induced by accurately measured wind fluctuations over a short period amount to a relatively straightforward exercise. Paleoclimate changes, on the other hand, occurred over such prolonged periods that the available computer resources permit simulations of only extremely brief intervals. Furthermore, the available information is incomplete and uncertain. Consider, for example, the hypothesis that the prolonged cold period approximately 14,000 years ago, known as the Younger Dryas, could have been a consequence of a freshening of the surface waters of the Atlantic Ocean. Testing that idea quantitatively is almost impossible because of huge uncertainties in the volume, location, a b Surface Increasing depth West East West East Figure 2 Schematic diagram of equatorial thermocline displacements involving (a) an adiabatic, horizontal redistribution of warm surface waters, as occurs during El Niño; and (b) a diabatic deepening of the thermocline that can induce permanent El Niño conditions. www.annualreviews.org • An African Perspective on Global Warming 7 ARI 27 March 2009 14:52 and timing of the freshening. As a consequence, current explanations for the Younger Dryas and related phenomena have a “dream-like quality.” Progress in the study of paleoclimates is likely to be more rapid for phenomena such as the Milankovitch cycles, which have forcing functions that are known precisely. The challenges nonetheless remain very formidable. I learned this when I became interested in the Early Pliocene, the period some three million years ago (Ma), when the Milankovitch cycles started amplifying. Fortunately, my colleague and friend Tony Dahlen offered me sound advice. When I became a member of the department of geosciences at Princeton University in the early 1990s, my efforts to learn about geology included a field trip to the Delaware Water Gap. On a sunny October Sunday, when fall colors were at their peak, I joined Tony Dahlen, who was taking his freshman class to have a look at evidence that the continents drift and that the Earth experienced an ice age in the distant past. During the scenic trip, we stopped at a few places, waded through the brush, found rock outcrops, and listened to Tony explain their significance. In the afternoon, we hiked up a hill onto bedrock, found a position where sunlight reflected off the rock at just the right angle, and then discerned faint scratches on the rock, all in the same general direction. At the end of that enjoyable trip, I thanked Tony for taking me along but expressed disappointment that, on the basis of the evidence presented to me on that day, I could accept neither the idea that continents drift nor the theory that much of North America had been covered with glaciers in the past. The evidence was too flimsy and unpersuasive. Tony explained that the scientific community is convinced of the reality of drifting continents, and of recurrent ice ages, because there is a wealth of evidence, a huge number of separate observations of different variables, all consistent. There are a few exceptions that do not fit the pattern, that may even be contradictory, but they must be weighed in the context of all the other available information. Too narrow a focus on isolated measurements covering a brief period in a small region can lead to serious errors. These insights are proving invaluable in our efforts to resolve controversies concerning conditions during the Early Pliocene and simulations of those conditions with climate models. That period, approximately three million years ago, is of interest because the Earth at that time was significantly warmer than it is today, even though the positions of the continents, the intensity of sunlight, and the atmospheric carbon dioxide levels were essentially the same. Why was the Early Pliocene so warm? An important hint is the finding that, at that time, sea surface temperatures were as high in the eastern as in the western equatorial Pacific (Ravelo et al. 2004). Such permanent El Niño conditions will strongly contribute to an increase in globally averaged surface temperatures by decreasing the areal extent of highly reflective, low-latitude stratus clouds, thus decreasing planetary albedo, and by increasing the atmospheric concentration of the powerful greenhouse gas, water vapor. Huybers & Molnar (2007) confirm that perennial El Niño conditions during the Early Pliocene would have inhibited glaciation. The hypothesis that El Niño was permanent during the Early Pliocene is currently in question because of recent observational and modeling results. (a) Although some observations show that sea surface temperatures in the eastern equatorial Pacific were high approximately three million years ago, other observations indicate the opposite, namely cold surface waters in the region at that time (see Fedorov et al. 2006 for references). (b) Certain very complex climate models, developed for the purpose of predicting climate changes that will accompany future global warming, fail to reproduce permanent El Niño conditions (Haywood et al. 2007). To resolve these controversies, let us return to Tony Dahlen’s advice on that field trip to the Delaware Water Gap. The inconsistent estimates of sea surface temperatures mentioned in (a) should be assessed in the context of conditions elsewhere on the globe at that time and in the context of preceding and Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 8 Philander ANRV374-EA37-01 ARI 27 March 2009 14:52 a 0 δ18O (ppt) 1 2 3 5 60 40 20 3 2.5 2 1.5 1 0.5 0 Millions of years before present b 300 260 0 CO2 (ppm) 380 340 Temperature (°C) Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. 