Global Change in the 

I Geosphere-Biosphere 

Initial Priorities for an IGBP 

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NF00454 
Global Change in the 

Geosphere-Biosphere 

Initial Priorities for an IGOP 

U.S. Committee for an 

International Geosphere-Biosphere Program 

Commission on Physical Sciences, Mathematics, 

and Resources 

National Research Council 

NATIONAL ACADEMY PRESS 

Washington, D.C. 1986 
NOTICE: The project that is the subject of this report was approved by the 

Governing Board of the National Research Council, whose members are drawn 

from the councils of the National Academy of Sciences, the National Academy 

of Engineering, and the Institute of Medicine. The members of the committee 

responsible for the report were chosen for their special competences and with 

regard for appropriate balance. 

This report has been reviewed by a group other than the authors according 

to procedures approved by a Report Review Committee consisting of members 

of the National Academy of Sciences, the National Academy of Engineering, 

and the Institute of Medicine. 

The National Research Council was established by the National Academy of 

Sciences in 1916 to associate the broad communjty of science and technology 

with the Academy's purposes of furthering knowledge and of advising the 

federal government. The Council operates in accordance with general policies 

determined by the Academy under the authority of its congressional charter of 

1863, which establishes the Academy as a private, nonprofit, self-governing 

membership corporation. The Council has become the principal operating agency 

of both the National Academy of Sciences and the National Academy of 

Engineering in the conduct of their services to the government, the public, and 

the scientific and engineering communities. It is administered jointly by both 

Academies and the Institute of Medicine. The National Academy of Engineering 

and the Institute of Medicine were established in 1964 and 1970, respectively, 

under the charter of the National Academy of Sciences. 

This study was supported by the following agencies: the National Aeronautics 

and Space Administration, under contracts NASW 3985 and NASW 4056; the 

Department of the Interior, under Purchase Order 42000-0666; the Department 

of Energy, under Grant DE-FG05-84ER-602777; and the Department of the 

Navy under Grant N00014-84-0196. 

Copies available from: 

The Board on Atmospheric Sciences and Climate 

National Research Council 

2101 Constitution Avenue, NW 

Washington, DC 20418 
U.S. Committee for an International Geosphere-Biosphere Program 

John A. Eddy, National Center for Atmospheric Research, Cha£rman 

D. James Baker, Joint Oceanographic Institutions, Inc. 

Wallace S. Broecker, Lamont-Doherty Geological Observatory, Columbia University 

Charles Drake, Dartmouth College 

Peter Eagleson, Massachusetts Institute of Technology 

William S. Fyfe, University of Western Ontario 

W.Lawrence Gates, Oregon State University 

John Imbrie, Brown University 

Robert Loomis, University of California, Davis 

James J. McCarthy, Harvard University 

Michael B. McElroy, Harvard University 

Mark F. Meier, U.S. Geological Survey 

Harold Mooney, Stanford University 

Andrew Nagy, University of Michigan 

Ronald Prinn, Massachusetts Institute of Technology 

S. Ichtiaque Rasool, Jet Propulsion Laboratory, California Institute of Technology 

Roger Revelle, University of California, San Diego 

Norman J. Rosenberg, University of Nebraska-Lincoln 

NRC Staff 

Peter Abel 

Robert S. Chen 

John S. Perry 

iii 
Board on Atmospheric Sciences and Climate 

Charles L. Hosler; Jr., Pennsylvania St.ate University, Ohairman 

Louis J. Battan, University of Arizona 

Kirk Bryan, Princeton University 

William C. Clark, International Institute for Applied Systems Analysis 

Robert A. Duce, University of Rhode Island 

John A. Eddy, National Center for Atmospheric Research 

John Gerber, University of Florida 

John B. Hovermale, Naval Environmental Prediction Research Facility 

Francis S. Johnson, University of Texas, Dallas 

Michael B. McElroy, Harvard University 

Volker A. Mohnen, State University of New York, Albany 

Andrew F. Nagy, University of Michigan 

Julia N. Paegle, University of Utah 

Roger R. Revelle, University of California, San Diego 

Juan G. Roederer, University of Alaska 

John W. Townsend, Fairchild Space & Electronics Company 

Warren Washington, National Center for Atmospheric Research 

Ex-Officio Members 

Werner A. Baum, Florida State University 

Devire Intriligator, Carmel Research Center 

Joseph Smagorinsky, Princeton University 

Verner E. Suomi, University of Wisconsin, Madison 

iv 
Commission on Physical Sciences, Mathematics, and Resources 

Herbert Friedman, National Research Council, Chairman 

Clarence R. Allen, California Institute of Technology 

Thomas Barrow, Standard Oil Company, Inc. (Retired) 

Elkan R. Blout, Harvard Medical School 

Bernard F. Burke, Massachusetts Institute of Technology 

George F. Carrier, Harvard University 

Charles L. Drake, Dartmouth College 

Mildred S. Dresselhaus, Massachusetts Institute of Technology 

Joseph L. Fisher, Office of the Governor, Commonwealth of Virginia 

James C. Fletcher, University of Pittsburgh 

William A. Fowler, California Institute of Technology 

Gerhart Friedlander, Brookhaven National Laboratory 

Edward D. Goldberg, Scripps Institution of Oceanography 

Mary 1. Good, UOP, Inc. 

J. Ross MacDonald, University of North Carolina 

Thomas F. Malone, Saint Joseph College 

Charles J. Mankin, Oklahoma Geological Survey 

Perry L. McCarty, Stanford University 

William D. Phillips, Mallinckrodt, Inc. 

Robert E. Sievers, University of Colorado 

John D. Spengler, Harvard School of Public Health 

George W. Wetherill, Carnegie Institution of Washington 

Raphael G. Kasper, Executive Director 

Lawrence E.McCray, Associate Executive Director 

v 
This Page Intentionally left Blank 
FOREWORD 

Cooperation in observation and research has long been the hallmark 

of the earth sciences. In the seventeenth century, Hadley laboriously 

developed an understanding of the global atmospheric circulation and the 

trade winds from carefully collected ships' logs. By the nineteenth century, formally organized international scientific activities began to take 

shape, such as the First Polar Year of 1882-1883. In the same period, 

international networks of weather observations emerged that have continued through the present. In our own century, the International Geophysical Year (lGY) of 1957-1958 not only created an unprecedented treasure 

trove of coordinated data but also spawned a host of successor programs, 

some of which are still in progress. 

For the most part, these programs focused on one or another component of our complex planet and primarily involved the scientific disciplines specialized to address that component. For example, the Global 

Atmospheric Research Program (GARP) addressed the large-scale circulation of the atmosphere; through its observational programs and coordinated research efforts, meteorologists and oceanographers greatly 

advanced our understanding of the processes determining weather and 

climate variability. The power of space-based observations of solar radiation and its role in global stratospheric photochemistry has further 

exposed the vast complexity of atmospheric processes at high altitude. 

The very success of these endeavors within the various disciplines of 

the earth sciences, however, has made us aware of their limitations. As 

we have learned more about the workings of the Earth's atmosphere, oceans, biota, space environment, solar variability, and indeed the solid 

Earth itself, we have become increasingly aware of the interactions 

among these components. Indeed, it has become increasingly evident 

that the most scientifically challenging and socially important problems 

facing the environmental sciences lie at the interfaces between these components, and thus between the established disciplines of the sciences of 

the geosphere and biosphere. 

The modern view of the Earth as a scene of continual change, and of 

mankind as an increasingly potent agent for change, heightens the 

vii 
importance of these interactions. The richly detailed chronology of 

massive global changes in the Quaternary associated with the advance 

and retreat of the great ice sheets can be understood only in a framework 

that encompasses ocean chemistry and biology, lithospheric dynamics, 

solar and orbital variations, and the terrestrial biota. Understanding 

future environmental changes that may be induced by mankind's 

transformation of the Earth's surface and the atmosphere's composition 

will require an even greater breadth of investigation that includes the 

social sciences. 

Such considerations, inspired by the twenty-fifth anniversary of the 

IGY, have generated a number of initatives aimed at fostering 

international, interdisciplinary, and global-scale studies. A unifying 

theme was cogently stated by George Garland in an International 

Council of Scientific Unions (ICSU) lecture commemorating the twentyfifth anniversary of the IGY. He remarked that the "mysteries" that 

remain in our understanding of the planet involve the interaction 

between physical and biological processes, including those processes 

dominated by human actions. A group of scientists advising the National 

Aeronautics and Space Administration (NASA) under the leadership of 

Richard Goody called for a program to address the continued 

"habitability" of the planet. Within the National Research Council 

(NRC), I encouraged discussions of future international interdisciplinary 

programs by the several units of the NRC concerned with the natural 

sciences. The latter round of consultations led to the organization of a 

major workshop held at Woods Hole, Massachusetts, in the summer of 

1983. This workshop addressed a broad range of research problems in 

the atmosphere, oceans, lithosphere, biosphere, and solar-terrestrial 

relationships. The report of the workshop emphasized the importance of 

the topic of global change and urged the further development of 

programmatic concepts on the national and international levels. 

At about the same time, the NASA Advisory Council appointed an 

Earth System Sciences Committee chaired by Francis P. Bretherton to 

formulate an implementation strategy. This Committee is focusing its 

attention on the problems of global changes that will occur in the next 

decade to century and seeking to integrate the earth sciences in a broad, 

global perspective. 

The broadly based recommendations of the NRC group were carried 

to ICSU and were enthusiastically received. Under the leadership of Juan 

Roederer and Thomas F. Malone, a wide-ranging symposium was 

organized in conjunction with the 1984 ICSU General Assembly in 

Ottawa. Motivated by this sweeping panorama of vital and challenging 

problems, the General Assembly appointed a steering group and set in 

motion a two-year study of .the requirements for international programs 

to address global change, a study that is in progress as I write. 

Another outcome of the NRC workshop was the establishment of a 

U.S. Committee for an International Geosphere-Biosphere Program, the 

viii 
name we had provisionally attached to a yet-undefined effort. This 

distinguished group, led by John A. Eddy, sought to focus on a 

manageable number of important and timely scientific issues and research 

problems within the scope of this evolving international effort. The 

Committee's report emphasizes the interactions that influence globalscale changes on time scales of decades to centuries, and particularly the 

interactive physical, chemical, and biological processes that regulate the 

Earth's unique environment for life. Importantly, the programs they 

propose address the insights we can hope to gain into these interactions 

by reconstruction of the Earth's past natural experiments in global 

change, observation of contemporary conditions from earthbound and 

spaceborne platforms, and coordinated research to achieve understanding 

and permit prediction. 

As the International Geosphere-Biosphere Program evolves, other 

scientists will be motivated by the intellectual challenge of understanding 

even the most remotely coupled elements of the terrestrial system from 

the core of the sun to the center of the earth. Such themes are emerging 

from scientists concerned with solar-terrestrial physics and solid earth 

sciences. 

The Committee has deliberately focused on a set of problems never 

adequately addressed in a comprehensive interdisciplinary thrust: a set 

that seem particularly pressing and timely for attack. We hope that 

these recommendations will contribute to the great dialogue now 

developing among scientists of many nations· and diverse agendas aimed 

at understanding the nature of global change and the processes that 

determine it. In this dialogue, these specific proposals almost certainly 

will be further developed, augmented, and reshaped. What we all wish 

to emerge is more than a collection of narrow disciplinary investigations. 

The problems of global change in the geosphere-biosphere, such as those 

identified in this report, call for a renaissance in the study of the SunEarth system as a dynamic, physical, chemical, living environment that 

is yielding more and more evidence of cross linkages between all its 

traditional disciplinary domains. That is the challenge of global change 

to the international community of science and the ultimate goal of these 

first initiatives. 

ix 

Herbert Friedman, Chairman 

Commission on Physical Sciences, 

Mathematics, and Resources 
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--------------------------------------J---------------
PREFACE 

The notion of uniting certain efforts of the earth and biological 

sciences in a common, international research program began to take form 

in the United States through actions of a number of groups and 

individuals over the past three years. In September 1984, the concept 

was formally presented and favorably received at the 20th General 

Assembly of the International Council of Scientific Unions held in 

Ottawa. The goal as originally conceived was to mount an effort to 

address an array of problems of global scale within disciplines of earth 

science, oceanography, atmospheric science, solar-terrestrial physics, and 

biology. The proposed theme, as enunciated in a preliminary U.S. 

National Research Council (NRC) Summer Study of 1983, was global 

change and the implications of environmental change for man and the 

future. A rallying point for a great number of scientists was the 

realization that most of the pressing environmental issues that now face 

us transcend the bounds of traditional scientific disciplines and that as 

global problems they require more t~an national efforts for their solution. 

The NRC 1983 Summer Study laid out a long list of questions that 

might be addressed in a proposed International Geosphere-Biosphere 

Program (IGBP). The charge to the U.S. Committee for an IGBP, 

formed early in 1984, was to take the next and harder step: to give the 

program a clearer focus, by selecting a cohesive set of compelling 

problems that clearly require an international effort--questions for which 

we now have adequate technology and a sound scientific base, which 

truly need a new program for successful resolution, and which can be 

expected to attract the involvement of a multidisciplinary community of 

creative scientists. 

Our Committee met for a week at the National Academy of Sciences 

Woods Hole Study Center in June 1984 and for shorter meetings on four 

other occasions during the year. As a group we represented a wide range 

of scientific disciplines and a diverse background of experiences and 

philosophy. Yet there was from the start a remarkable agreement 

* Toward an International Geo8phere-Bio8phere Program, National Academy Press, 

Washington, D.C., 1983. 

xi 
as to the need for a coherent international program, and a real 

enthusiasm for it. 

In this report we outline the elements of a program that is focused 

sharply on fundamental problems that have urgent practical implications. 

These elements define a program that would attempt to understand the 

workings of the Earth and the living organisms on it as a coupled system 

--- a challenge in science that holds the promise of elucidating many of 

the global concerns of the present day. It would require the participation 

of many nations and draw upon the efforts of many fields of science. It 

would be made up of an array of planned, cooperative programs of 

observation, modeling, and process studies with organized opportunities 

for joint discussion and interpretation. It would lean on spaceborne 

observations for global perspective, but it is not a "space program," for 

the preponderance of needed science would deal with processes of change, 

and the vast majority of necessary measurements would need be made on 

the ground and on the oceans, from within the habitat of life. AB an 

international program it would stand as a separate, focused endeavor 

that interacts with related, disciplinary programs to increase their 

effectiveness but without attempting to subsume them or to dictate their 

goals. And, it is a program that to us seems so clearly needed and 

compelling that it must be started now. 

What we have drawn is not a set of blueprints but an architectural 

plan: a reasoned design for a needed program of world research, with 

suggestions of the sorts of research efforts that are central to its success. 

The more elaborate plans of these various endeavors need to be made 

internationally and with the counsel of a much larger number of 

specialists in all the fields involved. 

We acknowledge contributions from Herbert Friedman and Thomas 

F. Malone, Advisors to the Committee, and the financial support of the 

Day Fund of the National Academy of Sciences and the National 

Aeronautics and Space Administration (NASA), the National Oceanic 

and Atmospheric Administration (NOAA), the Department of Energy, ; 

the Department of Interior and the U.S. Navy. Joseph Berry, Thomas 

Donahue, Devrie Intriligator, and Juan Roederer gave their time as 

invited participants at Woods Hole, as did Louis Brown (National Science 

Foundation), Robert Mahler (NOAA), and Robert Murphy, Shelby 

Tilford, and Robert Watson (NASA). We also thank John Perry, Robert 

Chen, Peter Abel, William Easterling, Nancy Maynard, Judith Marshall, 

and Doris Bouadjemi for staff support. 

xii 

John A. Eddy, Cha£rman 

U.S. Committee for an International 

Geosphere-Biosphere Program 
CONTENTS 

1. INTRODUCTION 1 

2. RECORD OF ENVIRONMENTAL CHANGE 7 

Introduction, 7 

Sediments, 9 

Ice Cores, 13 

Tree Rings, 15 

Coral Deposits, 18 

3. THE ENVIRONMENT FOR LWE 20 

Introduction, 20 

Observational Programs, 22 

Observations of the Sun, 23 

Atmospheric and Oceanic Observations 

and Monitoring, 25 

Geologic Processes, 26 

Measurements of Soil Moisture, Chemistry 

and Soil Dynamics, 27 

Observations of Snow and Ice, 29 

Modeling, 30 

Atmospheric and Hydrologic Models, 31 

Models of Ocean Circulation, 33 

Models of Agricultural Carrying Capacity, 33 

Models of Ice, Snow, and Permafrost, 35 

Solar and Solar Terrestrial Models, 38 

Coupled Environmental Models, 39 

4. THE BIOSPHERE 40 

Introduction, 40 

The Need for a Global Ecology, 41 

A General Approach, 43 

The Heritage, 43 

The Challenge of Scale and Integration, 46 

A Program, 47 

Linking Local with Regional Approaches, 48 

A Hierarchy of Levels, 48 
Global Circulation Model Cells, 50 

Regional Units, 51 

Global Inventories of Species Diversity, 53 

Experimental Approaches to the Study 

of Ecosystems, 55 

5. GLOBAL BIOGEOCHEMICAL CYCLES 57 

Introduction, 57 

Carbon, 58 

Nitrogen, 62 

Sulfur, 63 

Phosphorus, 64 

Carbon Dioxide, 65 

Methane, 67 

Nitrous Oxide, 68 

Discussion, 69 

6. GLOBAL HYDROLOGIC CYCLE 72 

Introduction, 72 

Description of the Cycle, 72 

Reservoirs, 72 

Fluxes, 75 

Coupling and Impacts, 75 

Ocean Circulation and the Global 

Water Budget, 76 

Chemical and Biological Considerations, 78 

Problems, 78 

Program Goals, 79 

Some Program Elements, 80 

Observations, 80 

Modeling, 82 

7. ELEMENTS OF A PROGRAM 83 

Summary, 83 

General Program Elements, 84 

Observations, 85 

Process Studies, 86 

Models, 87 

Tests, 88 

Modes of Investigation, 89 

Relationship to Other Programs, 91 
1 INTRODUCTION 

There is a strong current felt by governments and policy makers 

throughout the world to come to grips with a series of growing concerns 

that deal with the global environment. To the layman these concerns are 

perceptible issues of air and water and a changing landscape, and a 

gnawing sense that the ever growing activities and numbers of man have 

already degraded the quality of life--if not the future habitability of the 

planet. To the scientist they are complex problems of atmospheric 

chemistry and ocean dynamics, of hydrology and biology that involve but 

also reach beyond the conventional, bounded fields of disciplinary study. 

Their solution, almost all would agree, rests in strengthening the base of 

knowledge in all the sciences that deal with the Earth. But it requires 

something more that is harder to obtain: a global view and a new effort 

to study the Earth and its living inhabitants as a tightly connected 

system of interacting parts--an endeavor in which scientific disciplines 

forsake their accustomed imperatives and serve as tools rather than ends 

in themselves. An effort so defined has no real precedent, for it would 

require not only the cooperation of nations but an intercourse and 

sharing between fields of study that are often seen as isolated and 

territorial We think the need for action is so great as to warrant the 

mounting of a bold new program, and the issues so urgent and 

compelling that it must be started now. It is propitious that today we 

hold the means, in recent advances in science and technology, to mount 

such a program and to expect a measure to expect a measure of success. 

We live on a unique planet with an ocean of liquid water and an 

atmosphere capable of sustaining and protecting life. Moreover the 

atmosphere, hydrosphere, and surface layers of the Earth are not the 

product of inorganic processes alone but the result of a synergism 

between living and nonliving parts, with the former often dominant. 

What must impress us is the delicacy of the balance that obtains. What 

must alarm us are the pervasive changes that we have wrought--in air 

and water and soils--in but the last instant of geologic time. Among 

these are the dramatic, year-to-year increases now documented in 

atmospheric CO2 and methane and other greenhouse gases that through 

natural processes regulate the surface temperature of the Earth. 

1 
2 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

The bulk of the changes that affect the course of life and the 

environment of Earth are natural ones, induced by such inexorable forces 

as natural selection, the Sun-Earth distance, the shifting of winds and 

rivers, the turbulent dynamics of the atmosphere and ocean, the drifting 

of continental plates, the building of mountains, and the expansion and 

contraction of ice. masSes. But imposed on these is now another set of 

changes; more recent and immediate in consequence, that are the clear 

result of the hand of man. Human energy production and intensive 

farming and technology have altered the albedo of the Earth, the 

composition of the soil and waters, the chemistry of the air, the areas of 

forests, the forests, the balance of the global ecosystem, and the diversity 

of plant and animal species. 

More than 10 percent of .the land area of the Earth is now under 

cultivation. More than 30 percent is under active management for 

purposes of mankind. Chemical compounds for which there are no 

natural analogues are being produced and released into the air and water 

in ever growing proportions, and rates of natural chemical and hydrologic 

cycles have been altered with currently unpredictable consequences for 

climate and the local and global environment. Policy makers are faced 

with a baffling array of problems--apparent damage to large forest regions 

in Europe, deterioration of lakes in Scandinavia and eastern North 

America, climatic impacts of deforestation in the tropics, fluctuations in 

the extent of deserts in Asia, Africa, . and North America, depletion and 

pollution of groundwaters, and growing levels of tropospheric oxidants, to 

mention but a few. There are increasing demands for action and for 

reliable information. In many cases uncertainties in our understanding of 

the complex interdependencies of the geosphere and biota hamper our 

ability to identify causes or effects or to anticipate the costs and benefits, 

economic and environmental, of possible responses. 

In spite of the need and desire to know how Nature will respond to 

these perturbing human actions, we are obliged to admit that reliable 

predictions of neither the occurrence nor the consequences of such 

changes is currently possible. There are two reasons for this. The first is 

that we lack an adequate understanding of the way in which the global 

environmental system operates. We know there are strong interactions 

between such elements as solar radiation, atmospheric circulation, cloud 

cover, ocean currents, the Earth's biota, sea-ice cover, and atmospheric 

chemistry . Yet as a rule we know too little about the global dimensions 

and physics of these phenomena to offer more than a qualitative (and 

often speculative) description of their connections. A major challenge for 

an International Geosphere-Biosphere Program (IGBP), therefore, is to 

marshal the resources needed to advance our understanding of the way 

that individual elements operate. Only when this is achieved can the 

larger questions regarding feedbacks among many of the elements be 

properly understood and satisfactorily incorporated into useful, coupled 
INTRODUCTION 3 

models of the coupled environment. The second reason that 

environmental forecasting is difficult is that the impacts of human 

actions are convolved in a natural pattern of environmental change. In 

effect, the environmental scientist is asked to read an anthropogenic 

"signal" imbedded in an incompletely defined background of natural 

processes and to forecast what the combined consequences will be. 

Clearly this is no easy task. 

In the past 30 years the world community of scientists through the 

International Council of Scientific Unions has undertaken a number of 

broadly based international programs, such as the International 

Geophysical Year, the International Biological Program, the International 

Lithosphere Project, and the Global Atmospheric Research Program. 

These and other major international efforts were each directed at a part 

of the Earth's environment. A common finding in all these programs was 

the realization that we must look much more carefully at interactions 

among parts of the global system if we are to understand the major 

issues of global change. For example, the World Climate Research 

Program now includes studies of the ocean, ice, and certain land surface 

processes. Further understanding requires that we integrate studies of 

the physical and biological realms to understand the ways in which 

Earth's living creatures, including man, modify the physical and chemical 

characteristics of their planetary home and the ways in which Earth's 

unique physical and chemical conditions in turn determine the 

development and characteristics of life. 

We human beings who are privileged to live on this benign planet 

can also hope to understand it; indeed, such understanding may well be 

essential for our survival. The challenge of an IGBP is to 'gain this 

understanding by an integrated, global study of the physical, chemical, 

and biological processes that have produced and now maintain the 

environment needed for life on Earth. 

We urge the following as a focused objective for such a study: 

To describe and understand the interactive physical, 

chemical, and biological processes that regulate the Earth's 

unique environment for life, the changes that are occurring 

in this system, and the manner in which they are influenced 

by human actions. 

We visualize an IGBP as a tightly defined program of research directed 

at providing the body of knowledge needed to assess the near-term--

perhaps 100-year--future of the Earth. The adoption of this time scale 

for program emphasis provides another key element of focus, directing 

the effort at an array of emerging issues that promise most to affect the 

course of life in the ensuing century. 

The purposes of the program would be both fundamental and 
4 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

practical. A better description and a deeper understanding of the planet 

on which we live will provide the bases for rational management of 

resources and at the same time will improve the reliability of warnings of 

significant global change. 

Such an effort, planned now, could begin in the 1990s--a significant 

period of projected change during which we can expect the first 

observable climatic impact of increasing CO2, the continued depletion of 

much of the tropical forest reserve, and increasing use of resources by an 

expanded world population. The long time scales of many of the 

processes involved as well as the magnitude of the task dictate that an 

IGBP of this nature should continue well beyond the dawn of the next 

century. Such a program would be based on a well-planned series of 

observations and modeling and process studies. It should also include 

increased efforts to recover a much longer history of the Earth and its 

environment, from geological records and the records preserved in trees 

and ice, for we recognize that changes on a wide range of time scales, 

from years to hundreds of millions of years, are a significant feature of 

Earth history. Knowledge of the past is essential to the tasks of 

understanding the present or predicting the future. We envisage an 

IGBP as a program of cooperative efforts of varied disciplines--with 

biospheric interactions as the focus and discriminator in setting priorities 

and principal emphases. These critical iinkages between living and 

nonliving components, involving physical, chemical, and ecological 

processes are in our view the outstanding unknown in our present 

understanding of the Earth as a system. 

