Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 31
4
System Interactions:
Atmosphere, Oceans,
Land, and Humans
Over the past several decades, scientists' understancting of
the complexities of the earth system has evolved to the point
where they now recognize that the components of the system-
the atmosphere, oceans, land, and associated living beings in-
cluding humans are inextricably intertwined. A change in one
part of the earth system has repercussions for other parts often
In ways that are neither obvious nor immediately apparent. It is
beyond the human ken, however, to study the whole, multicli-
mensional system at once. As the following sections attest, the
effort to understand the dynamics driving change in the global
environment is clesigned along the academic lines that essen-
tially define classical disciplines. In fact, though, researchers are
ever-aware that the various sciences of the atmosphere, ocean,
land, and water are connected in countless ways. The intrica-
cies of the earth system range from the obvious links between
currents in the ocean and atmosphere, to the all-encompassing
global cycles of carbon and water, to the subtle, distant effect of
clearing a tract of tropical forest on the amount of carbon in the
atmosphere.
While each major component of the earth system holds its
31
OCR for page 32
32
THE EARTH AS A SYSTEM
mysteries, the effect of human activity on the system can be the
greatest wildcard of all. For the first time, the social sciences
are assuming substantial weight in the study of the earth sys-
tem as researchers and policymakers struggle to discern how
humankind, this relatively recent, terribly powerful feature of
the earth, affects the age-old forces that also dictate our planet's
future.
ATMOSPHERE
Many of the earth's inhabitants live far from the oceans;
concerns about tropical forests may seem remote to farmers on
the American Plains, or to women gathering firewood in the
Himalayas. But the atmosphere touches each of us.
The atmosphere, a gaseous envelope that surrounds the
earth, is the engine of the physical climate system. When ra-
diation from the sun enters the atmosphere, some is reflected
back upward by clouds and dust, and some continues on to the
land surface. Of that radiation that strikes the surface, some
is absorbed by the earth, but some is reflected back to space
by ice, snow, water, and other reflective surfaces. In addition,
infrared radiation is emitted by the earth. A portion of this en-
ergy gets trapped by certain atmospheric gases whose particular
chemistries do not allow the outgoing, longer-wave infrared ra-
diation to escape. Insteacl, this bounces back to the earth, raising
the surface temperature. This phenomenon, which has operated
throughout earth's history, is well known as the greenhouse ef-
fect.
Without the atmosphere and the greenhouse effect, the
earth's surface would be frozen, and life would not be possible.
At the other end of the spectrum, the atmosphere on Venus is
so dense with carbon dioxide and the greenhouse effect is so
intense that the planet's surface is everywhere as hot as cooling
lava on earth.
The composition of the atmosphere determines the earth's
ability to maintain a balance between the energy coming in and
the energy released. The main gases in dry air are nitrogen (79
OCR for page 33
SYSTEM INTERACTIONS
33
(79 percent), oxygen (20 percent), and argon (1 percent). Water
vapor, present in variable concentrations up to a few percent,
is the major gas responsible for the greenhouse effect on earth.
Other greenhouse gases are present in trace amounts, usually
measured in parts per billion (ppb). The trace gas that has
recently received the most attention is carbon dioxide, which
currently constitutes 0.034 percent, or 344 parts per million, of
the atmosphere.
In addition to carbon dioxide, other trace gases-two chIo-
rofluorocarbons (CFC-~1 and CFC-12, which also destroy the
protective ozone layer that shields us from harmful ultraviolet
radiation), methane, nitrous oxide, and tropospheric ozone are
efficient at absorbing infrared radiation emitted by the earth.
They are of special interest now because their concentrations in
the atmosphere are rising. As they do, less radiation escapes
from the surface into space, and the earth's temperature rises.
The future of the earth's climate and, perhaps, its inhabi-
tants, depends on how much concentrations of carbon dioxide
and other trace gases are likely to rise. Carbon dioxide poses
the single greatest threat because it is the most abundant of
these gases. It occurs naturally in the atmosphere and is cy-
cled through nearly all living organisms. Animals, including
humans, exhale it as a waste product, whereas plants "breathe"
it, using the carbon to make the carbohydrates they require in
the processes known as photosynthesis.
