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Annu. Rev. Energy Environ. 1998. 23:25–82
c 1998 by Annual Reviews. All rights reserved
Copyright °REWARDS AND PENALTIESOF MONITORING THE EARTHCharles D. Keeling
Scripps Institution of Oceanography, La Jolla, California 92093-0220
KEY WORDS:

monitoring carbon dioxide, global warming

ABSTRACT
When I began my professional career, the pursuit of science was in a transition
from a pursuit by individuals motivated by personal curiosity to a worldwide
enterprise with powerful strategic and materialistic purposes. The studies of the
Earth’s environment that I have engaged in for over forty years, and describe inthis essay, could not have been realized by the old kind of science. Associated with
the new kind of science, however, was a loss of ease to pursue, unfettered, one’s
personal approaches to scientific discovery. Human society, embracing science
for its tangible benefits, inevitably has grown dependent on scientific discoveries.
It now seeks direct deliverable results, often on a timetable, as compensation
for public sponsorship. Perhaps my experience in studying the Earth, initiallywith few restrictions and later with increasingly sophisticated interaction withgovernment sponsors and various planning committees, will provide a perspectiveon this great transition from science being primarily an intellectual pastime ofprivate persons to its present status as a major contributor to the quality of humanlife and the prosperity of nations.

CONTENTSPROLOGUE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1928–1953: GROWING UP WITH SCIENCE AND THE ARTS . . . . . . . . . . . . . . . . . . . . . .
Parents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Early Years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
School Years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Graduate School . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1953–1956: A PERIOD OF GREAT OPPORTUNITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I Find A Research Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1956–1963: IMPLEMENTING A GLOBAL PROGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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KEELINGThe International Geophysical Year . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
First Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mission Accomplished . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1964–1975: THE STRUGGLE BEGINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rising Interest in Rising Carbon Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
First Signs of Trouble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Real Trouble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1976–1980: THE RISE OF MISSION-ORIENTED RESEARCH . . . . . . . . . . . . . . . . . . . . . .
The Department of Energy Embraces Carbon Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Negotiating with Three Agencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MORE OBSTACLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A Short Reprieve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A Mandated “Convergence” Effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Struggling with the Standardization Issue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCIENCE IN SPITE OF POLITICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Why Go On? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
More Discoveries from Time-Series Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Linking CO2 Data to Global Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Where Do We Stand? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EPILOGUE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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PROLOGUE
At editorial request, the following sketch is focused on a particular aspect of
my career: my desire to measure atmospheric carbon dioxide. For much ofmy professional career, this desire met with heavy opposition from certain
agencies of the US Government that wanted such measurements to be managed
principally, or even solely, as in-house programs of the federal bureaucracy. I
have attempted to intertwine the portrayal of this struggle with a narrative of the
concurrent gain in knowledge from my measurements which repeatedly helped
me to argue for their continuance.
As biographical background, I begin with a general account of my childhoodand school years, followed by how I first became involved in measuring carbon
dioxide. With the beginning of the disputes with the agencies, most of what
follows bears, however, specifically on my studies of atmospheric carbon dioxide, although throughout my career at the Scripps Institution of Oceanography
I also pursued studies of the carbon cycle in the oceans. Near the end I remark
on some of the consequences of the inexorable increase in carbon dioxide in
the air, which I have witnessed first hand for over 40 years.

1928–1953: GROWING UP WITH SCIENCEAND THE ARTS
Parents
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homestead. After completing the eighth grade in a two-room school house, hewent to work as a farm hand and lumber jack. In contrast, my mother grew up
near Boston in a family that cherished tracing its ancestry back to the American
Revolution.
Shortly after my father finished grammar school his mother died. Soon after
that, his father contracted Rocky Mountain spotted fever and almost died. The
farm was abandoned. Moving with his father and two sisters to the West Coast
just as the First World War was ending, he worked in a Seattle shipyard andthen joined the Merchant Marine. On his first cruise he aspired to become an
officer. Told that this required a high-school education, he returned to Seattle,
completed high school in 3 years, and won a scholarship to Yale University.
Lacking a knowledge of Latin, necessary for earning a Bachelor of Arts degree,
he was awarded the rarely bestowed degree of Bachelor of Philosophy when hegraduated in 1927.
At Yale he met my mother, who had become a graduate student in English
Literature—rare for a woman at that school in those times. Marriage terminatedher graduate work. I was born in 1928. Two years later the family, now including
a baby sister, moved to Illinois where my childhood was spent in a successionof Chicago suburbs.
My father was profoundly influenced by his education at Yale. His childhood
beliefs, strongly conditioned by teachings from the Bible, were repeatedly challenged by his studies in sociology and natural history. In 1929, in Chicago justbefore the stock market crashed, he joined an investment banking firm. During
the ensuing Great Depression, although personally successful, he became distressed about the economic future of our nation. In the late 1930s he quit his
work in order to study, teach, and preach banking reform, thereby plunging ourfamily into the poverty he was distressed about. Toward the end of his relatively
short life, he collaborated with economists of the University of Chicago in trying to explain the business cycle. He had become convinced that booms andbusts stemmed from expansions and contractions of the money supply largely
under control of the banking system.

Early Years
Growing up in the midwest near Chicago, I was exposed so extensively to
my father’s ideas in economics and banking that I abandoned a curriculum inchemistry at the University of Illinois simply to avoid taking a required coursein economics. I was nevertheless sympathetic to his ideas and to his faith thatthe world could be made better by devotion to just causes.
My father had a general knowledge of science and mathematics, which hemade use of near the end of his life while studying the business cycle. When I
was about five years old, he excited in me an interest in astronomy. In a darkened

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KEELINGroom, he showed me how the seasons came about. He carried the “Earth,”
represented by a globe, with its north pole always pointed in the same direction,around the “Sun,” represented by an electric light placed in the middle of theroom. With a child’s urge to imitate, I volunteered to repeat the demonstration myself, beginning a life-long curiosity about the universe. I even made anuisance of myself in the fourth grade by attempting to correct a teacher who
was telling the class that the phases of the Moon were caused by eclipses. My
father taught me to recognize the constellations of the stars and to be in aweof the smallness of our Earth in a vast universe. As soon as I could, I began
reading about astronomy, especially a popular book on cosmology by Sir James
Jeans that I found in our small town public library.
My mother brought to my childhood a different perspective. She confessedto an almost total lack of understanding of science, which she illustrated bysaying that physics had something to do with a straight line being the shortest
distance between two points. She had a high regard for books and literature,and encouraged my sister and me at an early age to read the great childhoodclassics. She also sang and played the piano, starting me on piano at the ageof five. I took formal lessons through my childhood. For a time my parents
expected me to become a professional musician. When I was in the eighth
grade, they allowed my overzealous piano teacher to arrange that I be booked
to play for various women’s clubs in Chicago. Every few weeks that year I had
to find my way alone to luncheon meetings in Chicago suburbs, situated morethan an hour by train from our home. As prearranged the previous fall, I would
play for the ladies either a short concert for $5 or a longer one for $10. After
short concerts, I usually had to endure a speaker who shared the program withme. I often felt out of place but did not know how to excuse myself. After thatexperience, as far as seeking a livelihood was concerned, my interest in science
prevailed over music, although I continued to pursue music as an avocation.

School Years
In Libertyville, Illinois, where I attended school from the fifth grade on, formal
training in science began in high school. The offerings were limited. Though
I was not predominantly interested in science, I took all the advanced courses
offered: biology, chemistry, physics, and preflight aeronautics, the latter a special wartime offering that gave me glimpses into aerodynamics, meteorology,
navigation, combustion engines, and radio. All of these courses were taught by
the same instructor.
In the late spring of 1945, with the Pacific Rim still a theater of war, I
enrolled in a summer session at the University of Illinois to acquire a year of
higher education before being drafted into the army. I had just turned 17. It
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choice. Engineering and physics, however, were taught on a different semester
sequence than liberal arts. In physics I was able to take only an introductory
course, taught without calculus to huge classes of freshmen. I chose to major
in chemistry. I didn’t particularly like chemistry and repeatedly doubted that I
had made the right choice.
Soon the war was over and the draft age was raised to 19. I kept going tocollege.
At the beginning of my third year at Illinois, I abandoned the school’s curriculum in chemistry. This was partly a result of being disenchanted with arequired course on how to use the library for such boring tasks as looking
up organic chemicals in a compendium called “Beilstein.” The direct reason,
however, was to avoid a required course in economics. I felt quite passionatelythat my exposure to economics at home had been enough. Refused a waiveron the grounds that chemists should all be exposed to economics, I elected to
become a general liberal arts major. As an unexpected outcome, I needed fewer
credits to graduate. After 7 semesters, I graduated in the spring of 1948 andhad to decide what to do next. When entering the university, I had drifted into
chemistry without much thought of the consequences. Now I took the easiest
route again.