In concentrating on the interactive areas of the physical, chemical, 

and biological realms we of necessity put less emphasis on studies that, 

though they have great strengths and momentum of their own, would less 

clearly contribute to our understanding of the changing nature of the 

environment of life. Priority in an IGBP of this design would fall on 

those areas of each of the fields involved that show the greatest promise of 

elucidating interactions that might lead to significant change in the next 

100 years, that most affect the biosphere, and that are most susceptible to 

human perturbation. 

An IGBP that would satisfy such ::i, need should take full advantage 

of the modern ability to study the Earth's surface, oceans, biota, and 

inputs from the Sun from the vantage of space. Indeed the new 

technologies of spaceborne instrumentation and of high-speed computers 

allow, for the first time, the global synthesis of information needed for 

scientific understanding. These new technologies are central to advances 

in such fields as oceanography, geophysics, atmospheric dynamics, and 

solar-terrestrial physics. But an IGBP cannot be based on space 

techniques alone. It would demand an even larger observational effort 

from the ground, on land and sea and ice, as well as from supporting 
INTRODUCTION 5 

aircraft. A part of this ground-based effort would be needed to validate 

and calibrate spaceborne measurements, but a larger part would be 

devoted to local studies of biomes and climatic zones in selected land or 

water regions. 

An IGBP must be truly international, for the concerns of the 

program are those of the entire globe. Considerations of access alone will 

require the participation of scientists and technicians from both the 

advanced and the developing countries representing all areas of the 

world. But a need equally great is that of the active involvement of the 

nations and the governments that must ultimately use the knowledge 

gained to make economic and policy decisions. 

A charge to our Committee was to define a number of specific areas 

of study that could be put forth as typical or exemplary of an IGBP and 

that would particularly benefit from an international effort· and a 

multidisciplinary approach. In ensuing chapters we explore five such 

areas and offer preliminary suggestions for program elements that should 

be undertaken to further understanding in each of them. In Chapter 7 

these suggestions are brought together and summarized. At this stage of 

general definition we have made no attempt to define the details of a 

final program. Individual elements that might eventually form an IGBP 

will need to be more thoroughly studied and more explicitly defined by a 

larger number of specialists who have particular interests in the problems 

involved and expertise in the techniques of measurement and analysis 

required. This could be completed in a carefully planned series of 

international workshops over the next two years. These workshops could 

be organized through ICSU and coordi~ated by the Ad Hoc Planning 

Group on Global Change that was recently established by that body. 

Particular care should be taken in selecting workshop topics to ensure 

that their aims are a needed part of a cohesive and focused program. 

Reports of these workshops should propose a timetable of specific 

recommendations for action. 

The problem areas that we recommend for inclusion in an IGBP are 

as follows: 

o The Recovery of the Past History of Environmental Change, 

involving studies of ocean and earth sediments, ice cores, tree rings, coral 

deposits, and sea-level changes for what they tell of past climate, ocean 

circulation, solar inputs, distribution of plants, and chemistry of the 

atmosphere, earth, and oceans. 

o Changes in the Current Physical Environment, involving the 

observation and understanding of fundamental phenomena of the Sun 

and near-Earth space, the atmosphere, snow and ice, oceans, and the soils 

and land surface of the Earth, as well as progress in the development of 

comprehensive, coupled models of the whole environment. W e recogniz~ 
6 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

that some of the needed research is already being undertaken under the 

World Climate Research Program sponsored jointly by the World 

Meteorological Organization and ICSU. 

o Global Changes £n the B£osphere, involving efforts to initiate a 

study of global ecology, an assessment of the Earth's metabolic capacity, 

an inventory of changes in biota, and an investigation of the role and 

effects of human activities in altering the number and distribution of 

plant and animal species. 

o Global Biogeochemical Cycles, involving the study of 

biogeochemical cycles of carbon, nitrogen, sulfur, phosphorus, and other 

essential elements and compounds in the atmosphere, solid Earth, oceans, 

and biota. 

o The Global Hydrolog£c Cycle, with emphasis on the reservoirs and 

fluxes of water, their coupling with plant life and biogeochemical cycles, 

and definition of the impacts of modern agriculture and industry. 

The questions involved in each of these are urgent, fundamental, and 

hard. They are urgent because of the necessity to meet the needs and 

respond to the aspirations of the large human population that will live on 

the Earth within the next century. They are fundamental because they 

involve understanding of the Earth as a whole and the functioning of 

interacting forces and complex processes under changing conditions. And 

they are hard because they require that most difficult of scientific 

enterprises--interdisciplinary comprehension and collaboration--and they 

must be studied on the Earth as a whole, requiring international scientific 

cooperation. Their solution, in. our view, requires the scope and approach 

of a dedicated international program. Such an effort, though long 

needed, could not have been mounted 20 years ago or even 10 years ago. 

Nor can it be completed in the next 10 years or the next 20. But it must 

be begun, and the time to make a beginning is now. That we can start 

today stems from our new-found ability to observe and comprehend the 

complexity of the Earth on all spatial scales--from atomic to planetary--

and, equally new and necessary, our capability through worldwide 

computer access to manage and disseminate the vast amounts of data 

that need to be acquired. 
2 RECORD OF ENVIRONMENTAL CHANGE 

INTRODUCTION 

Environmental change is a fact of life, and one that is felt on all 

times scales. For example, meteorological station records compiled 

during the past century show that the global temperature rose during this 

time by about 0.5 0 C (Figure 2.1). In high northern latitudes the 

warming was three times greater. During the 1940s and 1950s, however, 

the trend of northern hemisphere temperatures turned downward--so 

sharply that concern was expressed at the time that the world might be 

heading into a new Ice Age. The nature of the trend in the most current 

measurements--since about 1960--is now being watched with particular 

care: Does it signal, like the first robin of spring, the onset of steep 

warming now anticipated from increasing global CO2 and other 

greenhouse gases? 

Two lessons can be drawn from our meteorological experience over 

the past century. The first is that satisfactory predictions are not safely 

made by extrapolating past trends. They can come only from a 

knowledge of the driving forces involved. The second lesson is that 

environmental changes occur on a hierarchy of time scales. Year-to-year 

oscillations of the 1940s and 1950s, for example, are superimposed on a 

20-year cooling trend, which in turn modulates a 100-year warming trend 

that is a ripple on a complex of longer cycles of oscillation between 

glacial and interglacial epochs. Our ability to forecast the future or to 

assess any of the impacts of human activities rests critically on our 

knowledge of the processes that lie behind trends occurring on a wide 

range of time scales. A reliable record of past environmental changes can 

enlighten the development of environmental models and provide needed 

tests and constraints. 

We now have in hand from paleoclimatic research a reasonably good 

picture of the main climatic events and trends of the past half million 

years that are most relevant to IGBP objectives. From a variety of 

sources we have reasonably good histories of glacier extent, global ice 

volume, surface ocean temperature, atmospheric CO2 content, vegetative 

cover, lake levels, and soil types. The stage is now set for an intensive 

7 
8 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

~--------------------------------~ 1.2 

0.8 

0.4 

o 

-0.4 

1880 1920 1960 

YEAR 

FIGURE 2.1 Measured surface temperature trends in degrees Celsius 

for the period 1880-1980 as a global mean (lower curves, annual and 5-

year running mean) and for stations poleward of latitude 64 0 N (upper 

curve, 5-year running mean). After J. Hansen et at., 1983. 
RECORD OF ENVIRONMENTAL CHANGE 

look at the dynamic content of these records. What forces induced these 

changes? What feedback mechanisms were at work? 

To answer these questions requires rigorous study of continuous 

records that contain quantifiable environmental indicators such as isotope 

ratios, chemical ratios, species ratios, and accumulation and deposition 

rates. Four types of natural history hold the most promise for these 

ends: the records kept in sediments, ice caps, tree rings, and coral 

deposits. These natural diaries provide individual and different insights 

into the past history of the Earth; each covers a characteristic span of 

time, and each has a different temporal resolution. Here we consider the 

principal records in turn, illustrating the kinds of insights that have been 

provided and assessing the promise that each of them holds for an IGBP. 

We begin with the sediment record, not because it necessarily holds the 

most promise but because it is the longest and thus provides the clearest 

perspective of global change. 

SEDIMENTS 

Environmental records that span half a million years and more are 

all dominated by dramatic swings between glacial and interglacial stages. 

The marine sediment record makes it clear that the benign global 

climates that characterized the past 10,000 years (the Holocene Epoch) 

are but the interglacial phase of an ongoing gladal-interglacial cycle 

(Figure 2.2E). Only 18,000 years ago, our ancestors lived in an ice-age 

world, with ice sheets covering all of Canada, part of the United States, 

and much of Northern Europe, with sea level some 60 to as much as 140 

meters lower, and with a climate much cooler and drier than today. 

From sediment records on land comes evidence that the pattern of iceage vegetation in temperate North America was very different from that 

of today--and a clear picture of how the vegetation responded during the 

past 18,000 years to a continually changing climate (Figure 2.3). 

Two important conclusions can be drawn from these sedimentary 

records. The first and perhaps more important is that global ecosystems 

are never static. Communities of animals and plants continually shift in 

response to changes in their physical environment. As every species now 

alive must be adapted to survive diurnal and annual cycles of 

environmental change, so every enduring species has also adapted to 

endure the range of conditions encompassed in the much longer cycles of 

glacial-interglacial succession. A second conclusion is that the Earth's 

climate system appears to be surprisingly sensitive to small changes in 

external boundary conditions. The natural factors that pace the most 

dramatic climate variations known--the glacial-interglacial succession--are 

subtle changes in the seasonal and latitudinal distribution of sunlight. 

These changes,· which for any latitude are no more than about ±5 

percent, are in t\lrn the consequence of small, secular variations in the 

orbit of the Earth about the Sun (Figure 2.2, Panels A, B, and C). 
10 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

0.06 

0.025 

o 24.5 

f!l23.3 

Q 

22.0 

-0.07 

-0.016 

..... 

b 

0.04 

0.6 

2.6 

-2.1 

o 

2.1 

i i 

o 100 i • i • 

200 300 400 600 

®

TIME(K y® ... ago) 

41 KY 23 KY 

eO I 40 

'If' 1 I>~ I 

Il. 

i 

~OO 

i 

700 i 800 

A6''c 

FREQUENCY (f') 

100 

41 23 

18 

C(f') 

5% SIS 

FREQUENCY (f') 

FIGURE 2.2 Changes in the orbit and climate of the Earth during the 

past 800,000 years. Time series in rows A-C (left) are variations in the 

eccentricity of the orbit, the obliquity of the ecliptic, and an index of the 

climatic effect of precession P = .6.e sin w, a measure of the Earth-Sun 

distance on June 21) as calculated by Berger (1976). The corresponding 

spectra display variance density (C) as a function of frequency; the 

dominant periods of conspicuous peaks are labeled in thousands of years 

(kyr). These orbital variations cause changes in the seasonal and 

latitudinal distribution of incoming solar radiation that are on the order 
RECORD OF ENVIRONMENTAL CHANGE 11 

of ±5 percent for particular latitudes and seasons; the total annual 

income is nearly constant. The time history of these radiation anomalies 

is a strong function of latitude and season. 

The time series in row E is a set of oceanic 8180 observations 

obtained by averaging planktonic data from five widely separated deepsea cores. Variations in this curve are highly correlated with changes in 

the global volume of glacial ice; an approximate scale of equivalent sealevel change is given at the right (meters); the scale at the left is in units 

of standard deviation ( (J'). Significantly, the spectrum of this time series 

(Row E, right) has concentrations of variance at the same periods that 

dominate orbital history: 19 kyr, 23 kyr, 41 kyr, and 100 kyr. In each of 

these narrow frequency bands, moreover, the isotopic variations display a 

high degree of linear correlation (r ,....., 0.9) with variations in one of the 

orbital curves, as shown by the coherency spectrum (Row F, far right). 

As shown by the phase diagrams (Row F, left), the variations in 8180 lag 

significantly behind orbital variations in each frequency band. This 

would be expected, given the long time constants of ice-sheet growth and 

decay (,.....,15 kyr). This statistical evidence of a close relationship 

between the time-varying amplitudes of orbital forcing and the timevarying amplitudes of the 8180 response implies that orbital variations 

are the main external cause of the succession of late Pleistocene ice ages 

(Imbrie et al., 1984). This conclusion is strongly supported by numerical 

experiments with climate models (Kutzbach and Otto-Bliesner, 1982; 

Kutzbach and Gietter, 1984; North et al., 1983). 

The time series in row D (left) are observed differences in 13C 

concentration between surface and deep-dwelling foraminifera, expressed 

as .6.813C (parts per mil). This high-resolution (6 cm/kyr) record was 

obtained from a deep-sea core at an eastern Equatorial Pacific site 

(Shackleton et at., 1983; Shackleton and Pisias, in press). Based on a 

model advanced by Broecker (1982), the same authors have argued that 

an increase in the vertical oceanic 13C gradient reflects an increase in the 

proportion of upwelling carbon removed by photosynthesis and that such 

an increase is associated with a decrease in the eoncentration of CO2 

both in the surface ocean and in the atmosphere. The right-hand scale is 

an estimate of atmospheric CO2 concentration (ppm). Significantly, the 

(low) estimates of atmospheric CO2 during the last ice age that were 

obtained in this way agree with independent estimates obtained earlier 

from bubbles in Ice Age ice (Neftel et al., 1982). 

The spectrum of this carbon isotope time series (Row D, right) has 

concentrations of variance at three of the same periods that dominate the 

orbital and 818 0 records (23 kyr, 41 kyr, 100 kyr). Moreover, the .6. 13C 

and 180 records are highly coherent at these frequencies (left-hand 

coherency spectrum, Row F). Significantly the phase diagrams (Row F, 

left) show that changes in 8180 lag systematically behind variations in 

.6.813C. This suggests that the concentration of atmospheric and oceanic 

CO2 varies in response to orbital forcing (by mechanisms yet to be 
12 GLOBAL CHANGE IN THE GEOSPHERE·BIOSPHERE 

Recent evidence suggests that one of the major mechan£sms by which the 

climate system responds to these subtle forcings involve global changes in 

the carbon budget (Figure 2.2D). 

Although much effort has gone into the study of isotopic and biotic 

records in deep-sea cores, many important problems remain to be solved. 

Notable among these are problems of reconstructing the circulation 

patterns and nutrient chemistry of the oceans. Detailed geochemical 

measurements of cadmium and of 130/120 ratios in foraminiferan shells, 

of calcite dissolution indices, and of indices related to bottom water O2 

content are needed to understand the circulation of the paleo-ocean and 

its impact on regional climates and on atmospheric 002' Atomic 

accelerator analysis of minute amounts of carbon now make it feasible to 

measure 140 in co-existing surface and bottom-dwelling foraminifera, and 

this offers an opportunity to establish paleo-ocean ventilation rates 

during the past several tens of thousands of years. 

Finally, the record of pollen; dust, and ice-rafted material in 

sediments from the margins of the sea must be studied to establish a 

correlation with continental climatic events, with particular attention to 

sediments from high latitudes. The techniques of spectral analysis can 

now be applied to assess the importance of astronomical cyclic forcing of 

climate and to correlate cores from different geographic regions. Joint 

efforts similar to those now being conducted by the NSF Oooperative 

Holocene Mapping (COHMAP) and Spectral Mapping (SPECMAP) 

groups should be encouraged. 

In addition to marine sediments, far more attention must be given to 

sedimentary records from lakes and other inland bodies, and particularly 

in lakes that existed during glacial times. To date these studies have 

focused chiefly on the floral transition that followed the end of the last 

glacial period. The possible finding in Greenland ice of discrete warm 

events of about 800 years' duration 45,000 to 25,000 years ago clearly 

calls for a careful search for these events in continental records covering 

the same interval. The 140 content of older lake sediments can be used 

also to estimate atmospheric 002 concentrations in past times. 

Studies of sediments formed in lakes, bogs, and river terraces have 

much to offer regarding the history of man's full impact on the 

environment. For example, records of sediment accumulation rates 

provide one way of assessing the extent to which natural soil erosion 

rates have been modified. The study of the amount and distribution of 

pollen grains offers a powerful means of determining changes in 

discovered) and that these changes are part of the complex of 

mechanisms which make the Earth's climate system so sensitive to the 

relatively modest orbitally driven changes in the radiation budget. 
RECORD OF ENVIRONMENTAL CHANGE 13 

vegetational distribution; moreover, the charcoal content of sediments 

indicates the frequency of forest fires, and the metallic content records 

the flux of airborne pollutants. 

ICE CORES 

The history of past climate is nowhere better preserved than in the 

ancient ice of Greenland and Antarctica. These valuable deposits, some 

as thick as several kilometers, preserve the fallen snow for several 

hundred thousand years. The list of measurable properties is already 

long and growing rapidly. Annual increments of local precipitation are 

directly obtained, and annual seawater temperatures are now routinely 

derived through analyses of 160: 180 and H:D ratios. In addition, the 

chemical and solid fallout, the lOBe content of the ice, and the CO2 and 

CH4 content of entrapped air have all been studied. Each of these 

r~cords has revealed an astounding encoded message, and each has given 

us powerful new insights into past environmental change. They show, for 

example, that CH4 has doubled in the air since A.D. 1600 through sources 

of production that are yet unknown. They show that the CO2 content of 

the air was 30 percent lower during glacial time than in the Holocene. 

They show that the polar atmosphere was far dustier during glacial 

interludes, implying a possible, significant connection between 

atmospheric turbidity and major climatic change. Rates of past 

deposition of cosmiogenic lOSe in polar ice call into question the 

canonical picture of variations in the strength of the Earth's magnetic 

moment in the past 10,000 years that was based on the initial 

interpretation of secular changes in tree-ring radiocarbon in the same 

period; the same measurements of iceborne lOBe promise to open new 

vistas on the behavior of the ancient Sun. Ice-core analyses provide 

direct measures of the change in polar temperatures between glacial and 

interglacial epochs. They indicate that very rapid changes in climate 

may have occurred during glacial time, leading to the suggestion that the 

Earth may operate with more than one mode of ocean-atmosphere 

interaction. 