Analysis of air bubbles trapped in glacial ice and contem-
porary measurements reveal that carbon dioxide concentrations
have increased by nearly 25 percent since the eighteenth century,
when industrialization began. The main cause is the combustion
of fossil fuels, which produces compounds that also contribute
to problems such as local air pollution and acid deposition.
During combustion, carbon is oxidized to carbon dioxide and
released to the atmosphere. The destruction of forests for settIe-
ments or cultivation contributes to this rise also. When land is
cleared, the trees either decompose or are burned, and the car-
bon stored in the plant material is released to the atmosphere.
We have accurate records of modem carbon dioxide levels
OCR for page 34
34
'I ~ ~W
I'
UJ A:
_ ~
o
~ :\N ~ ~ ~
~),~\
~m
C9Z
ZO
o X
.°
=
o ~ ~ ~
~ C ~ 'A U
C ~ =` ~
=.Q
.~ ~ 3 .s ~
'
`_,
~ ~ ~ ,~ ~
.5 te 3` too
X o ~:s
C ~ ~ ~ ~ ~s
X bO.5 in ~ °°
C ~
~ m/~:
~ , U ~ ~ ~ y
c { '' ~
3 - C
ct' ~ 4,, ~ o 3
,-v ~ o ·, U) ~
O ~ C Ct. ._
~ ~ "' :; ~ 'a e
~ 'X ~-
OCR for page 35
SYSTEM INTEMCTIONS
35
since 195S, when Charles D. Keeling, of Scripps Institution of
Oceanography in La lolIa, California, began measuring concen-
trations of atmospheric gases from a research station high on
Mauna Loa in Hawaii. His records cover a relatively brief in-
terval, but are treasured by scientists: They clearly show that
carbon dioxide is increasing in the global atmosphere, anct they
also show a striking sawtooth pattern that reflects the entire
biosphere of the Northern Hemisphere "breathing in" as plants
grow in the warm months and "exhaling" when they are dor-
mant. From studies of glacial ice samples, scientists know that
the level of carbon dioxide during ice ages was about 200 parts
per million. in between glacial periods, when the earth was
warm, it was about 280 parts per million. Today we are at 350
parts per million and climbing.
The other trace greenhouse gases methane, nitrous ox-
ide, chIorofluorocarbons, and ozone-absorb infrared radiation
much more effectively than carbon dioxide cloes, but they are
present in much smaller quantities. Their combined effect may
well cause half of the global warming projected for the next
century.
The atmosphere's methane content is particularly worri-
some because it is rising at a much faster rate than even carbon
dioxide. Systematic measurements of methane concentrations
did not begin until the late 1960s. During the 1980s, levels of
this gas rose sharply, at a rate of about l.1 percent per year. Stud-
ies of ice cores show that the methane increase over the centuries
parallels the swelling of human population, a logical connection
because methane is produced through the rumination of increas-
ing numbers of cattle and through rice paddy cultivation, which
is also increasing. Like carbon dioxicle, methane concentrations
in the atmosphere vary with the glacial cycle. During the ice
ages, methane was present in the atmosphere at roughly 300
parts per billion. During interglacial periods, the atmospheric
levels doubled to perhaps 600 parts per billion. Now we are
at 1800 parts per billion and climbing. The sources for this rise
include melting of tundra permafrost, biomass burning, leaks
OCR for page 36
36
355
350
-
Q
o
z
C:
z
o
on 320
345
340
335
330
325
315
310
THE EARTH AS A SYSTEM
If__ ~
58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90
YEAR
Concentration of atmospheric carbon dioxide in parts per million of dry air (ppm)
versus time for the years 1958 to 1989 at Mauna Loa Observatory, Hawaii. The
dots indicate monthly average concentration. (Reprinted, by permission, from C. D.