Graduate School
My mother had grown up next door to a family named Dole. One of the sons,Malcolm, about her age, had graduated from Harvard, married, and become aprofessor of chemistry at Northwestern University. During my childhood, theDoles and my parents often played card games together. I attracted Dr. Dole’s
attention at the age of 5 or 6 by multiplying two-digit numbers, using sometrick technique I had learned from my father but can today no longer recall.
I probably hadn’t mastered all combinations, but my demonstration evidently
impressed Dr. Dole. He kept me in mind and in 1948 offered me a graduate
fellowship at Northwestern. I accepted without applying to any other school.
Accepting so soon was probably a mistake. I had just turned 20 with only
a minimal education in chemistry, albeit from a university department with agood reputation. My work ethic was to follow directions on a short-term basis.
On my first day at Northwestern, Professor Dole asked me to clean up thechemistry laboratory where I would work. When I reported back for the next
assignment, Dr. Dole dropped what he was doing and found me a new task. I
donned pallbearer’s gloves, provided for cleanliness, and he taught me to makeweight measurements on an analytic balance. Over the days that followed, Iinterrupted him many times, asking for additional instructions.
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KEELING

to appreciate. I tried for a long time to read the texts, but I couldn’t concentrate.
Dr. Dole was freed from having to give me close attention, but gradually he had
deeper and deeper misgivings about his choice of a new graduate student.
For the next two years I took the prescribed graduate courses. I worked hardand passed the courses, but I allowed myself little time to accomplish anything
in the laboratory to earn my fellowship. During the second year, by department
rules, I was obliged to declare a “noncontiguous minor” area of study. The
chemistry students usually chose a subject area as close to chemistry as possible. I saw an advantage to the flexible rule, however. I proposed astrophysics,
a subject in which I had no previous instruction, but which was related to mychildhood interest in astronomy. Dr. Dole surprised me by asking if I might
not want to major in astrophysics.
Upon investigation, I found that Northwestern University did not offer thenecessary instruction. Some months passed. One day while visiting a college
friend who was still at the University of Illinois, I noticed a text on his shelf inwhich even the title contained a word incomprehensible to me: Glacial Geology and the Pleistocene Epoch, by John Foster Flint. I read into the book far
enough to learn what Pleistocene meant. Back at Northwestern, I bought a copy.
Reading it was pleasurable between experiments in the laboratory. I imagined
climbing mountains while measuring the physical properties of glaciers. Herewas a new idea for a noncontiguous minor. I proposed geology to Dr. Dole,
again a subject in which I had no previous instruction.
Dr. Dole looked at me thoughtfully. “Would you perhaps like to major ingeology?” he asked. I said no, I would still major in chemistry. This settled,
I started taking undergraduate classes in geology, beginning with engineering
aspects, because the course being offered quickly covered the fundamentals. I
went on to complete most of the basic undergraduate courses, except for lengthy
labs and field excursions that I couldn’t find time for.
Twice I interrupted my studies during the summer to hike and climb inthe glacier-decked Cascade Mountains of Washington State. I prolonged thesecond of these excursions by accepting an invitation to join a canoe trip in
Ontario, Canada, when one of the scheduled canoeists had to drop out. Of thistrip I have lasting memories of great “jack pine” forests and muskeg swamps in
the rain. Dr. Dole was more than a little upset by these diversions, but I rationalize now that they were worth the price, not only for my exposure to landscapes
but also because I later married a sister of the canoeist who had dropped out.
In 1953, I completed a dissertation on polymers under Dr. Dole, taking
what was then the extraordinarily long period of five full years. I had alsoacquired a working knowledge of geology, weak in laboratory and field work,
but adequate for me to consider applying for a postdoctoral fellowship in ageology department.

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On the other hand, my thesis in chemistry had received national attention.
The cover of an issue of Chemical and Engineering News in 1953 showed
Dr. Dole standing beside a complicated apparatus built by another graduate
student for a different project. Dole was quoted as the discoverer of a new kindof “long-range migration of chemical activity.” This was because my thesis had
suggested that double bonds between carbon atoms in polyethylene moved tothe ends of polymer chains when subjected to a high-energy beam of neutrons.
Although I hardly grasped it then, the opportunities for new PhDs were atnearly an all-time peak. There had been a shortage of PhD chemists ever since
the recent world war. The shortage was still acute. Few chemistry majors at
Northwestern investigated low-paying postdoctorals at universities. Dr. Dole’s
graduates were going directly to major oil companies and the like. I was offeredemployment by large chemical manufacturers, most of which were located in
the industrialized cities of the eastern United States. Polymer chemistry was
important to industry because exciting new plastics were being developed.
There were few new PhDs versed in polymer chemistry. Moreover, I had
acquired a modest understanding in another important field, nuclear chemistry,
because my thesis, suggested by Dr. Dole, had involved irradiating polymers
with neutrons. In more recent times it would have been risky to pass up such
good job offers. To Dr. Dole it even then seemed foolhardy to do so. He told
me that I shouldn’t shun a job just because it was located in the eastern UnitedStates: One could enjoy life wherever one ended up working.
I had trouble seeing the future this way. I wrote letters offering my services as
a PhD chemist exclusively to geology departments west of the North American
continental divide. In general, I received back polite declining letters, but I
got two offers. I accepted an invitation from Professor Harrison Brown of the
California Institute of Technology in Pasadena, California, where he had recently started a new department in Geochemistry. I became his first postdoctoral
fellow.

1953–1956: A PERIOD OF GREAT OPPORTUNITY
California
Southern California was enthralling even though, owing to a peculiar haze inthe air, the high mountains immediately behind Pasadena remained steadfastly
invisible for weeks after my arrival. I penetrated them by car on winding roads
that took me into clear air and pristine pine forests. A visitor from Switzerlandroomed with me. He had relatives living nearby who had built a stone cabinhigh in the San Bernadino mountains, accessible only by foot. We visited itafter the first autumnal snowfall. Also, I soon found musicians to play ensemble
music with, and I got married.

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KEELINGMy only problem was finding a scientific research topic to pursue at Caltech.
A graduate student was assigned by Professor Brown to help me. In a dark
subbasement of the Caltech geology building was an ear-piercing, dust-belchingrock crusher. The student needed to have a lot of rock crushed for an experimentfunded by the US Atomic Energy Commission. He asked me to crush rock for
two weeks to gain practical experience in geochemistry.
A grant from the Atomic Energy Commission was paying my salary. I had
agreed in advance to work for the grant’s principal objective—to derive nuclear
power from the uranium contained in ordinary granitic rock. It was logical to
ask me to learn to crush rocks, but I was very proud of my new PhD. I didn’t
think two weeks were needed to master the science of rock crushing.
I hesitated to get started, sitting in my new office space each succeeding day
reading about geology. I began to audit geology courses. I probably made aterrible impression on some of my associates, who expected me to commencesome visibly useful activity; but Professor Brown didn’t express concern.
One day, while I was in his office with some others of his group, Brown
illustrated the power of applying chemical principles to geology. He suggested
that the amount of carbonate in surface water and near-surface ground watermight be estimated by assuming the water to be in chemical equilibrium withboth limestone and atmospheric carbon dioxide.
To test his idea, I decided to set up a field experiment. This would provide
me with the kind of practical experience I really wanted. I could fashion chemical apparatus to function in the real environment. The work could take place
outdoors.

I Find A Research ProjectWith Professor Brown’s consent, I postponed the study of uranium in graniteand set about building a device to equilibrate water with a closed air supply. I
acquired a hand-operated piston pump. Through a nozzle it could spray waterfrom a natural source onto the wall of the glass chamber to bring about athermodynamic equilibrium between the carbon dioxide (CO2) dissolved in thestream of water and gaseous CO2 in the chamber. The water then exited througha drain, and I stored the equilibrated air in the chamber, which was exchanged
for another in the next sampling exercise. Also, I saved a separate portion of
the sampled water. This I acidified back at Caltech to convert the dissolved
bicarbonate and carbonate salts to CO2 gas. I built a vacuum extraction system
to isolate, in a cold trap, the CO2 gas from each sample of air and acidified water.
As a refrigerant I used liquid nitrogen, which had recently become available
commercially.
To measure the precise amounts of CO2 trapped by the liquid nitrogen somekind of gas manometer was needed. Searching about, I found a 1916 journal

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article describing a device that confined a space above a column of mercury,the latter held at a fixed height by gas pressure, which could be adjusted andmeasured precisely. I modernized the design and engaged a glass blower toconstruct the instrument from drawings. This constant-volume manometer performed to an imprecision of about one thousandth of the measurement, as wellas or better than any other available procedure for measuring CO2 in air or
carbonate in water.
The equilibrator seemed to work when I tested it out on a tiny creek near
Pasadena. The setting was not very natural, however, and the measurements
didn’t appear to be very valuable. Permission was granted for me to go up
the California coast to a state park near Monterey, where the Big Sur Riverflowed out of a mountain wilderness into the Pacific ocean. The area contained
calcitic rocks where the ground water would presumably be in good contact
with limestone.
Before going to Big Sur I began to worry, however, about assuming a specified
concentration for CO2 in the air based on a search of the scientific literature. This
concentration had to be known precisely for comparison with the CO2 measured
in the equilibrator. Published values of atmospheric CO2 concentration varied
widely. After finding little guidance beyond an oft-repeated statement that theconcentration was about 0.03% of the content of air, I decided to make direct
measurements. To do so I had a dozen 5-liter glass flasks constructed, eachclosed off with a stopcock to hold a good vacuum. I weighed them empty
and filled them with water to determine their volumes. As a rehearsal for fieldstudies, I collected sequences of air samples on the roof of the geology building
at Caltech. I extracted the CO2 with my vacuum line, measured its amount withmy new manometer, and calculated its concentration in each sample.
The concentrations that I found varied significantly. It was obvious that
Pasadena’s air was often affected by CO2 emissions from industry, car exhaust, and backyard incinerators. Further measurements in the city seemed
unproductive. I turned my attention to sampling air and water in Big Sur StatePark.
It was a full day’s drive to Big Sur. Not being sure that the CO2 even inpristine air next to the Pacific Ocean would be constant, I decided to take air
samples every few hours over a full day and night, as well as a series of water
samples.
Why did I devise such an elaborate sampling strategy when my experiment
didn’t really require it? The reason was simply that I was having fun. I liked designing and assembling equipment. I didn’t feel under any pressure to produce
a final result in a short time. It didn’t occur to me that my activities and progressmight soon have to be justified to the sponsoring Atomic Energy Commission.
At the age of 27, the prospect of spending more time at Big Sur State Park toP1: PSA/spd