4 220 –4 –8 400 350 300 250 200 150 100 50 0 Thousands of years before present Figure 3 (a) Variations in δ18 O over the past 60 million years. Higher values of δ18 O indicate colder climate (greater global ice volume). The gradual cooling over the past 50 million years is evident. Note that the timescale changes at three million years ago. The Milankovitch cycles are modest in amplitude up to three million years ago but then start amplifying (Zachos et al. 2001). (b) Fluctuations in temperature and in the atmospheric concentration of carbon dioxide over the past 400,000 years, as inferred from Antarctic ice core records (Petit et al. 1999). The vertical red bar is the increase in atmospheric carbon dioxide levels over the two centuries prior to 2006. subsequent developments. The Pliocene is then seen as not merely a warm period in the recent history of the planet but as a far more interesting and important stage in the prolonged transition from a warm to a cold planet. In Figure 3, the irregular global cooling, because of processes associated with the drifting of continents, started early in the Cenozoic some 60 million years ago. Superimposed are Milankovitch cycles that are modest up to the Early Pliocene, whereafter they start amplifying and in due course grow into dramatic, recurrent ice ages. What happened approximately three million years ago? Climate models are required to interpret the observations of different variables from different parts of the globe. This presents us with an apparent paradox because we need the observations to establish the validity of the models. How can we use a model (or theory) to explain observations, which in turn are needed to test the model? To progress, we are obliged to engage in a continual interplay between observations and models—not only complex models that are deemed realistic, but a hierarchy of models, some of which are highly idealized (Held 2005). If simple models yield www.annualreviews.org • An African Perspective on Global Warming 9 ARI 27 March 2009 14:52 results that complex models fail to reproduce, then it is possible that the idealizations suffer from the neglect of certain important processes. However, it is also possible that the complex models are flawed. The failure of the complex model, mentioned in (b), to simulate a permanent El Niño could indicate that the model has serious deficiencies. Resolution of the Early Pliocene controversies could lead to improved climate models for the prediction of future climate changes. To explore how El Niño, which is intermittent today, could have been permanent in the past, we have to identify processes that can deepen the thermocline, as shown in Figure 2b. Such a change, unlike the adiabatic one in Figure 2a, is diabatic and implies a change in the oceanic heat budget. It follows that not only the eastern equatorial Pacific but also other parts of the globe must be involved. Can information from those other regions shed light on the controversy concerning measurements in the eastern equatorial Pacific? For an initial answer, let us turn to the results from idealized models. The ocean gains heat mainly in low latitudes, especially where cold water rises to the surface in upwelling zones, such as along the equator. The cold water gains heat as it flows poleward in the surface layers and loses that heat in the extratropics, especially in winter when cold continental air flows over warm currents such as the Gulf Stream and Kuroshio. Next, the water sinks in subduction zones and then, in subsurface layers, returns to the equator. In a state of equilibrium, this meridional overturning component of the wind-driven circulation ensures a balanced heat budget, with the ocean gaining as much heat as it loses. Whereas the loss of heat to the atmosphere depends on atmospheric conditions, the gain at the equator depends on oceanic conditions, on the depth of the thermocline. Suppose that the heat lost extra-equatorially decreases because of a warming of the atmosphere. Warm water then accumulates in low latitudes and the equatorial thermocline deepens, thus decreasing the oceanic heat gain and, in due course, establishing a new balanced heat budget. A change in the oceanic heat budget can be either direct, as described above, or indirect, when the surface waters are freshened. In the latter case, an increase in surface buoyancy (which depends on temperature and salinity) reduces the meridional overturning, decreases the poleward transport of heat, and deepens the equatorial thermocline. Hence, a change in rainfall patterns in the extratropics can induce El Niño conditions in the tropics. These results, established by means of highly idealized models of the ocean, indicate that a change in extratropical conditions (a reduction in the oceanic heat loss, or a freshening of the surface waters, or both) can cause El Niño to become permanent (Boccaletti et al. 2004, Fedorov et al. 2006). It is conceivable, even plausible, that these conditions were satisfied during the very warm Early Cenozoic so that the thermocline would have been sufficiently deep for El Niño to be permanent. The theories indicate that the subsequent global cooling over tens of millions of years was accompanied by a shoaling of the thermocline, which, at a certain stage, was so shallow that the winds were capable of exposing cold water to the surface in the tropics and subtropics. If this hypothesis is correct, because the shoaling of the thermocline was global, cold surface waters