By examining the acidity of ice cores, it is possible to recover a 

temporal history of the atmospheric concentration of acid aerosols at 

high latitudes. There is good evidence that this record primarily registers 

the volcanic flux of sulfate particles whose increase is known to affect the 

Earth's radiation budget so as to induce global cooling. In this way the 

ice-core record provides not only a quantitative record of explosive 

vulcanism that can be compared with other geologic records but also an 

enhanced ability to assess the role that such activity plays in altering 

global climate. 
14 

LEAFY 

HERBS 

SEDGES 

SPRUCE 

PINE 

OAK 

GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

. ' . . '8 ~ • ..~ 

~IJ~~~ . : .J'. :;. ~ .... I,.... I 

~~~~ , .:: ~:. .. ~.\ . ~ J ...... ~:.:. :::: ~ '., y ~~..I" 1 . .'.: I .' ~ j ... . '. . 

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.. '. .:.' ":: 't - , .,.~e', 

~tJlJ[t18 [f'\ I ::::.::. .:t······ ,:::' .'::' .:.,: (: 

18,000 12,000 10,000 6000 

• 

TIME IN YEARS BEFORE PRESENT 

500 

FIGURE 2.3 Vegetation change in eastern North American during the 

past 18,000 years from full glacial conditions (18,000 years ago) until just 

before European settlement (500 years ago), Cross-hatched area is the 

ice sheet. Areas with heavy stippling (HS) and light stippling (LS) show 

regions with different concentrations of pollen types, expressed in percent 

of the total pollen rain observed at fourteen 18-kyr sites, fifty 12-kyr 

sites, and over two-hundred sites at younger times. The distribution of 

leafy herb and sedge pollen (>5%, LS; >10%, HS) represents various 

types of prairie, tundra, and open woodland vegetation. The distribution 

of spruce pollen (> 5%, LS; >20%, HS) indicates the development of 

spruce woodlands and (since 6000 B.P.) the boreal forest. The changing 
RECORD OF ENVIRONMENTAL CHANGE 15 

Exploitation of the ice-core record has only begun. By judicious 

choice of drilling sites, older ice can be reached that allows the study of 

full cycles of glaciation--far beyond the currently available span of about 

75 percent of the most recent major oscillation. More precise dating can 

be accomplished through 14C/2C and by lOBe/36CI ratio measurements 

using .accelerator mass spectrometry by taking advantage of the 

differences in half-life of these and other isotopes. It should be possible 

to secure continuous records of abundances of greenhouse gases, the 

13C / 12C record for atmospheric CO2 and CH4, the influx rates of the 

cosmogenic isotope lOBe, and long-term records of explosive vulcanism. 

A high-priority item in an IGBP should be efforts to strengthen and 

expand the existing international ice-core drilling programs and to widen 

participation in laboratory studies of this unique record. Cores from 

West Antarctica, where ice as old as 500,000 years may yet survive, may 

help to answer whether the West Antarctic ice cap disappeared during 

the last interglacial, as suggested by the existence of a 6-meter terrace in 

shorelines in many parts of the world that can be dated at 125,000 years 

ago. 

TREE RINGS 

Trees are compulsive diarists. The thickness of wood in an annual 

tree ring provides a direct measure of growth in that year, and hence of 

local environmental conditions. For some applications seasonal resolution 

can be obtained by analysis of early and late wood in a single ring. In 

many areas of the world, such records can be extended back several 

hundreds of years, and in some cases several thousand years. The study 

of tree rings, therefore, provides unique insights into the history of our 

environment--and with one-year resolution. Records of this kind will 

clearly become more important as we attempt to assess, for example, the 

impact of acid rain and increase in carbon dioxide. To illustrate how 

distribution of pine pollen (>20%, LS; >40%, HS) represents the 

northward movements of northern pine forests from South Carolina and 

Georgia to the Midwest, and the recent development of the southern pine 

forests. The distribution of oak pollen (>5%, LS; >20%, HS) reflects 

the extent of deciduous forest. Note that the regional vegetation pattern 

is always changing in response to natural changes in radiative and 

climatic boundary conditions. A particularly rapid change in vegetation, 

ice volume, and climate occurred between 12,000 and 10,000 years ago 

(coinciding with a maximum in northern hemisphere summer insolation), 

whereas the major change in· the area of the North American ice sheet 

occurred later (unpublished pollen data from the COHMAP project; ice 

margins derived from Mayewski et al., 1981). 
16 GLOBAL CHANGE IN THE GEOSPHERE.BIOSPHERE 

important such studies may be, we cite a recent large-scale analysis of 

growth trends in subalpine conifers in the western United States. This 

study finds evidence of a systematic increase in ring widths since the 

middle nineteenth century that is consistent with the enhanced growth 

expected from the known increase in global carbon dioxide. The 

increase, of more than 70 percent in California samples, seems unrelated 

to local climate. Whether that is so is subject to question. But if carbon 

dioxide is indeed the cause, it provides key information on the response 

of biota to anticipated increases in atmospheric CO2, 

Tree-ring samples that predate the era of instrumented weather 

records are available from almost all temperate regions. For this reason, 

studies of ring widths and wood density have been extensively used to 

reconstruct histories of river flow, drought, air temperature, and, through 

multivariate analysis, of atmospheric pressure and circulation patterns. 

This information, when combined with studies of the chemical 

composition of the cellulose itself, provides a revealing record of past 

environmental change. Ring-by-ring analyses of stable isotope ratios of 

H/D, 180j160, and 13C/12C, for example, provide a measure of tree 

temperature and metabolism. Moreover, through their photosynthetic 

intake of carbon dioxide, trees take up atmospheric radiocarbon that is 

formed in the high atmosphere through the impact of high-energy 

galactic cosmic rays. The analysis of 14C j12

C ratios in dated wood tells 

us much of what we know of the past history of radiocarbon production 

and hence about the history of cosmic ray fluxes at the orbit of the Earth 

(Figure 2.4). From these data has come a 7500-year record of solar 

activity and possible information on climate, the carbon cycle, and the 

varying strength of the Earth's magnetic field. The comparison of treering radiocarbon variations with cosmic-ray-induced 1Dr3e in ancient ice 

offers the hope of disentangling the convolved histories of solarmagnetic-field variations, geomagnetic changes, and climatic effects. The 

most .recent 350 years of the tree-ring radiocarbon record overlaps the era 

of telescopic observation of the Sun; comparison of the two reveals an 

almost identical picture of solar behavior, thus providing a reliable 

template for interpreting the earlier radiocarbon data that extend to the 

time of the late Stone Age. This long tree-ring record comes from the 

bristlecone pines that live as individual specimens for as long as 5000 

years. Older, undated samples of wood have been found that evidently 

come from late glacial time. Because of their acute environmental 

sensitivity, tree rings offer our best hope of recovering the history of 

climate of the continents over the last several thousand years. 

Although the tree-ring record offers great promise, its interpretation 

is extremely complex. If we are to learn to read it properly, a 

considerabie effort will. have to be made. An expanded but judicious 
© Wolf Spoerer Maunder 

r 

Minimum 

~ II T T T 20 H 

~t~{···· ~·,·i 

Ii' 

200 

100 

~ "j'" I.e 10 

1008 1208 14H lS88 18H 

FIGURE 2.4 Three indices of solar activity compared as a function of time for the period since A.D. 1000. The 

observed annual mean sunspot number (r, scale at right, from Eddy, 1976) is shown by the thin line beginning in 

A.D. 1650, with pronounced ll-yr cycles visible after about A.D. 1700. The heavier curve (c, scale at left) 

extending from A.D. 1000 to A.D. 1900 is a proxy sunspot number index derived by Stuiver and Quay (1980) from 

their measurements of tree-ring 140. As a proxy it successfully replicates the envelope of observed sunspot number 

(r) in the period of overlap--which ends about 1900 owing to the overwhelming presence of fossil-fuel carbon in 

tree rings after that date. Open circles (a, scale at left) are an index of the occurrence of northern hemisphere 

aurorae, another measure of solar activity, in sightings per decade (from Eddy). The three independent indices 

confirm the existence of significant, long-period changes in the level of solar activity, including three prolonged 

periods of depressed behavior labeled as the Wolf, Spoerer, and Maunder minima. 

~ 

t:'j 

("} 

o 

~ 

o 

o 

"'1 

t:'j 

2! 

~ o 

t:'j 

~ 

t"' 

~ o 

= > 2! 

o 

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18 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

sampling of the tree-ring sites must be undertaken, and in often remote 

areas of the world where environmentally sensitive species are found. In 

addition, growth-chamber experiments and purposeful field experiments 

will have to be conducted to improve our knowledge of the response of 

trees to various stresses. An IGBP will call for a considerable expansion 

of the existing modest effort in this area. 

CORAL DEPOSITS 

The production of calcium carbonate in the shells of mollusks and in 

corals is a function of local conditions, and hence another potential 

source of environmental history. Moreover, these shells and deposits, 

which are recoverable in fossil form, have been demonstrated to grow in 

many cases in discrete annual and even daily steps, offering 

environmental diaries of unusual temporal resolution. Attempts to rea.d 

and exploit this potential source of Earth history have been limited 

chiefly to the coarser coral record. 

One aspect of the coral record requires special attention. World sea 

level is expected to reflect long-term changes in mean global temperature 

through changes in the storage and release of water in polar and other ice 

reserves. As noted earlier in this chapter, the argument has been made 

that raised coral reefs with radiometric dates of about 125,000 years 

found, for example, on Bermuda, Australia, the Bahamas, and Hawaii, 

demonstrate that the world sea level stood about 6 meters higher at the 

time of the last interglacial maximum. The source of the extra water is 

conjectured to be the melting of the predecessor to what is now the West 

Antarctic ice sheet. The implication drawn is that the global warming 

now expected from increased fossil fuel CO2 in the atmosphere could 

cause a repeat of this phenomenon. Related to this argument, however, 

is the question of whether the coastlines where uplifted corals are found 

were themselves subjected to a few meters of tectonic uplift during the 

same period, thus altering the reference of measurement. A more 

extensive study of coastal contours must therefore be made in these 

regions, to determine whether on these coasts there exist the subsiding 

counterparts of those elements on which raised corals are found. If so, it 

may imply that sea level stood no higher during the last interglacial than 

it does today. The question is one of such fundamental importance that 

it demands resolution. The international and multidisciplinary features 

of an IGBP would lend themselves well to such a study. 

REFERENCES 

Berger, A. L., 1976. Long-term variation of the Earth's orbital elements. 

Celestial Meeh. 15, 53-74. 

Broecker, W. S., 1982. Glacial to interglacial changes in ocean chemistry. 

Prog. in Oeeanog. 11, 151-197. 
RECORD OF ENVIRONMENTAL CHANGE 

Eddy, J. A., 1976. The Maunder Minimum. Science 192, 1189-1202. 

Hansen, J., D. Johnson, A. Lacis, S. Lebedeff, P. Lee, D. Rind, and G. 

Russell, 1983. Climatic effects of atmospheric carbon dioxide. 

Science 220, 874-875. 

Imbrie, J., J. D. Hays, D. G. Martinson, A. Mcintyre, A. C. Mix, J. J. 

Morley, N. G. Pisias, W. L. Prell, and N. J. Shackleton, 1984. The 

orbital theory of Pleistocene climate: support from a revised 

chronology of the Marine 8180 record, in A. L. Berger et al. (eds.), 

Milankovitch and Climate, D. Reidel Publ. Co., Dordrecht. Part I, 

pp. 269-305. 

Kutzbach, J. E., and B. L. Otto-Bliesner, 1982. The sensitivity of the 

African-Asian monsoonal climate to orbital parameter changes for 

9000 years B.P. in a low-resolution general circulation model. J. 

Atmo8. Sci. 39, 1177-1188. 

Kutzbach, J. E., and P. J. Gietter, 1984. The sensitivity of monsoon 

climates to orbital parameter changes for 9000 years B.P.: 

experiments with the NCAR general circulation model. In A. L. 

Berger et al. (eds.), Milankovitch and Climate, D. Reidel Publ. Co., 

Dordrecht. Part 2, pp. 801-820. 

Mayewski, P. A., G. H. Denton, and T. J. Hughes, 1981. Late Wisconsin 

ice sheets of North America. In Denton, G. H. and T. J. Hughes 

(eds.), The Last Great Ice Sheets, John Wiley, New York, pp. 67-

178 and Fig. 2.2. 

Neftel, A., H. Oeschger, J. Schwander, B. Stauffer, and R. Zumbrunn, 

1982. Ice core sample measurements give atmospheric CO 2 content 

during the past 40,000 yr, Nature 295, 220-223. 

North, G. R., J. G. Mengel, and D. A. Short, 1983. Simple energy 

balance model resolving the seasons and the continents: application 

to the astronomical theory of the ice ages, J. Geophys. Res. 88, 

6576-6586. 

Shackleton, J. J., M. A. Hall, J. Line, and C. Shuxi, 1983. Carbon 

isotope data in core V19-30 confirm reduced carbon dioxide 

concentration in the ice age atmosphere. Nature 306, 319-322. 

Shackleton, N. J., and N. G. Pisias (1985). Atmospheric carbon dioxide, 

orbital forcing and climate. Geophysical Monograph #32, American 

Geophysical Union, Washington, D.C., 303-317. 

Stuiver, M., and P. D. Quay, 1980. Changes in atmospheric carbon-14 

attributed to a variable sun. Science 207, 11-19. 
3 THE ENVIRONMENT FOR LIFE 

INTRODUCTION 

We all experience to some degree the consequences of change in our 

physical environment. Often they are adverse. For some it is the 

destruction of property by a flood; for others, the disaster brought about 

by prolonged drought. For still others it is the decline of agricultural 

productivity through soil impoverishment, the depletion of coastal 

fisheries, or the damaging of lakes and trees by acid rain or by other air 

or water pollution. Some of these changes are natural and recurrent; 

others may be attributed to the hand of man, as the consequence of his 

ever-increasing presence on the globe. To anticipate global changes, 

including those induced by man, we need to understand their causes and 

natural variations; yet in this endeavor we often deal with interacting 

and synergistic processes that are beyond the scope of isolated physical or 

biological studies. 

International concern over long-term global environmental changes 

arises in part from the realization that the impacts of man's activities are 

not always confined to the area in which the primary intervention arises. 

For example, much of the chemical effluent released to the atmosphere 

from heightened industrial smoke stacks--installed to solve local 

problems--now passes across state and national boundaries where it can 

reach the ground as acid rain. Similarly, although CO2 , CH4, N20, and 

halocarbons are introduced locally and unevenly into the atmosphere, 

their consequence is now predicted to be global climatic changes whose 

potential impacts we are just beginning to grasp. We are also concerned 

that man-made dust may playa role in changing the planet's climate and 

that the diversion of rivers for irrigation may significantly change the 

large-scale patterns of evaporation and rainfall. 

We know that, quite independent of human intervention, the 

environment has changed substantially over a wide range of time scales 

in the past, and there is no reason to think that similar changes will not 

recur. Some of these changes--such as tropical cycles of dry and wet or 

the astronomically paced Ice Ages and the associated shifts in the 

distributions of animals and plants and soil features--occur so slowly that 

20 
THE ENVIRONMENT FOR LIFE 21 

they will have little detectable impact in the course of the next century. 

At the other end of the spectrum are natural climatic events that occur 

on time scales from a year to decades. Most notable among these is EI 

Nino, which introduces abrupt and dramatic changes in the circulation of 

the tropical oceans and of the global atmosphere and which appears to be 

driven by strong interactions between the atmosphere and ocean. 

Another, less predictable example, is that of explosive vulcanism and 

resultant global cooling. Between these extremes are the largely 

unexplained climatic events whose durations are measured in centuries, 

such as the Little Ice Age of about A.D. 1500 to 1850, or the recurrent 

warming episodes, each lasting a millennium or less, that appear to have 

punctuated the most recent major glaciation. 

As discussed in the preceding chapter, we are only now learning to 

read the record of these events in tree rings and ice cores and other 

natural diaries, and it is essential that we achieve a better understanding 

of the range and course of natural variability on all time scales. Until we 

develop a more thorough knowledge of the natural background of change 

in the physical and chemical environment and the processes of feedback 

and interaction, we have little hope to isolate and identify the impacts of 

man's intervention. 

Finding a Solution 

Three major approaches must be taken if significant progress is to be 

made: 

o The taking of synoptic observations directed at illuminating the 

way in which present environmental systems operate. These 

observational programs will require satellites orbiting the globe, ships 

traversing the world's oceans, and field stations on the ground--some in 

remote regions of the globe. 

o Directed efforts to understand the past record of environmental 

change contained in meteorological records or preserved in tree rings, ice, 

geologic strata, and in the sedimentary layers of lakes, bogs, and the 

seafloor. As noted in Ohapter 2, these records provide our main source of 

information about the natural variability of the environment and the role 

of external inputs to the system, such as solar and geomagnetic 

variations. They also yield important insights into the effects of natural 

feedback mechanisms that can amplify man's impacts on the 

environment. Since we cannot perform field experiments of global scale 

and geologic duration, we must make every effort to utilize the record of 

experiments already conducted by Nature. 

o The development of new models of the coupled environmental 

system. Dynamical models currently used for weather forecasting, 

general circulation studies, and climate simulation now include many of 
22 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

the important physical processes at work in the atmosphere. The new 

challenge is to create coupled physical, chemical, and biological models 

for the environment as a whole. To do this will first require major 

improvements in the manner in which processes such as cloud formation 

and precipitation and factors such as sea ice and soil moisture are 

handled by atmospheric models. The interpretation of these data will 

also require the development of fully interactive ocean-atmosphere-Iand 

surface models that include wind- and density-driven (thermohaline) 

ocean circulation and the formation and melting of sea ice. Models of 

this kind will need to include the effects of chemical changes in the 

atmosphere and more realistic parameterizations of vegetation, since this 

variable component of the environment interacts profoundly with the 

heat and moisture budget of the land surface. It is safe to say that if we 

are to gain a reliable and comprehensive assessment of the environmental 

consequences of human activities, it must come ultimately from such 

models. 

OBSERVATIONAL PROGRAMS 

The greatest impediment to more reliable prediction of 

environmental change is our lack of understanding of many physical and 

chemical processes that are key to the operation of the current 

atmospheric, oceanic, and biospheric systems. In most cases existing 

observations have been worked and reworked to the extent that little 

more new insight can be expected. As is so often the case in science, 

significant advances await new observations. For some problems we have 

a clear idea of which data sets are critical; in these, progress awaits 

resources to launch satellites, to operate an ocean surveyor to install a 

set of ground-based monitoring stations. In other cases it is not yet 

known which of several available measurement strategies will provide the 

hoped-for advances. Since global observational programs are costly in 

both time and manpower, great care must be taken in deciding which 

strategies to implement and which experiments should be conducted. 

Since new observations will form the basis of any geospherebiosphere program, it is important that the best possible strategies be 

agreed on and implemented. Many of the feasible strategies have already 

been proposed and discussed as multidisciplinary initiatives in the World 

Climate Research Program. The programs suggested here are meant to 

build upon these exiSting and planned efforts, which indeed address many 

of the physical aspects of the global atmosphere and its interaction with 

the ocean. The initial job of an IGBP is to identify other promising 

options for understanding the working of the Earth as a system. Here we 

cite some examples of observational programs that we believe necessary 

for our understanding of the operation of individual environmental 

systems and that are critical to our understanding of important linkages. 
THE ENVIRONMENT FOR LIFE 23 

Observations of the Sun 

Essential to life is the continuous energy of sunlight that warms the 

Earth and oceans, stirs the air, and forges through photosynthesis the 

first essential links in the food chain. The bulk energy or integral of 

radiative energy of the Sun, centered in the visible and near-infrared 

wavelengths, serves as the principal driver of atmospheric circulation and 

thus, in a sense, powers the climate machine. The march of the seasons 

is ample evidence for the acute sensitivity of the environment of the 

Earth to changes in the distribution of solar radiation. A more sensitive 

gauge of the Sun's impact on climate, however, is found in the 

Milankovitch effect, by which slow and subtle changes in the latitudinal 

and seasonal distribution of insolation, smaller than seasonal variations 

but of much longer period, serve to pace the recurrence of major Ice Ages 

and other long-term climatic cycles. Solar ultraviolet radiation, rising 

and falling with solar activity, dictates the basic chemistry of the upper 

and middle atmosphere, including the equilibrium and balance of 

important trace gases such as ozone. The possible influence of 

atmospheric electricity on climate, atmospheric chemistry, and the 

biosphere is an intriguing question that has received little quantitative 

study. The potential of the global electric field is maintained by 

thunderstorm activity, but it may be perturbed by solar-induced 

variations in cosmic ray flux or by changes in the efficiency of coupling 

between the solar wind and the high latitude ionosphere. 

Each of these inputs has played a role, and often a crucial one, in 

setting the conditions for life on Earth, and everyone of them is variable, 

over a range of variation that is now only crudely known. 

The solar inputs to the Earth are today sufficiently steady that they 

are often taken as constant. In reality none of them is. Far and away 

the most energetic of inputs, the so-called "solar constant" (or integral of 

radiative flux at mean Sun-Earth distance), is now known to vary, and in 

several ways. Precision spaceborne measurements, made since 1978, have 

established that the total solar irradiance delivered to Earth fluctuates 

daily at the level of 0.1-0.3 percent in step with solar activity, and there 

is some evidence that it has also been decreasing at about 0.01% per year 

since these observations began. A change of 0.1% in the total radiative 

output of the Sun, if maintained for a decade or longer, will alter the 

surface temperature of the Earth by 0.1-0.20 C, and possibly by more if 

enhanced by a number of possible feedback effects, including links with 

the biosphere. We know nothing at all of solar energy variations on 

longer time scales. But a persistent change of 1 percent in the solar 

constant would alter surface temperature by an amount comparable with 

that currently projected from CO2 warming in the next 60 years, and a 

drop of this amount seems more than enough to induce the cooling that 

gripped Europe and North America in the Little Ice Age, between the 

sixteenth and middle nineteenth centuries. 

While far less energetic than the integral of visible and near-infrared 

radiation, the solar ultraviolet flux is characterized by greater variation: 
24 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

these changes, acting through the lever of atmospheric chemistry, can 

exert an influence on both climate and the conditions for life on the 

planet. 

Continuous measurement of the solar inputs to the Earth is a recent 

endeavor, spurred by a belated appreciation of their importance and 

made possible by spaceborne platforms and the development of reliable, 

precision instrumentation. An unbroken sequence of spaceborne solarconstant measurements is now available for about 6 years from Nimbus 7 

and for an interrupted 4 years from the more precise radiometer on the 

Solar Maximum Mission (SMM) spacecraft. Observations of the spectral 

irradiance, as in the ultraviolet, are more sporadic, as are measurements 

of the flux, velocity, and composition of the solar wind and in situ 

probing of the Earth's magnetosphere. Exploratory measurements have 

revealed the nature of short-term changes and the general response of 

most of these parameters to sporadic solar activity; but for none of them 

do we have a definitive description of its quantitative variation in the 

course of the ll-year solar cycle or even for some of whether such a 

generalized pattern even exists. 

An often-stated goal is that of continuous measurement of each of 

these fundamental inputs for a full magnetic cycle of the Sun, or 22 

years: such a goal is timely and appropriate for an IGBP effort, for it 

would be most efficiently done, and probably only done, through the 

cooperation of multinational space programs. The interpretation of these 

data would also require a program of continuous supporting observations 

of the Sun from the ground, which are also best accomplished by 

international coordination. While many of these spaceborne and 

ground-based measurements would add to our understanding of the Sun 

and the magnetosphere and their patterns of behavior, their primary 

value in an IGBP is a definitive description of variable solar inputs to the 

Earth. Such knowledge is essential if we are to make progress in defining 

and delimiting the terrestrial impacts of solar variability and of changes 

in the Earth's electric and magnetic fields on climate and on the 

evolution of the atmosphere and the evolution and response of the 

biosphere. 

The seat of solar activity lies beneath the visible surface of the Sun. 

Principal unknowns in understanding the physics of the solar cycle are 

conditions in the convective zone, including its depth and the scale and 

physical parameters of convective cells. It is now possible to probe 

conditions in the convective zone though the technique known as "solar 

seismology," by which interior conditions are deduced through the 

analysis of patterns of solar surface oscillations resulting from trapped, 

subsurface pressure waves. The measurements needed for these analyses 

are broadband, high-resolution observations of the brightness of the solar 

surface for continuous periods of at least tens of days. A feasible way to 

achieve such coverage is through a global, ground-based network .of 

observing stations, requiring international coordination and planning. 

Eventually, such measurements can be made, more accurately, from 

above the Earth's atmosphere. 
THE ENVIRONMENT FOR LIFE 25 

Atmospheric and Oceanic Observations and MonitM'ing 

Operational meteorological observing programs now exist to support 

global weather forecasting and climate research. These include surface, 

upper air, and satellite observational networks for atmospheric 

temperature, pressure, winds, radiation, and cloudiness and cloud 

structure. Under auspices of ICSU and the World Meteorological 

Organization (WMO) such efforts have been effectively planned and 

coordinated on regional and global scales, as. truly international 

endeavors. The Global Atmospheric Research Program, which 

culminated in a year-long program in 1979--the Global Weather 

Experiment--and the follow-on World Climate Research Program 

(WCRP), now in progress, are good examples. Of particular importance 

to an IGBP are data relevant to global environmental change and the 

monitoring of processes that exhibit a potential for significant biospheric 

interactions. Long-term records of global surface temperature, the 

atmospheric radiation balance, and the elements of the surface heat and 

moisture budgets are already being obtained under the WCRP. Special 

efforts should also be made to develop and maintain research-quality data 

sets of global snow and ice mass, surface soil moisture, and 

concentrations of atmospheric trace gases and aerosols. 

The WCRP places special emphasis on the interaction of clouds and 

radiation and on ocean processes and their interaction with the 

atmosphere. On the time scales relevant to an IGBP, the planned 

WCRP World Ocean Circulation Experiment (WOCE) is of particular 

interest. The primary goal of the WOCE is to understand the general 

circulation of the global ocean well enough to be able to model its 

present state and to predict its evolution in relation to long-term changes 

in the atmosphere. The WOCE is aimed at providing the scientific 

background for designing an observing system for long-term measurement 

of the large-scale circulation as a basis for operational climate prediction. 

This international experiment has as its centerpiece global satellite 

measurements of variations in ocean level, or surface topography, and of 

surface roughness. The objective of the surface topography program is to 

learn more about both the steady-state flow of water through the ocean 

and the variability in this flow. The objective of the roughness program 

is to measure the stress exerted on the sea surface by wind. Since wind 

stress drives surface currents and is involved in the exchange of heat, 

water, and various gases with the atmosphere, it is critical to define its 

geographic and seasonal means as well as its variability. In connection 

with satellite missions! plans have been made to make density sections 

within the ocean to couple with the surface topography measurements 

and to make ocean wind observations to aid in calibrating the remote 

roughness measurements. In addition there are plans for deploying 

neutrally buoyant floats at various density levels in the sea and plans for 

measuring the distributions of radioisotope and chemical substances as 

tracers to define the mean transports of water though the body of the 

ocean. The distributions of transient tracers such as Freons, radiocarbon, 
26 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

tritium, and helium-3 are ideally suited for testing general circulation 

models of the ocean. 

Geologic Processes 

Programs of observation in the solid earth sciences will represent an 

integral part of any investigation concerning the interrelationships of the 

physics, chemistry, and biology of the geosphere-biosphere. Many but 

not all aspects of geology involve processes that have operated over a 

time scale of millions--even billions--of years; none the less, short-term 