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myself carving out a new career in geochemistry.
I did not anticipate that the procedures established in this first experiment
would be the basis for much of the research that I would pursue over the next
forty-odd years. Nor did I give much thought to the consequences of following
up on a proposal of Professor Brown’s close associate Dr. Sam Epstein. Epstein
was carrying out new isotopic studies in geochemistry, following the lead ofDr. Harold Urey at the University of Chicago, where Epstein had earned his
PhD. Urey’s former chief engineer, Mr. Charles McKinney, had been hired at
Caltech and had built a mass spectrometer to measure the carbon and oxygenisotopic ratios of CO2. Epstein urged me to save the CO2 samples that I wasgathering from air and water and measure their isotopic ratios. I took his suggestion. This turned out to be an important addition to my study, although it
had no direct bearing on testing Professor Brown’s original hypothesis of acarbonate equilibrium in water.
Contrary to Brown’s hypothesis, river and ground waters at Big Sur andseveral other sites typically bore a higher pressure of CO2 than the equilibrium
value for the air. CO2 levels were so high in water issuing from a cold springin limestone near Big Sur that much of it was evidently coming from oxidizedorganic matter.
I soon focused my attention, however, on obtaining more measurements of
CO2 in air, because these data showed an intriguing diurnal pattern. The air
contained more CO2 at night than during the day. Also, the heavier carbon-13
isotope of the CO2 at night was depleted with respect to the lighter carbon12 isotope, as though the CO2 that caused the nighttime rise had been released by the plants and soil. The degree of depletion of carbon-13 for a givenrise in CO2 concentration varied from site to site in a manner suggesting thatthe plants during daytime at some sites reabsorbed CO2 previously released
into the air locally the night before. To understand these findings I began toread the literature bearing on plant growth and on the meteorological conditionof the air near the ground at night.
The diurnal patterns were similar everywhere I went, from the rain forestsof the Olympic peninsula near Canada to the high mountain forests of Arizonanear Mexico. (US National Forests at that time had large tracts of land notyet disturbed by logging.) Moreover, the air in the afternoon seemed always
to have nearly the same amount of CO2, about 310 parts per million (ppm) of
air, after correcting for water vapor. The concentrations were highly variable atnight and always higher than in the afternoon. Also, the carbon isotopic ratios
in the afternoon were all about the same, though systematically variable withconcentration at night.

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The scientific literature didn’t suggest that daytime concentrations should beso similar from place to place. A recently published book on geochemistry (53)indicated that arctic air could contain as little as 150 ppm, tropical air as much as
350 ppm. Moreover, photosynthesis by plants in the area of my sampling shouldhave drawn CO2 down during the day, making the concentration lower than in air
over bare ground. I broadened my study by sampling on a high mountain duringstrong winds over barren ground. Also, Professor Norris Rakestraw, a marine
chemist at the Scripps Institution of Oceanography in San Diego, California,
kindly took samples for me over tropical waters of the east Pacific Ocean.
Even at these places, sampled in the free atmosphere, the concentrations andcarbon isotopic ratios were nearly the same as in the afternoon near vegetation(30, 32). Why didn’t photosynthesis, which takes CO2 out of the air during theday, cause low and variable concentrations when respiration by plants and soil,
which puts CO2 into the air at night, causes high and variable concentrations?
I found an explanation in a book that attracted my attention because of its apt
title: The Climate Near the Ground (21). All of my forest measurements had
been made during fair weather. On such days heating by the Sun typically induces enough turbulence in air near plants to cause thorough mixing of thisair with the free atmosphere by early afternoon. Where I had sampled, the free
air evidently had been of nearly constant composition with respect to CO2. In
contrast, during the nighttime the air near the ground cooled, forming a stablelayer that allowed CO2 from respiration to build up within the forest canopy.
The highly variable literature values for CO2 in the free atmosphere were
evidently not correct.1 Rather, a concentration of 310 ppm of CO2 appeared toprevail over large regions of the northern hemisphere. I had detected this nearconstancy under the implausible circumstances of studying air in old-growthforests where variability was to be expected. By 1956 my broader findings ofsurprising near-constancy seemed to me secure enough to communicate themto others, including an employee of the US Weather Bureau. Meanwhile, I
gave up the study of river and ground water that had first led me to measuring
atmospheric CO2.

1956–1963: IMPLEMENTING A GLOBAL PROGRAM
The International Geophysical Year
In 1956, the US Weather Bureau was a decidedly lean federal agency, dedicatedto forecasting the next day’s weather. Nevertheless it included a Division of
Meteorological Research guided by an energetic director, Dr. Harry Wexler.
Wexler had deployed an ozone scientist, Dr. Oliver Wulf, to Caltech. I spoke
1 I believe now that some of the late nineteenth century data were nearly correct (20).

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to Wulf about my measurements of atmospheric CO2, and he told his boss
about them. Wexler invited me to Washington. There I showed him my datasuggesting that the amount of CO2 in the open atmosphere might be far lessvariable than was generally believed.
My trip to Washington was by air, my first-ever ride in an airplane. Wexler’s
haunts were a suite of crowded offices at the old Weather Bureau quarters at
24th and M Streets. Wexler seemed to be in a hurry, with many things on
his mind. He quickly accepted my new data as relevant to a major Weather
Bureau project recently formulated as part of a worldwide program identified
as the International Geophysical Year, IGY for short. The Weather Bureau wasalready planning to measure atmospheric CO2 at remote locations during the
IGY. Wexler showed a particular interest in my having successfully sampled
air on a high mountain and suggested an exciting prospect: sampling at a new
meteorological observatory that had been built by the Bureau the year before on
the Island of Hawaii. The site was on a slope near the top of a 13,000-foot-highvolcano called Mauna Loa. Wexler had taken a personal interest in getting thisobservatory built, and was keen on its being utilized.
I expressed to him a concern that conventional measuring of CO2 during the
IGY might just lead to more data of the kind that I believed to be unreliable. Hevery quickly seemed convinced, and we talked about beginning a new kind of
program. I had briefly investigated some commercially available instrumentsthat could measure atmospheric CO2 continuously. These devices detected infrared radiation from a glowing coil of wire after the radiation passed througha cell in which a stream of air flowed. A radiation detector at the other end of
the cell determined how much CO2 was in the air stream. Perhaps several ofthese infrared gas analyzers could be placed strategically around the world. I
proposed that my new manometric technique could be used to calibrate themprecisely. Also, samples of air could be collected in 5-liter glass flasks at additional locations and returned to a laboratory to be measured by one of these
instruments. Flask samples would furthermore provide much wider coverage,
since continuous gas analyzers would be difficult and expensive to operate atmore than a few remote locations.
Without hesitation, Wexler supported continuous CO2 measurements at
Mauna Loa and at Little America, the latter Admiral Bird’s famous Antarctic
station of the 1930s, to be reoccupied during the IGY. After less than an hour
had past, he directed me to files of Weather Bureau stations, so that I could
tentatively choose additional sites suitable for flask sampling. He also sent me
to Dr. Sigmund Fritz of the US Air Force to discuss sampling air on routine
reconnaissance flights of the Air Force’s Air Weather Service. The next day hesaw me again briefly and asked me whether I would like to come to Washington
to carry out this program.

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I was escorted to where I might work. There was no available space at thecrowded 24th and M Streets offices. I was sent to a dim basement of the Naval
Observatory where the only activity seemed to be a cloud-seeding study being
carried out by a solitary scientist named Ross Gunn. I had misgivings about
the prospect for adequate resources to start a project in such a place.
Meanwhile, Norris Rakestraw, who had collected air samples for me overthe Pacific Ocean, brought my atmospheric CO2 data to the attention of
Dr. Roger Revelle, Director of the Scripps Institution of Oceanography, situatedon the Pacific coast near San Diego, California, a two-hour’s drive by automobile south of Caltech. Revelle invited me to visit Scripps with the prospectof a job. I was given lunch in the back yard of the residence of his associate,
Professor Hans Suess, in brilliant sunshine wafted by a gentle sea breeze.
Rakestraw could give me a small room at Scripps. After briefly considering
the alternative of a basement room in Washington, I agreed to come. Wexler
was cordial about this arrangement, agreeing to donate a substantial sum of
Weather Bureau IGY money to supplement funds that Revelle said could be
provided to pay my salary and a little bit more.
I had taken a gamble in advocating continuous measurements of atmospheric
CO2 to both Revelle and Wexler. For only a couple of days at Caltech had I
tested a continuous gas analyzer that might accomplish this. Several companies were marketing such analyzers, developed for military purposes during
World War II. None were designed specifically to measure CO2 in ordinary
air. The manufacturers could not say how well they would work at such low
CO2 concentrations. I had tested a model manufactured by the Applied Physics
Corporation (APC), the only company in which I was able to get past a salesman
and talk directly with an engineer. The APC analyzer, manufactured conveniently close to Caltech, consisted of a thermostated cell, an optical system, andan electronic amplifier, all in a large heavy-metal case. By itself it cost the verylarge sum of $6000. It would cost still more to construct a gas handling system
for it and to provide it with calibrated reference gases and an electric power
supply for use in remote areas with poor electrical generation. Only after one
was purchased with these accessories and tested under field conditions could I
be sure how well such instruments would work.
The International Geophysical Year, in spite of its name, was scheduled to
run for 18 months, beginning in July, 1957. I moved to Scripps from Caltech
in August, 1956, less than a year before the program was scheduled to begin.
Its chemistry component, within the Weather Bureau, was not closely related
to the IGY’s primary mission to study the geophysical effects of an anticipatedmaximum in the solar sunspot cycle. Although I didn’t know it when I showed
up at 24th and M Streets, no one there really knew yet how to spend all thefunds awarded the Weather Bureau for atmospheric chemistry. My proposal toP1: PSA/spd

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Wexler to buy expensive new instruments helped him to allocate some of thismoney.