Keeling et al. 1989. "A Three Dimensional Model of Atmospheric CO2 Transport
Based on Observed Winds: Observational Data and Preliminary Analysis," Appendix
A, in Aspects of Climate Variability in the Pacific and the Western Americas, Geophysical
Monograph, vol. 55, Nov. Copyright (3 1989 by me American Geophysical Union.)
in natural gas pipelines, and emissions from rice paddies and
cattle, but they are far from quantified.
Atmospheric scientists try to decipher the workings of the
physical climate system by constructing what are known as
general circulation models. These computer models use math-
ematical equations to express the basic physical principles that
govern the global atmosphere and then use actual data to test
whether the models adequately simulate reality.
The general circulation models, as they now exist, simu-
late the physical climate and geographical features on a very
coarse scale. A country the size of Japan, for example, does
not appear on the computer-generated maps. Vast numbers of
calculations and large amounts of computer time and money
would be required to refine the scale.
OCR for page 37
SYSTEM INTERACTIONS
37
It is not only the coarse scale of the general circulation mod-
els that is proving problematic in using the models to answer
questions about climate change. The current models clo not in-
corporate other components of the earth system that are known
to exert strong influences on the physical climate. Scientists are
attempting to incorporate the dynamics of the ocean, and its
enormous abilities to absorb heat and carbon, into the climate
models. Cloud cover, too, has a strong moderating influence
on the greenhouse effect, but it is difficult to characterize and
incorporate into coarse-scale models. Even more clifficult to
model, and perhaps more important, are the living parts of the
world the forests, which store carbon and moisture, and the
marine biota, which sequester carbon. Scientists look longingly
to the day when enough is understood about these processes to
include them in the models. Perhaps such a grand mode! can
never be constructed, but the conceptual approach embedded
in the attempt lays the cornerstone for earth system science.
OCEANS
The worId's oceans are the atmosphere's partner in the phys-
ical climate system. Just as atmospheric chemistry fluctuates, so
does ocean chemistry, though not in the same ways. While
much is known about ocean circulation and its coupling to at-
mospheric currents and pressure, less is certain about its ability
to store additional carbon or about how much heat it will store
in response to rising surface temperatures.
The ocean is an immense reservoir of heat, holding the heat
it absorbs from solar radiation longer than the land does. As the
ocean water moves through its grand circulation scheme, heat is
transferred vertically from the surface waters to the deep ocean
and back, and horizontally from high latitude to Tow latitude
and from longitude to longitude.
As heat is released by the ocean in a region remote from
where it was absorbed, it interacts with the overlying atmo-
sphere, moderating the daily and seasonal cycles and tempera-
ture on the earth's surface areas. Thus the ocean helps to shape
OCR for page 38
38
THE EARTH AS A SYSTEM
the regional features of weather and climate. The episodic cli-
mate phenomenon known as the E} Nino/Southern Oscillation,
a change in atmospheric circulation that occurs irregularly every
2 to 7 years above the tropical Pacific Ocean, is the most notable
example that a local disturbance in the balance between ocean
and atmosphere can interact to cause an abrupt and dramatic
change in the circulation of the tropical oceans and the global
atmosphere. Kevin Trenberth, of the National Center for At-
mospheric Research in Boulder, Colorado, and colleagues have
shown that the hot and dry conditions in central North America
in the summer of 1988 could have been triggered by unusual
distributions in sea surface temperatures that occurred in the
aftermath of the 1987 E! Nino.
A critical unanswered question is, what is the ocean's role
in storing the carbon dioxide added to the atmosphere by hu-
man activity? Preliminary calculations suggest that about half
of the carbon dioxide added to the atmosphere by fossil fuel
combustion and deforestation remains there. At least part of the
carbon dioxide has been absorbed by the ocean, which holds
60 times as much carbon as there is In all of the atmospheric
carbon dioxide.
The ocean's carbon largely resides at the bottom of the
sea and has accumulated over billions of years. Photosynthetic
plankton in the ocean's surface waters are consumed by other
organisms; some of that carbon is returned to the atmosphere
through respiration, and part goes into storage in the deep-sea
sediment as detritus and shells or skeletons of marine organ-
isms. The free-fall of organisms from the surface to the ocean
floor and the subsequent release of carbon as deep ocean waters
are slowly recycled up to the surface waters have a profound
effect on the way carbon is apportioned throughout the earth
system.