(e.g., lOOO-year) changes on the Earth represent segments of a temporal 

continuum, and the orogenic and related physiochemical processes are 

geologic by definition. Many apparent short-term variations, such as the 

incidence of volcanoes, earthquakes, and prevalent climatic trends, can 

only be fully grasped if framed in the context of geologic time and 

viewed in the perspective of prolonged causative processes such as crustal 

deformation and the paleoclimatological evolution of the planet. 

Equally important, much ongoing geologic activity takes place over 

time intervals measured in years, decades, or centuries. Neotectonic 

processes (such as modern land subsidence, elevation changes, 

deformation, and seismicity), volcanism, landsliding, soil production, and 

erosion have undergone marked changes that have profoundly influenced 

the course of life and of civilization. Modern man with his ability to 

modify the landscape and his growing demands for natural resources 

(including minerals, water, and fossil fuels) has irrevocably altered 

superficial portions of the Earth's crust. The siting of critical facilities, 

the prediction and ameliorization of geologic hazards, and the 

containment and dispos'al of toxic waste products have been addressed 

but not solved. 

For civilization to utilize the environment more widely in the next 

century we will need to understand far better the complex interactions 

that thread the lithosphere, hydrosphere, atmosphere, .and biosphere. 

Ongo'ing geologic processes are part of this complex web. 

As but one example, volcanic activity--both contInental and 

submarine--can bea major perturber of the environment for life, on local 

to global scales. Volcanoes deliver sulfur, chlorine, and other chemical 

species and particulates to the troposphere and to the stratosphere, where 

residence times are long. Explosive injection of volcanic solids, liquid 

droplets, and gases to high altitudes in the atmosphere bring about 

measurable and sometimes dramatic changes in the turbidity and 

chemical properties of the global atmosphere. These changes can act to 

reduce the surface temperature of the Earth for periods of one to several 

years until diffusion clears the air, as demonsti'ated'in analyses of station 

weather records following the major known volcanic events of the past 

century. The record of mountain glacier oscillations suggests a possible 

connection with episodes of volcanic activity that would identify 

explosive vulcanism as a major perturber of world climate. 

What is less known are the detailed physical, chemical, and 
THE ENVIRONMENT FOR LIFE 27 

dynamical processes through which volcanic ejecta modify the threedimensional atmosphere, the relative and related roles of gases and 

particulates, and a more complete and quantitative history of past 

events. Added to this is the even more fundamental need for improved 

comprehension of vulcanism itself, leading to the ultimate goal of reliable 

prediction of these and other related seismic events. This will entail 

individual observations and measurements, the establishment of 

observing networks to make opportune use of natural events, and a close 

alliance with onging programs such as the International Lithospheric 

Study. 

Measu1'ements of So£[ Moisture, Chemistry, and Soil Dynam£cs 

Global measurements of soil moisture are needed both for climate 

models and for estimating the productivity of farms, forests, and grazing 

lands. Such measurements can best be accomplished by a combination of 

spaceborne and ground-based sensors. There are a number of techniques 

that can be employed for remote measurements. Microwave sounding of 

the top few centimeters gives information on recent wetting. 

Measurement of the thermal inertia of bare soils can distinguish soils 

with considerable water from those in which most of the water has been 

depleted. Infrared soundings of surface temperatures can be used to 

distinguish plant canopies suffering water stress from those well supplied 

with water. Near-infrared reflectance measurements will also distinguish 

hydrated plant tissue from that which is nonhydrated. 

What is needed is a practical global observing system for soilmoisture measurement in a number of carefully selected, representative 

regions. This should include: 

o Inventories of soils and their water holding characteristics. 

o Inventories of vegetation cover with consideration of season, stage 

of growth, and plant vigor. 

o Data from closely spaced networks of ground-based precipitation 

sensors and/or ground-based, airborne and space-based radars. 

o Data from similar networks of microclimate stations providing 

information on net radiation, air temperature, vapor pressure, and 

windspeed. 

o Regional measurement and study of the physical and biological 

processes that control evapotranspiration. 

FOr global or regional studies these data must all be combined into 

water balance schem~s that integrate upward from the smallest 

homogeneous area of measurement to the aggregate area of interest. 

Studies of the changing chemistry of soil and of soil erosion and 

formation are also sorely needed. Human influences on the landscape 

have coine to be important only within the past few centuries, but today 

they are a dominant factor in the metabolism of the planet. Very little of 

the Earth's surface remains free of human alteration, and large areas 
28 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

receive intensive management. More than 1 percent of the total land 

area of the Earth outside Antarctica is now given to housing, factories, 

schools, and transportation, 11 percent is cultivated, and over 30 percent 

is subject to grazing. Additional large areas of forestlands are subject to 

periodic harvests. 

Managed ecosystems, by their very extent, are significant elements in 

global change. Their role in hydrologic and biogeochemical cycles and in 

global metabolism are cited in ensuing chapters of this report. Another 

critical component is the soil as a substrate for life, although it has 

received little attention in this context. Soils serve as reservoirs of 

nutrients and water for the higher plants and the biota that inhabit the 

soil, they function as reactors and exchange elements in chemical cycling, 

and they are repositories for enormous quantities of organic materials. In 

spite of intensive study, we still know little with certainty about the 

dynamics of soil formation, change, and loss. Changes in global climate 

will alter soil dynamics; changes in soil, as from accelerated erosion, will 

alter the global storage of nitrogen and carbon as well as the global 

hydrologic and heat budgets and thus influence global climate. Human 

welfare is affected even more directly, since our basic food supply is 

dependent on the remarkably thin and fragile layer that is sufficiently 

porous, water retentive, and chemically constituted to serve as soil. 

There is a common tendency, particularly in North America where 

farming is a recent activity, to assess soil quality in terms of topsoil or 

the depth of the principal, upper zone of humus deposition and mineral 

leaching. In a virgin soil, this layer contains much of the inherent 

fertility. It is also the layer that is most subject to accelerated water and 

wind erosion when tilled. With continued cropping, the nutrient 

accumulations of the layer are eventually depleted, however, and after 

that it is useful mainly to support roots and to hold water. That topsoil 

is not always necessary for agriculture, however, is demonstrated at many 

sites in Europe and Asia that have been farmed for many hundreds and 

in some cases thousands of years and that now retain none of the features 

of the original topsoil. With adequate fertilization, yields at those sites 

are equal to those attainable anywhere else. When topsoil is lost, other 

parameters assume importance: soil depth and the characteristics of 

subsoils that determine water retention, n:utrient supply, and rooting. 

Unfortunately, these properties have not been surveyed and mapped 

nearly so well as have those of the surface. 

Our knowledge of processes requisite for the continued suitability of 

a soil for agriculture is surprisingly limited. In addition to a better 

understanding of soil biology, we need better measures of physical and 

chemical erosion rates (to include leaching of dissolved minerals), rates of 

downward movement and reformation of secondary minerals, and rates of 

weathering of the substrate parent materials. We also know little about 

how these processes may be altered in changed environments--for 

example, with different amounts of dissolved CO2 and added burdens of 

acidic oxides of Sand N in rainwater or with changes in agricultural 

practices. 
THE ENVIRONMENT FOR LIFE 2{) 

Nor do we have more than scant knowledge of the present state of 

the world's soils. The Food and Agriculture Organization (F AO) of the 

United Nations has worked toward the use of common systems for the 

classification and mapping of soils, but only general, large-scale maps are 

available for much of the world. Needed details of chemical and 

biological activities; accumulations of carbon, nitrogen, and other 

elements; and profile depths and substrata are generally lacking. We 

may also need more detailed information on local climates, since the 

distribution of rainfall and length of season are the main determinants of 

vegetative production and soil processes. 

There is, in short, a need for distributed, global studies of the 

present condition of the world's major soil types and the rates at which 

processes of soil formation and destruction are occurring. An IGBP 

should include studies of the following, to be carried out in concert with 

the F AO and other international and national agencies: 

o Rates and processes of soil formation, erosion, and soil dynamics in 

soils that typify the Earth's major agricultural systems, such as 

chernozem (or black prairie soil) in which most of the world's wheat is 

produced or alluvial soils in which rice is commonly grown. 

o Processes of soil chemistry, including ion exchange, the fluxes of 

salts and other materials in and through soils, the balance of organic and 

inorganic constituents, the effects of soil acids, the production of humus, 

and significant rates of change in any of these. What is important in soil 

is not so much its origin or intrinsic nutrient content as its capacity to 

hold water and nutrients and its texture; in other words, its quality in 

terms of sustained food production. 

o A worldwide inventory of soils, to include their important physical 

and chemical properties and factors of topography and slope, which are 

crucial in determining rates of soil erosion. There have been many soil 

surveys on a reconnaissance scale; to be most valuable, however, they 

need to be done in terms of soil characteristics and slope. Much of the 

cultivable land of the Earth is fragile because it is not sufficiently level. 

Observat£ons of Snow and Ice 

A change in the volume of polar ice is an obvious indicator of an 

increase or decrease in global temperature. Yet at present we have no 

reliable means to assess changes in the inventory of ice in the Greenland 

and Antarctic ice sheets. Variations in polar ice volumes should be 

detectable in sea-level measurements, but these data are noisy and 

influenced by the thermal expansion that results from global temperature 

change and by local tectonic movements related to the melting of the last 

major glacial ice sheet. Ground-based surveys are not definitive. A 

straightforward technique is through satellite altimetry, although to date 

no such program is planned or in operation. Support for such a program 

should be one goal of an IGBP. 

The glaciers and small ice caps of the world are important factors in 
30 GLOBAL CHANGE IN THE GEOSPHERE·BIOSPHERE 

high mountain and high-latitude environments,and their wastage has 

contributed about 5 cm to the observed rise in global sea level in the past 

century. In view of the possible rise in air temperature due to future 

increases in CO2, an IGBP should support continued glacier monitoring 

as part of an organized international program. 

Seasonal snow cover is a sensitive indicator of climate change; 

because of its high albedo it also has an important influence on the global 

radiation budget and therefore on global climate. Snow is critically 

important to the biosphere in many areas, insulating the soil from winter 

cold and providing soil moisture at the beginning of the growing season. 

Snow accumulation, melting, and runoff can, to some extent, be managed 

to aid agriculture, water supply, and the generation of electrical power. 

On the other hand, too much snow or too rapid snowmelt can have 

adverse effects: destructive avalanches, the crushing of structures, 

problems with transportation, and devastation by flooding. 

Unfortunately, our present ability to monitor the world's snow cover is 

very poor. Satellite observation using passive microwave radiation holds 

considerable potential, but more understanding and comparisons of 

satellite results with field data are needed. 

Sea ice, like snow on land, is a factor in global climate through its 

effect on planetary albedo. In addition, it influences mass, heat, and 

energy transfer between the atmosphere and oceans and affects the 

temperature and salinity structure of the ocean. It creates both an 

obstacle and an opportunity for economic development at high latitudes; 

and the seasonal sea-ice zone, especially in the southern ocean, is a place 

of enormous biological productivity. Sea-ice extent can be mapped by 

passive microwave sensors carried by satellites, and the ice concentration 

can be estimated. However, in order to incorporate sea-ice dynamics into 

atmosphere and ocean models, means will have to be found to make 

synoptic measurements of sea-ice thickness, the distribution of ice of 

differing ages, and the extent of surface melting. 

MODELING 

It is only through simulations with comprehensive models that we 

can hope to discern the impact of man's activities on the environment. 

Thus the development of more comprehensive and reliable models should 

be a clearly stated goal of an IGBP. Since all the components of the 

environmental system are linked through the atmosphere, the central 

part of a global modeling effort must be the development of improved 

climate and general circulation models. We note that this development 

is now one of the major objectives of the WCRP. What is particularly 

needed for an IGBP are more realistic treatments of clouds, atmospheric 

chemistry, ocean circulation, soil moisture, evapotranspiration, snow and 
THE ENVIRONMENT FOR LIFE 31 

ice cover, and biospheric interactions (Figure 3.1). Current atmospheric 

models include interaction among these systems in only a primitive 

manner. Based on past experience the task of building sufficiently 

realistic models will be a demanding one that will require several decades 

bf effort. While larger and faster computers will certainly be required, 

the limiting factor is likely to be gaps in our understanding of interactive 

processes that take place in the systems we seek to model, such as the 

complex relations that link soil moisture, rainfall, vegetation, and albedo. 

Atmospherz'c and Hyd1'ologz'c Models 

A first step in the improvement of current atmospheric general 

circulation models (GCMs) is to couple them effectively to the ocean and 

land-surface biomass. To do this their depiction of the surface fluxes of 

heat, moisture, and momentum must be significantly improved, along 

with their treatment of cloudiness and radiation. Ourrent GOMs 

generally do not include interactive atmospheric chemistry or aerosols 

and do not realistically allow for the interaction of the atmosphere with 

surface vegetation. The problem of parameterizing local geography in 

GCMs also needs further attention in connection with regional model 

validation. 

There are many aspects of the global water cycle that are not 

adequately treated in current models. Three stand out: the simulation of 

multilayered clouds, of precipitation, and of soil moisture and 

evapotranspiration in vegetation. In most of the models currently used 

cloud albedo is prescribed rather than generated by cloud microphysics. 

The problem is admittedly complex, but since cloud albedo-temperature 

feedback is potentially one of the strongest factors of the climate system, 

an improvement is clearly needed. We can hope it will be aided by the 

acquisition of new empirical data on global cloud cover and vertical 

structure. 

Among the questions involved in modeling precipitation are the 

following: What are the size distributions of rain drops or ice particles? 

At what rates do these particles fall or rise? Do solid-to-liquid transitions 

occur during this transport? How much evaporation takes place as water 

droplets fall toward the ground? The answers to these questions will 

require new observations as well as new model design. 

Almost all atmospheric GCMs have some means to account for 

changes in soil moisture. This is important because the evaporation (or 

transpiration) of soil water has a profound impact on air temperature and 

circulation over the continents. The schemes in use, however, are 

rudimentary ones that have been empirically adjusted to produce realistic 

surface air temperatures. To improve the models will require more 
SPACE 

Terrestrial 

Radiation 

H20, N2, °

2, CO2, °3, etc. 

Aerosols 

Changes in 

Solar Inputs 

Air-ice Coupling 

Changes of 

Atmospheric Composition 

Changes of Land Features, 

Orography, Vegetation, 

Albedo, etc. 

~ 

OCEAN 

Precipitation, 

Evaporation 

Wind Stress 

Changes in 

Ocean Circulation 

ATMOSPHERE 

Air-biomass-Iand 

Coupling 

BIOMASS 

Figure 3.1 The climate system, involving the atmosphere, ocean, ice, land, and biomass, with some examples of 

physical processes responsible for climate and climatic change (after Report of U.S. Committee for a Global 

Atmospheric Research Program, National Research Council, Understanding Climatic Change: A Program for 

Action, National Academy of Sciences, Washington, D.C.; 1975). 

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THE ENVIRONMENT FOR LIFE 33 

realistic treatments of such factors as vegetation cover, root depth, soil 

water capacity, water movement in soils, soil water throughput to the 

groundwater system, and runoff. Another factor that needs to be 

included in fully coupled models is the role of atmospheric aerosols, 

including the production of aerosols by plants, some of which occurs 

through the process of transpiration from leaf surfaces. Some of the 

needed information is available from agricultural and forestry research; 

some has yet to be determined by field observations. The impact of 

changing climate and of atmospheric 002 content on the soil parameters 

used in these simulations must also be known. 

Models 0/ Ocean C£rculat£on 

The ocean transports heat toward the poles and thereby influences 

regional climate. It also acts as a heat buffer, smoothing short-term 

climate variations and. delaying those of longer term. The ocean is the 

main sink in the global carbon cycle and hence the ultimate repository 

for fossil fuel 002' For all these reasons ocean circulation is a 

fundamental factor in models used for long-term environmental 

prediction. Yet, many atmospheric models use only passive oceans 

capable only of simulating their function in buffering heat. If we are to 

build adequate predictive models we must learn much more about the 

basic phenomena taking place in the sea. These include wind forcing at 

the ocean surface, the generation of deep and thermocline waters, and the 

rates of lateral and vertical transport and mixing within the sea. 

Although our present knowledge of these phenomena is incomplete, we 

should· strengthen efforts to build GOMs of the ocean while the data 

needed to define these parameters better are being gathered. The 

construction of a comprehensive and realistic ocean circulation model is 

one of the important tasks being undertaken by the WORP and is the 

principal justification for the World Ocean Oirculation Experiment 

described above. Indeed, the lack of an accurate atmosphere-ocean GOM 

now blocks progress in understanding major global changes of the past 

and stalls our ability to predict the global environmental changes of the 

future. 

Models of Agr£cultu1'al Carrying Capac£ty 

Behind many of the scientific questions of an IGBP is the 

fundamental issue of the human carrying capacity of the Earth, measured 

in terms ·of food and fiber production. An obvious, limiting factor is that 

of soil and soil quality. Since limitations of low soil fertility can be 

ameliorated through changes in farming systems or through energydependent inputs (such as chemical fertilizers), and since human diets are 
34 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

in principle flexible, there· is a wide range of possible estimates of 

ultimate regional and global carrying capacities. Calculations of carrying 

capacity made to date view soils as a static rather than a diminishing or 

accruing· resource; nor has adequate attention been given to the influences 

of changes in the mean or stochastic properties of climate. It is clear 

that we need to develop greatly improved abilities to assess agricultural 

potentials, including a range of assumptions regarding climate, 

technology, and water and resource availability--and that this capability 

must come from improved models. Increased and continuing attention to 

their development will help us to distinguish between perceived and real 

crises in food supply, to identify in advance particularly susceptible 

regions and circumstances, and to devise possible corrective strategies. 

The development of agriculture has enormously amplified mankind's 

ability to wrest food supplies from the biosphere. Since cropping extracts 

nutrients from the system, it was limited until recently by the nutrient 

supplies that were in the soils and by their natural replenishment through 

weathering, rainfall, flooding, dust deposition, and other processes. The 

yield levels possible with those sources of replenishment are very low: 

seed increase rates (the number harvested for each seed planted) before 

the seventeenth century seldom exceeded 3 or 4 to 1. During earlier eras, 

gradual increases in the human population were made possible mainly by 

the expansion of farming onto additional land. Quantum increases in 

productivity followed discoveries that nutrients, particularly nitrogen, 

could be refuged from adjacent grazing lands through collection of 

animal wastes, recycled through animal and human wastes, or enhanced 

by crop rotation with legumes. AB these practices spread through 

farming systems, they provided the basis for significant increases in the 

number of people that could be supported per unit area of agricultural 

land. The principal limitation on improved nutrient replacement and 

cycling in agriculture is, and always has been, the energy cost measured 

in human effort or fuel consumption. 

The high level of organic farming achieved early in this century in 

many parts of Europe and ABia through these techniques supported more 

than 2 x 109 humans.. By 1930, however, tillage had extended to 11 

percent of the ice-free area of the Earth and grazing to over 30 percent, 

and evidence had accumulated that we were approaching the humancarrying. capacity of the globe, based on that agriculture. The remaining 

lands were much less suited to tillage and grazing, and dietary standards 

were in. decline, even in North America. Further development and 

extensions of the legume-manure systems, even when supplemented by 

phosphate fertilizers, promised only moderate increases in food supply. 

These older systems .made only partial use of the sunlight and water 

that they received. World grain yields ranged from 800 to 1600 kg ha-1

, 

far below the photosynthetic potentials of cereal plants. In simple terms, 
THE ENVIRONMENT FOR LIFE 36 

cultivated land served more as a place for concentrating scarce resources 

of nitrogen than as a place for photosynthesis. The advent of abundant 

fertilizer nitrogen derived from the atmosphere (with the aid of fossil 

fuels) has changed those rules (Figure 3.2). Crops can now be brought to 

production rates that are limited mainly by the levels of water, radiation, 

or CO2, Soil acidification is accelerated by NH3-N additions, and other 

nutrients are removed more rapidly as yields increase; but with fertilizer, 

the role of soil as a source of nutrients is diminished while its importance 

in supplying water is greatly increased. Agriculture has since kept pace 

with the rapid expansion in human population, and although regions .of 

malnutrition remain, global dietary standards have improved. A world 

population of 10 billion people (roughly twice the present number) will 

require with. present methods of agriculture about one third of the 

cultivable land on· theplanet~-but for sustainable use the tilled fraction 

must be land that is .flat or only moderately sloped. There is nothing on 

the horizon in chemosynthesis, aquatic sources, or biotechnology that 

offers a significant alternative to the massive amounts of food that can be 

produced by higher plants grown on terrestrial sites. Perhaps we can find 

new and more efficient means of ensuring adequate supplies of nutrients, 

water, and 002 to crops, but until that happens our attention must 

remain focused on the adequacy of conventional agriculture. 

New and serious questions now arise. We are now closer to the 

practical limits of the photosynthetic productivity of crops. World food 

supplies are now dependent on energy supplies, and thus on the stability 

of a larg.er world society. Among the questions that must be answered, 

and that can be addressed in part by models, are the following: 

o What is the ultimate carrying capacity of the Earth under different 

assumptions as to the availability of energy and technology? 

o Are world soil resources being degraded by modern agricultural 

practices so as to limit present or future sustainable population levels? 

o How do changes in land and water use for cultivation, grazing, or 

forestry effect evaporation, aerosols, and regional or global climates, and 

how will world agricultural productivity be affected by changing climate? 

Models of Ice, Snow, and Permafrost 

The global heating expected from increases in atmospheric 002 and 

other greenhouse gases exposes another weak link in our understanding of 

the workings of the Earth as a system: namely, the interactive role of 

snow and ice. Among the major questions are the following: 

o How will seasonal snow and sea-ice cover change in the future, and 

how will this change influence the environment and the climate? 
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Figure 3.2 Trends in selected features of United States agriculture and food supply, 1909-1982, demonstrate the 

marked effects of changes in soil utilization in periods of decades. The retail meat supply per capita year declined 

steadily 'from 1909 to 1938 and has since increased dramatically. The U.S. depended on traditional methods of 

farming during the first third of the century and became a net importer of food in the 1930s. Hybrid maize with 

improved disease resistance and rapid expansion of the use of the legume alfalfa in grain rotations provided 

noticeable improvements from 1938 to 1950, but the most dramatic increases in grain yields (and thus meat 

supply) came with the use of nitrogen fertilizer. Meat supply includes fish (generally less than 10 percent of the 

total); maize yields are given as an index of feed production; and nitrogen fertilizer is the total applied to all 

crops. (Source of data: Agricultural Statistics, U.S. Dept. Agriculture, Washington, D.C.) 

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THE ENVIRONMENT FOR LIFE 37 

o How will the amount of ice stored in glaciers, ice caps, and the 

great ice sheets change in the future? What feedbacks on climate will 

follow, and how will this affect sea level and in turn the coastal 

environment? 

o To what extent will permafrost thaw, and how will this affect the 

use of northern or high-altitude lands? 

The answers to all of these can come only through realistic global models. 

Atmospheric GCMs simulate the growth and decline of snow cover, a 

variable important to the models because of its key role in determining 

surface albedo. However, existing models are less than precise in 

predicting precipitation patterns, and only rudimentary relations are used 

in simulating snow accumulation and melt. Furthermore, topography at 

subgrid scales is critical to the formation of snow cover in many regions, 

and this has not been adequately modeled. Considerable improvement is 

therefore needed before atmospheric GCM's can adequately simulate 

present-day patterns of snow cover or before they can hope to predict the 

pattern of future climate. In addition, new developments are required to 

provide the synoptic, remote sensing of snow that is needed to validate 

these models. 

Sea-ice models that include both thermodynamic and dynamic 

processes need to be coupled to atmospheric and oceanic GCMs because 

of the important role that sea ice plays in fixing planetary albedo and 

heat flux between air and sea. The task of modeling sea-ice formation is 

complicated by the role of ocean salinity and vertical mixing and by the 

intimate dependence of sea-ice extent and other characteristics such as 

the existence of polynias--or areas of open water--on wind speed and wind 

direction. Although complex sea-ice models exist that include most of 

the essential physical processes, there are no simple, efficient models of 

demonstrated validity for use in comprehensive, coupled atmosphereocean circulation models. Considerable model development, field studies 

[such as the International Marginal Ice Zone (MIZEX) program], and 

improved remote sensing are all required. 

Global effects of changes in land-ice cover, particularly on global sea 

level, needs to be understood better. The present-day rates of change of 

the major ice sheets (in Antarctica and Greenland) are not known but are 

thought to be close to zero. Major questions pertain to iceberg discharge 

from Greenland and Antarctica, melting at the base of ice shelves in 

Antarctica, and surface melting in the ablation zone of Greenland. The 

mass balance of the smaller glaciers of the world has been generally 

negative for the last century, and their wastage has contributed about 0.5 

mm/year to sea level rise. In order to predict what will happen to sea 

level in the next century, greatly improved models will be required. Of 

special importance is a better knowledge of the processes that might 
38 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

allow warm, deep ocean water to penetrate onto and under the Antarctic 

ice shelves, since the thinning or loss of these ice shelves might allow 

rapid ice stream flow and the loss of ice from land. Along with this, an 

understanding of iceberg calving and the factors that determine the 

seaward limit of ice shelves is needed. Better atmospheric circulation 

models, with attention to parameterization of topography at subgrid 

scales, will be required to predict the likely wastage of small glaciers and 

parts of the Greenland ice sheet. An additional problem is that of the 

prediction of future accumulation in Antarctica; some climate models 

suggest that snow accumulation will increase, taking water out of the 

oceans. 

The warmer temperatures anticipated in polar regions as a result of 

greenhouse warming will likely cause the permafrost to thaw. Attempts 

must be made to model the penetration of heat and liquid water through 

the soil zone into the underlying frozen ground. Long-term melting of 

these deeper horizons must be considered, not only for the direct effects 

on soil stability but also because deeper layers of permafrost are thought 

in some areas to consist in part of methane clathrates, whose melting 

could release methane to the atmosphere. 

Solar and Solar Terrestrial Models 

Two parallel efforts are needed to provide the theoretical basis 

through which measured changes in solar inputs can be interpreted and 