First Results
As one might have expected, some members of the US IGY steering committee
were not immediately persuaded that it was worthwhile to acquire expensive
equipment to achieve high accuracy in atmospheric CO2 measurements, when
all the published data pointed to high variability. The distinguished Swedish
meteorologist Dr. Karl Gustav Rossby, a strong advocate of CO2 studies, contrasted my grandiose proposal to the traditional approach of making chemicalmeasurements of CO2, adopted in Scandinavia as a prelude to the IGY. Indeed,data already obtained by the traditional method showed a high degree of variability, which Rossby’s researchers ascribed to variable origins of the air masses(18). Indeed, Rossby’s interest in atmospheric CO2 lay largely in using it totag air masses. When he met me during a visit to Scripps, he dubbed me “theman with the machine” (37). Others worried about possible interference fromvolcanic gases at Mauna Loa Observatory because it was situated on an active
volcano. Harry Wexler made a considerable effort to ward off these criticisms(37).
Given the short time before the IGY was to begin, I was allowed right away topurchase four continuous gas analyzer systems. One system each was needed
to measure CO2 continuously at Little America and Mauna Loa. A third wasbought because Revelle wanted one installed on a ship. A fourth was neededin our laboratory to cross-calibrate reference gases and replace the slow direct
manometric procedures for analyzing flasks that I had used at Caltech.
The first APC analyzers didn’t arrive till November. Assembly of the firstsystem in time to be placed on the last ship to go to Antarctica in 1956 was barely
possible. Fortunately this ship was berthed in San Diego. A graduate student
and I worked into Christmas eve to get all of our equipment for Little America
Station on board. The effort to get ready, however, had been too hasty. The
air pumps, copied from those used at Little America for ozone measurements,
failed to deliver pure air. A year went by before suitable replacements arrived
in Antarctica. Flask samples, however, were deployed to the South Pole. In
early 1957 these provided the earliest precise time-series measurements ofatmospheric CO2 at a remote location (19). In 1957, because Little America
was being shut down, our continuous analyzer system was moved to the South
Pole, where it remained until 1963.
Soon after the Antarctic equipment had been sent off in 1956, Wexler, tohasten progress, sent Dr. Gene Wilkens, a full-time Weather Bureau employee,
to Scripps to help me. Meanwhile, Revelle was anxious that the analyzer
designed to measure CO2 at sea, be ready in time for an IGY cruise in the fall

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of 1957. It was to be used to measure CO2 in the water as well as in the air,a logical extension of my equilibrator experiment at Caltech. The equilibrator
system, however, now had to be partially automated for continuous operation.
Prior to the main expedition at sea we ran test cruises, including a long cruise
to Alaska and back.
Revelle was also anxious for the planned aircraft sampling program to start.
The complexities of working with military aircraft made progress slow, evenwith much help from Wilkens. Revelle insisted that this aircraft project take priority over starting up measurements at Mauna Loa, because he believed that themain objective of my program should be to gain a “snapshot” of CO2 around theworld. He still held to the prevailing belief that the CO2 concentration in air was
spatially variable and that therefore sampling must be widespread to establish
a reliable global average during the IGY. Measurements should be repeated in,say, 20 years to see whether the global concentration had noticeably changed.
Averages of the highly variable published data for the twentieth century had
been scrutinized by GS Callendar, an English engineer (12). These data indicated that CO2 in air had been increasing. The rate of rise could be accounted for
if CO2 emitted by burning coal, natural gas, and petroleum had all remained in
the air. Revelle distrusted these data because he thought that the oceans must be
absorbing somewhere near half of this CO2 from “fossil fuel.” Comparing two
carefully documented snapshots would provide a reliable estimate of oceanic
CO2 uptake, given that enough time elapsed to determine precisely the fractionof emissions observed to be staying in the air.
In the fall of 1957, with the IGY under way, I became concerned about thedelay in establishing measurements at Mauna Loa Observatory. The equipment
was ready for installation, but Revelle was reluctant to sign travel orders for me
to go to Hawaii because the aircraft program was not yet operational. Then,in November, Mr. Ben Harlan, who had operated the CO2 equipment at Little
America, conveniently returned to the United States. To prevent further delay
Wexler enlisted him to install the APC analyzer system on Mauna Loa. Thishe did in March, 1958, with the help of Jack Pales, a recently arrived physicistin-charge of the observatory. In advance, I gave advice including a suggestionof what CO2 concentration to expect if the equipment worked correctly. By
assuming that the concentration there would match closely with test measurements of presumably unpolluted air made shortly before at the Scripps pier, I
told Harlan to expect 313 ppm.2 As I recalled (37):
To our great surprise, on the first day of operation it delivered within one ppm
the CO2 concentration that I had told Harlan to expect on the basis of my earlier
manometric data and preliminary test data obtained at Scripps. Of course this2 A provisional value later adjusted (35).

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Figure 1 The daily average concentration of atmospheric CO2 at Mauna Loa Observatory for thecalendar year 1958, shown as dots. (Source: Ref. 51)

agreement was an accident. The mean of the daytime manometric and Scripps data
just happened to be close to the value typical for the month of March. Indeed, thenext month’s data did not agree—the concentration rose by over one ppm. The
following month’s mean concentration was still higher. Electrical power failures
then shut down the equipment for several weeks. When measuring resumed in July,
the concentration had fallen below the March value. I became anxious that theconcentration was going to be hopelessly erratic, especially when the computed
concentration fell again in late August. Then there were more power shutdowns.

Finally, in November I was allowed to visit Mauna Loa and restart the analyzer. As new data emerged without further interruption, the concentrationrose steadily (Figure 1). Then in May it started to decline (Figure 2). A regular seasonal pattern began to emerge, but it differed markedly from earlier
published northern hemisphere data in which the maximum concentration was
typically in January, a month when CO2 from burning is likely to accumulate in
the air near the ground because of temperature inversions (9). The maximum
concentration at Mauna Loa occurred just before plants in temperate and boreal
regions put on new leaves. At Mauna Loa the regular seasonal pattern almost

Figure 2 Same as in Figure 1, but for 1959. (Source: Ref. 51)

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exactly repeated itself during the second year of measurements (Figure 2). We
were witnessing for the first time nature’s withdrawing CO2 from the air forplant growth during the summer and returning it each succeeding winter.
In April, 1958, aircraft sampling came into operation, but I still lacked manometric calibrations. The constant-volume manometer that I had built at Caltech
had remained there for possible further use in other projects. I was determined
to build a more elaborate manometer which allowed very precise determinationsof CO2 over a much wider range of concentrations by having a larger seriesof fixed volumes, all controlled by columns of mercury. Assembly work went
slowly; it took several months to calibrate the fixed volumes using a precise
cathetometer to measure the mercury heights. Not until the spring of 1959, after
the IGY was over, was it possible for me to determine the concentrations of
CO2 in the reference gases employed to calibrate the gas analyzers. I made justenough manometric measurements of reference gases to report the field data ata meeting of the International Union of Geodosy and Geophysics (IUGG) in
Helsinki in August, 1960. The manometer, designed to yield measurements of
CO2 to an imprecision of one ten-thousandth of the measurement, performed
at about one part in four thousand, yielding atmospheric CO2 measurements
precise to 0.1 ppm (22).
At the IUGG meeting there were also presentations of CO2 data obtained by
the chemical methods, and an honorary address by Dr. Kurt Buch, who had
championed atmospheric CO2 measurements in Finland as early as 1920. Atmospheric CO2 measurements at an array of stations over Scandinavia, reported
routinely since 1955 in a new journal, Tellus, were presented.
This Scandinavian program, started by Rossby in 1954, had been a major
factor in triggering interest in measuring CO2 during the IGY. Neverthelessit was quietly abandoned after the meeting, when the reported range in concentrations, 150–450 ppm, was seen to reflect large errors.3 Rejected alongwith the Scandinavian sampling program was Rossby’s hypothesis that CO2
concentration data could be useful to tag air masses (14).
I don’t know how my data were received in Helsinki. The termination of
Scandinavian CO2 data reporting was never explained in Tellus. Probably themain reaction was surprise.
The Scripps CO2 data through March, 1960 appeared in the geophysics journal Tellus the following June, prior to the IUGG meeting (31). The article was
the shortest I ever wrote. The text, under 1200 words, described the main findings: a distinct seasonal cycle of CO2 concentration in the northern hemisphere
3 At two stations in Finland, samples collected by station personnel had been sent to Scripps.
These samples yielded nearly the same concentrations as those measured at Mauna Loa Observatory, proving that the errors in the Scandinavian program were mainly analytical rather than due
to variable CO2 in the air being sampled.