The movement of carbon through the earth system would
be quite different if noting lived in the ocean. If one could con-
sider the influence of physics and chemistry alone, carbon diox-
ide in the surface waters would be evenly distributed. In fact,
however, there is a distinct physical and chemical difference be-
tween the capacities of waters at different latitudes to sequester
OCR for page 39
SYSTEM INTERACTIONS
39
and release carbon dioxide. The food webs of organisms deter-
mine to what degree the carbon that is fixed photosynthetically
will go back into the water and to what degree it will go into
the creep ocean. in other words, the physics of the system that
provides nutrients such as carbon, nitrogen, and other elements
from the deep ocean to the surface and that moves surface wa-
ters from one location to another also influences the nature of
the food web. In turn, the nature of the food web influences the
partitioning of carbon dioxide.
lames McCarthy, a biological oceanographer at Harvard
University, believes that assumptions about the ocean's capacity
for storing added carbon must be looked at carefully. What is
it, he asks, that determines the capacity of the ocean today to
absorb carbon? Why is it not half that amount, or twice that
amount? How might the capacity of the ocean to absorb the car-
bon dioxide that is being released from fossil fuel combustion
change in the future? What are the implications of this for the
ocean carbon cycle? What would happen if the surface ocean
conditions were to change?
Scientists have not yet answered these questions, but the
record of the past provides some valuable clues in addressing
them. The distinct correlation between the concentration of car-
bon dioxide and the surface temperature of the planet during
the glacial cycles over the last 160,000 years must have involvecl
the ocean. Researchers believe the carbon cannot move through
any other reservoirs in the earth system efficiently enough over
those time periods to account for these changes in carbon diox-
ide concentrations.
While there are many questions in urgent need of answers,
in the last decade the ocean science community has developed
new and powerful techniques for addressing them. Scientists
have increased their understancting of the coupled nature of
the atmosphere-ocean system, and of ocean physics and bio-
geochemistry. increased computing and modeling capability
improves researchers' ability to handle large data sets and to be
able to put those data into forms that can be subjected to critical
analysis.
The developments in remote sensing in the last decade have
OCR for page 40
40
THE EARTH AS A SYSTEM
been extraordinary. Until fairly recently, oceanographers based
their studies of ocean processes on samples of ocean water gath-
ered while aboard ships an extremely slow, labor-intensive
process. Ships move at roughly 10 knots, but weather patterns
can move across the surface of the earth much faster. Indeed,
much of the data collected from the ocean surface is biased be-
cause of problems of space and time scale. Now, satellites have
made it possible to measure not only the ocean surface tem-
perature but also how the surface currents are moving. Surface
winds can be tracked with instruments aboard satellites, anct
the height of the ocean surface can be precisely gauged. These
measurements reveal valuable information about ocean circu-
lation. And, finally, the color of the ocean can be assessed to
approximate the concentration of plankton pigment, and thus
biological activity, at the ocean's surface.
LAND
Nothing seems more solid than a tract of land, and yet the
plants and animals, the soil, and the life-supporting nutrients
provided by that land make up a single interdependent unit an
ecosystem that is dynamic on time scales ranging from days to
seasons to years to millennia. Over days and seasons, the earth's
plant communities absorb and release carbon in a breath-like
rhythm. Over years and decades, ecosystems respond to the
natural patterns of plant succession and occasional events such
as E1 Nino or drought. At the far extreme, ecosystems on land
change on time scales of tens to thousands of years according
to the earth's glacial cycles.
Ecosystems function metabolically, producing and consum-
ing many of the gases that drive the earth system. Plants capture
energy from the sun and carbon dioxide from the atmosphere
in their growth process. Terrestrial plants take up more than
100 billion metric tons of carbon each year and return approx-
imately as much to the atmosphere as plants die and decay.