should have appeared nearly simultaneously at the various oceanic upwelling zones in regions as far apart as California and southwest Africa. Observations indicate that this threshold for thermocline depth was indeed reached simultaneously in various regions approximately three million years ago (Fedorov et al. 2006). From this perspective, it seems plausible that the surface waters around the Galapagos Islands also experienced cooling at that time. Corroborating evidence comes from developments since three million years ago, specifically from the amplification of the Milankovitch cycles seen in Figure 3. The appearance of cold surface water at the equator affected the oceanic heat budget and permitted regions of heat loss in the extratropics to influence conditions in equatorial regions of heat gain, as explained earlier. A decrease in heat loss when obliquity (the tilt of the Earth’s Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 10 Philander Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 ARI 27 March 2009 14:52 axis) is large and thus high latitudes receive more sunlight can cause a deepening of the equatorial thermocline and an increase in sea surface temperatures. Tropical ocean-atmosphere interactions of the type involved in El Niño amplify and modify this response because they amount to positive feedbacks. This link between the tropics and extratropics operates on timescales comparable to or longer than that of the wind-driven oceanic circulation, i.e., a few decades. The link therefore does not affect the response to precessional changes in sunlight because those occur at too high a frequency. (Precessional changes, when averaged over a year, are zero.) These results explain why obliquity and not precessional signals are observed to be dominant in equatorial Pacific sea surface temperature fluctuations (Ravelo et al. 2004, Lawrence et al. 2006). The signals became prominent approximately three million years ago, consistent with the proposal that cold waters appeared at the surface in the eastern equatorial Pacific at approximately that time. Results from a variety of idealized models of the ocean, the atmosphere, and the coupled system, provide the faint outlines of a consistent picture in which the Early Pliocene is a crucial stage in the transition from a warm to a cold planet (Fedorov et al. 2006, Barreiro et al. 2008, Barreiro & Philander 2008). To determine whether the processes neglected in the simple models are indeed negligible, we need calculations with complex climate models. However, the complex models introduce new approximations, the validity of which needs to be checked. Could the failure of the complex models to simulate a permanent El Niño be an indication that they are flawed? The first attempts, in the 1960s, to model the Earth’s climate reproduced too warm a world because, in the simulations, the planetary albedo was too low. The major problem was the absence of the low stratus clouds in the tropics. Advances in model development eliminated that flaw so that in the realistic simulations of the climate of today those clouds are present. But are the computer codes that determine the clouds appropriate for a radically different climate such as that of the Early Pliocene? In simulations of that period, sea surface temperature gradients along the equator persist, as does the Walker Circulation and, as a result, the low level stratus clouds of the eastern equatorial Pacific. The albedo of the planet hardly changes from its value today. Is it possible that the remedy for the original problem, simulation of a world that is too warm, now mars the simulation of a warm world in which the Walker Circulation collapses permanently? Are the models too inflexible in their treatment of the low stratus clouds in the tropics? The controversies concerning the Early Pliocene are by no means settled; thus, Tony Dahlen’s advice, to broaden the context of the observations and theories, remains valuable. For example, we should guard against the tendency to focus, in isolation, on only one of the various phenomena that are part of the response to Milankovitch forcing. That forcing corresponds to modest changes in the seasonal cycle, which has different signatures in different regions: monsoons in India, severe winter storms in central Canada, and oceanic upwelling at the Galapagos Islands. To a first approximation, these phenomena are independent of each other and can be studied separately. Links between them become apparent when the appearance of El Niño is associated with a failure of the Indian monsoons and with mild winters in Canada. It is very likely that the response to Milankovitch forcing also involves several different phenomena. In this article, the results in Figure 3 are discussed strictly in terms of vertical movements of the thermocline. Usually, discussions of Figure 3 focus attention on the waxing and waning of glaciers. The variation in the atmospheric concentration of carbon dioxide is yet another part of the story, and further parts probably remain to be discovered. The seemingly independent phenomena, each with its own explanation, are connected in ways yet to be explained. Studies of paleoclimates are at an exciting stage. Rapid progress could be imminent, but certain developments over the past few decades, the enormous growth in the size of the scientific enterprise for example, are creating hurdles. That growth, along with global political changes, have caused the pendulum that was on the side of Venus after the launching of Sputnik to swing to the side of the www.annualreviews.org • An African Perspective on Global Warming 11 ARI 27 March 2009 14:52 bride (Figure 1). Both the acquisition of data of the kind shown in Figure 3 and the development of complex climate models amount to “bride-like” activities. These activities are essential, but their value is diminished in the absence of complementary “Venus-like” activities. The few ideas that are available to explain climate changes, a shutdown of the thermohaline circulation for example, are invoked so often, for such a variety of phenomena, that one is reminded of the adage: If a hammer is your only tool, then everything resembles a nail. A further problem is the insufficient attention given to possible flaws in the complex climate models. For a long time, many oceanographers were skeptical of the value of numerical models of the ocean on the grounds that the simulations represent possible worlds but are not directly relevant to the world we observe. Rapid progress led to a realistic numerical simulation of El Niño of 1982–83. It persuaded several people that the models can be powerful oceanographic tools. A little more than a decade later, complex climate models are being embraced so enthusiastically that words of caution are necessary. Those models are imperfect tools. Furthermore, discussion and comprehension of the results from complex models depend on the results from idealized models. To solve the important puzzles posed by the results in Figure 3, we need scientists who succumb to Cupid’s designs while working in an unstructured environment that encourages bold, risky ventures and that tolerates failures. Those solutions are needed so that we can reduce uncertainties in the prediction of future climate changes. Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 THE OPPORTUNITIES THAT GLOBAL WARMING PRESENTS In March 2005, at the invitation of the Academy of Sciences of South Africa, I visited several universities and research institutions in that country. Afterward, I was asked for recommendations on how to attract more students to science and engineering. South Africa, with a population of 48 million, of whom nearly 80% live in abject poverty, has a dire need for technically trained people. The transition from apartheid to postapartheid during the 1990s was accompanied by the exodus of close to a million people, practically all of whom were highly educated. Many of the positions they left vacant are still unfilled even though unemployment is in the neighborhood of 40%. The vacancies are likely to increase over the next decade because of imminent retirements. In South Africa, and more generally in all of Africa, education is a high priority because it is essential for the alleviation of poverty. Fortunately, global warming, even though it is usually associated with imminent environmental disasters, presents splendid opportunities for education and research. Unfortunately, it is difficult to take advantage of the opportunities, in part because of developments in wealthy countries. The award of the 2007 Nobel Peace Prize to Al Gore and the IPCC has enormously increased public awareness of issues related to global warming. Many people now associate it with imminent environmental disasters that call for prompt “adaptation” and “mitigation.” To some, the award of the Nobel Peace Prize is a signal that scientific disputes concerning global warming have been settled and that the science “is over.” This, regrettably, is the message that some foreign advisors bring to Africa in their zeal to promote “adaptation and mitigation.” This message harms not only the poor but also the rich countries that are concerned about a public that is poorly informed about science in general. It is therefore important to recognize that global warming is not only a threat but also an opportunity. Growing concern about global warming is intensifying the passions of many people to be responsible stewards of planet Earth. Many of those people are handicapped because they have to take, on faith, the alarms that scientists sound without comprehending the scientific reasons. Their response to the threat of global warming will be far more effective if it is motivated by a rudimentary understanding of why the Earth is habitable. Taking care of our immensely complex 12 Philander Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 ARI 27 March 2009 14:52 planet can be a challenge; thus, the success we have with an even more complex system, the human body, is encouraging. Education plays a major role in that success; every educated person is expected to know how the human body functions and to be aware of the importance of hygiene, diet, and exercise. By contrast, laymen have scant knowledge of the reasons ours is a habitable planet and do not appreciate how their way of living impacts the environment. Education is most effective if it involves everyone (university students, school children, and their parents) and if it deals with issues and phenomena all of us care about dearly. Because we all love and cherish nature and wish to be responsible custodians of this remarkable planet, the Earth is an ideal focus for an educational program. The landscape anywhere has a wealth of information about our planet, but most people are unaware of it. Every classroom should have a thermometer so that children can document diurnal and seasonal changes in temperature. In the process, they will learn a great deal about mathematics and statistics. Concern about global warming is a vehicle for teaching those and other topics, such as chemistry and physics, while encouraging the