Download Where Are You From? Why Are You Here? An African Perspective

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