This cyclical exchange involves 20 times the amount of carbon
released through combustion of fossil fuels. Microorganisms in
OCR for page 41
41
8 ~
~ ~ E
_ ~a),o~.=
_# 1 A_
i: 0 7
_'.''2:'". .,. ~ S t~0
.
on
Hi
-
._
lo
U
U.
CJ
._
Cal
LO
^
00
O ~
- ' . _
O C)
a, ~
O
'~ ~
~ O
V]
q.) ·-
O ~
O ~ ..
S
_ ~ I; '~
Ub ~ U)
_ Cq
al ~ C,)
"Y ~0
O
U) 10,
q) As,
0
_
~0
·
U
U
_ O .s
.~ Go, ~
_
O U) 00
-
- o ~ ~
boo=
~ ·z ·m
OCR for page 42
42
THE EARTH AS A SYSTEM
the soil release carbon dioxide and methane as end products
and nitrogen-containing trace gases as by-products. As is the
case with carbon, the amount of nitrous oxide cycled through
terrestrial ecosystems is much greater than the amount released
through combustion of fossil fuels.
Of the three main components of the earth system-atmo-
sphere, oceans, and land the land is the most heterogeneous.
The earth's surface is a mosaic of different types of ecosys-
tems ranging from arid desert to tropical forests to tundra to the
more familiar temperate forests. Each harbors distinct plant and
animal communities, and each uniquely contributes to the func-
tioning of the earth system. Tropical rain forests, for example,
with abundant moisture and high temperatures that facilitate ex-
ceedingly rapid plant growth and decomposition of dead plant
material, cover about 7 percent of the earth's land area but con-
tribute a much larger share of the worId's annual turnover of
biomass. At the other end of the spectrum, the cold tempera-
tures In the tundra inhibit decomposition of plant material, and
so the carbon in the biomass is stored there for long periods.
Though change is a quality intrinsic to all ecosystems,
changes to the plant cover from agriculture, clearing of forests,
and other human activities are not just another sort of change
imposed on the background of natural variation. Rather, they
profoundly alter the amount of light reflected back to the atmo-
sphere from the land, the roughness of the land surface, which
influences wind patterns, and the cycling of materials through
the earth system.
For studies of the short-term dynamics of terrestrial ecosys-
tems, biologists, like oceanographers and climatologists, have
benefited from advances in satellite technology. One of the most
important short-term dynamic effects is the seasonal variation
in vegetation, which can be seen from space and recorded in
snapshots. Some of these images show where plants are active
at any given time and are extremely useful because the informa-
tion can be accumulated daily, summed annually, and compared
with measurements of the atmosphere. Peter Vitousek, a biolo-
gist at Stanford University, explains that results are particularly
OCR for page 43
SYSTEM INTERACTIONS
43
striking when the seasonal variation in the amount of light ab-
sorbed globally by vegetation is compared to the relative carbon
dioxide concentration over the same seasons. "If you do this,"
Vitousek says, "not only do you see the biosphere inhale and
exhale seasonally, but you actually see the distribution of the or-
ganisms over the surface of the earth engaged in that process."
In trying to assess what is in store for terrestrial ecosystems,
researchers are drawn to the most recent instance when global
climate changed on a massive scale: an ice age. The ice age is of
particular interest in light of projections for the planet in the next
century. Even during glaciation and the retreat of glaciers, which
occurred much more slowly than the rate of warming projected
for the planet in the next 100 years, the rate of change was so
fast that only some species were able to adapt to the changes.
Associations between species were severed. Eventually those
species that survived recolonized into new communities, often
in unfamiliar areas and in different combinations of members.
As a result, many ecosystems were composed of wholly different
combinations of species than are found anywhere today.
During the ice age, the major vegetation zones shifted thou-
sands of kilometers from their current positions, and so the frac-
tion of the earth's surface covered by specific types of vegetation
also was altered substantially. What is in store for ecosystems in
the future, and how these changes will feed back to other parts
of the earth system, are open questions.