eventually predicted in terms of terrestrial effects. As discussed in the 

previous sections, the first is an improvement in global models of the 

atmosphere, biosphere, and oceans and their coupling. Such models need 

to be expanded to include the effects of changes in latitudinal insolation, 

for example, and the imperfectly understood effects of solar irradiance 

variations on the upper and middle atmosphere and their coupling to the 

troposphere. Spaceborne observational programs such as the Upper 

Atmosphere Research Satellite (UARS) will do much to provide the data 

needed for these analyses. An ultimate understanding must also include 

the role of the biosphere and the levers of atmospheric chemistry, 

dynamics, electricity, and biogeochemical and particle precipitation. 

processes, as probable amplifiers of small changes in solar fluxes at the 

orbit of the Earth. 

A second need is an improved theoretical understanding of the 

mechanism of solar variability itself. In spite of the presence of a long 

and well-documented record of the ll-year activity cycle of the Sun, we 

are still unable to explain its cause, other than through elementary 

dynamo models that· couple solar differential rotation with hypothesized 

subsurface magnetic configurations. Such models replicate the observed 

solar cycle only crudely and are as yet wholly unable to give meaningful 
THE ENVIRONMENT FOR LIFE 

information on cycle amplitudes or on long-term secular effects such as 

the Maunder Minimum that depressed solar activity for 70 years in the 

late seventeenth and early eighteenth centuries (see Figure 2.4). 

Predictions of solar activity and of the timing or amplitude of any future 

ll-year cycle are today done almost entirely by statistical methods whose 

accuracy is far from adequate for many practical purposes. 

Ooupled Env£ronmental Models 

A pervading physical element of the environment is the coupling or 

interaction between the atmosphere, solar inputs, ocean, snow and ice, 

soil, and biota that determines the course of global change. To portray 

and possibly to predict these changes adequately, it is essential that 

realistic models of the entire coupled global system be developed. Not 

only must atomspheric GOMs be coupled at the air-sea interface with 

realistic fluxes at the ocean surface, they must also be meshed 

interactively with appropriate models of the land surface and its 

vegetative cover and the other factors noted above. Models developed 

for individual subsystems need to be tested in interactive mode, first 

from the point of view of identifying obvious incompatibilities and 

interactive instabilities and then against observation. Steps toward this 

end have already been taken, but the ultimate goal is a major challenge. 
4 THE BIOSPHERE 

INTRODUCTION 

Almost all known forms of life have evolved in, and are confined to, 

the Earth's surface and its waters, at or near the interface with the 

atmosphere. Within this remarkably thin realm reside millions of 

different organisms, all exhibiting many similarities at the genetic, 

metabolic, and biochemical levels but each distinctive in how it interacts 

with the physical and biological environment. At work throughout the 

history of life on Earth has been a strong interaction between the activity 

of organisms and the development of soils and sediments, the cycling of 

constituent elements, the movement of water, and the composition of the 

atmosphere. Global climate and the chemistry of air and water and soil 

would all be different from what they are today were there not life. 

The nature of this interactive relationship has changed through time 

as new organisms have come into dominance in response to the 

continually changing physical and biological environment. The change 

has not always been gradual; from time to time episodic, cataclysmic 

events have apparently caused large and rapid environmental 

perturbations resulting in wholesale extinctions of certain species. In 

evolutionary time the relationship between the survival of any given 

organism and the suitability of the changing environment of Earth is a 

tenuous one. 

Man is a very recent player in the evolutionary pageant, and he 

differs in many ways from his predecessors and contemporaries. He alone 

has the capacity to comprehend the nature of his relationship with his 

environment, and with other organisms. He also has the capacity to 

modify not only his own environment, but that of other organisms as well 

in a substantial way. Unfortunately, our understanding of the 

relationships and dependencies of organisms with one another and with 

their physical environment has not developed as quickly as our capacity 

to modify them. Anthropogenic changes in the planetary environment 

are a unique feature in that they may well exceed the limits of natural 

regulation. There are many indications that human-induced changes are 

substantive enough to affect the survival of other organisms, both 

directly and indirectly, and to pose a potential threat to mankind itself. 

40 
THE BIOSPHERE 41 

We are now at a critical juncture in the history of mankind. Because 

of our sheer numbers and our increasing capacity to manipulate or affect 

large regions, our impact is now globally pervasive. Fortunately, we are 

also beginning to develop the tools with which we can view, for the first 

time, the total global environment. At the same time we have in hand 

extensive methods to measure and evaluate the interactions and 

dependencies of organisms with their physical and biological environment 

on the microscale. We must become more informed of human-induced 

environmental changes and plan for their eventual impacts. This will 

require large conceptual and technological advances, particularly in 

applying biological and ecological information derived from local studies 

to an understanding of global-scale processes. We must develop the 

potential to assess the full impact of ongoing environmental modifications 

as well as to predict the consequences of projected changes. We need to 

make an inventory of the Earth's resources and .to develop an 

understanding of the important links between the biotic and physical 

environment. By such methods we can hope to evolve a global strategy 

for the development and protection of resources that is compatible with 

the maintenance of the health of the global life-support system. 

The Need for a Global Ecology 

Events of the past several decades have provided dramatic examples 

of our need to develop a global ecology--a way to perceive and predict 

the biological consequences of global changes in the environment. We 

need to know the causes and extent of change and its magnitude and 

potential duration. Further, we need to be able to predict how organisms 

will respond to these changes either metabolically or genetically, and how 

these responses may in turn influence the environment. 

The first evidence of human-induced changes in the biosphere on a 

global scale came. with the atmospheric testing of nuclear weapons as a 

result of which the transcontinental transport of mutagenic agents was 

clearly demonstrated. The use of exotic pesticides on a large scale (e.g., 

DDT) again demonstrated that no ecosystem--no matter how remote--is 

isolated from the global dispersion of materials, toxic or benign. Since 

then, long-distance movement of metabolically active substances in the 

atmosphere, rivers, and oceans has been demonstrated over and over 

again. Dramatic recent examples of human-induced changes having a 

transnational impact are the combustion of fossil fuels contributing to 

acid rain, air and water pollution, and the increase in atmospheric CO2• 

It is this latter phenomenon, perhaps, which points most emphatically to 

the need for a global ecological perspective. The increase stems chiefly 

from the combustion of fossil fuels and a possible shift in the ratio of 

production to decomposition (including fire) in the Earth's ecosystems 
42 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

owing to biomass harvesting and land clearing for agriculture and human 

settlement (Figure 4.1). These changes influence atmospheric CO2 

concentration directly, and in turn affect plant production. 

It is now clear that there will be a marked enrichment of CO2 in the 

atmosphere that seems destined to alter the world: directly through 

modification of the global energy balance and indirectly through effects 

on biota. Yet the interactions among atmospheric and oceanic CO2 

content, climate, anthropogenic sources of nutrients, and the biota are 

exceedingly complex and only poorly known in quantifiable terms. We 

do not have sufficient information to make precise predictions of the full 

impact of CO2 changes because of uncertainties in the effects on climate, 

as well as a lack of precise information on the biotic responses to either 

CO2 or nutrient enrichment or to climate change. We do know that 

different species will respond differently to CO2 enhancement: a fact that 

complicates simple predictions. Furthermore, CO2 enrichment may affect 

decomposition as well as production processes. 

At present, there is no objective way to extrapolate point 

measurements of terrestrial CO2 fluxes to global scales. For example, 

most recent assessments of global carbon storage and fluxes depend 

entirely on disparate data for such factors as net primary productivity, 

litter production, deforestation, soil erosion, river transport, and marine 

sedimentation. Such efforts draw upon research performed at different 

places, with differing objectives and assumptions and with widely varying 

analytic procedures, quality control, and accuracy. Considerable 

judgment is needed in formulating consistent regional and global totals 

and in estimating aggregated uncertainties. The reliability and 

intercomparability of the results are thus likely to be limited. 

Furthermore, it is important to understand the dimension of the 

responses of the global system. Presently used approaches are not 

capable of considering the mechanistic links that drive these large-scale 

changes. 

Remote-sensing instruments on spacecraft using radiation from 

visible to microwave wavelengths can now provide objectively averaged, 

regional data for important parameters such as albedo, temperature, 

vegetative cover, and plankton biomass over large areas of the Earth. 

However, remote sensing by itself cannot supply the detail and accuracy 

essential to understand the complexities of geosphere-biospheric 

interactions. In situ measurements and large-scale models of biosphere 

processes are also clearly required. 
THE BIOSPHERE 43 

A GENERAL APPROACH 

The Her£tage 

The study of the relationships among terrestrial nonagricultural 

organisms and their physical-chemical environment is a relatively old 

science. It has progressed along two more or less parallel pathways: one, 

examining detailed environmental relations of individual organisms and 

the other, making correlative observations of the character and 

distribution of communities of organisms with climate and soils. Only 

recently have attempts been made to examine the environmental 

interactions of entire communities or landscape units. These studies were 

stimulated in part by the International Biological Program (IBP) and in 

part by the development of watershed approaches to the study of 

ecosystem function. Such studies provide the basis for estimates of the 

productivity of the diverse biomes of the Earth. 

The close dependence of man on a very few organisms for food has 

resulted in detailed and extensive studies of crop-environment 

interactions. The heritage of these studies is a body of information on 

the productive capacity of crops in diverse climates and under different 

cultural regimes. 

Such investigations have developed from initially descriptive to 

increasingly predictive ones. Methods utilized for. building a predictive 

capacity have employed a combination of experimentation and modeling. 

The quantitative models that now exist link rates of certain biological 

processes with conditions in the physical environment. Models of water 

transport and utilization exist for individual leaves, whole plants, entire 

canopies, and complete watersheds, though with decreasing precision at 

higher levels of organization where experimental verification is more 

difficult to achieve. Similarly, there are models that predict the intake of 

carbon dioxide by plants through photosynthesis, for chloroplasts, 

individual leaves, whole canopies, and even biomes. The accumulation of 

carbon by primary producers can be predicted reasonably well for crops 

under a range of climatic conditions, though less accurately for natural 

plant communities. 

Models for the uptake of nitrogen and phosphorus through the soil 

and into primary producers are now being developed. The turnover rates 

of minerals between plants and soil are also known at a descriptive level 

but are to a large extent species specific. 

We thus have a fairly good foundation for quantitatively linking the 

interaction of plants with the movement of carbon from the atmosphere 

into plants and of nutrients from the soil into plants. We also have 

information on the interaction of biota with solar and terrestrial 

radiation as well as with such atmospheric properties as air movement. 
44 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 
THE BIOSPHERE 45 

We have less capability to predict the movement of carbon and nutrients 

through animal and microbial components of ecosystems back to the soil 

or atmosphere. 

In sum, we know, and have known for some time, most of the 

interactive processes linking organisms with their physical environment 

and how they in turn affect such physical parameters as the soilatmosphere radiative" and thermal balance, the water balance, and the 

movement of elements within ecosystems. For most of these processes 

we have a solid capability to interrelate them quantitatively, at least on 

smaller scales. 

Similarly, studies of the physiology of the dominant marine plants 

(unicellar phytoplankton) have led to a quantitative understanding of 

response of growth to a suite of environmental variables. Dissolved 

inorganic carbon is sufficiently abundant in seawater to preclude the 

possibility that its availability could limit rates of primary production. 

Rather, it is sunlight and the rate of supply of dissolved inorganic 

nutrients, mainly Nand P, that limit marine photosynthetic production. 

A substantial portion of the demand for Nand P nutrients is met by 

recycling processes in the upper, sunlit portion of the oceanic water 

column. Rates of these processes can now be quantified, and these values 

provide an indirect estimate of the portion of primary production that is 

FIGURE 4.1 (Top) LANDSAT scene, central Rondonia, Brazil, June 

1976. The center of this scene is 10 0 S, 62 0 W. The grid pattern is the 

result of clearing forests along roads cleared by the Brazilian federal 

government with aid from international development banks. The area is 

in the southwestern Amazonian Basin close to the Bolivian frontier. 

Radar imagery from the early 1970s showed clearing only along the main 

highway and two adjacent roads. (Imagery obtained from the Brazilian 

Institute of Space Studies, INPE.) (Bottom) LANDSAT scene, central 

Rondonia, Brazil, May 1981. The area shown is identical to that of (top). 

A comparison of these two scenes showed that 2200 square kilometers of 

forest were cleared between 1976 and 1981. The total area of the scene is 

about 34,200 square kilometers. During the latter half of the period the 

rate of clearing was twice what it was during the first half of the period. 

[G. M. Woodwell, R. A. Houghton, T. A. Stone, and A. B. Park (in 

press). Changes in the area of forests in Rondonia, Amazon Basin, 

measured by satellite imagery. In The Global Carbon Cycle: Analys£s of 

the Natural Cycle and the Impl£cations of Anthropogen£c Alterations for 

the Next Century. J. R. Trabalka and D. E. Reichle, eds., SpringerVerlag, New York.] 
46 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

exported from the near-surface waters by gravitational settling; they 

complement direct measurements of particle fluxes made with sediment 

traps. This sinking process for intact organisms, fragments, and feces 

constitutes the dominant source of food for deep-sea organisms: the 

unused residual, when integrated over the water column, results in 

sedimentary accumulation on the seafloor. 

The amounts of C, N, and P that are exported from near-surface 

waters must be replaced to keep the system in balance. For marine 

plankton these elements occur in the relatively constant atomic ratio of 

106C:16N :lP. The limiting nutrients Nand P are replenished by an 

upward flux from reserves of nitrate and phosphate that exist worldwide 

in the deep ocean; these reserves in turn are replenished from animal and 

microbial processing of material that settles from the surface layer. The 

carbon in this organic matter is part of the same cycle, and a part of the 

C, N, and P that sinks as organic matter is lost from the cycle as a result 

of long-term burial in sediments. The processes of sediment burial and 

gas exchange across the air-sea interface together with biological 

processes in the ocean both serve to regulate the Earth's atmospheric 

content of CO2. 

The Challenge of Scale and Integration 

The production and decomposition of organic matter on the Earth is 

of course closely linked to climate--it influences, and is influenced by, 

such climatic elements as temperature, humidity, radiation, and wind. 

Further, these biotic processes represent significant controlling points in 

the cycling of mineral elements. Such processes, when viewed at the 

biospheric level, can be considered to represent the global metabolism. 

The balance between production and decomposition has a direct influence 

on the sizes of the nonorganic pools of C, N, P, and S. Changes in the 

balance of production and decomposition thus signal, for example, 

potential changes in climate. In recent years, the balance may be 

shifting owing to major changes in landscape use associated with 

cultivation, irrigation, deforestation, and desertification. At the same 

time the factors that control global plant productivity are also changing 

owing to anthropogenic alterations in the environment. Productivity, for 

example, may increase with increasing CO2 but decrease with air and 

water pollution. 

At present we are unable to measure total global metabolism, but we 

can measure or estimate it for large areas of the ocean and for specific 

ecosystems or smaller units on the land. Spaceborne sensors now being 

considered for deployment in the 1990s will make it possible to obtain 

estimates of certain components of global productivity, but extensive 

verification by in situ methods will be needed in order to calibrate these 

results. This effort is important since once the validations are made, we 

will have the capability of determining the metabolic status of the 
THE BIOSPHERE 47 

Earth's biotic systems both quickly and continuously. The linking of 

levels of approach--from local to global scale--in the study of biospheric 

metabolism will constitute an important step forward since it will involve 

the linking of biological and geophysical models that have been 

developed in isolation. The important interactions noted earlier between 

the world's biota and atmospheric and geospheric processes make this 

linkage a crucial step in understanding the Earth as a system--and our 

best hope for better global predictive models. 

A Spec2'jic Approach 

What is needed is an assessment of the Earth's metabolic capacity, 

which involves studies at overlapping levels of resolution and is fully 

integrated with geophysical measurements and modeling. There are 

three specific goals: 

o To quantify our knowledge of production and decomposition 

processes both regionally and globally and to determine the factors--

climate, soils, nutrients, water, and competition by other organisms, for 

example--that control them. 

o To obtain data on the details of the biological inputs into 

biogeochemical cycles and microscale and mesoscale climate processes. 

o To account for the diversity and the losses and additions of major 

biological participants in the global metabolism, as well as the changes in 

biomass distribution. 

In pursuing these objectives it should be noted that important events 

may take place in very short time intervals, that very limited areas may 

playa disproportionate role in the global balance, and that not all species 

are equally important in their contribution to the global metabolism. 

Special attention should be paid to the interactions of climate, soils, and 

crops, since it is these relationships that are most crucial in supporting 

the growing human population. 

In addition to studies of global metabolism, which would link 

directly with coincident studies of the atmosphere and geosphere, we 

need global inventories to assess the changing balance between species 

extinctions and invasions and experimental manipulations of entire 

ecosystems to determine the mechanics of geosphere-biosphere 

interactions. 

APROGRA:M 

The task of unraveling the complex and detailed interactions that 

link the Earth's physical-chemical environment and its biota is a 

monumental one, for which 10 or 20 years is a very short time. It is 

essential that a comprehensive program such as an IGBP sharply focus 

on a restricted set of problem areas that would most benefit. from a 
48 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

multidisciplinary approach and that might lead to a new understanding 

of the central processes maintaining life on Earth. 

What follows are three new approaches to the study of biospheric 

phenomena that promise comprehensive and basic information on 

biospheric structure and function. 

The first represents an effort of measurement and modeling designed 

to make the essential links between local, regional, and global 

observations. The second proposes an inventory of the changing nature 

of the Earth's biota. (This latter effort would not endeavor to account 

for those factors controlling species interactions, distributions, or 

metabolism--the main focus of much of biology; instead it would 

concentrate on building the data base to provide a necessary view of the 

changing distribution of the Earth's biota.) The third is ail experimental 

program to provide new information on the nature of geosphere 

interactions at the level of ecosystems. 

The general questions posed are the following: 

o What techniques can best be used to refine our estimates of the 

total exchanges of mass and energy between the geosphere and biota, and 

what is the best means to monitor these exchanges continuously? 

o What are the impacts of an anthropogenic ally modified 

environment on the production and decomposition processes of biotic 

systems? 

o How are the Earth's biotic resources restructured by human 

influences? 

LINKING LOCAL WITH REGIONAL APPROACHES 

A major problem in studies of global ecology is how to relate local or 

small-scale observations to questions of regional or global scale (Figure 

4.2). 

A Hierarchy of Levels 

An obvious nesting of units of study would proceed from a global 

view (utilizing satellite imagery) to regional units (or macrocells, utilizing 

aircraft and above-canopy climate towers or ships and instrumented 

buoys) to the level of relatively homogeneous ecosfstem units (or 

microcells, utilizing in situ measurements and experimental techniques). 

At each level there must be an accounting for interaction between models 

developed separately for physical and biological realms. Where models 

do not exist in common scale they would need to be developed. As an 

example, the atmospheric general circulation models (GCMs) generally 

utilize a grid size of hundreds of kilometers, at which scale there are no 

analogous biological models. The development and inclusion of 

biologically realistic energy balance models at this scale would expand 

the power o'f the GCMs and would provide an important input to the 
THE BIOSPHERE 40 

\ 

\ 

\ 

\ 

\ 

"" 

\ \ \ 

\ \ 

'" \ \ \ "'- \ 

\ , \ 

\ \ 

FIGURE 4.2 Studies of global ecology rest on . nested studies at 

progressively higher resolution, proceeding from a global view to a 

microcell. Macrocell units, about 100 km2 in area (middle), are proposed 

as possible Biosphere Observatories in an IGBP. 
50 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

assessment of global metabolism. It would also provide a link to 

smaller-scale approaches. It will be necessary also to link models of the 

various scales (global, macro, and micro) within the separate biological or 

physical realms. In these linkages, measurements at one scale can 

provide validation for models at other scales. 

Satellites and Global Metabolism 

Satellites offer global coverage of Earth surface properties at 

resolutions extending from hundreds of kilometers to 1 km or less. It is 

expected that measurements of a number of biological and environmental 

properties will eventually be made routinely from satellites, including 

ocean plankton concentration, terrestrial biomass, moisture content, and 

perhaps even leaf area index and a measure of leaf protein content. 

Correlations of these variables with spectral reflect.ance and emittance 

properties are now being made, although at this stage these studies are 

exploratory and the identifications are dependent on site or species. 

Absorbed photosynthetically active radiation and surface temperature 

can now be measured in both marine and terrestrial systems. These 

measures can give a low-resolution estimate of the changing productive 

capacity of the Earth over the course of a year, although plant 

decomposition, among other things, cannot be accounted for in this 

manner. 

One of the most rewarding activities of an IGBP would be efforts to 

improve the capability of satellite-based measurements of biological 

properties. Such efforts would compare spaceborne observations of 

spectral reflectance with continuous in situ measurements made at 

replicated, macrocell stations on land and at sea. Only through such a 

comprehensive validation program can we hope to make more realistic 

estimates of regional and global metabolism. 

Global Circulation Model Cells 

The global climate simulated in GCMs includes wind, temperature, 

and humidity at the Earth's surface as prognostic variables, together 

with diagnostic values of cloudiness, precipitation, and radiative flux--

each of which is calculated with a horizontal resolution of several 

hundred kilometers. Such GCMs require the specification or 

parameterization of the surface fluxes of heat, water vapor, and 

momentum on the same spatial resolution. Currently used flux 

parameterizations are based on bulk aerodynamic formulas and are 

applied uniformly for all land-surface conditions. 

A number of problems arise when one attempts to couple these 

models with local surface vegetation, which is characterized by elements 

of much smaller scale. One needs a method both for aggregating the 

fluxes from local surfaces onto the larger scale of climate models and for 

distributing the model's large-scale meteorological variables onto the 
THE BIOSPHERE 61 

smaller scales of local surface vegetation. Such problems typify the steps 

needed to achieve an effective, interactive coupling between atmospheric 

and biomass models. 

Reg£onal Unt"ts 

Landscapes 

The Earth's topography is complex at all scales, providing a mosaic 

of habitat types that differ in suitability for different organisms. Adding 

to this complexity is the fact that any habitat presents an assemblage of 

organisms whose makeup is a function of the time since the last 

ecological disturbance. Communities of organisms generally progress 

through a series of distinct stages. The activities of man have greatly 

increased the complexity of these' landscape units by a variety of 

manipulations. Accounting for the detailed interactions of these 

landscape units with the atmosphere and geosphere is obviously a 

complex task, yet it is essential that we do so in order to assess fully the 

consequences of the increasing tempo of landscape modification. 

It should be possible to view the metabolism of landscape units as a 

function of time as well as to account for their changing biological 

complexity. A possible way to accomplish this is to establish a number 

of local Biosphere Observatories, each of which is a regional research 

station that defines a landscape unit (or macrocell) covering about 100 

km2 (Figure 4.2). Utilizing instrumented probes extending above the 

influence of the immediate vegetated cover, it might be possible to 

measure the atmospheric and radiative properties that characterize the 

macrocell--although this would require the development of a reliable 

means to assess the local variations in fluxes of gases such as water 

vapor, CO2, N20, NO;r, and methane. Such measurements have been 

made, although they are of low precision and limited by conditions, 

season, and level of flux. Continuous measurements of gas fluxes at the 

Biosphere Observatory were they proven possible would be of enormous 

value in themselves, although considerable development would be needed 

to establish their applicability to a larger domain. The long-term 

measurements of CO2 in Hawaii, for example, demonstrate a marked 

seasonal change in abundance that gives an index of globally integrated 

landscape metabolism. 

Measurements at such Biosphere Observatories could provide a 

measure of the metabolism of a landscape unit and furnish the smallscale information necessary to build toward larger cells in modeling 

efforts. They could serve also as a fixed network of stations for 

validating satellite measurements of spectral reflectance and other surface 

properties. Airborne probes and satellite imagery could in turn provide 

information on the changing configuration of homogeneous unit.s 

(microcells) within the zone monitored by the Biosphere Observatory. 
52 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

Microclimate arrays within each microcell could typify climate-ecosystem 

interactions as well as track the changing composition of the atmosphere. 

These measures could then be related to direct measures of biological 

productivity and decomposition. 

The methodology for modeling and measuring ecosystem-level 

processes (such as productivity, water, and nutrient balance) at the 

microcell level was extensively developed by agrometeorologists, soil 

scientists, and ecologists working both independently and in the IBP. 

The present challenge is to integrate results from microcells to derive 

values for larger landscape units and to develop sufficient resolution in 

these measurements to account for the changes in system processes that 

may result from changing climate or atmospheric composition. 

Marine Habitats 

Regional studies of the marine habitat are necessary to refine our 

understanding of certain important biospheric processes. Although 

perhaps 80 percent of marine primary production occurs seaward of the 

continental shelf, more than 95 percent of the world's marine fish harvest 

comes from nearshore regions. Moreover, these coastal waters and 

estuaries are most heavily affected by human activities. Weare today 

unable to provide a quantitative basis for relationships among the 

physical, chemical, and biological processes that regulate primary 

production and fish yield in these important habitats. Lacking, in most 

cases, is a sufficient base of background data and observations. The 

natural variability of the system must be documented and understood 

before we can hope to ascertain the magnitude of anthropogenic effects. 

The role of coastal regions in sequestering carbon, and how this function 

has adjusted in response to anthropogenic inputs of nitrogen and 

phosphorus, are examples of other important unknowns. 

In large part, these gaps in our knowledge of interrelated systems 

stem from a less than adequate match of the scales, both temporal and 

spatial, at which related natural processes are studied. The decade of the 

1970s literally opened our eyes, through global satellite sensors, to the 