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Figure 3 Variation in concentration of atmospheric CO2 in the Northern Hemisphere. (Source:
Ref. 31)(Figure 3) that diminishes southward, and possibly a worldwide rise in CO2
from year to year. Because I could by then, in retrospect, see a seasonal variation in the carbon isotopic ratios of CO2 in my earlier afternoon data from
Caltech, I proposed that the activity of plants growing on land was the cause of
the seasonal cycle. This activity explained why maximum CO2 concentrations
in both hemispheres were observed in the spring, when most plants begin to
grow. The observed year by year rise in concentration was close to that expected if all of the industrial CO2 from combustion of fossil fuels remainedin the air. Aware, however, of Revelle’s conviction that the oceans must be
absorbing some of that CO2, I noted that longer records might cause a revisionin the estimated rise. This was a good judgment call. In the 1970s, with much
longer records of CO2, a coworker, Robert Bacastow, discovered that a transient
release of CO2 from natural sources, associated with a powerful E1 Niño eventin 1958, had exaggerated the average rise in these early data.

Mission Accomplished
The Scripps CO2 program continued undiminished through 1962, supported by
an extension of funding from the National Science Foundation. In addition tocontinuous measurements at Mauna Loa and at the South Pole, and repetitive
flask sampling with aircraft, measurements were made on suites of flask samples collected on ships. The Weather Bureau continued to supply me with atechnician and took care of operating the continuous gas analyzers at the South
Pole and Mauna Loa Observatory. The CO2 data, registered on continuous strip
charts, were worked up at the sites and on board ship by scaling distances between pen-traces of reference gas and air levels of CO2 by hand. The distances

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were averaged, using adding machines, and then converted to concentrationdifferences by comparison with additional reference gases. The immediate result of my program was to realize the “snapshot” of CO2 from the arctic to theSouth Pole that Revelle had wished for as part of the IGY. Ironically, most of
the data had been gathered after the IGY was over.
Even before the IGY, Rossby had been warned by doctors that he was working
too hard and should take a rest. He paid the ultimate price of not heeding
their advice, dying suddenly of a heart attack in 1957 (6). The Institute ofMeteorology in Stockholm, which he had founded, was left without an obvious
successor. Dr. Bert Bolin, about my age, took over the directorship. He was myhost when I chanced to visit the institute after the IUGG meeting in Helsinki, andhe invited me to spend a year there. He had been trained in the new professionof numerical weather forecasting but took an interest in the chemistry program,started by Rossby. In the summer of 1961, with permission from NSF to takea year’s leave of absence from Scripps, I went to Stockholm with my wifeand three children and began to assess the significance of the “snapshot” dataenvisioned by Revelle. Mr. Tom Harris, who had replaced Gene Wilkens, onloan to the program from the US Weather Bureau, kept the field program goingat Scripps while I was away.
Freed in Stockholm from the daily routine of running a field program, I
assembled all of the Scripps CO2 data. A long-term increase in concentration was present in the data at every location, most clearly seen at Mauna Loa
Observatory (Figure 4). The data showed a distinct seasonal cycle in the northern hemisphere (Figure 5), a weaker seasonal cycle in the southern hemisphere.
These cycles and spatial gradients in the data seemed to reflect natural sources

Figure 4 Annual average concentration of atmospheric CO2 at Mauna Loa Observatory, Hawaii.
(Source: Ref. 8)

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Figure 5 The concentration of atmospheric CO2 at various altitudes in the northern tropics as afunction of the month of the year. January through June (months 1 to 6) are plotted twice to reveal
the seasonal pattern more fully. (Source: Ref. 8)

and sinks of atmospheric CO2, produced by the oceans and terrestrial vegetation,
as well as CO2 from combustion of fossil fuels.
Bolin estimated these presumed sources and sinks using a set of mathematical
functions called Legendre polynomials to characterize the north-south gradients in the mean annual CO2 concentration and in the amplitudes of the seasonal
cycles seen in the data. He applied this technique the next summer while residing on a family farm in central Sweden. It is difficult to imagine in today’senvironment of fast digital computers how he did this analysis. Relying on his
training in numerical forecasting, he copied by hand, to two-figure accuracy, themagnitudes of the first four Legendre polynomials for different latitude bands
and then fitted the CO2 data to these polynomials. Subsequently, also by hand,
he computed the second derivatives of these polynomials and the resulting estimates of the inferred sources and sinks of atmospheric CO2. We reported ourstudy at a meeting on atmospheric chemistry in Utrecht in August, 1962.
While in Utrecht, I learned that Harry Wexler had suddenly died of a heart
attack, probably for reasons similar to those that had contributed to Rossby’s

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death. It was very sad news, which I found out about from his close friend in
the Weather Bureau, Dr. Lester Machta.
My study with Bolin was reported more completely the next summer inBerkeley, California, at an IUGG meeting. By using only the first four Legendre
polynomials in our analysis, Bolin and I focused our analysis on estimating
average CO2 fluxes between the northern and southern hemispheres, between
each pole and the equator, and between middle latitudes and the rest of eachhemisphere. Our analysis was more detailed than an earlier attempt to explain
the Scripps data by Christian Junge (28), but our computed fluxes, in retrospect,
were too large. We had characterized the global atmospheric circulation as
being caused by eddy diffusion. The intensity, assumed to be of the same
magnitude everywhere, was estimated indirectly by supposing that a peak in
CO2 in the middle of the northern hemisphere was due solely to the releaseof industrial CO2 from fossil fuel. This approach wrongly assumed that theCO2 concentration would be the same in both hemispheres in the absenceof fuel combustion. Although the mechanisms are still not well understoodeven as I write, some process causes the concentration of CO2 in the northernhemisphere to be lower than expected in comparison to CO2 in the southernhemisphere (52). Our results could not be seriously challenged, however, until
digital computers, atmospheric circulation models, and considerably more CO2
data all became available two decades later.
During 1963, the first signs appeared that unfettered support of my studies ofatmospheric CO2 wouldn’t be sustained indefinitely by the United States government. The US Congress mandated agency budget cuts for 1964 that seriously
affected any Weather Bureau studies not directly related to weather forecasting.
Mauna Loa Observatory was threatened with closure. Harry Wexler was notalive to defend it. Lester Machta argued strenuously for its survival, using theCO2 program as one of the arguments to prevent its closure. It was saved,
but the staff was drastically reduced from eight to three, including the transfer,
without replacement, of Jack Pales, the physicist-in-charge. Our equipment,at the first glitch in performance, was shut down by the remaining station personnel. Even earlier, in August, 1963, my assistant from the Weather Bureau,
Tom Harris, had been reassigned and left my program. I ordered the continuous
analyzer from the South Pole returned to Scripps but, without Harris’ help, I
did not attempt to send flasks to the South Pole for the next field season. The
ship and aircraft programs were also ended. Suddenly there were no precise
measurements being made of atmospheric CO2 anywhere.
Furthermore, I had postponed investigating possible systematic errors thatmight arise from replacing direct manometric assays of flask samples in themanner of my Caltech study with infrared gas analyzer data obtained by comparing air with manometrically calibrated reference gases. I should have paid

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more attention to a discussion I had had with a spectroscopist, Dr. Lewis
Kaplan, who had viewed our gas analyzer setup early in the program. At theoutset I had been afraid that oxidation might affect stored reference gases, andhad calibration gases prepared as mixtures of nitrogen gas and CO2. Underthe rush of the IGY program I had neglected to prepare at least a few special
gas mixtures in which nitrogen was partially replaced by oxygen to see what
difference this substitution would make. What came to be called the “carrier-gas
effect” was not investigated carefully for almost another decade.
I had seen the budget cut coming early in 1963 and had tried to prevent
its terminating the CO2 program at Mauna Loa Observatory. I even went toWashington to plead for supplemental funding. This had no tangible effect,
however, until the cessation of measurements actually occurred. The National
Science Foundation then found funds to pay for an additional technician at
Mauna Loa. In May, 1964, with Mr. John Chin hired for the task, CO2 measurements were restored there. Through most of 1964 I had the services ofa returning South Pole Observer, Mr. Craig Brown, who helped me to workup for publication the eight years’ worth of data acquired from Antarctica.
This work-up showed that a flask program at the South Pole would suffice toestablish a long-term record now that it was too expensive to maintain a continuous analyzer there. Ironically, the cessation of time-series studies cameafter Bolin and I had published enough results to show that such data wereclearly valuable. I learned a lesson that environmental time-series programs
have no particular priority in the funding world, even if their main value lies inmaintaining long-term continuity of measurements.