discovery that the familiar world is full of mysteries and wonders. This is an opportune time for such a program because the Earth sciences are entering an exciting new phase. What had been separate disciplines are being integrated in order to address a host of important questions, some of which concern future climate changes. The results in Figure 3 offer an excellent introduction to the Earth sciences because all youngsters are already experts on dinosaurs but are unaware of the weird and astonishing developments subsequent to the demise of those beasts. Figure 3 tells a strange story of drifting continents, the waxing and waning of glaciers, and the appearance of “new” animals, of which the most interesting are humans. We developed with such astonishing rapidity over the past few millennia that we have become geologic agents capable of interfering with the processes that make this a habitable planet. Figure 3 tells us that we live in an era that began a few hundred thousand years ago in which climate is very sensitive to modest perturbations. Slight variations in sunlight can induce dramatic climate fluctuations such as recurrent ice ages. Even though we cannot yet explain those phenomena, we know enough to realize that to introduce a perturbation that grows exponentially is to play with fire. We, the fortunate inhabitants of a most unusual planet at an unusual moment in its history, a moment that calls for circumspection, should remember that we call ourselves homo sapiens. Global warming can be an effective vehicle for promoting education in all parts of the globe, but putting it to this use in Africa is a special challenge. The reasons should have been obvious to me more than forty years ago, but I did not realize it at the time. WHERE ARE YOU FROM? WHY ARE YOU HERE? “Where are you from?” the Boston policeman asked me. We were in his patrol car, waiting to find out whether the borrowed car I was driving before he stopped me—a car that lacked a rear light—had perhaps been stolen. My answer, “South Africa,” met with impatience. “Yes, but which country?” Once he grasped that South Africa is a country, the policeman quickly came to the obvious conclusion: An African studying at Harvard University will be in a position to appoint a chief of police once he returns home. The policeman proceeded to apply for the position, regaling me with colorful anecdotes of his varied accomplishments in the field of law enforcement. This incident occurred shortly after my arrival in the United States in the early 1960s, when South Africa was in no need of advice on how to improve enforcement of its cruel apartheid laws. It was my introduction to a representative of the large number of well-intentioned people who are woefully ignorant of Africa but nonetheless are firmly convinced that their expertise is exactly what Africa needs. For example, some students of biodiversity are passionate about advising Africans on www.annualreviews.org • An African Perspective on Global Warming 13 ARI 27 March 2009 14:52 how to live on the savannah in harmony with the wild animals. These ecologists seem not to realize that Africans have aspirations indistinguishable from theirs—to live in the suburbs and to drive large, fast, shiny cars. Not only a few ecologists but also many non-Africans who are eager to help the continent are convinced that their particular fields of expertise are what Africa needs most. After a few decades in the United States, I returned to South Africa to become involved in establishing ACCESS (Africa Center for Climate and Earth System Science), which offers educational programs and information concerning global warming and related environmental issues. (The website www.Africaclimatescience.org has more information.) Upon my arrival in Cape Town, a few of my new colleagues asked me a question I never was asked in the United States: “Why are you here?” These people, even though they are from a country that is admired worldwide for the impressive manner in which it has started to bring abominable apartheid to an end, are unaware that South Africa can be a leader in additional ways, that it can be prominent in efforts to deal with global warming, for example. “I am back in South Africa for the same reason that I originally left: to explore opportunities,” I said. “Concern about communism created opportunities in the 1960s and 1970s. Concern about global warming is doing the same today, offering exceptional opportunities for research and for the promotion of education.” I explained that, because the rich countries have dominated discussions of global warming in a polarizing manner, everyone would benefit if Africa were to have its own independent voice on the matter, if it were to draw attention to important but neglected aspects of this multifaceted issue. “What does it mean for Africa to have its own voice? Haven’t Al Gore and the IPCC spoken? What more is there to say?” To appreciate why an African voice is necessary, it is vitally important to keep in mind that the ethical dilemmas of global warming call for compromises based on the acceptance that different people can have different values and priorities. How do we find a balance between our responsibilities to future generations and our obligations toward those who are suffering today? The wealthy are reasonably satisfied with current conditions and weigh responsibilities to future generations heavily. To the poor, however, the threats of global warming decades hence are meaningless because, to them, the present is barely tolerable, the future is bleak. That is why our