complexity of structure in the world's oceans. Sea-surface temperature 

and ocean color data from spaceborne sensors afforded a previously 

unseen view of the complex temporal and spatial variability of major 

ocean currents like the Gulf Stream, Kuroshio, East Australian, and 

California Current. No longer can one assume that the biologically 

important features of such currents can be adequately studied from 

occasional transects -across the currents as was done in the past. Eddylike features, some persisting for months, are common, and their effect on 

the distribution of biota and rates of activity for organisms at all trophic 

levels can be profound. 

Dramatic examples of temporal variability can also be seen in 

satellite imagery of the open ocean. The spring bloom phenomenon is 
mE BIOSPHERE 53 

common to temperate coastal waters. Yet in at least one case, the New 

England coastal waters, decades of shipboard studies ha'd failed to reveal 

the extraordinary synchrony of this process over the entire shelf and 

slope region. In general, the biological response to physical processes in 

the upper ocean, such as convection and stratification, occur rapidly. 

With greater use of instrumented buoys and satellite observations, the 

detailed in situ study of production processes can be conducted with an 

efficiency never before possible by shipboard studies alone. 

Many generalizations have been drawn about the biological 

homogeneity of major ocean basins. Again, however, satellite 

observations have revealed physical structure that was previously 

unknown. Compilations of direct and indirect estimates of the openocean production of biota are currently in poor agreement. Data sets 

from in situ studies are small and will remain so, because of the expanse 

of these regions and the limitations of shipboard studies and resources. 

Some of the differences in these estimates could result from poor 

sampling of episodic events that stimulate production. Global coverage of 

the oceans is therefore a high-priority goal for the proposed mission of 

the next generation color scanner, the Ocean Color Imager (OCI). 

A multiplatform strategy that includes satellite sensors, ships, and 

buoys will greatly facilitate the study of regional scale phenomena 

. relevant to biological production. A convergence of interests among ocean 

scientists with biological, chemical, and physical perspectives has led to a 

determination to take full advantage of a major program involving ocean 

satellite sensors early in the 1990s. 

GLOBAL INVENTORIES OF SPECIES DIVERSITY 

Evolutionary processes have resulted in the development of complex 

assemblages of organisms that operate in an interactive manner to 

capture and process solar energy and mineral resources. These 

assemblages of plants and animals are in general uniquely adapted to the 

particular physical and biological regime under which they have evolved. 

Isolation of the Earth's land masses has promoted this development of 

biotic diversity. 

The activities of man 'have massively disrupted these natural 

assemblages through direct destruction of total ecosystems for alternate 

uses, through selective alteration (as in the case of forestry and range 

utilization), and even inadvertently by breaking down geographic barriers 

so that processes of biological invasion are greatly accelerated (Figure 

4.3). 

We have no global inventory of the magnitude of these biotic 

disruptions and thus cannot assess their consequences in terms of 

alterations of ecosystem function. What data we have indicate that two 

processes are proceeding that are indeed related: the first is an 

accelerating rate of species extinctions and population reductions; the 
54 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

900 (al 

800 • Total California flora (/) 

w o Southern California flora 

U 

w 700 a. 

(/) 

Z 

w 600 ::::i 

<{ 

0 

w 

N 500 

::::i 

<{ 

ex: 

:::> 

I- 400 

<{ 

Z 

u. 

a 300 

ex: 

w 

CD 200 :E 

:::> 

z 

100 

0 

1750 1800 1850 1900 1950 2000 

YEAR 

(/) (b) w 

U 

w 700 a. 

(/) 

Z 

w 600 ::::i 

<{ 

0 

w 500 N 

::::i 

<{ 400 ex: 

:::> 

~ 300 z 

u. • ald. a 200 o Viet. ex: 

w "1 N.S.W. CD 

:E 100 o S. Aust. :::> 

Z 

0 

1860 1900 1940 1980 

YEAR 

FIGURE 4.3 Rate of increase of alien, higher plants in the last 200 

years in California (a) and in four states of Australia (b): Queensland, 

Victoria, New South Wales, and South Australia. (Compiled by R. H. 

Groves from various sources.) 
THE BIOSPHERE 66 

second is a dramatic homogenization of the Earth IS biota reduction of 

genetic diversity. AB but one example, annual plant species that have 

coevolved with man in the Mediterranean Basin are becoming weeds with 

world wide distributions. These invasions are most prevalent in 

ecosystems that have been disturbed in one way or another by man, but 

they are also occurring in natural communities. The economic costs of 

controlling certain invasive species in agricultural areas. are enormous. 

The ecosystem consequences of these invasions and extinctions are largely 

unknown. 

An IGBP would offer the opportunity to gain a world view of the 

extinction-invasion problem. An initial effort could involve the study of 

information that is available on the rates of change in species 

distribution. For example, there are data bases available that give the 

distribution of endangered species in the United States. A time analysis 

of this data base would yield an indication of rates of extinction. There 

are also data available on the rates of spread of a number of particularly 

invasive organisms. A world survey of invasion characteristics of various 

taxonomic groups would give the information necessary to improve 

existing models of the process of establishment, rate of spread, and 

nature of such invasions. Such an analysis is a necessary first step in 

assessing the ecosystem impact of these processes with respect to 

productivity and the movements of water and nutrients. 

EXPERIMENTAL APPROACHES TO THE STUDY OF ECOSYSTEMS 

It is becoming increasingly clear that we lack not only the basic 

information on how intact natural systems function and interact with 

their physical~chemical environment but also the basic tools to unravel 

these relationships. 

As one example, it is generally perceived that acid precipitation is a 

major factor contributing to an observed decline in forest productivity in 

the eastern United States and parts of Europe. There are, however, a 

multitude of atmospheric, soil, and biotic factors that affect tree growth. 

These factors are interactive and are not changing in concert. We can 

assess how individual factors affect tree . growth under controlled 

conditions in growth chambers. What we cannot duplicate in this way is 

the complex play of factors that characterize· the real environments of 

natural ecosystems. The difference is both profound and crippling. 

What is obviously needed is the design and execution of ecosystemlevel experiments under natural conditions to assess environmental 

interactions. Because of the cost and complexity of such experiments 

there are not many precedents and few models to point to in evaluating 

this complex approach. Two that can be cited are the Hubbard Brook 

study in 1965 of forest control of nutrient cycling in a controlled drainage 

basin and the chemical manipulation of confined lakes in the 

Experimental Lakes Area in Western Ontario beginning in 1970, to 
56 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

demonstrate the impacts of added Nand P. Both were enormously 

revealing in providing information on system processes that could not 

have been obtained otherwise. Their successes suggest that such studies 

could afford to be much more, daring and more widely applied as, for 

example, in tests of effects of acid rain or of processes of soil degradation 

or the chemical manipulation of soils. 

Appropriate in an IGBP is the development of a series of 

experiments at the ecosystem level designed to study the system impacts 

and responses of modified atmospheres, soils, and biomass configurations. 

These experiments should be conducted on systems for which the need 

for knowledge is most acute (such as temperate and tropical forests, polar 

regions, or desert areas) and at sites where the potential interactions 

between scientific disciplines would be greatest. A possible candidate, 

appropriate for an IGBP, is the comprehensive tropical basin study 

suggested in connection with hydrologic studies in Chapter 6. Such 

experimental initiatives would be most effective if closely allied with 

programs proposed earlier in this chapter that endeavor to relate local or 

small-scale processes to areas of larger scale. 
5 GLOBAL BIOGEOCHEMICAL CYCLES 

INTRODUCTION 

The elements carbon, nitrogen, sulfur, and phosphorus are of special 

interest in the study of life on this planet. With water, they are often the 

limiting components of living systems, whose growth and decay depend 

on the supply, exchange, and transformation of these elements. We can 

begin to understand how the biosphere works by following the 

transformations that make up the biogeochemical cycles of the individual 

elements. The need for such investigations has become apparent with 

growing evidence of anthropogenic perturbations to the chemical, 

physical, and biological state .of the atmosphere, land, and ocean. The 

magnitude of manMmade perturbations is significant; yet we have only a 

primitive understanding of their causes and ultimate impact. 

There is abundant evidence for change at present. Most obvious 

perhaps are changes in the composition of the atmosphere--or CO2, CH4, 

CO, N20, NOz , SOz, and Oa--and changes in the chemistry of 

precipitation. There are more subtle effects associated with altering 

practices of land and energy use and of waste disposal. Anthropogenic 

changes are superimposed on natural fluctuations, and it is difficult to 

separate the anthropogenic from the natural changes that are taking 

place today. There are clues, however, from the record of the past. 

An impressive body of information haS accumulated recently to 

suggest that fluctuations in CO2 may have played an important role. in 

regulating at least some of the major changes in climate of the past. The 

level of CO2 was approximately 200 ppm during the last Ice Age. It rose 

by about 50 percent, to approximately its present value, in only a few 

thousand years, 10,000 to 12,000 years ago, ushering in the present 

in terglac ial. 

We can reconstruct the history of CO2 back to about 60,000 years 

before present using air trapped in bubbles in ancient ice preserved in 

Greenland and in Antarctica. A more indirect technique, based on 

analysis of the isotopic composition of carbon in the carbonate skeletons 

of marine organisms in ocean sediments, has allowed us to extend the 

record even further, to about 400,000 years ago. The correlation with 

57 
68 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

climate is striking. High CO2 is invariably associated with warm 

conditions, low CO2 with cold; and indeed, changes in CO2 appear to 

precede changes in climate. This suggests that the geologic record can 

provide an important means to check and refine models for the present 

climate and that it can enhance our ability to predict the response of the 

atmosphere-biosphere system to modern changes in CO2• 

Carbon dioxide is but one of several gases with the potential to raise 

the temperature of the Earth. Infrared radiation from the planetary 

surface is absorbed also by methane (CH4), nitrous oxide (N20), and 0 3 

and by the industrial halocarbons, OF 2Cl2 and CFCI3. On a moleculeper-molecule basis, these gases are much more efficient than CO2 in 

altering the radiative balance of the present Earth, and their 

concentrations are also changing. Their cumulative effect on climate over 

the past several decades may be comparable with that of CO2. The 

complex nature and diverse reasons for the changes observed in the 

composition of the atmosphere require an analysis more comprehensive 

than any performed to date. Changes in the atmosphere can induce 

changes in the ocean and biosphere and in the storage and transfer of 

H20, which may in turn affect the functioning of many other parts of the 

planet. 

To illustrate the nature of the scientific challenges that we face, we 

address here the biogeochemical cycles of C, N, S, and P and the 

processes affecting several of the important greenhouse gases. This 

should not be construed, however, to minimize the scientific importance 

of cycles of a number of other elements--halogens and metals, for 

example. 

Most of the world's C resides in sediments as calcium carbonate and 

in organic C. Most of the planet's supply of P is also in the sedimentary 

reservoir, while N is found for the most part in the atmosphere as N2. 

Schematic views of the C, N, and P cycles, as currently understood, are 

presented in Figures 5.1-5.3. 

CARBON 

Carbon has a lifetime in the sedimentary reservoir measured in 

hundreds of millions of years and is released to the atmosphere by 

volcanic eruptions and by weathering following the uplift of sedimentary 

rocks. Carbon is then exchanged rapidly, on time scales of tens to 

hundreds of years, between the atmosphere, biosphere, soils, and the 

upper ocean,- with occasional, more prolonged periods of residence in the 

deep sea pending ultimate return to the sediments. Carbon, as CO2, is 

the fuel for photosynthesis. It is returned to the atmosphere from the 

biosphere and soils by respirl;l.tion and as a product of microbially 

mediated decay. The predominant role of CO2 in the budget of 

atmospheric carbon today reflects the . pervasive presence of aerobic 

respiration. 
FOSSIL 

FUEl 

~ ATMOSPHERE 

728 (ANNUAl INCREASE = 3) 

110 52 60 70 80 35 . 22 

40 

BIOTA -+- WARM SURFACE 

15 

COLD SURFACE 

560 60 600 300 

SOIL AND DETRfTUS 

1200 

BIOTA + 20 

2 18 

BIOTA .+9 

1 10 

RNERS 2 37 1 0.5-2 

• 

;SERVOIRS IN 10159 

INTERMEDIATE AND DEEP WATERS 

34000 

.UXES IN 10159 yr 

-1 

FIGURE 5.1 The global carbon cycle, showing the present (perturbed) 

content of major reservoirs and estimated rates of transfer between them. 

The discrepancies between the outputs and inputs of individual reservoirs 

reflect present uncertainties in the global carbon budget. 

37 

1 

i 

'-l 

t'" 

o 

~ 

f: 

~ 

o 

'-l 

!:'j 

o 

Q 

:= 

!:'j 

~ 

~ Q 

Q 

~ 00 

<:n 

c 
LIGHTNING 

COMBUSTION 

0.00 

ATMOSPHERIC N2 , 

4 x 106 

ATMOSPHERIC FIXED N BIOFIX 

RAIN NOX 

0.003 

NH3 RAIN 

AND 

BIOF IXAT ION DEN ITRIF !CAT ION DENITR. 

0.18 0.13 0.24 0.2 10-4 0.1 0.015 0.1 

DECAY 

2.3 RIVERS 

LAND BIOTA LAND SOIL 0.025 OCEAN BIOTA 

UPTAKE 

OrgN 2.5 OrgN, NH3

+, N03

- OrgN 

10 70 1 

DECAY UPWEl 

1.6 

DEEP OCEAN 

RESERVOIRS IN 1015 9 OrgN, N03

-

FLUXES IN 1015

g )'l'-1 

800 

FIGURE 5.2 The global nitrogen cycle, showing contents of major 

reservoirs and estima.tes of fluxes between them. Discrepancies between 

outputs and inputs of specific reservoirs reflect uncertainties in the global 

nitrogen budget,. 

1.6 

L 

c::D 

e 

~ 

r" 

o 

~ 

> r" 

C 

:= 

> 

~ t'1 

Z 

"'" := 

t'1 

~ 

t'1 

o 

00 

"0 

:= 

t'1 

~ 

r:" 

~ 

o 

00 

"0 

g; 

~ 

t'1 
LAND BIOTA 

2000 

2501 1250 

1.5 

RIVERS 

SOILS (PREHISTOR1C) 

150,000 

, 

, 

, 

\ 

, 

120 

UPWELLING 

, 10 

,UNAVAILABLE) 

flUXES OF TOTAL P 

1012g yr-1 

PREHiSTORIC 10 

DENUDATION 25 

FERTILIZER 15 

OCEAN BIOTA 

140 

2.5 

WITH 

'CoC03 

100.5 

PART ICU LATE 

ORGANIC 

DEEP OCEAN 

100,000 

20 

DEEPWATER 

FORMATION 

\ 

r---L-l 

I SEDIMENTS\ I 

I 109 \ I '- ____ ,...J , ~, ~------~----~~~ 

\ 

, 

, 

RESERVOIRS IN 1012g , 

, 

, 

FLUXES IN 1012 -1 , .... gyr " *" ----

0.5 2.0 0.5 

BELOWCCD 

100 

REGENERATION 

0.5 BURIAL 

FIGURE 5.3 The global cycle of chemically available phosphorus, 

showing contents of major reservoirs and rates of transfer between them. 

Discrepancies between outputs and inputs of specific reservoirs reflect 

uncertainties in the global phosphorus budget. 

Q 

b 

~ 0;, 

o 

Q 

l!!J 

o 

~ 

~ Q 

~. 

Q 

o 

~ 00' 

CD 

~ 
62 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

Methane is the second most abundant form of carbon in the 

atmosphere. Its presence reflects the importance of localized media where 

oxygen is deficient, as in swamps and the soil of rice paddies, for 

example, or in the digestive tracts of ruminants and a variety of other 

animals, including termites. 

Carbon doxide enters the ocean from the atmosphere mainly at 

middle and high latitudes. It is transformed in the sea from 002 to 

HC03-, with some additional production of C03

- -. It is transferred to the 

deep sea either in the form of organic detritus or as the structural CaC03 

of organisms living in the mixed layer or in inorganic form as a 

constituent of cold dense waters that sink to depth at high latitudes. The 

waters that leave the surface at high latitudes are replaced by extensive 

upwelling of bicarbonate-rich deep waters. Upwelling is most intense near 

the equator and in the eastern portions of the major ocean basins. The 

slow turnover of the ocean is controlled by the distribution of ocean 

currents, heat, and salinity. It is thus ultimately linked to the external 

climate and may be particularly sensitive to the manner in which 

moisture is transferred from one ocean to another by the air. 

The fall of organisms from surface waters and the subsequent release 

of constituent carbon at depth has a powerful influence in apportioning 

carbon between the deep ocean on the one hand and the surface ocean 

and atmosphere on the other. The process has been called a biological 

pump. If the pump acts with high efficiency, we expect that the level of 

atmospheric CO2 will be relatively low, and conversely, an inefficient 

pump will serve to raise the level of 002' It is obviously important to 

define the complex physical, chemical, and biological factors that 

combine to determine the efficiehcy of the pump. The overall cycle of 

carbon among the atmosphere, biota, soils, and ocean has an associated 

residence time of about 100,000 years, with most of this time spent in the 

deep sea. The cycle involving the atmosphere, biota, soils, and upper 

ocean is mediated for the most part by biological processes, limited in 

many cases by the supply of constituents other than C--N, P, and water, 

for example. The biogeochemical cycles of these elements are thus 

inextricably connected. A disturbance in the cycle of one element leads 

almost inevitably to changes in the functioning of all the other major 

cycles, with complex eventual effects on the biosphere and potential 

impact on the physical and chemical states of both the atmosphere and 

the ocean. 

NITROGEN 

Nitrogen occurring in compounds as single atoms (fixed nitrogen) is 

chemically versatile and essential for life, with a range of oxidation states 

from -3 to +5. Processes that break the N-N bond (nitrogen fixation) a.re 

relatively slow, a.mounting to less than 0.2 X 1015 g of N yr-1

. 

Recombination of fixed nitrogen to form N2 is also slow, owing largely to 
GLOBAL BIOGEOCHEMICAL CYCLES 63 

the kinetic stability of inorganic, fixed nitrogen (NH4+, N02-, NOa-) in 

solution. The recombination reaction is carried out biologically by 

bacteria using NOa and N02

- as electron acceptors (denitrification). 

Denitrification takes place in anoxic, organic-rich locations such as 

flooded soils and estuarial sediments, bottom waters of some deep ocean 

basins and trenches and in low-oxygen or anoxic waters at intermediate 

depths in coastal upwelling regions. Denitrification is essential to the 

preservation of the present level of atmospheric N2. In the absence of 

biological processes, the atmospheric nitrogen cycle would be open 

(Figure 5.2), leading to accumulation of N02

- and NOa

- in the oceans. It 

is unclear how the global system acts to establish a balance between 

fixation and denitrification. Mechanisms directly coupling nitrogen 

fixation to denitrification have not been identified, and indirect 

connections are not obvious. 

Nitrogen is cycled through the biosphere at rates 10 to 100 times as 

large as the rate for fixation of Nz. Inorganic fixed nitrogen (NH/, N02

-, 

NOa-) is assimilated into terrestrial biomass at a rate of about 

3 X 1015 g of N yr-1

, but this influx is balanced by decay of organic 

material. The rate at which inorganic fixed nitrogen is consumed and 

recycled by biota in the oceans is roughly 2 X 1015 g of N yr-1 with a 

large uncertainty. Internal cycles of mineral and organic nitrogen 'are 

essential links in the life-support system of the planet. 

We now know that NO plays an important role in the removal of 

stratospheric Oa under, natural conditions. It is derived mainly from 

oxidation of N20 formed by microbial activity in soils and aquatic 

systems. Nitrous oxide is a by-product of both oxidation (nitrification) 

and reduction (denitrification) of fixed nitrogen by microbes, with an 

additional contribution from combustion. 

Nitric oxide is also involved in the chemistry of tropospheric Oa. If 

the concentration of NO is high, above about 70 parts per trillion ( 

70 X 10-12 ), as it is for example in cities and over large regions of the 

continents, oxidation of CO and hydrocarbons leads to net production of 

Oa through photodissociation of N02• Otherwise, removal of CO and 

hydrocarbons results in consumption of Oa. The abundance and spatial 

distribution of tropospheric Oa is linked, therefore, in a rather direct way 

to the processes that control the levels of atmospheric CO, hydrocarbons, 

and NO. 

The supply and distribution of fixed nitrogen affects thus not only 

the productivity of the biosphere but also the chemical and radiational 

environments.for life. 

SULFUR 

Sulfur, like N, occurs in a wide variety of oxidation states and is an 

essential element for life. In contrast to N, atmospheric and biological 

transformations between these various states are relatively rapid and· 
64 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

there is no abundant stable S compound in the atmosphere. 

Nevertheless, the fluxes of S species into and out of the atmosphere are 

large--sufficiently large that the removal of the element from the 

atmosphere in the form of wet and dry deposition of S02 and sulfuric 

acid is now affecting the pH of North American and European lakes and 

forest soils. The impact of this process of removal on the health and 

productivity of forests and the ecology of lakes is now an issue of 

international concern. 

Sulfur enters the atmosphere in two dominant ways. Oombustion of 

fossil fuels add sulfur in the form of S02. Microorganisms in soils and in 

the surface waters of the ocean putatively contribute additional amounts 

in the form 9f (OH3hS, H2S, and other reduced sulfur gases, but the 

precise amount is unknown and controversial. These reduced gases are 

oxidized to S02 on time scales of hours to days. Anthropogenic and 

natural inputs of S02 to the atmosphere are apparently comparable in 

amount. 

The S02 is oxidized to sulfate and in this way removed from the 

atmosphere on time scales of several days. The sulfur oxidization 

processes depend on atmospheric levels of the OH radical and thus on the 

abundances of atmospheric 0 3, H20, nitrogen oxides, and hydrocarbons. 

In the soil and in the ocean photic zone, sulfate is taken up by 

plants and microorganisms. The sulfur is then recycled to the 

atmosphere through processes of decay; some accumulates in organic 

matter in ocean sediments. On geologic time scales, sedimentary sulfur is 

returned to the ocean-atmosphere system through vulcanism. 

PHOSPHORUS 

Atmospheric transfer processes are unimportant for phosphorus, in 

contrast to the cases for 0, N, and S. Key exchanges for P are associated 

with dissolved and particulate transport in rivers, with weathering 

processes, and with diagenesis in soils and sediments. Much of the P in 

rivers is in particulate form and is biologically unavailable. A major 

question here concerns the fraction of riverborne P that participates in 

the marine cycle and the time scale for effective transfer to the ocean. 

There is evidence that biologically available P increases dramatically in 

the mixing zone between fresh river water and saline ocean waters, at 

least for some of the world's major rivers. Some or all of this input may 

come from desorption or dissolution of particulate riverine P, enhancing 

the effective input to coastal ecosystems and to the ocean as a whole. 

The added P could also arise from marine biota, and much work remains 

to be done to resolve this question. Additional uncertainty is associated 

with the storage of P in estuarine and coastal sediments. This phosphorus 

may be mobilized during periods of lowered sea level. 

Biological uptake by P in the sunlit or photic zone of the ocean is 

extremely rapid, and surface waters are typically low in mineral 
GLOBAL BIOGEOCHEMICAL CYCLES 

phosphorus, excep£ in upwelling zones where P IS relatively plentiful 

throughout the year. Nitrogen and P are present in the ocean in almost 

exactly the ratio required by phytoplankton (16:1), and it is therefore 

difficult to discern whether marine productivity is limited by N or P. 

There is frequently a small residual of soluble P in upwelled waters, after 

inorganic N has been exhausted, and hence the role of P is often assumed 

to be secondary. The minor role of nitrogen fixation in this system is a 

puzzle. It has been argued that nitrogen fixation may be inhibited at low 

levels of P. Thus the marine cycles of Nand P may be tightly coupled in 

subtle ways. It is important that we unravel the essential 

interconnections, since fixation and denitrification can provide possibly 

rapid sources and sinks for fixed N, with potential impact on C and on 

the life cycle of major ecosystems. 

CARBON DIOXIDE 

Carbon dioxide plays an important role in the radiative budget of 

the atmosphere, intercepting heat reradiated by the planet's surface. AB a 

greenhouse gas it regulates the transfer of energy within the atmosphere 

and controls the ultimate release of heat to spac.e. An increase in 

atmospheric CO2 may be expected to bring about an increase in the 

global average surface temperature with a compensating decrease in the 

temperature of the stratosphere. Changes in the lower atmosphere will 

almost certainly change the behavior of weather systems and hence the 

climate, but current models may not be able to predict the eventual 

impacts on the hydrological cycle, on biota, ocean currents, and on the 

overall biogeochemical cycling of materials in the near-surface regions of 

the Earth. An accurate assessment of the impact of CO2 released by 

burning fossil fuel or by deforestation requires, therefore, a 

comprehensive understanding of the atmosphere, biosphere, soil, and 

ocean as an integrated physical-chemical-biological system. A 

fundamental overall goal of an IGBP should be to provide the 

information necessary to advance our understanding of and appreciation 

for the essential linkages that regulate this system. 

Fortunately, there is an excellent, essentially continuous, record for 

the change in atmospheric CO2 over the past 25 years. The concentration 

has risen from about 315 parts per million (ppm) in 1958 to almost 345 

ppm today. Much of the rise can be attributed to release of CO2 from 

combustion of fossil fuel. There are problems, however, in accounting for 

details of the observed trend. The rise is less than one might anticipate 

given the magnitude of the fossil source. The difficulty is compounded in 

that we might have expected that, over the period of these observations, 

burning of vegetation would have provided a source of CO2 perhaps 

comparable with that from fossil fuel. 

Estimates of CO2 production due to burning are based on data 

defining the area of land cleared annually for agriculture, mainly in the 
66 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

tropics, and are quite uncertain. The net source of CO2 depends on the 

abundance of C stored in both the biomass and soils of the area subjected 

to fire and on the fraction of bound C released to the air. We must 

account also for a net uptake of CO2 in areas recently cleared but 

subsequently abandoned and allowed to return to forest. There are major 

gaps in our knowledge of the C content of tropical ecosystems and 

further uncertainties in our ability to predict the fractional yield of CO2 

from fire. A significant portion of the C involved in burning vegetation 

may be converted to charcoal, which is relatively inert and could be 

stored for long times in soils or in river and estuarine sediments. Careful 

studies of tropical systems are needed to document conditions before, 

during, and after fire. We need also improved data on the extent of the 

land area that is burned annually. Observations from space could play an 

invaluable role but they must be carefully coordinated with ground-based 

observations and theoretical analysis if their full potential is to be 

realized. In this connection, space observations have yet to make a 

significant impact. 

The largest known sink for fossil-fuel-derived CO2 is the ocean. 

Carbon is removed from the atmosphere-upper ocean system by turbulent 

mixing and downwelling of bicarbonate-rich water in polar regions. As 

noted earlier, gravitational settling of particulate organic material 

produced by organisms in the open ocean serves as an additional but not 

well quantified sink. The calcium carbonate contained in structural 

material of these organisms is the primary source of mineral carbonate in 

marine sediments. By these mechanisms the ocean is estimated to take 

up between 2 X 1015 and 3 X 1015 g of C yr-1 from the atmosphere, 

approximately half the rate estimated for release of CO2 due to burning 

of fossil fuels, 6 X 1015 g of C yr-1. 

Published values for the net transfer of carbon from the biosphere to 

the atmosphere range from zero to about 3 X 1015 g of C yr-1. 

Combining these values with the value· for the fossil fuel source 

(6 X 1015 g of C yr-1

) and the range of values for ocean uptake 

[(2-3) X 1015 g of C yr-1)], suggests a range of values between 

3 X 1015 g of C yr-1 (6 + 0-3) and 7 X 1015 g of C yr-1 (6 + 3-2) for the 

net release of CO2 to the atmosphere. The observed increase in 

atmospheric CO2 leads, however, to a lower value for net CO2 release, 

2.5 X 1015 g of C yr-1

, indicating either an additional sink for CO2 

derived from burning of fossil fuel or an error--or at least an 

underestimate of the uncertainty in other terms of the atmospheric 

budget. Largest present uncertainty attaches to the values adopted for 

the biospheric contribution. As noted in Chapter 2, there is recent 

evidence for enhanced growth of trees in the past 100 years at temperate 

latitudes, stimulated perhaps by higher levels of CO2 , by enhanced 

supply of nutrients, by more favorable climatic conditions, or by a 

combination of all these factors. Also, the soil represents a large reservoir 

for carbon, but we have little direct information on possible changes in 
GLOBAL BIOGEOCHEMICAL CYCLES 67 

the 0 content of soils. There is an urgent need for better data on all the 

processes noted above, including the role of the ocean, if we are to 

formulate a credible model for the future evolution of atmospheric 002, 

METHANE 

The situation for CH4 is even less satisfactory. Methane, like 002, 

has an important effect on the radiative budget of atmosphere. It has a 

residence time in the atmosphere of about 10 years and is removed 

ultimately by reaction with the free radical OH. Oxidation of CH4 in the 

troposphere leads to production of CO and perhaps 0 3, Oxidation in the 

stratosphere provides a major source of stratospheric H20. Methane is 

essentially linked to the chemical cycles controlling the concentration of 

both stratospheric and tropospheric 0 3, Thus it can influence the 

transmission of solar-ultraviolet radiation to the Earth's surface as well as 

the infrared radiative balance of the troposphere. These perturbations 

can exert important effects on the biosphere and significant related 

consequences for the cycling of critical chemical elements. 

The stratosphere is very dry: the abundance of H20 amounts to 