THE WATER CYCLE
it is easy to take water for granted. Rain, a lake, dew, waves
crashing along a shoreline, snow, fog, a freshwater spring sur-
rounded by desert palms-water in these and many other fa-
miliar forms means that life can be sustained. Nowhere else in
the solar system does water currently exist in its liquid state;
nowhere else has life taken root and flourished. Here water
connects the various components of the biosphere, driving pro-
cesses on land, sea, and air.
Like the other components of the earth system, water is
OCR for page 44
44
THE EARTH AS A SYSTEM
mobile on time scales ranging from the gradual advance of
glaciers to the pelting of raindrops. It resides temporarily in
oceans, groundwater, lakes, ice, and clouds and flows between
them through rainfall and snow, evaporation from surfaces and
through plants, and runoff across the earth's surface. Nearly ev-
ery process in the earth system requires it. It sculpts the earth's
topography, pushing vast amounts of debris ahead of advanc-
ing glaciers, compressing the land beneath mountains of ice.
Soil particles caught up in river flows traverse great distances
to the oceans and lakes, where they settle to the bottom and
eventually harden into sedimentary rock. Water also destroys
rocks, acting as a solvent in the weathering process or splitting
them mechanically, pushing into crevasses where it freezes and
expands.
Most aspects of the water cycle are poorly understood:
There is simply too much of it in too many places for the many
reservoirs, flows, and fluxes to be measured accurately. We do
know that oceans hold the lion's share, over 97 percent, of the
earth's water, followed by glaciers and ice caps. Lakes, rivers,
and other surface water hold a mere one or two ten-thousandths
of the global water stock.
People have affected the water cycle by constructing dams
and reservoirs, which alter river flow and evaporation. Cities
are built and paved, creating new patterns of runoff and pre-
venting rainwater from entering the ground. Forests are cleared,
reducing the ability of the soil and plants to retain water. Peo-
ple also consume water for drinking, cooking, and bathing and
use it to irrigate their fields and to cool industrial plants. Such
human actions raise the possibility that availability of water for
future human use will be altered.
in light of the massive transformation under way in the
global environment, water is of special interest because it exerts
a strong moderating influence on the global climate system.
Oceans, ice and snow, and clouds determine the earth's ability
to reflect incoming radiation back to space, thereby helping to
regulate temperature. in the form of water vapor a greenhouse
gas water joins the other trace gases to absorb radiation leaving
OCR for page 45
SYSTEM INTERACTIONS
45
the earth's surface. Scientists are fairly certain that the water
cycle, which transports and distributes most of the solar energy
reaching the planet, will change in response to a warmer climate.
Changes in factors such as the area of the earth covered by
reflective polar ice or the abundance of clouds over the oceans,
for example, would have a further effect on global temperature.
As temperature and hence evaporation from oceans and
land increase, global precipitation is expected to increase by 5
to 10 percent. The timing and quantity of runoff may change,
as will the amount of moisture stored in soil, with implications
for world agriculture. Changes in vegetation in response to a
warmer climate may profoundly affect patterns of evaporation
and also whether precipitation seeps into the soil anct ground-
water for future use or runs off directly once it hits the ground.
With current understanding, scientists cannot say how large the
shifts in precipitation will be or where they will occur.
HUMAN INTERACTIONS
The recent furor over the changes humanity has wrought in
the global environment since industrialization began invites the
assumption that human alteration of the earth's landscape is a
fairly recent phenomenon. In fact, many of our effects on the
environment did not reach their global scale until the latter half
of the twentieth century. But studies of many parts of the world
suggest that as we extended our natural abilities with tools and
later learned to cultivate plants, we became an effective agent
of environmental change.
Ecologists Robert Peters, of the World Wildlife Fund, and
Thomas Lovejoy, of the Smithsonian Institution, traced the rec-
ord of human activity and its effect on terrestrial plant and
animal life in several regions of the world. One of the areas
they studiecl, the Mecliterranean, provides a telling example.