1964–1975: THE STRUGGLE BEGINS
Rising Interest in Rising Carbon Dioxide
In 1964 I became a junior faculty member of the Scripps Institution of Oceanography, which had recently become part of a new campus of the University ofCalifornia. With added responsibilities, I only slowly expanded my atmospheric
CO2 program beyond continuing measurements at Mauna Loa and the South
Pole. With the help of former field personnel, I reported the previously collected data (11, 33, 61). I also assisted Mr. John Kelley, who had set up an APC
gas analyzer at Point Barrow, Alaska in 1960 and was obtaining continuous
CO2 data there. I was grateful to NSF for continuing my funding in spite of thefact that published results were slow to appear.
In 1966, a physicist, Mr. Arnold Bainbridge, joined my program and assumed
responsibility for operating the atmospheric CO2 field program. His knowledgeof the emerging computer technology soon made the processing of our data
easier. In 1969 he augmented the program by installing a continuous CO2 gas

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analyzer in his native country, New Zealand. The same year Dr. Chi Shing
Wong, formerly my graduate student now working in Canada, began flask
sampling for us from a weather ship at 50◦ N in the eastern Pacific Ocean(39). By 1970 my program was gathering CO2 data at four stations strategicallyspaced in both hemispheres.
Meanwhile, Mr. Walter Bischof, an engineer working at Bert Bolin’s Institutein Stockholm, set up an aircraft sampling program that led to a better understanding of the vertical mixing of atmospheric CO2 (5). Lester Machta, following
a meeting in 1966 which I attended, laid plans for the US Weather Bureau tobegin a Bureau-run program to measure atmospheric CO2 at fixed locations.
In 1969, I spoke on invitation before the American Philosophical Societyon the implications of rising atmospheric CO2. This rise was of interest, I
said, because if it persisted it was likely to inhibit the escape of heat radiating
upward from the Earth’s surface and bring about a warmer climate—the socalled “greenhouse effect,” although I didn’t use that expression. The Mauna
Loa record, as I had stated on previous occasions, showed a “cyclic patternowing to a seasonal variation in plant activity.” Now we could clearly see that
this pattern was superimposed on a rising trend (see Figure 6). A surprisingfeature in the second half of the record was an “apparent falling off of the slopeof the trend during a period when the rate of CO2 input [from fossil fuels] wasincreasing.” No simple mechanism of oceanic uptake could explain this fall-off.

Figure 6 Long-term variations in the concentration of atmospheric CO2 at Mauna Loa Observatory, with data through 1967. The oscillatory curve is a least squares fit to monthly average
concentrations, shown as dots. The curve is based on an empirical equation containing 6- and
12-month cyclic terms and a secular cubic trend function. The latter is shown separately as a slowly
rising curve. (Source: Ref. 34)

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Perhaps it was a result of plants on land growing more rapidly in the recent past
as a result of “fertilization” caused by higher concentrations of atmosphericCO2, an unusual idea at the time.
The remainder of my talk (34) was inspired by my having helped to write areport for the President’s Science Advisory Council. Roger Revelle, the leadauthor of the report (57), was struck by the fact that the human race was returning
to the air a significant part of the carbon that had been slowly extracted by plants
and buried in sediments during a half billion years of Earth history. He thoughtthat measurable, perhaps even marked, changes in climate might occur from anincreasing greenhouse effect. He believed that careful measurements should
be made to check such predictions.
Echoing Revelle’s concern before the American Philosophical Society, I too
pondered the significance of returning a half a billion years’ accumulation ofcarbon to the air (33). I appreciated his concern because of direct personal
experience, watching CO2 rise from near the oft-stated background level ofapproximately 300 ppm (0.03%) to over 320 ppm. I wondered what the consequences of rising CO2 would be in, say, 30 years:
The rise in CO2 is proceeding so slowly that most of us today will, very likely,
live out our lives without perceiving that a problem may exist. But CO2 is just one
index of man’s rising activity today. We have rising numbers of college degrees, rising steel production, rising costs of television programming and broadcasting, highrising apartments, rising numbers of marriages, relatively more rapidly rising numbers of divorces, rising employment, and rising unemployment. At the same time
we have diminishing natural resources, diminishing distract-free time, diminishing
farm land around cities, diminishing virgin lands in the distant country side... .
[Viewed over thousands of years] I am struck by the obvious transient nature of
the CO2 rise. The rapid changes in all factors I [have just] mentioned, including the
rapid rise in world population, are probably also transient; these changes, so familiar to us today, not only were unknown to all but the most recent of our ancestors
but will be unknown to all but the most immediate of our descendants.

I noted in closing my talk that people held widely divergent views concerning
a possible peril attending rising CO2, but that in 30 years “if present trends are
any sign, mankind’s world, I judge, will be in greater immediate danger than it
is today.”
As it happened I would have little leisure time to pursue such philosophicalthoughts during the next 30 years.

First Signs of Trouble
In the fall of 1969, I and my family spent a pleasant year in Germany as guests
of Dr. Karl Otto Münnich of the University of Heidelberg. I found time to travelwith my wife and five children, ages 2 to 14, packed together in a Volkswagen

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van along with baggage, tent, and an ample supply of German apple juice andAmerican peanut butter, as far south as the Aegean Sea of Greece and northas far as Trondheim, Norway. Although I completed no scientific projects thatyear, I gained an impression of European scientific research that, in my eyes,
fully justified the visit.
Early in my stay, I was asked to be part of a small committee chaired byProfessor Christian Junge, of the University of Mainz, to prepare recommendations for an international program to measure atmospheric CO2. This request of the World Meteorological Organization (WMO) was an opportunity
for me to promote a long-term global-scale CO2 program of the kind I had
started during the IGY. I helped the committee to write a strong recommendation to heed Revelle’s admonition that the carbon cycle should be carefully
watched.
With my family I returned to the United States in the fall of 1970. The report of the Junge Committee had been accepted by WMO and was alreadyinfluencing international planning and even leading to some implementation.
I was surprised to learn that during my stay in Germany, the US Weather
Bureau, now absorbed into a new agency called the National Oceanic andAtmospheric Administration (NOAA), had purchased a CO2 gas analyzer belonging to my program without my being informed. It had been installed
alongside our Applied Physics Corporation (APC) analyzer at Mauna Loa. Thisseemed disturbing. I had arranged the purchase of this instrument together with
two others from a German company, Hartmann and Braun, shortly before thefunding cut of 1964. All three analyzers had remained unused until two had
been taken to New Zealand by Arnold Bainbridge, leaving one at Scripps forparallel testing with our APC analyzers. No testing had taken place, however.
I now protested that the analyzer’s installation at Mauna Loa was premature,and it was returned to Scripps for testing.
Bainbridge meanwhile accepted a managerial role in a new oceanographic
program named GEOSECS. Mr. David Lowe, hired by Bainbridge in
New Zealand, and Peter Guenther, a chemist hired to join my group in 1968,
assumed responsibility for running our continuous CO2 gas analyzer there.
Dr. Carl Ekdahl, another physicist, hired to replace Bainbridge, undertook theparallel testing. This task was not straightforward because we had encounteredelectrical shorts in several of the radiation detectors of our APC analyzers. A
new company that had bought the rights to maintain the APC line of commercial
analyzers had been unsuccessful in repairing the shorts, and the problem had
gradually worsened. Ekdahl arranged for the Scripps machine shop to refurbish
all of the faulty detectors. When at length this work was completed, he began athorough parallel testing of the two kinds of analyzers and even of a third kind,with a still different optical system, called the UNOR.

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KEELINGOne day while we were parallel testing all three types of analyzers, Lowe,
who happened to be visiting us at the time, glanced at the pen traces andsuddenly exclaimed that the UNOR instrument registered atmospheric CO2
concentrations above the reference gas being used as a comparison, while theother two registered below. This seemed impossible! After some moments ofshared astonishment, I felt a sinking feeling as I recalled my conversation 15
years earlier with Lewis Kaplan about a possible carrier-gas effect. Samples of
CO2 diluted with air might register differently from those (like our standards)
diluted by nitrogen gas.
To test for this effect we quickly prepared provisional reference gases containing oxygen as well as nitrogen. We found that different analyzers could havesubstantially different responses to CO2 depending on the proportion of oxygen. The correction for the Hartmann and Braun analyzer was nearly the same
as for the APC but was distinctly different for the UNOR, causing the reversal
we had witnessed. Since all of our data, except those from New Zealand, werebased on APC analyzers and had been calibrated in the same way, our published scientific findings, which depended on spatial and temporal differencesin concentrations, were not seriously affected. Obviously, however, we needed
to establish calibrations based on CO2-in-air standards to compare with otherinvestigations and to allow for a nearly constant bias caused by the carrier-gas
effect.
I was worried, though, that reference gases containing oxygen might be lessstable than gases with only inert nitrogen gas as the carrier. I decided that weshould continue to rely on primary standards containing CO2 in nitrogen; atthe same time, we should prepare new standards of CO2-in-air, thus doubling
our calibration effort. The NOAA people, not waiting for us to complete our
testing program, purchased a new Hartmann and Braun analyzer, which they
installed at Mauna Loa.