only a few parts per million of the total air above the tropopause. The 

factors that determine the level of stratospheric H20 are as yet poorly 

understood. The conventional explanation suggests that air enters the 

stratosphere mainly at low latitudes where convection is most intense and 

where the tropospause is highest and coldest. Recent observations 

indicate, however, that the tropical tropopause is not cold enough, at 

least on average, to account for the exceptionally low values observed for 

the concentration of stratospheric H20. Exceedingly vigorous convection 

in localized regions of the tropics may provide the answer. It has been 

suggested that cumulus convection over Indonesia, for example, or above 

the Western Amazon Basin, can penetrate to altitudes as high as 20 km. 

The tops of associated clouds are extremely cold and offer a potential 

trap for H20 in the lower stratosphere. The abundance of stratospheric 

H20 may be linked therefore in a rather direct way to the climate of 

particular regions of the tropics. Vertical and horizontal transfer of OH4 

and subsequent oxidation at higher levels of the atmosphere provides a 

mechanism whereby H , and subsequently H20, bypass the tropical cold 

trap. We would expect an increase in CH4 to lead to an increase m 

stratospheric H20. 

The hydroxyl radical, the sink for CH4, is a central player in 

tropospheric chemistry, yet estimates of its concentration and variability 

over the globe are very uncertain. If we accept current ideas, atmospheric 

CH4 is removed from the atmosphere at a present rate of about 

3.6 X 1014 g of C yr-l. Approximately 4 X 1013 g of C yr-1 of CH4 is 

accumulating in the atmosphere at the present time, indicating a global 

source of about 4 X 1014 g of C yr-1

. This number is relatively well 

defined (±50 percent), limited mainly by our ability to estimate the mean 
68 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

concentration of tropospheric OR. The individual contributions to the 

global source are poorly known however. One can argue that agricultural 

activities may contribute as much as 50 percent of the total emission of 

CR4, with an additional 20 percent from fossil fuels and from burning of 

biomass. It appears that the tropics could account for about one fourth of 

the global source and for perhaps two thirds of what the undisturbed 

level would be in the absence of human influence. 

Analysis of air trapped in polar ice cores indicate that the 

concentration of atmospheric methane was constant for many thousands t years prior to about A.D. 1600, and that it began to rise rapidly about 

[50-400 years ago. Methane appears to have increased by about a factor 

of 2.2 since the Industrial Revolution. Perhaps half of the rise can be 

attributed to reductions in OR caused by anthropogenic emissions of CO, 

but our understanding of source mechanisms is inadequate to allow a 

more definitive conclusion. Clearly, improved definition of sources, and 

the factors that influence them, is needed if we are either to account for 

the past or predict the future course of CR4. 

NITROUS OXIDE 

Nitrous oxide is removed from the atmosphere mainly by photolysis 

in the stratosphere. The removal rate is calculated to be 10.5 (±3) 

X 101Z g of N yr-1, using observed distributions for NzO and calculated 

rate coefficients for photolysis. The rate of increase in the atmosphere is 

currently 0.7 ± 0.1 ppb yr-1 (3.5 X 101Z g of N yr-1), with an indication 

that growth may have accelerated since 1965. Total emissions for NzO 

therefore amount to 14 ± 3 X 101Z g of N yr-1. The magnitude of the 

annual increase, though small, implies a discrepancy in excess of 30 

percent between current sources and sinks, a consequence of the long 

atmospheric residence time (.........,150 yr) for NzO. 

Nitrous oxide is an obligatory free intermediate in denitrification. 

Sequential reduction of the N atom provides a respiratory path for a wide 

variety of bacteria under anaerobic conditions. Denitrification is most 

often observed in environments isolated from atmospheric oxygen and 

supplied with abundant sources of oxidizable organic matter in organicrich sediments, flooded soils, and closed ocean basins, for example. Such 

systems were once thought to be the principal sources for atmospheric 

NzO, but this idea has proven incorrect. Anaerobic ecosystems contain 

typically very low concentrations of NzO, indicating that virtually all the 

NzO produced by denitrification is consumed in situ. 

Significant quantities of NzO are produced, however, by a variety of 

aerobic environments. The most intense emissions are associated with 

rapid oxidation of organic matter, and it appears that the NzO is 

produced mainly as a by-product of primary nitrification. This process, 

carried out by certain autotrophic bacteria, yields 1-3 molecules of NzO 

per 1000 nitrite molecules produced under fully aerobic conditions. The 
GLOBAL BIOGEOCHEMICAL CYCLES IU} 

yield of N20 increases dramatically under low-oxygen conditions, rising 

to 10 percent of the nitrite production rate for partial pressures of O2 

below 0.1 atm. It is interesting to note that nitrifying bacteria also 

produce NO, with release rates similar to N20. We expect, therefore, 

that soils producing large quantities of N20 might also form copious 

amounts of NO, although direct observations of NO release are currently 

scant. 

It appears that soils in tropical forests emit N20 at rates far in 

excess of those observed in most other environments. An interesting 

inverse relationship is observed between fluxes of CH4 and emissions of 

N20: sites that are net sinks for atmospheric CH4 have lower emissions 

of N20. The latter sites tend to be waterlogged, or nearly so. Microbial 

production of CH4 is a strictly anaerobic process, while consumption 

generally requires oxygen. The anticorrelation noted between N20 and 

CH4 emissions therefore provide' support for the view that N20 is 

produced in forest soils by an oxidative process. 

It appears that the anthropogenic processes of agriculture, waste 

disposal, and combustion account for about one third of current emissions 

of N20. If the present pattern of emissions persists, the abundance of 

atmospheric N20 should grow slowly to about 400 ppb. However, there is 

little reason to project that emissions should remain constant in the 

future. Sources associated with combustion and with intensive agriculture 

are likely to increase, and we might expect increased fluxes of N20 from 

tropical forests disturbed by exploitation. A doubling of N20 within the 

next century is not out of the realm of possibility. Such a change would 

significantly reduce the abundance of stratospheric 0 3 and would also 

lead to an increase in average surface temperature. A much improved 

understanding is needed to predict future emissions of N20, and studies 

of tropical forests, agricultural soils, and aquatic systems are clearly 

important to this aim. 

DISCUSSION 

Our ability to predict changes in atmospheric CO2, CH4 , and N20 

may be even more uncertain than we have portrayed here, for we cannot 

assume that the existing imbalance of sources and sinks for these 

compounds will not change in the future. To understand how the CO2 

content of the atmosphere will change, we need accurate predictive 

models that include processes regulating rates of oceanic deep-water 

formation, global primary production, and fluxes of organic and inorganic 

particulate carbon to the deep sea. For CH4 we need to understand the 

processes controlling levels of tropospheric OH--a topic complicated by 

the fact that CH4 and other biologically produced hydrocarbons (such as 

isoprene and terpenes) can serve as either net sources or sinks for OR, 

depending on the ambient level of atmospheric NOz . This comes about 

because, as alluded to earlier, when NOz is deficient the hydrocarbon 
70 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

chemistry of the atmosphere leads to the destruction of 0 3; when it is 

high, as in polluted urban areas, there is net production of 0 3• 

To predict the future course of N20 we need a deeper appreciation 

of the nitrogen cycle. AB noted above, CO2, CH4, and N20 are 

greenhouse gases with recognized potential influences on climate. At the 

same time their budgets may be altered in important ways by the very 

climate changes that they instigate. The existence of feedback processes, 

both positive and negative, demands more realistic predictive models and 

new observations of many of the governing processes and fluxes. 

Theoretical calculations demonstrate that increases in CO2 , CH4, and 

N20 in the atmosphere will not only increase the average global 

temperature by several degrees but also substantially modify global 

rainfall patterns. Such changes in precipitation will also have a direct 

impact on the global distribution of the biomass and perhaps the 

distribution of salinity in the surface ocean. AB an important factor in 

global albedo, biomass regulates the amount of solar energy absorbed by 

the surface of the Earth. Changes in plant cover and plant moisture can 

also affect the distribution of cloud cover. It is an open question whether 

this biologic feedback will accentuate or allay the first order climate 

effect of increasing CO2, CH4, and N20. 

It is clear through the known effect of greenhouse gases that the rate 

of cycling of carbon and other elements through the atmosphere, oceans, 

and biosphere can perturb the global climate and that climate change, in 

turn, can lead to significant changes in rates of cycling. It is this 

interdependence that makes the problem of predicting the impact of 

human perturbations so complex, and why it is the major challenge for a 

program like IGBP. There is hope that we can begin now to identify 

certain cause and effect relationships by coordinated studies in different 

disciplines, by examining the problem at many different time and space 

scales, and by obtaining new data from a wide variety of sources. For 

example: 

o A better understanding of the combined influences of biological 

cycling and large-scale ocean circulation on the quantity and distribution 

of various nutrient constituents within the sea will help to quantify the 

ability of the oceans to take up fossil-fuel CO2• Three planned or 

existing programs can be identified that will help accomplish this 

objective: The World Ocean Circulation Experiment and the program to 

study transient tracers in the sea are designed to improve our knowledge 

of how the ocean IS mixed. The Particle Flux program is intended to 

improve our knowledge of the space and time patterns of production and 

distribution of organic tissues and associated calcium carbonate and opal 

within the sea. 

o A careful measurement of the rate of change of biomass on the 

Earth's surface during the next few decades will help to identify the role 

of land biota in determining the concentration of CO2 in the atmosphere. 
GLOBAL BIOGEOCHEMICAL CYCLES 71 

This might be achieved through (1) observations of surface vegetation by 

spacecraft to define global plant cover and density; (2) analysis of the 

changing amplitude of the seasonal modulation in measurements of 

atmospheric CO2; (3) measurements of changes in the 13Cj12C ratio in 

plants and in the atmosphere; and (4) the careful analysis of tree growth 

as reflected in tree-ring widths, as cited earlier in Chapter 2. Studies are 

also required to define and to investigate possible changes in the carbon 

content of soils. 

o A study of the processes involved in the cycling of nitrogen and 

phosphorus in a variety of ecosystems would clarify the impact of 

combustion-related sources of nitrogen and the importance of the 

extensive agricultural applications of nitrogen and phosphorus that 

characterize modern agriculture. 

o A field program to identify and quantify the major sources of CH4 

and N20and their response to environmental factors, plus improved 

estimates of the rate of b~ildup of these gases in the global atmosphere 

will provide essential information needed to predict future changes and to 

provide understanding of past changes in these chemically and 

radiatively important gases. 
6 GLOBAL HYDROLOGIC CYCLE 

INTRODUCTION 

The global water cycle is in many respects the most fundamental of 

the biogeochemical cycles. It strongly influences all the other 

biogeochemical cycles and also plays a direct role in atmospheric 

chemistry and global circulation, and hence in the shaping of weather 

and climate. Much of the heat that drives the atmospheric circulation is 

derived from phase changes of water. Clouds, ice, snow, and surface 

moisture have important influences on the Earth's radiation budget. The 

runoff of water from the continents together with precipitation and 

evaporation at the ocean surface are important determinants of oceanic 

salinity and thus of oceanic vertical mixing rates. 

The intensity of the hydrologic cycle is demonstrated by the fact 

that an amount equal to the entire global inventory of tropospheric 

moisture is exchanged with the ocean and the land surface through 

precipitation and evaporation every 10 days and that the global 

inventory of surface freshwater could be drained by rivers in 10 years or 

by evaporation and transpiration in 5 years. The major reservoirs of the 

water cycle along with the connecting fluxes are illustrated in Figure 6.1. 

DESCRIPTION OF THE CYCLE 

Reservoirs 

The great bulk of water on Earth lies in the oceans. This enormous 

reservoir is involved in processes of exchange with water on and under 

the land and in the atmosphere on many different time scales. The 

transport of heat in the ocean is a major factor in determining 

continental climate. The physical dynamics of the upper layers of the 

ocean and the exchange of these layers with the ocean below are 

important factors in the biogeochemical cycles of carbon and plant 

nutrients. 

Another great repository are the extensive reservoirs found deep 

beneath the land surface and oceans of the Earth. This underground 

72 
TERRESTRIAL r-----

LAND 

'--_---'I Reservoirs, volumes in l(y5kg (103 km3 ) 

b ) Fluxes, in 1015kg yr-l (103 km3 yr-l ) 

MARINE 

ATMOSPHERE 

11 

OCEAN 

FIGURE 6.1 The global water cycle, showing estimates of contents of major reservoirs and rates of transfer 

between them. Knowledge of water contained in the ground is particularly poor; this fundamental parameter is 

known to only a factor of 2 or perhaps 4. 

~ 

t" 

o 

~ t" 

~ ~ 

o 

t" 

o 

~ .... 

a 

a 

-< a 

t" 

t"j 

... 

~ 
74 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

water ( or groundwater) stored in porous materials beneath the top meter 

or so of soil has typical and in some cases as much as 106 residence times 

of from 10 to 103 years. Groundwater is sometimes highly mineralized or 

contaminated with anthropogenic wastes, including toxic ones. An even 

larger mass of freshwater exists as ice in the Antarctic and Greenland ice 

sheets. This ice, with an average residence time of 103 to 105 years, 

participates very slowly in the global cyc1e. However, it is so large a 

reservoir that small percentage changes in ice volume can cause major 

changes in sea level on time scales of 102 to 104 years. The addition or 

subtraction of ice from smaller, mountain glaciers, reacting on time scales 

of 10 to 100 years, may appreciably affect runoff of certain rivers. The 

melting of ice in these glaciers appears to have caused a third to a half of 

the sea-level rise observed in the past century. Snow cover on land and 

sea ice on the ocean vary rapidly and seasonally and exert a major 

influence on the Earth's radiation budget and atmospheric and oceanic 

circulation. 

Part of the precipitation on land runs off in streams, ~nd some of the 

remainder infiltrates into the ground. The topmost meter or so of soil is a 

chemical and biological reactor, and the water stored there plays an 

important function in coupling the various biogeochemical cycles. 

Retained moisture affects the albedo of bare soil and controls the 

partitioning of net solar radiation at the land-atmosphere interface. Soil 

moisture, with typical residence times of days to months, provides the 

potential for moisture fluxes: upward as evaporation and to the roots of 

plants and downward in recharging groundwater. It serves the same 

storage and driving functions for dissolved chemical species. Both the 

carrier and the solutes interact with the soil medium. Soil moisture also 

plays important roles in soil formation, directly through chemical 

weathering of rock and indirectly through life support of soil biota. Soil 

moisture is an active agent as well in the depletion of soil minerals 

through leaching, and it influences the resistance of soils to erosion. 

Finally, it also has an obvious and direct effect on the growth of 

vegetation and hence on global food production. 

The volume of water stored as snow can be measured readily, 

allowing localized forecasts of river runoff, water supply, flooding, and 

agricultural production. Variations in the areal extent of snow from 

season to season are greater than that of any other contributor to global 

albedo changes. Because snow has the highest albedo of any abundant 

substance on the Earth's surface, its presence or absence drastically alters 

the amount of absorbed radiation and therefore the surface air 

temperature. 

Just as snow modifies the albedo of the land, sea ice drastically 

modifies the albedo of the surface of the sea. In the Arctic and subArctic the area of sea ice doubles between summer and winter, from 

7 X 106 to 14 X 106 km2• In the unconfined ocean waters of Antarctica 

the seasonal variation in sea ice extent is much larger--from 2 X 106 to 
GLOBAL HYDROLOGIC CYCLE 76 

20 X 106 km2

. The presence of sea ice modifies the Earth's seasonal 

temperature cycle, delaying temperature extremes through the release of 

latent heat by freezing in the autumn and by the absorption of heat 

through melting in the spring. The growth of sea ice also raises the 

salinity of the surface ocean waters from which it forms, and locations of 

extensive sea ice growth are the probable sources of the cold saline water 

that ultimately forms the bottom water of the world's oceans. The 

location of the ice edge may also affect the path of cyclonic disturbances 

in the atmosphere and perhaps the generation of large eddies in the 

ocean. The seasonal sea-ice zone is also a region of great marine 

biological productivity. 

Fluxes 

Solar energy drives the water cycle. Evaporation from the oceans 

and, to a lesser extent, from the, land and its vegetation supplies water 

vapor to the atmosphere. The atmospheric water vapor is redistributed 

globally by winds and then condensed and returned to the surface of the 

land and the ocean as rain or snow. Water reaching the land surface 

that does not eyaporate again is returned to the oceans primarily by 

rivers but also through subsurface (groundwater) movement and by the 

calving of icebergs from glaciers and ice shelves. 

Coupling and Impacts 

Condensation of atmospheric water vapor in clouds and its 

precipitation as rain or snow are major inputs and driving forces in the 

hydrologic cycle. The release of lat~nt heat by condensation is one of the 

strongest forcing factors in global climate. Because of its inherent links 

with river runoff, soil moisture, snow, and underground storage, 

precipitation is the critical element for agricultural production and 

domestic water supply. Floods or droughts, often with catastrophic 

consequences, can result from an overabundance or marked deficiency of 

precipitation. Approximately 70 percent of the precipitation falling on 

the land surface is returned to the atmosphere by evapotranspiration, 

where it provides a source of subsequent precipitation. 

Evapotranspiration is vital to plant growth and development and serves 

as a natural regulator of the surface temperature. It is also a factor in 

the production of atmospheric aerosols, which are released to the air from 

leaf surfaces with the evaporation of water. 

Storage and depletion of precipitated moisture and the growth of 

vegetation have characteristic time scales that determine the temporal 

persistence of hydrologic variations. These dynamic properties are 

central to modeling the perturbations, trends, and possible instabilities in 

land-surface biological systems. 

The distribution of freshwater is highly variable over the globe and' 
76 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

is poorly correlated with either the density or rate of growth of the 

human population. Similar inequities arise in the temporal distribution 

of available water. Rainfall integrated over periods as short as a week is 

important to the productivity of unirrigated soils. Surface freshwater 

reservoirs are sensitive to rainfall or snowmelt integrated over time scales 

of 1 to 10 years; groundwater responds to rainfall integrated over time 

scales of 10 to 103 years. An ability to predict and thus to manage better 

the delivery of water to food crops on the 1- to 100-year time scale would 

be an invaluable aid to world agriculture. 

The temporal and spatial feedback mechanisms that operate between 

atmosphere and water are important in defining seasonal cycles and the 

variability of seasonal and interannual components of the hydrologic 

cycle. During the winter months, the continental land surfaces are net 

sinks for atmospheric moisture picked up over the oceans; whereas in the 

summer, when thermal convection is the predominant precipitation 

mechanism, the depletion of soil moisture by evaporation and 

transpiration transforms the continents into net sources of water for the 

atmosphere. Understanding these scales is vital in forecasting the 

location and size of anomalies in the cycle and in specifying the 

environmental impact of changes in the land surface. 

Some of the problems related to the cycling and availability of water 

may be considered as local, such as water quality--defined in terms of the 

content of dissolved and suspended substances. Others transcend 

national boundaries and may be properly defined as regional or even 

global problems. 'fhese affect, for example, the variability of rainfall on 

regional and larger scales, changes in gross vegetative type and cover on 

the land, salinity changes of the oceans, and the long-term availability of 

freshwater. 

Ocean Oirculation and the Global Water Budget 

The way in which water is transported through the atmosphere plays 

a critical role in establishing ocean circulation. A most dramatic example 

is the contemporary formation of deep water in the North Atlantic 

Ocean. The best meteorological estimates indicate that evaporation of 

water from the North Atlantic and its adjacent seas (the Mediterranean, 

Arctic, and Caribbean) exceeds what is added .by precipitation and 

continental runoff by about 15 percent. The resultant rate of water loss 

is 0.3 X 106 m3 s-1 (or 0.3 Sverdrup). This loss of water must of course 

be balanced by a net return flow of 0.3 Sverdrup through ocean 

circulation. 

There must also be a balance in the salt budget of the North 

Atlantic. Excess evaporation results in a salinity (and hence density) 

increase that must be reduced by exchange with less salty water from 

other oceans. This is thought to occur through a vertical circulation 

pattern: a shallow, northward flow of less saline waters from the 
GLOBAL HYDROLOGIC CYCLE 77 

Antarctic into the North Atlantic and a compensating southward flow of 

more saline, deep water. The difference in salinity between these two 

waters is about 0.5 part per mil compared with a mean ocean value of 35 

parts per mil. Hence the portion of flow from the Antarctic to the North 

Atlantic required for salinity balance is (35/0.5) X 0.3 or about 20 

Sverdrups. This predicted flux agrees with that estimated from 

oceanographic observations. 

The mode of operation is thus as follows. As salt increases in the 

North Atlantic, waters are generated that are dense enough to sink to 

abyssal depths and flow southward to the Antarctic where a shallow, 

return flow is generated. The product of deep water flux and salt excess 

must balance the rate of salt enrichment provoked by excess evaporation 

in North Atlantic seas. Thus a fundamental ocean circulation is driven 

by an aspect of the atmospheric moisture budget. 

The formation of deep water in the North Atlantic is a process that 

has wide-reaching consequences. It is responsible for maintaining the 

benign climate of northern Europe. For every cubic centimeter of deep 

water formed, about ten calories of heat are released to the atmosphere. 

This heat input from ocean waters is equal to about 25 percent of the 

solar energy that impinges on the North Atlantic over the course of a 

year. 

For these reasons it is important to understand how patterns of 

ocean circulation change with climate. In the process described above it 

is clear that the rate of formation of deep water in the North Atlantic 

must respond to changes in evaporation excess, as for example, through 

variations in insolation or atmospheric. circulation. This linkage provides 

a good example of the strong interdependence of various parts of the 

environmental system. It also demonstrates how much we have to learn 

before we can hope to predict climatic changes. 

The example is but one of many. We need a better understanding of 

the factors governing the transport of water in the air and in the oceans. 

Our knowledge of this aspect of the hydrologic cycle is surprisingly 

limited, owing largely to the difficulty of obtaining the basic data that 

are needed. It is almost impossible to determine the net flow of water 

across geographic boundaries. The net fluxes between land and air and 

between land and water are also poorly known. Nor are there obvious 

ways in which any of these measurements might be accomplished. 

One approach may offer hope. In atmospheric GeMs the net 

transport of water across geographic boundaries can be determined. By 

"tagging" the water that enters the atmosphere from any grid square one 

can follow its subsequent path through the model system to answer 

questions about, for example, (1) the fraction of local precipitation 

derived from local evaporation, a measure of hydrologic sensitivity to 

local landwater change; (2) the regional origin of local precipitation; and 

(3) the locus of precipitation of locally evaporated water. Moreover such 

models can be perturbed to determine the response of the hydrologic 
78 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

cycle to a wide variety of factors and conditions. Since these simulations 

are inexact and often model-dependent, they do not provide exact 

answers to real-world problems. They can, however, give valuable clues 

that can lead to the design of field programs. Observational results can 

then further adjust the models. 

The stable isotopes 180 and 2H should be employed as natural 

tracers to verify and improve these model studies, as should the historical 

record of the spread of tritium from nuclear tests. We now have global 

information regarding the distribution of these isotopes in rain, vapor, 

and groundwater that should prove valuable in this regard. 

Chemical and Biological Considerations 

There are important couplings between the hydrologic cycle and the 

biogeochemical cycles of C, N, P, S, trace metals, and minor constituent 

gases of the atIllosphere. For example, the runoff of water toward and 

within streams is an agent for the entrainment, transport, and ultimate 

deposition of sediments, anthropogenic chemicals, and dissolved and 

absorbed nutrients. The structure of the stream channel and the 

biological systems that it supports are significantly influenced by the 

concentration and the character of these constituents. The eventual 

concentration of these substances in freshwater lakE~s and reservoirs is a 

common cause of ecological change. These changes are exemplified by 

the effects of acid precipitation on lake environments. 

The deleterious effects of man on the quality of water in rivers and 

lakes and harbors are generally reversible in a relatively short time 

because of the rapidity with which water cycles through these surfacewater systems. However, when toxic materials become incorporated in 

river or lake sediments it is difficult or virtually impossible to remove 

them. 

Far more serious in the long run may be the injection of toxic or 

harmful substances into the soil and groundwater reservoirs. Complex 

chemical and biochemical reactions in the unsaturated soil zone may 

occur that are difficult to model and predict. Once they have entered the 

groundwater system, harmful substances may move great distances and 

remain in the system for centuries to millennia. Because of the complex 

reactions with soil and rock particles, the long time-constants involved, 

and our inadequate knowledge of groundwater flow rates and trajectories, 

this type of pollution is particularly difficult to trace or manage. The 

unnoted intrusions of today can pose a subtle and serious hazard for the 

future. 

PROBLEMS 

Our quantitative knowledge of the global water cycle is surprisingly 

poor. The volume of underground water is not known to within a factor 
GLOBAL HYDROLOGIC CYCLE 19 

of 2 or perhaps 4; our knowledge of surface water and of frozen water 

reserves is somewhat better. Far more serious is our insufficient 

knowledge of changes in these reserves of liquid and frozen water. We 

lack understanding of both the rates of change and their causes, as well 

as the influence of man in provoking these changes. 

A major uncertainty concerns the rates of evaporation over land, 

evaporation and precipitation over oceans, and cloud formation and 

precipitation processes. Precipitation minus evaporation over land and 

ocean (or equivalently, the net flow of water from land to oceans and the 

net advection of moisture from the marine to the terrestrial atmosphere) 

is not known globally to sufficient precision for understanding and 

predicting the delivery of water, for example to land-based biota. 

Improved understanding of the relation of the hydrologic cycle to the 

biological, chemical, and geological environment and the development of. 

reliable predictive capability will require answers to a number of 

important questions: How is the distribution of groundwater .over the 

globe changing both in quantity and composition as a consequence of 

human activities? What are the spatial and temporal distributions of 

rainfall, evapotranspiration, and runoff over the Earth, and how do these 

distributions interact with changes. in regional land use and climate? 

How does the volume of snow and ice on the land and on the sea vary in 

space and time, and how do these changes influence sea level? What is 

the net flow of water to the oceans via rivers and aquifers, and how do 

these affect ocean circulation? 

PROGRAM GOALS 

We propose four general goals for the study of the global hydrologic 

cycle: 

o To determine the dynamics of the major global reservoirs of 

freshwater: atmosphe1'e, surface, soil, and underground water; snow, sea, 

and lake ice; and glacial ice. This goal recognizes the need to understand 

the roles of these reservoirs in the hydrologic cycle and their relationship 

to weather, climate, the global energy budget, and global water supply. 

o To define and unde1'stand the mechanisms for the transfers of water 

between the major global reservoirs. This goal recognizes the need to 

understand the processes of evapotranspiration, condensation, 

precipitation, river flow, glacial flow, melting, and freezing that are 

responsible for the major fluxes in the hydrologic cycle. 

o To predict on app1'opriate time scales, changes in distributions, 

volumes, chemical composition and fluxes of water resulting from climatic 

change and from human activities in (a) the atmosphe1'ej (b) land-surface, 

soil, and underground water reservoirs; (c) snow cover; (d) sea ice; and 

(e) glacial ice. The relevant time scales are days for atmospheric water, 

weeks for land-surface water and snow, weeks to years for soil moisture 
80 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

and sea ice, and years to millennia for underground water and glaciers. 