Destruction of natural habitats around the Mediterranean
began at least 7000 years B.C. Excavations show that by 6000
B.C., the bones of wild animals in kitchen refuse heaps were
replaced by the bones of domestic sheep. In the fifth and fourth
OCR for page 46
46
THE EARTH AS A SYSTEM
centuries B.C., forests began to dwindle as wood was harvested
for fuel and construction. Around the Mediterranean, the re-
searchers explain, humans have disrupted natural communities
for so long that "it is difficult to determine which plants are
natural or introduced, or what the original vegetation was like."
Throughout the region, degradation of forested areas is so ex-
treme that even if an area is protected, original vegetation often
will not regenerate. Over the centuries, forests were converted
to pasture, and grazing pasture was then replaced by thorny
plants over enormous areas. Animal communities, displaced as
their habitat disappeared, shrank in size and diversity.
Scientists have found patterns of human-induced change
in other regions. Aborigines are thought to have walked into
Australia from Indonesia about 40,000 years ago, when sea level
was lowered during a glacial episode. Almost immediately,
Australian vegetation became dominated by the fire-resistant
eucalyptus tree. In Britain, habitat destruction over the last
3,000 to 4,000 years has caused 90 percent of its forest and most
of its wilderness to vanish. In North America, as in Europe,
marshes were clrained, rivers dammed, and prairies plowed.
And in Brazil's Atlantic forest, clearing began in earnest in the
seventeenth century and continues today. -From an original one
million square kilometers, the Atlantic forest has been cleared
until now, only fragments remain less than 7 percent in any
condition and less than ~ percent undisturbed.
The message in these examples is clear: With longer human
occupation and greater population density, the influence of hu-
mans on other parts of the earth system grows. Now we know
that human activities have become so pervasive that the effects
are no longer local but are regional and even global in scale.
Forest clearing is eliminating habitats where millions of species
reside, acid rain is affecting lakes and streams in North Amer-
ica and Europe, and pollutants are changing the makeup of the
atmosphere in ways that can affect climate and the protective
ozone layer.
This awareness that humanity is an intrinsic part of the
OCR for page 47
SYSTEM INTERACTIONS
47
earth system is causing a fundamental shift In the way science is
pursued. No longer is it sufficient to explore only the physical
dynamics of the earth system. This effort, ciaunting in itself,
may be dwarfed by the effort to decipher the confounding be-
havior of Homo sapiens, the planet's most powerful inhabitant.
Thus, as physical scientists join together to study, model, and
predict changes on the earth's surface and in its atmosphere,
their traditional focus on the physical and biological aspects of
change is shifting to include the social sciences. For the first
time, scientists from disciplines ranging from geochemistry to
ecology are realizing that human action is the critical element
in their studies. So potent is the human impact on the earth
system that knowledge of physical processes ruling terrestrial
or atmospheric change will be incomplete until scientists better
understand the human dimensions of that change.
While studies in fielcls including economics, psychology,
and communication provide an invaluable research foundation,
they have, for the most part, focused on what determines and
controls individual behavior. Roberta Balstad Miller, director
of the Division of Social and Economic Science of the National
Science Foundation, stresses that the study of human aspects of
global change must consider not only individual behavior but
also entire institutions national laws and regulations, profit
margins, transportation patterns, agricultural markets, and tax
structures that are significant for the environment. The re-
search must also address the history of environmental change,
dealing with human and institutional activities over long pe-
riods of time. "Research on the human dimensions of global
change that ignores these factors would be nearly as inadequate
as research that ignores the human dimension altogether," Miller
said. "Will a social science research effort on global change be
expensive? No question. But we must never forget that the
costs of cloing nothing are even greater."
The effort to discern the human causes of global change
is complicated because the target changes over time: humans
both act on and react to their environment. Using their unique
OCR for page 48
48
THE EARTH AS A SYSTEM
capability to choose, people can perceive and assess possible
future changes that they hope to encourage or avoid. Accord-
ing to Harvard University's William C. Clark, "Ultimately, it is
certain patterns of human behavior that lead to environmental
degradation, and other patterns that result in sustainable devel-
opment. We need to establish how relevant human behaviors
are shaped, and how they can be altered as part of efforts to
manage the long-term, large-scale interactions between people
and their environments."
Representative terms from entire chapter:
physical climate