Real Trouble
In 1971, shortly before NOAA installed their own analyzer at Mauna Loa, I
submitted to the Atmospheric Sciences Section of the National Science Foundation (NSF) a proposal to support eight full-time scientists and technicians tocontribute to the emerging global atmospheric CO2 program under the auspicesof the World Meteorological Organization. I felt honored when the program
manager for meteorology asked me to expand my funding request to include
a laboratory manager, to give me more time for scientific direction of my program. The proposal was then funded with seven full-time and four half-time
staff positions to assist me. We soon enlarged our array of CO2 stations witha flask sampling site on Fanning Island at 4◦ N in the equatiorial Pacific, andwe began to make continuous measurements of CO2 at the end of an ocean

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pier near our laboratory. Besides a laboratory manager, a second physicist,
Dr. Robert Bacastow was hired to assist Carl Ekdahl in the interpretation of ourdata.
While this new funding cycle was still in its first year, a friend, Dr. RobertCharlson, who was measuring aerosols with a new “nephelometer” that hehad invented (1), sent me copies of letters he had exchanged with the headof the Atmospheric Sciences Section of NSF. He had been informed that his
studies were repetitive and therefore no longer suitable for NSF support. He
protested that his nephelometer had led to well-regarded data and that he wanted
to continue his studies. The NSF section office held fast to its new doctrine.
Charlson lost all NSF support for his research.4
A few months later I was called by the program manager who had awarded
me more funding than I had requested the year before. He now told me thatmy program probably had strayed from basic science. I should tell him whatfraction of my effort was routine. I declared, as had Charlson, that noneof my work could be deemed routine. NSF’s response was that the agency
would decide for me. Half of my program was declared routine. I learned
from Charlson that a NOAA administrator, recently transferred to NSF to become head of the Atmospheric Sciences Division, had introduced this new
doctrine.
After some fruitless additional protesting to NSF, I wrote to Christian Junge
in Mainz, explaining that evidently I couldn’t be part of the new WMO program
unless NSF changed its mind. He wrote to NSF questioning the funding cut.
Here, in part, is the reply from NSF, dated May 17, 1973:
Dear Professor Junge:
I have delayed replying to your letter of March 20 until I had an opportunity tovisit Dr. Keeling and discuss his work with him. I can assure you that we have nointention of unilaterally discontinuing support for Dr. Keeling and his work on CO2
measurements. However, I believe that we in this program must tread a narrow line
between that work which constitutes basic research and that work which constitutes
fairly routine monitoring... . I believe that Dr. Keeling’s work is of sufficient statusthat the scientific community will urge us to continue his support of basic research[italics added].

At first I thought that this last remark might mean that I could continue
my work if I claimed that my measurements were nonroutine. The letter went
4 Charlson continued limited research with funding from the US Environmental Protection
Agency until 1976, when the agency insisted that he address urban aerosols. For the next five years
he managed to investigate natural aerosols, his main interest, during extended visits to Sweden,
where Bert Bolin arranged European funding. He has survived as a distinguished experimental
scientist thanks to this European connection and reinstatement of aerosol funding by the National
Science Foundation in the 1980s.

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KEELINGon to say, however, that, as an “interested scientist,” I would “presumably
be willing” to work on “technical problems” of a “WMO network” of CO2
stations. This evidently meant that I was expected to turn over all actual CO2
measurements under my supervision to agencies dedicated to “monitoring.”
This latter term, new to me in the context of my program, stuck in my mind.
Soon it would be in use in the Atmospheric Sciences Section of NSF as abasis for separating all repetitive observations of nature from the scope of basic
science.
A few weeks after I received this letter, it became clear on which side of
the “narrow line” trodden by NSF I was judged to be. NSF cut my previously
awarded second-year budget from nine to five staff positions. I now appealed
to Dr. Junge for help, stating that I would not be able to solve the carrier-gas
problem without supplemental funding. This was a persuasive argument for
restoration of some of the lost funding, because my program had been the sole
supplier of calibrated reference gases to WMO programs just starting up inother countries, as well as by NOAA, so that their measurements could all be
reliably intercompared. No one else so far had prepared their own standards,
although NOAA personnel were attempting to do so.5
Junge, in response, called for an international meeting of prospective participants in the new WMO program. At this meeting, which took place at Scripps
in 1975, it was agreed to designate our laboratory a “Central CO2 Laboratory of
WMO” to supervise calibrating worldwide and to assist with evaluating instruments and procedures for this new program (59). After protracted procedural
difficulties dealing with the United Nations bureaucracy, Scripps was awarded
start-up funds for two years to carry out calibrating via the recently inaugurated
United Nations Environment Program (UNEP).

1976–1980: THE RISE OF MISSION-ORIENTEDRESEARCH
The Department of Energy Embraces Carbon Dioxide
In 1972, before the funding cut by NSF had taken effect, Dr. George Woodwellof the Brookhaven National Laboratory convened a symposium of biologists
and ecologists to contemplate how increasing atmospheric carbon dioxide might
affect the environment of the Earth’s plants and animals. Invited to participate,
I set about, with my new associates Ekdahl and Bacastow, to explain the significance of this rise in the context of geochemical models of the global carbon
5 NOAA personnel met with me twice, as I recall, to discuss calibrating. They were not impressedby the manometric method, declaring that they had devised a volumetric method that was more
precise. It wasn’t working yet, however.

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cycle (3, 15). Imitating some earlier modeling attempts, we represented thiscycle by interconnected reservoirs of carbon residing on land, in the oceans, andin the atmosphere. We asserted that carbon was exchanged among these reservoirs according to identified physical processes (such as turbulent gas exchange
at the sea surface) and biological processes (such as photosynthesis and respiration of land plants). Aided by new measurements of the radioactive isotope
carbon-14, many of which had been made recently by Professor Hans Suess at
Scripps, we could estimate realistically the amount of carbon passing among
the identified reservoirs. Indeed, Revelle and Suess (56) had already estimatedin this way that about half of the CO2 from fossil fuel production was being
absorbed by the oceans. We now showed that their estimate of oceanic uptake
was close to what we observed in our measurements of rising atmospheric CO2.
We noticed, however, that the measured rate of rise of CO2 didn’t seem steady.
When I had spoken to the American Philosophic Society in 1969 the rate had
recently slowed down, although fossil fuel emissions were increasing. Now in1971 the rate was speeding up. This wasn’t particularly obvious when looking
at the actual Mauna Loa record (Figure 7) but could be clearly seen when a
cubic function, such as I had used in 1969, was fit to the data after subtracting
the average seasonal cycle (Figure 8). This approximately decadal feature, seen
also in the South Pole record, did not correspond to variations in fossil fuel use,
nor could the speeding up of the rate of rise recently be caused by an increase

Figure 7 Long-term variation in the concentration of atmospheric CO2 at Mauna Loa Observatory,
with data through 1971. Monthly data are shown as dots. The oscillatory curve was obtained using
the same function as in Figure 6. (Source: Ref. 15)

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Figure 8 Secular trend of atmospheric CO2 concentration at Mauna Loa. Circles represent monthly
averages, seasonally adjusted by subtracting the 6- and 12-month cyclic terms used in deriving the
curve of Figure 7. The rising curve is a cubic secular trend function as in Figure 6. (Source:
Ref. 15)in plant growth by CO2 fertilization. Thus we didn’t really understand what
was going on.
A year later, in 1973, still another feature of the CO2 rise was discovered.
Bacastow, whose employment had survived the NSF funding cut, noticed that
if he removed the influence of fossil fuel combustion from the South Pole andMauna Loa records, which he could do approximately by subtracting a constantfraction of the computed fuel emissions, residual fluctuations showed up, shorterin duration than the decadal pattern reported at the Woodwell symposium.
Looking for clues in an extensive treatise on climate that had just been published (46), Bacastow6 found a reference to the “southern oscillation,” a featureof tropical climate that neither of us had heard of, consisting of a quasi-periodic
strengthening and weakening of the air pressure difference across the equatorial
Pacific Ocean. He saw that time variations in this gradient matched closely with
6 This occurred, one day, when he was standing in the check-out line at the Scripps Library.
The line was long, but for the diversion of waiting customers there was an inviting display of newbooks on a nearby table. To pass the time, he began examining the table of contents of one of thesebooks and saw an entry labeled “cyclic and quasi-periodic phenomena.” Turning to the text, he
was surprised to find a description of a feature called “The Southern Oscillation.” He had no prioridea that any interannual variation like this existed. He checked out the book, by HH Lamb (46),and soon saw that a plot of the Southern Oscillation (on page 246) tended to match the feature that
he had seen in our CO2 records.

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Figure 9 Southern Oscillation, expressed as an index, and residual rates of change of atmospheric
CO2 at the South Pole and Mauna Loa. The CO2 data were first seasonally adjusted and the influenceof fossil fuel combustion removed. The resulting rates are inverted in the plots for easier comparison
with the Southern Oscillation index. Fully developed El Niño events occurred in 1965, 1969, 1972,
and 1976, and a weak El Niño occurred in 1975. (Source: Ref. 4)

the rate of change in the residual fluctuations for both the South Pole and Mauna
Loa Observatory (see Figure 9). He published his discovery, even though thephenomenon’s cause was elusive (2). The correlation continued to appear inour data (4), as did decadal irregularities in the rate of rise of CO2.
In 1976 we published 14 years’ worth of measurements for Mauna Loa andthe South Pole (35, 36) showing the unmistakable rise in CO2 concentration andits irregular pattern. The long wait to publish after the Brookhaven symposium
was due to my hesitation to present our data to the public formally until thedata could be properly adjusted for the carrier-gas effect. Because of the lossof almost half of our staff in 1973, it took us several years to establish thisadjustment for our laboratory.7
This same year the issue of rising atmospheric CO2 attracted the attentionof a new US administrative division called the Energy Research and Development Agency (ERDA). It had recently been carved out of the US government’s
Atomic Energy Commission (AEC) along with a new Nuclear Regulatory Commission, following accusations that the AEC had not adequately addressed risks
7 It took substantially longer to establish carrier-gas corrections for participants of the WMO
CO2 program, who depended on our laboratory for reference gases.