response to global warming has to become a vehicle for transporting the poor out of their misery. The historical path to wealth, industrialization, has two equally important requirements. One is a supply of energy. The other is an educated populace that includes a scientifically and technically trained workforce. China is sprinting ahead not only because it burns huge amounts of coal but also because it has an educated populace. Global warming presents us with splendid opportunities to promote education, and thus can help with challenges that extend far beyond adaptation and mitigation. For Africans to take advantage of the opportunities global warming presents, they should be not merely the recipients of advice but participants in discussions of how we can best cope with this problem. Consider, for example, how India learned to deal with the problem of reduced crop production associated with failure of the monsoons. In the 19th and early part of the 20th centuries, these events contributed to the deaths of millions of people (Davis 2000). The British, while they were in charge of India, saw accurate predictions of the monsoons as an important step toward a solution. To that end, the young Cambridge mathematician Gilbert Walker was sent to India after the famine of 1899. He made important discoveries concerning the Southern Oscillation but was unable to develop methods for the prediction of the monsoons. A century later, the monsoons still defy accurate predictions and still fail occasionally, but for several decades now there have been no massive famines. The solution depended less on science than it did on India becoming a democracy in which the government is held responsible if it fails to solve certain social problems (Sen 1981). Merely knowing that the monsoons will fail sooner or later is enough scientific information to Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 14 Philander Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 ARI 27 March 2009 14:52 develop policies to start coping with such problems. Accurate scientific information is of course invaluable, but much can be done until such information becomes available. An event that impressed on me the need for an African voice was a fascinating meeting on “Origins of Man” I recently attended in Mosselbay, a seaside village some 500 km east of Cape Town. Apparently, it is possible that all humans, approximately 150,000 years ago, had ancestors living in the neighborhood of Mosselbay! For three days in May 2008, more than 30 scientists and their students from South Africa, the United States, Israel, Australia, and several European countries discussed the genetic, archaeological, climatic, and botanical results that suggest this possibility. This stimulating meeting had one strange feature: there were no black participants other than the lady serving tea and myself. (I invited myself; she was less presumptuous.) When I pointed out to a visitor from the United Kingdom that this meeting, in Africa, about the origins of man, attended by people from all over the globe, had no black participants, he remarked that he had not noticed. I am sure that he spoke the truth. “THE FAIREST CAPE IN ALL THE CIRCUMFERENCE OF THE EARTH” Africans suffer from an excess of advice and a paucity of opportunities. An urgent need is an increase in educational opportunities. Attracting students to science is a major goal; the success of the workshops, which were held in Cape Town this year and last, to explain to participants why the present is a special moment in the history of a special planet, confirms that Earth science can be a magnet for attracting students (see Figure 4). “The fairest Cape,” in the words of Sir Francis Drake, is the perfect location for such workshops because the southern tip of Africa is a region of astonishing geological, botanical, oceanographic, and climatic diversity. It is even possible to Figure 4 Participants at the workshop “How to Build a Habitable Planet,” held in Cape Town, South Africa in July 2007. www.annualreviews.org • An African Perspective on Global Warming 15 ARI 27 March 2009 14:52 Water: Chlorophyll a concentration (mg m–3) Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 > 0.01 0.2 1 10 50 Land: Normalized difference vegetation index Maximum Minimum Figure 5 Chlorophyll distribution in Africa and the adjacent oceans, from the NASA website http://oceancolor.gsfc. nasa.gov/SeaWiFS. test the hypothesis that the striking temperature contrast between Cape Town’s cold Atlantic and warm Indian Ocean beaches is a major contributor to the region’s botanical diversity. This can be done by traveling three million years back in time by visiting a fossil park in Langebaan, an hour north of Cape Town. That park is rich in the remains of the very different fauna and flora of the Early Pliocene, when sea surface temperatures were as high along the western as along the eastern coast of southern Africa. An African center of excellence with a strong focus on the Earth sciences can be a beacon that attracts students to science. The southern part of the continent is an ideal location for such a center as is evident from the distribution of chlorophyll in Figure 5. From this perspective, southern Africa is a peninsula with remarkable climatic and biological diversity, surrounded by three strikingly different oceans. Whereas the western coast is cold and highly productive, the eastern coast is warm and supports entirely different species, and the underexplored Southern Ocean absorbs much of the carbon dioxide humans inject into the atmosphere. An