This goal recognizes the societal importance of the water cycle and the 

need to predict changes in important reservoirs and interreservoir fluxes. 

o To understand better the coupling and reactions involving water in 

biogeochemical cycles. This goal recognizes the pivotal and complex role 

of water in man's environment, with opportunities to improve water 

quality and to optimize food production. 

SOME PROGRAM ELEMENTS 

Observations 

Observations related to the hydrologic cycle have traditionally been 

made using networks of stations on the land surface. These networks 

and their instruments are highly developed in Europe, North America, 

and other industrialized regions where some records exist that span more 

than a century. Elsewhere in the world observing networks are sparse or 

absent, and the records are of a few tens of years at best. More complete 

global coverage is needed, but there is no current technology for 

measuring many of the quantities from space. It will therefore be 

necessary to expand the global networks of on-site station measurements 

of 

o Precipitation quantity and burden of dissolved and suspended 

substances (or "quality"), 

o Streamflow quantity and quality, 

o Sediment transport by streams, 

o Groundwater quantity and quality, 

o Atmospheric humidity, and 

o Soil moisture. 

In conjunction with this expanded observing effort it is essential to 

provide centralized data retrieval and archiving to make the data 

available to the user community. 

Since rainstorms are a critical factor in the dynamics of the 

hydrologic cycle, it is necessary to observe their spatial extent. It is now, 

or soon will be, possible to do this from space using microwave radiation. 

Ground-based radar can also be used. Here, as with station observations 

of storm intensity and duration, it is the statistics of a region's 

precipitation climatology that are important and not the recording of 

every storm event on Earth. 

A number of important hydrologic quantities can be observed from 

space, however, and an IGBP should pursue them vigorously. These 

include 

o The mass balances of the Antarctic and Greenland ice sheets are 
GLOBAL HYDROLOGIC CYCLE 81 

still unknown in spite of an extensive field effort since the International 

Geophysical Year (1957-1958). It may soon prove possible to determine 

these fundamental quantities by repeated altitude surveys, using laser or 

radar altimeters on polar-orbiting spacecraft. The measurement should 

be pursued as part of an IGBP because of the role of these reservoirs in 

climate and in determining global sea level. 

o Glaciers and Small Ice Caps: The wastage of these secondary ice 

reservoirs, especially those in the mountains bordering the Gulf of 

Alaska, in Central Asia, and in southern South America, has contributed 

significantly to the contemporary rise in sea level. The contribution is 

likely to increase, given the probability of warmer surface temperatures 

through global greenhouse gas enhancement. Yet little is known about 

the current mass balance of glaciers in many parts of the world. 

Spaceborne methods to measure and monitor volume changes have not 

been developed, and research on such techniques should be encouraged. 

In the meantime existing methods of aerial photography and 

measurements made on the glacier surface should be extended and 

intensified. 

o Snow and Sea Ice: The remoteness and scale of snow and sea ice 

make real-time, global-scale data acquisition practical only with 

satellite borne sensors. Over 50 percent of the land is covered and 

uncovered by snow each year, and sea ice covers about 10 percent of the 

world's oceans. 

o The Secular Change in Sea Level: In many areas the sea level 

varies seasonally and interannually with changes in the heat content of 

the upper layers and in the velocity and location of ocean currents. 

These short-period changes may ultimately be best measured from radar 

altimeters on satellites such as the NASA Ocean Topography Experiment 

(TOPEX), but the altimeters will need calibration from a network of tide 

gauges on open coasts and islands. 

Long-term changes in sea level can also be expected to follow the 

climatic changes now anticipated from rising concentrations of CO2 and 

other greenhouse gases. A worldwide network of individual tide gauges 

would probably be the best method for measuring this secular change. A 

network of measurements of salinity and temperature in the upper 1000-

2000 meters of the oceans will also be necessary to separate changes in 

ocean volume due to thermal expansion from changes in total ocean 

water mass resulting from glacial melting. Measurements of secular 

changes in the position of the Earth's pole of rotation and in the speed of 

rotation would also be useful in making this separation. Possible secular 

changes in the elevation of individual tide gauges with respect to the 

center of the Earth must also be determined; this can now be done to an 

accuracy of about 1 cm by measurements of the acceleration of gravity at 

the location of the gauge and by satellite geodesy using lasers ranging 

and radio interferometry. 

o Precipitation and Evaporation over the Ocean: At present there are. 
82 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

no suitable means for measuring precipitation and evaporation over the 

ocean, even though an understanding of these processes is essential for 

interpreting the role of the ocean in climatic change and for a complete 

picture of the hydrologic cycle. One promising means of point 

observation of precipitation is by acoustic measurements, made from 

submerged hydrophones, of the noise made by raindrops falling on the 

sea surface. Both the size of the drops and their frequency can be 

determined from the level and spectrum of the acoustic signal. Auxiliary 

ship borne radar observations are needed in conjunction with this 

technique to define the spatial extent of oceanic storms. 

No satellite-based measurements of evaporation rate are currently in 

sight, and estimates will continue to be made using the traditional bulk 

aerodynamic formulae. Controlled experiments are needed to evaluate 

the diffusion coefficients for water vapor in the presence of breaking 

waves and consequent aerosol formation. 

o Tropo8pheric Moi8ture: Estimates of the vertical profile of water 

vapor in the troposphere can be made from space and should be 

encouraged and exploited. 

Modeling 

Major efforts should be made to develop conceptual models to better 

understand why changes are taking place in the hydrologic cycle and to 

integrate these models with global-scale atmospheric and oceanic GCMs 

for studies of climate change. Analytical work is needed to develop 

hydrologic models that successfully simulate such factors as streamflow. 

Such models should make it possible to predict the hydrologic 

consequences of postulated environmental changes, such as the higher 

surface temperatures and altered circulation and precipitation patterns 

now anticipated in a COz-enriched atmosphere. 

A Oomprehen8ive Experiment 

An integrated observational program, such as those suggested in 

Chapter 4 as "ecosystem experiments," might meet many common goals 

of an IGBP and be of particular value to local studies of the hydrologic 

cycle. Such a program might undertake an integrated study of a tropical 

basin such as the Amazon basin. This 'would involve study of the cycling 

of water, chemical species, aerosols, and other constituents between 

surface water, soil, groundwater, sediment, atmosphere, ocean, and 

biomass. Circulation would be explored at scales ranging from microcells 

to regional scale, with emphasis at the mesoscale. The program would 

involve data collection at each of these scales as well as intensive process 

studies and modeling. The results would be applicable to an 

understanding of the global carbon and other biogeochemical cycles; 

prediction of climate change in the future due to anthropogenic release of 

CO2; the role of tropical rainforests in the global hydrologic, atmospheric, 

and oceanographic circulation; and the effect of man's actions--especially 

deforestation--on the global environment. 
7 ELEMENTS OF A PROGRAM 

SUMMARY 

We have outlined in preceding chapters some of the factors that lead 

us to endorse the concept of a focused, international geosphere-biosphere 

program, whose goal is to understand the interactive physical, chemical, 

and biological processes that regulate the Earth's unique environment for 

life, the changes that are occurring in this system, and the manner in 

which they are influenced by human actions. There is a pressing need to 

assess the consequence of human activities in the context of natural 

global change and to provide the body of knowledge necessary to chart a 

wise course to the future. We believe that· the state of our science is 

ready now to accept this demanding challenge and that the task is 

sufficiently urgent and of such a scale as to require international and 

multidisciplinary attention. 

Mankind has developed the capacity to influence the environment of 

the Earth on a global scale--a situation unparalleled in the history of the 

planet. Our presence is detectable in the remotest regions of the globe in 

the form of significant changes in the chemical composition of the 

atmosphere. We have altered not only the air but the soils and albedo of 

the Earth, the surface and subsurface waters, and the working of the 

hydrologic cycle itself. On every continent we have so perturbed the 

natural distribution of plant and animal species that today the world is 

characterized by an accelerating rate of species extinctions and a 

dramatic homogenization of biota. No corner of the Earth is free of 

human influence. More than 30 percent of the land is under tillage, 

active grazing, and managed forest. Ohemicals unknown in nature are 

being introduced in the air and water and soil in ever-growing quantities. 

It is we who now fix (and greatly accelerate) the pace of many of the 

processes that cycle chemical elements essential to life. Yet we know 

only vaguely the results of these sometimes massive perturbations, or 

indeed the background of natural process in which they work. In this 

context the earth and biological sciences have not yet been able to 

answer the modern, practical questions most often asked of them--in part 

because we lack a holistic understanding of the Earth and its biota as an 

interrelated system. 

83 
84 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

Our present understanding of the Earth has come in discrete pieces 

from an agglomeration of loosely connected disciplines, such as 

meteorology and aeronomy, solar-terrestrial physics, ecology, 

oceanography, hydrology, seismology, and geochemistry. The hope of a 

geosphere-biosphere program rests on the established prowess and modern 

capabilities of these and other fields, but its objectives require something 

more--a synthesis of specializations, directed to provide a deeper 

understanding of the natural world, to improve the general condition of 

mankind. The problems outlined in this report are unquestionably of an 

interdisciplinary essence, with the biosphere as the common link. As an 

example, we cite the burning of fossil fuel that releases CO2 to the air, in 

such increasing amounts in the present era as to evoke global concern. It 

is generally conceded that the increase in CO2 abundance in the 

atmosphere will eventually lead to a significant increase in the globally 

averaged temperature of the surface of the Earth. But knowledge of a 

modeled, climatic trend is of limited use. To foresee the practical 

impacts in quantitative terms we need to define the response of the 

Earth's biota to increasing CO2, as well as that of the soil, the hydrologic 

cycle, and the ocean, to trace the complex feedbacks that are involved 

and to determine the ultimate response of the composite system. The 

need is to predict the regional impacts of change, not simply its global 

average, and the ultimate impacts of local or regional changes in climate. 

This task is obviously demanding, and it requires a new step forward, not 

only in the disciplinary but also in the interdisciplinary dimensions of our 

science. 

GENERAL PROGRAM ELEMENTS 

A number of specific objectives have been developed in the preceding 

chapters. They have in common the need for new programs of 

ob8ervation of the Earth as a planet, a better understanding of the 

interactive proce88e8 that govern its changes, the development of a new 

generation of coupled mode/8, and the design of suitable te8t8 to guide 

the development of these models and the understanding of the processes 

involved. 

We summarize below the general recommendations in each of these 

four categories, condensed from the more specific recommendations given 

in earlier sections. We emphasize that the list is neither complete nor all 

inclusive but rather an indication of the sorts of efforts that must be 

undertaken to meet the goal of a focused IGBP. Moreover, a number of 

the programs mentioned are already planned or under way, as features of 

other international, research programs. 
ELEMENTS OF A PROGRAM 86 

OBSERVATIONS 

Observations of the present and evolving state of the Earth are 

essential to the aspirations of an IGBP. They provide the input for 

models. They play a central role in raising questions, stimulating 

hypotheses, and identifying needs for specific process-related studies. 

They can substitute, at least on a temporary basis, for gaps in 

understanding, allowing phenomena not well understood to be 

represented in an empirical fashion in models. Particularly needed are 

the following: 

o Continuing, long-term observations of parameters that may 

provide composite indications of change in global climate. These include 

sea level, volume of land and sea ice, surface temperatures, clouds, 

regional and global albedos, and the vertical structure of the atmosphere 

and oceans. The initiation and maintenance of long-term time series of 

fundamental measurements are an obvious requirement of any program 

that endeavors to document and understand global changes. They may 

well form the principal bequest of an IGBP for future generations of 

scientists, for questions that we cannot anticipate and problems that we 

cannot foretell. 

o New observational programs that trace the movement of water 

within terrestrial ecosystems, the ocean basins, and between sea and 

land, since these flows are critical to the function of ecosystems and 

fundamental to the state of the climate. There is also a need to 

determine rates for evaporation and precipitation and to determine the 

moisture content of soils. Current observations must be extended to 

provide better coverage of remote environments. 

o Programs that study the world's current soil resources including 

key factors of slope, roughness and soil thickness, the physical and 

chemical properties of soils, and the relative balance or imbalance 

between soil formation and erosion in representative areas of the world. 

o Observations to define the extent and to monitor change in the 

distribution of selected, representative ecosystems--tropical forests, for 

example. 

o A continuing record of extinctions of native species and the 

colonization of intrusive varieties of plants and animals in sensitive 

ecosystems. These processes are accelerated by human activities and 

they may alter the geosphere-biosphere interactions of entire ecosystems. 

o Data to define quantities of important chemical elements--carbon, 

nitrogen, and phosphorus, for example--stored in major ecosystems. A 

sampling strategy must be devised to provide early detection of possibly 

significant changes in the holding capacity of these environments. 

o Continuing measurements of basic ocean variables such as current, 

temperature, and salinity over the entire globe. 
86 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

o Extensive observations of the ocean to define rates at which 

materials are distributed from place to place and from depth to depth. 

Satellite studies of physical and biological properties together with in situ 

measurements of chemical tracers, both natural and anthropogenic, can 

make an important contribution to this objective. 

o Continuing measurements of the composition of the atmosphere at 

a number of geographically dispersed stations to identify changes in the 

abundance and altitude profiles of specific gases and to aid in diagnosis of 

factors responsible for the observed changes. Gases that should be 

included in this program include CO2, CH4, CO, N 20, NO z, SO z, and 

0 3, Observations defining the changing chemistry of precipitation are 

also needed. 

o Continuing observations of 0 3 and other selected gases in the 

troposphere and stratosphere to distinguish changes due to human 

activity and natural variability. 

PROCESS STUDIES 

Resolution of many of the most . critical uncertainties in our 

knowledge of geosphere-biosphere interactions will require experimental 

studies in both the field and the laboratory. Testable hypotheses now 

exist for some of these processes; new global observations will be required 

to design studies to investigate others, and the studies necessary to 

understand some will be guided by new models that appropriately 

address geosphere-biosphere interactions. In some cases this will involve 

an elaboration of existing or planned programs, while in others it will 

require a new synthesis of ideas and strategies. In an IGBP the emphasis 

of process studies should be both global and interdisciplinary. Many 

topics for these studies are proposed in the preceding chapters; 

summarized below are examples that demonstrate the need for an 

international program. Particularly needed are studies of 

o Processes controlling concentrations of CH4, OH, NOz , and other 

important trace gases in the troposphere and stratosphere, to understand 

the role of these substances in global chemistry and climate. We need to 

identify and quantify the major sources and sinks of gases whose 

concentrations are known to vary and to determine the environmental 

factors that are important in regulating release rates from specific 

habitats, such as tropical forests, peatlands, permafrost regions, and the 

oceans. Laboratory studies of some of the organisms involved will also be 

essential. 

o Variations in solar inputs to the atmosphere, such as the total 

irradiance and those inputs that influence the concentration of 

stratospheric and tropospheric oxidants, to identify and delimit the role 

of solar variability as a perturber of climate and of other significant 

global change. An interplay of models and relevant observations is here 

particularly needed. 
ELEMENTS OF A PROGRAM 87 

o The processes responsible for the formation of deep ocean water, to 

understand the fundamental circulation of the ocean and the basic 

interactions between ocean and atmosphere that influence climate. We 

need to know the factors that determine the geographic extent of these 

regions and the magnitude and frequency of downwelling events. It now 

appears that both physical and biological process in regions where deep 

water is formed play an important role in the carbon and nutrient cycles 

of the sea. 

o Whole ecosystems--both natural and man-made--to illuminate the 

real impacts of environmental perturbations. Such studies would employ 

controlled experiments in regions of perhaps 1000 to 10,000 acres. Good 

examples are the studies performed in recent years in Canada in the 

Experimental Lakes Area of Western Ontario. 

o The effects of variations in CO2, nutrients, and other 

environmental conditions on selected ecosystems--such as the effects of 

industrial effluents or of increased carbon dioxide on tree growth--to 

specify how these changes influence biological processes and the cycling 

of water and chemical elements through biosphere-geosphere systems. 

o The role of physical processes in the ocean and their influence on 

the production and burial of organic carbon in the sea, to quantify 

important components of the global cycles of C, N, and P. These will 

require intensive investigations of representative regions of the ocean. 

They are essential if we are to make optimal use of the potential of space 

measurements of ocean color to estimate ocean biomass and production. 

o Processes of soil formation and degradation, the salinization and 

chemical balance of soils and of soil erosion, to understand the impacts of 

modern agriculture on the global soil resource and to specify the ultimate 

agricultural carrying capacity of the Earth. 

o Specific aspects of the hydrological cycle--for example, the 

exchange of water between the troposphere and stratosphere, the 

investigation of dynamical and radiative feedbacks involving clouds, or 

studies of exchange of waters between soils and the atmosphere. 

Relevant processes are complex and must be understood better if they are 

to be incorporated reliably in models. 

MODELS 

A major challenge for an IGBP is to develop an integrated view of 

the Earth as an interactive physical, chemical, and biological system. 

This is required if we are to provide a comprehensive assessment of the 

complete effects of modern technology on the global environment. We 

need to forecast, for example; the changes in climate and weather 

patterns induced by release of CO2 from the combustion of fossil fuel. 

To do this successfully presumes an ability to predict changes in 

atmospheric circulation, associated changes in the biota, global snow and 

ice cover, and the ocean, recognizing that the eventual impact involves a 
88 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

variety of subtle, complex, and poorly understood feedbacks. To address 

these issues we need a better understanding of a variety of processes, as 

noted above, and improved observations. We also need improved models 

for 

o The circulation of the atmosphere, with better means to describe 

the radiative feedback of clouds and improved definition of processes 

controlling exchange of heat momentum, H20, and other chemicals at the 

surface. Radiative-dynamical-chemical feedbacks with the stratosphere 

are fundamental parts of such improved models. 

o The circulation of the ocean, both surface and deep water, 

including definition and quantitative description of mechanisms 

responsible for upwelling and downwelling. We need an ability to 

describe the response of the ocean to externally imposed conditions at the 

surface and also models to describe the ocean and atmosphere as an 

interactive system. 

o The responses of sea ice, major ice sheets, continental glaciers, and 

of world sea level to climatic change. 

o The metabolism of ecosystems accounting for changes in species, 

and for the exchange of H20 and chemicals with other reservoirs, in 

response to variations in the external environment. 

In addition we need to develop the techniques of integrating ecosystem 

models with global models of the physical and chemical environment of 

the Earth, leading to eventual coupled models that describe all the basic 

features of the global environment. Immediate needs in this endeavor are 

joint agreements between disciplines as to scale and the ensuing 

challenges of aggregation and disaggregation of relevant data. 

TESTS 

A necessary part of model development is the synergistic use of tests 

in natural systems to evaluate and perfect the model's performance. 

Many of the observations and process studies listed earlier will serve this 

function. In addition, one can learn much from reading the record of the 

past, where Nature has conducted grand experiments of her own. If we 

can but read it, the past history of the Earth will provide surprises that 

will stimulate new ideas and suggest new observations, which in turn will 

lead to the refinement of models and the definition of further tests. In 

this regard, the environmental record discussed in Chapter 2 becomes a 

particularly valuable resource for an IGBP. The following steps are 

needed to exploit it: 

o Expanded, cooperative programs of polar ice core retrieval and 

analysis to reconstruct the history of world temperature, atmospheric 

chemical and particulate properties, terrestrial vulcanism and its effect on 
ELEMENTS OF A PROGRAM SD 

climate, and the history of galactic cosmic-ray flux for studies of solar 

and terrestrial magnetic-field variations. For some of these studies, cores 

will need be taken from middle- and low-latitude glaciers in areas such as 

the Alps, the Himalayas, and the Andes. 

o Intensification of efforts to recover and analyze sedimentary 

records from the seafloor from a large area of the globe for studies of past 

climate, ocean circulation patterns, cosmic-ray fluxes, and the nutrient 

chemistry of the oceans. Appropriate numerical models need also to be 

developed to further our understanding of the dynamics of the inferred 

changes. 

o Expanded efforts to collect varved sediments in lakes and estuaries, 

to refine their temporal resolution and to expand the regions sampled for 

reconstructions of past climate, biotic distributions, and the chemical and 

particulate content of the atmosphere. 

o Expanded efforts to determine the temporal extent and geographic 

coverage of the tree-ring record as a repository of information on 

climatic, hydrologic, volcanic, and solar history over the past several 

thousand years. Trees that are most sensitive to environmental stress are 

generally found in arid or mountainous regions that are often remote. 

o Expanded efforts to establish the record of changes in sea level; 

studies of tropical coral growth and deposition as an indicator of past sea 

level and climate. 

MODES OF INVESTIGATION 

The research described in this report represents an exciting new 

challenge for earth and biological scientists. The opportunities for 

individual involvement range from participation in small, focused 

experiments with relatively simple hardware demands all the way to the 

large and technologically challenging endeavors exemplified by Earthorbiting satellites. The need for interdisciplinary cooperation in scientific 

planning has been emphasized in the preceding chapters. There will be a 

need for similar cooperation during the design and execution of the 

measurements themselves. Physical, chemical, and biological data will 

often be required for the same locality and can often be obtained most 

economically using the same surface station, aircraft, ship, or satellite. 

There are certain modes of observation needed in an IGBP that are 

worthy of particular emphasis. We see the need for a globally 

distributed, low-density network of surface stations for long-term 

measurements of atmospheric trace species. In addition, we identify the 

need for higher-density networks of surface stations for intensive shortand/or long-term studies of vegetation, hydrology, and sources and sinks 

for trace species. These networks would operate in land areas of high 

biological and chemical activity such as tropical forests and other critical 

ecosystems. The need for stations similar to both of the above types of 

networks has already been emphasized as an essential element in the 
00 GLOBAL CHANGE IN THE GEOSPHERE-BIOSPHERE 

proposed Global Tropospheric Chemistry Program. 

For the ocean, the acquisition of a global data set and a long-term 

record is even more challenging than for the land or atmosphere. 

Regular sampling schemes that include more frequent visits to the 

remoter parts of the world's oceans and efficient methods for sampling 

will all be necessary in order to provide physical, chemical, and 

dynamical data at the required temporal and spatial resolutions. 

While long-term measurements are an essential feature of an IGBP, 

a wide variety of shorter-term experiments will also be necessary. For 

example, experiments designed to identify the currently elusive sources of 

atmospheric methane and nitrous oxide and to understand better the 

processes responsible for the formation of ocean bottom water are equally 

important. 

Satellite observations have been recognized as important potential 

contributors to further advances in almost all of the earth sciences. For 

an IGBP we emphasize specifically the essential role of satellite 

observations for studies of the global physical environment and global 

biota. However, we also emphasize that for some objectives satellite 

measurements alone are of limited use and that in situ measurements are 

essential to aid in the interpretation of remotely sensed data. 

In addition to observations, an IGBP will clearly demand significant 

new efforts in data processing and analysis and in the further 

development of global models incorporating all the important biological, 

chemical, and physical processes. In this respect we emphasize two 

particular needs: first, interactions among the involved disciplines and 

second, intensive work in areas of particular need or current relative 

ignorance One useful way to address both of these needs is to conduct 

focused workshops with well-defined goals at both the national and 

international levels. 

While activities such as the launching of satellites and the 

development of general circulation models are capabilities possessed by 

relatively few countries, many other experimental and theoretical 

activities in an IGBP (such as surface observing networks and many 

aspects of data analysis) provide the opportunity for all countries with 

interested scientists to make fundamental and essential scientific 

contributions. In this respect, we emphasize that the extensive data base 

relevant to an IGBP should be quickly accessible to all interested 

scientists, as should the results of the associated analyses, models, and 

tests. A comprehensive data bank employing modern techniques of data 

storage and worldwide access is a task of great magnitude--and perhaps 

the largest single challenge of an IGBP. The Committee recognizes this 

requirement as essential to the success of the program. 
ELEMENTS OF A PROGRAM 

RELATIONSHIP TO OTHER PROGRAMS 

There are now in progress a number of international research 

programs aimed at specific components of what we have called the 

geosphere-biosphere system. Many of these, with others now in planning 

stages, will continue into and indeed beyond the era of an IGBP. What 

is the optimum relationship between these more disciplinary programs 

and a multidisciplinary IGBP? 

A possible model, which we reject, is a simple federation. of the 

varied, international disciplinary programs under a single banner of 

coordinated research: in effect, the erection of an umbrella over all the 

diverse activities that study the Earth and its biota and near 

environment. Such an approach seems to us neither workable nor 

desirable, nor one that would meet the goal of understanding the Earth 

as a coupled system. 

We propose instead a separate and more restricted endeavor, defined 

by a focused objective of the kind that we have developed here. An 

IGBP of this design would not subsume or replace other more 

disciplinary programs. It would communicate with and to some extent 

depend on them, however; and the existence of one would enhance the 

scientific returns of the other. The principal goal of an IGBP--to 

understand the Earth as a coupled, interactive system--and the new 

information that it seeks to find are not the primary ends of other 

international programs of research. Certain elements of the World 

Climate Research Program, the International Lithosphere Programs or an 

International Solar Terrestrial Program, for example, will make necessary 

inputs to an IGBP, and other elements will not. 

A final point is the relationship of preliminary studies within this 

country, such as that described here, to an eventual plan for an IGBP. It 

is clear to all that an international program must be internationally 

planned and internationally agreed on if it is to be internationally 

executed. At this time the International Council of Scientific Unions is 

considering the implementation of an International Geosphere-Biosphere 

(or Global Change) Program, with inputs solicited from many nations 

and international scientific organizations. We hope that the 

recommendations developed here will be useful contributions to this great 

dialogue. 
End of Document