African climate center for studies of the continent, the surrounding oceans, and the interactions among them will have its own niche in the competitive world of science. Everyone will benefit from an African center of excellence that deals with the research questions posed by Figures 3 and 5, and also with the wrenching ethical dilemmas global warming presents. Africa should have its own voice on these matters because, thus far, the debate about global warming has been dominated by people in rich countries in a manner that inadequately takes into account the needs of the poor. Many of the rich are eager to assist Africa, but unfortunately it is often in a spirit not unlike that of the Boston policeman I briefly met more than forty years ago, the one who was unaware that good intentions are not enough. Africans usually get advice that is of little relevance to the problems they face. Instead of advice, they need opportunities not merely to participate in research projects that are mainly of interest to wealthy countries but to establish African centers of excellence that provide obvious answers to the question, “Why are you here?” 16 Philander ANRV374-EA37-01 ARI 27 March 2009 14:52 Many of the gifted, young, potential scientists who should populate such centers are currently unaware that science can be a career. They need to be identified and nurtured. This is particularly important in a country where, for a long time, the regrettable views on race recently expressed by the Nobel laureate James Watson informed the government’s education policies. The opportunities in the Earth sciences today are as exciting as those in oceanography in the 1960s, and the need to attract young students is as strong now as it was then. Africa can provide some of those students. Of its huge number of young people, some, as in any population, are bound to be exceptional scientists. We have to make sure that “time and chance happeneth to them all.” Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. DISCLOSURE STATEMENT The author is not aware of any biases that might be perceived as affecting the objectivity of this review. ACKNOWLEDGMENTS I am indebted to Michael Bender, Mark Cane, Ping Chang, John Compton, David Halpern, Johann Lutjeharms, Laurel Lyman, and Carl Wunsch for valuable comments that improved an earlier draft of this paper significantly. For generous support of my research, I am indebted to NOAA and NASA, in addition to NRF, DST, and CSIR in South Africa. LITERATURE CITED Barreiro M, Fedorov A, Pacanowski R, Philander SG. 2008. Abrupt climate changes: how freshening of the northern Atlantic affects the thermohaline and wind-driven oceanic circulations. Annu. Rev. Earth Planet. Sci. 36:33–58 Barreiro M, Philander SG. 2008. Response of the tropical Pacific to changes in extra-tropical clouds. Clim. Dyn. 31:713–29 Boccaletti G, Pacanowski R, Philander SG, Fedorov A. 2004. The thermal structure of the ocean. J. Phys. Oceanogr. 34:888–902 Bjerknes J. 1969. Atmospheric teleconnections from the equatorial Pacific. Mon. Weather Rev. 97:163–72 Cane MA, Sarachik ES. 1976. Forced baroclinic ocean motion I. J. Mar. Res. 34(4):629–65 Davis M. 2000. Late Victorian Holocausts. El Niño Famines and the Making of the Third World. New York: Verso. 464 pp. Fedorov A, Philander SG. 2000. Is El Niño changing? Science 288:1997–2002 Fedorov AV, Harper SL, Philander SG, Winter B, Wittenberg A. 2003. How predictable is El Niño? Bull. Am. Meteorol. Soc. 84:911–19 Fedorov A, Dekens P, McCarthy M, Ravelo C, deMenocal PB, et al. 2006. The Pliocene paradox (mechanisms for a permanent El Niño). Science 312:1485–89 Halpern D. 1987. Observations of annual and El Niño thermal and flow variations along the equator at 110W and 95W during 1980–1985. J. Geophys. Res. 92:8197–212 Hayes S, Mangum L, Picaut J, Sumi A, Takeuchi K. 1991. TOGA-TAO A moored array for real-time measurements in the tropical Pacific Ocean. Bull. Am. Meteorol. Soc. 72:339–47 Haywood A, Valdes P, Peck V. 2007. A permanent El Niño-like state during the Pliocene? Paleoceanography 22:1213, doi:10.1029/2006PA001323 Held I. 2005. The gap between simulation and understanding in climate modeling. Bull. Am. Meteorol. Soc. 86:1609–14. Huybers P, Molnar P. 2007. Tropical cooling and the onset of North American glaciation. Clim. Past 3:549–57 Lawrence KT, Liu Z, Herbert TD. 2006. Evolution of the eastern tropical Pacific through Plio-Pleistocene glaciation. Science 312:79–83 www.annualreviews.org • An African Perspective on Global Warming 17 ARI 27 March 2009 14:52 Leetmaa A, Ji M. 1989. Operational hindcasting of the tropical Pacific. Dyn. Atmos. Oceans 13:465–90 Matsuno T. 1966. Quasi-geostrophic motion in equatorial regions. J. Meteorol. Soc. Jpn. 2:25–43 Moore DW. 1969. Planetary-gravity waves in an equatorial ocean. PhD thesis. Harvard Univ. 311 pp. Petit JR, Jouzel J, Raynaud D, Barkov NI, Barnola J-M. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399:429–36 Philander SGH, Seigel AD. 1985. Simulation of El Niño of 1982–1983. In Coupled Ocean-Atmosphere Models: Papers Presented at the 16th International Liege Colloquium on Ocean Hydrodynamics, ed. JCJ Nihoul, pp. 517–41. Amsterdam, Holland: Elsevier Philander SGH. 1985. El Niño and La Niña. J. Atmos. Sci. 42:2652–62 Philander SG. 2004. Our Affair with El Niño: How We Transformed an Enchanting Peruvian Current into a Global Climate Hazard. Princeton, NJ: Princeton Univ. Press. 288 pp. Philander SG. 2006. Sextant to satellite: the education of a land-based oceanographer. In History of Physical Oceanography—Developments since 1960, ed. M Jochum, R Martugudde, pp. 153–64. New York: Springer Ravelo AC, Andreasen DH, Kyle M, Lyle AO, Wara MW. 2004. Regional climate shifts caused by gradual global cooling in the Pliocene epoch. Nature 429:263–67 Schopf PS, Suarez MJ. 1988. Vacillations in a coupled ocean-atmosphere model. J. Atmos. Sci. 45:702 Sen A. 1981. Poverty and Famines: An Essay on Entitlement and Deprivation. Oxford: Clarendon Press. 257 pp. Stommel H. 1995. Why do our ideas about the ocean circulation have such a peculiarly dream-like quality? Or examples of types of observations that are badly needed to test oceanographic theories. In Collected Works of Henry M. Stommel, ed. NG Hogg, RX Huang, 1:124–34. Boston: Am. Meteorol. Soc. Stommel H. 1948. The westward intensification of wind-driven ocean currents. Trans. Am. Geophys. Union 29:202–6 Wunsch C, Gill AE. 1976. Observations of equatorially trapped waves in Pacific sea level variations. Deep Sea Res. 23:371–90 Wyrtki K. 1973. Teleconnections in the equatorial Pacific Ocean. Science 180:66–68 Zachos J, Pagani M, Sloan L, Thomas E, Billups K. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292:686–93 Zebiak SE, Cane MA. 1987. A model El Niño-Southern Oscillation. Mon. Weather Rev. 115:2262–78 Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. ANRV374-EA37-01 18 Philander AR374-FM ARI 27 March 2009 18:4 Annual Review of Earth and Planetary Sciences Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. Contents Volume 37, 2009 Where Are You From? Why Are You Here? An African Perspective on Global Warming S. George Philander p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 1 Stagnant Slab: A Review Yoshio Fukao, Masayuki Obayashi, Tomoeki Nakakuki, and the Deep Slab Project Group p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p19 Radiocarbon and Soil Carbon Dynamics Susan Trumbore p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p47 Evolution of the Genus Homo Ian Tattersall and Jeffrey H. Schwartz p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p67 Feedbacks, Timescales, and Seeing Red Gerard Roe p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p93 Atmospheric Lifetime of Fossil Fuel Carbon Dioxide David Archer, Michael Eby, Victor Brovkin, Andy Ridgwell, Long Cao, Uwe Mikolajewicz, Ken Caldeira, Katsumi Matsumoto, Guy Munhoven, Alvaro Montenegro, and Kathy Tokos p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 117 Evolution of Life Cycles in Early Amphibians Rainer R. Schoch p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 135 The Fin to Limb Transition: New Data, Interpretations, and Hypotheses from Paleontology and Developmental Biology Jennifer A. Clack p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 163 Mammalian Response to Cenozoic Climatic Change Jessica L. Blois and Elizabeth A. Hadly p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 181 Forensic Seismology and the Comprehensive Nuclear-Test-Ban Treaty David Bowers and Neil D. Selby p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 209 How the Continents Deform: The Evidence from Tectonic Geodesy Wayne Thatcher p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 237 The Tropics in Paleoclimate John C.H. Chiang p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 263 vii AR374-FM ARI 27 March 2009 18:4 Rivers, Lakes, Dunes, and Rain: Crustal Processes in Titan’s Methane Cycle Jonathan I. Lunine and Ralph D. Lorenz p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 299 Planetary Migration: What Does it Mean for Planet Formation? John E. Chambers p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 321 The Tectonic Framework of the Sumatran Subduction Zone Robert McCaffrey p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 345 Annu. Rev. Earth Planet. Sci. 2009.37:1-18. Downloaded from arjournals.annualreviews.org by Annual Reviews on 05/18/09. For personal use only. Microbial Transformations of Minerals and Metals: Recent Advances in Geomicrobiology Derived from Synchrotron-Based X-Ray Spectroscopy and X-Ray Microscopy Alexis Templeton and Emily Knowles p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 367 The Channeled Scabland: A Retrospective Victor R. Baker p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 393 Growth and Evolution of Asteroids Erik Asphaug p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 413 Thermodynamics and Mass Transport in Multicomponent, Multiphase H2 O Systems of Planetary Interest Xinli Lu and Susan W. Kieffer p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 449 The Hadean Crust: Evidence from >4 Ga Zircons T. Mark Harrison p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 479 Tracking Euxinia in the Ancient Ocean: A Multiproxy Perspective and Proterozoic Case Study Timothy W. Lyons, Ariel D. Anbar, Silke Severmann, Clint Scott, and Benjamin C. Gill p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 507 The Polar Deposits of Mars Shane Byrne p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 535 Shearing Melt Out of the Earth: An Experimentalist’s Perspective on the Influence of Deformation on Melt Extraction David L. Kohlstedt and Benjamin K. Holtzman p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 561 Indexes Cumulative Index of Contributing Authors, Volumes 27–37 p p p p p p p p p p p p p p p p p p p p p p p p p p p 595 Cumulative Index of Chapter Titles, Volumes 27–37 p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p 599 Errata An online log of corrections to Annual Review of Earth and Planetary Sciences articles may be found at http://earth.annualreviews.org viii Contents