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KEELINGattending the use of nuclear energy. ERDA continued the AEC task of overseeing national laboratories devoted to nuclear studies but was mandated toconsider energy issues more broadly than the AEC.
Pursuant to this new mandate, the director of ERDA’s Oak Ridge National
Laboratory, Dr. Alvin Weinberg, appointed a Study Group on the Global
Environmental Effects of Carbon Dioxide (58). He did not hide his motive. The
application of nuclear energy to electrical power generation was regarded as
unsafe by a vocal group of objectors to nuclear energy. Owing to the CO2 greenhouse effect, the burning of fossil fuels might be more dangerous to mankind
than any perceived side effects of nuclear energy. It was time to find out.
After brief deliberations the Study Group, chaired by Weinberg, recommended that ERDA sponsor a Carbon Dioxide Effects Research Program. In
July, 1977, as a first step, a group of scientists was asked to prepare a development paper (58). NOAA’s leading proponent of CO2 research was asked to be“interim director.” A “broadly based group of experts” was called on to prepare
papers recommending “what should be done.” I was asked to participate. My
assigned subject area was “the exchange of CO2 gas at the interface of air andsea.” Assigned to set up a worldwide program of “atmospheric monitoring of
CO2” was Dr. Kirby Hanson, a solar energy scientist from NOAA.
The papers we prepared were reviewed at a meeting in February, 1978, shortly
after ERDA had been restructured as the Department of Energy (DOE). As acourtesy, because I was suffering from back pain and didn’t want to travel, themeeting was held at Scripps. The participants were specifically asked in advanceof the meeting to provide advice “on the most constructive way to start spending
DOE CO2 funds to help resolve the uncertainties in the CO2 problem.” This
advice was sought relative to each participant’s assigned area of expertise. Dr.
Hanson, now identified as a CO2 monitoring expert, recommended an extensive
NOAA-funded CO2 program. I stated the case for pursuing the possibility,
highly speculative at the time,8 that the CO2 gas exchange between the air andthe oceans could be established quantitatively by direct eddy flux measurements.
The consequences of these combined recommendations were soon to have a
profoundly negative impact on my ability to pursue CO2 studies.
The first direct signs of this appeared in a hand-delivered copy of an internal“diary note,” which I received in April, 1977. Prepared by the manager of a new“climate dynamics program” of NSF, it memorialized an agency meeting. NSF
staff at this meeting disclosed that funding of “routine monitoring” activities
had continued in my program despite NSF’s doctrine to the contrary. However,1977 would be “the final year” of this support. NOAA personnel at the meetingthen stated that they weren’t ready to assume full responsibility for monitoring
8 And still so, as I write.

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yet. They would assist my program with temporary funding through 1979.
After that, however, “of course they intend to phase out Dr. Keeling’s work
including the providing of standard gases.” WMO personnel, also present at
the meeting, declared that the UNEP funding to Scripps would be phased out
in two more years, since it was only granted to “initiate monitoring activities
throughout the world.” I now realized that there was a coordinated plan to phaseout my entire atmospheric CO2 measuring program.

Negotiating with Three Agencies
At about the same time, I was visited by Willem Mook of Groningen University
and Karl Otto Münnich, my host eight years earlier in Germany. They arrived
together with a mission in mind. Why had I given up measurements of the13
C/12C ratio of atmospheric CO2? Isotopic data of the kind I had collected at
Caltech would obviously furnish valuable additional insight on the working of
the global carbon cycle.
I explained that I had planned to make isotopic measurements when I firstcame to Scripps in 1956. I had even set up and tested an extraction vacuum line
to prepare samples for isotopic analysis back in 1957. Ample air for isotopic
analysis remained in the flasks of our collection program after concentration
analysis. Difficulties with getting isotopic analysis carried out at Scripps, followed by mounting demands on my time, had thwarted my plans till now.
Professor Mook proposed a remedy. A student of his, Pieter Tans, would
soon complete a PhD thesis. He could spend a year at Scripps as a paid-for
postdoctoral fellow. If we prepared isotopes of CO2 from our flask samples,
Mook’s laboratory would run the samples on a mass-spectrometer in Groningen.
The plan was implemented. Dr. Pieter Tans arrived in April, 1978, and withina few weeks activated the extraction line that I had set up 21 years earlier. We
soon had a year’s worth of isotopic measurements completed for La Jolla,
Mauna Loa Observatory, and the South Pole. We published a paper showing
a distinct shift in 13C/12C ratio since 1955 related to fossil fuel combustion(38).
In June, 1978, it was formally announced that DOE had agreed to fund
NOAA to measure atmospheric CO2 in flasks at 20 stations. Soon after this I
was told by the interim director of the DOE CO2 program that, regrettably, theUS government couldn’t continue funding my studies of atmospheric CO2.
The NSF program manager, who in 1972 had said that at least the “basic
research” component of my atmospheric CO2 studies was fundable by his
agency, had left NSF. His replacement, in the new Climate Dynamics Research
Section of NSF, declared to me that I should not apply for any further funding.
I protested, stating that I had just begun a cooperative program with Groningen
University to gather valuable CO2 isotopic ratio data. Soon thereafter I learned

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that NOAA had just arranged to have the US Geological Survey make isotopic
measurements for their CO2 program, disposing of that argument.
In late 1979, after I pressed the issue, the same manager at NSF agreed
to consider funding my program for two more years, if I agreed in advancenot to apply again. To reinforce his determination, and evidently mindful that
NSF relied on peer review to judge proposals, he warned me that he could find“calibrated reviewers” should I be unwise enough to apply again.9 Funding
was then provided for two years, for eight full-time salaries. NOAA and DOE
together contributed 80% of the funding, assuring that managers in these two
agencies were in control of funding, not NSF. A fixed ending date of July, 1982,
was set.
Now I risked taking a sabbatical leave from Scripps. Overcoming my concerns about future funding were the urging of my family, a desire to broaden
my perspective by a second stay in Europe, and an opportunity to interact withProfessor Hans Oeschger and his associates at the University of Bern, who weredeveloping measurements of CO2 trapped in glacial ice in hopes of extending
atmospheric CO2 data over thousands of years.
One of my sons, Ralph, who had just begun graduate studies in environmental
science, was also invited to come to Bern to assist a graduate student working in
the ice core program. When my family and I arrived in Switzerland, Oeschger’s
student had not been able to achieve a clean separation of CO2 from water in theice samples. He had been told by the overseeing ice crystallographer to thaw
the samples before extraction of the CO2. The student had felt that he couldn’t
defy authority, but with Ralph’s assistance in running experiments and mybacking he had an excuse to try a dry extraction. It led to successful collectionof CO2 data from ice cores. Ralph, who had planned to be theoretician, changed
advisors the next year at Harvard University and became an experimentalist.
Watching the ice core program become a success was one of the motivations
for his change of mind.
Professor Oeschger very graciously provided a highly talented graduate student, Martin Heimann, to work with me on interpreting the Scripps CO2 data.
With a geochemical model portraying sources and sinks of CO2 with northsouth resolution (23, 40), we refined the regional representation of the carbon
cycle that I had worked on earlier with Bert Bolin in Sweden (8). Still more
important as groundwork for a later study, we worked to identify all of the mostimportant components of the global carbon cycle, and to characterize themusing up-to-date geochemical data.
9 While writing this biographical chapter I learned from Dr. Robert Charlson that during thesame year he was advised by the program manager of the atmospheric chemistry program of NSF
not to seek funding for his nephelometer studies. Exactly the same term, “calibrated reviewers,”
was used to reinforce this advice.

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Halfway through my year’s stay in Bern, I was abruptly reminded that myoverall program was supposed to terminate. From the former interim director of
the DOE CO2 program, now in his capacity as director of the new DOE-funded
NOAA program, I received a polite letter, asking me to prepare a “protocol”
to transfer responsibility of my CO2 measurements to NOAA. This letter dated
February 8, 1980, read in part:
Dear Dave: You may recall that as part of the arrangement for funding Scripps
for two years by NSF, DOE and NOAA, it was agreed that you and I (or our
staffs) ought to almost immediately agree on some protocol whereby, if we jointly
agree, responsibility for preparing CO2 standards and measuring atmospheric CO2
at Scripps stations would be transferred to NBS and NOAA respectively. Sucha transfer from Scripps would not reduce funds from the NSF to Scripps during
the two-year period of the most recent contract renewal but it likely would affectthe kinds of work which the three supporting agencies would grant funds for any
further renewal... . Do you have suggestions on how to start our preparation of sucha protocol?... . I hope that we can get past the preliminary exchanges well before
your return to the States, which I presume will be during the summer of 1980... . I
hope you and your wife are enjoying Bern.

I wrote back that I didn’t agree to discontinue my program, citing that the
NOAA program and the USGS isotopic data hadn’t been demonstrated to be ofa quality to make my studies redundant.

MORE OBSTACLES
A Short Reprieve
I returned from Switzerland with my family early in the fall of 1980. I renewed
my protest of the imminent termination of my program. NOAA personnel
at length agreed to a meeting at Scripps where I would have an opportunity toplead that my studies were not redundant with theirs. During the morning on themeeting day in January, 1981, I gave my arguments to the NOAA people withlittle feedback. The director of the DOE-funded NOAA CO2 program complimented my program but once again expressed regrets that the US government
couldn’t any longer afford to fund it.
After lunch, the director of Scripps, Dr. William Nierenberg, presided overa wrap-up session in his outer office. We sat down together around a big table.
Dr. David Slade, now the permanent director of the DOE CO2 program, hadarrived. I regretted that it was he who must ultimately decide the funding issue,
and that he hadn’t heard any part of my morning pleadings. Nierenberg briefly
outlined the problem, and a general discussion ensued. At some point, without
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By accident I happened at that moment to be looking at the director of the
NOAA CO2 program. For a fraction of a second his facial muscles tensed
involuntarily. It was quickly over, but I was sure that he was as much surprised
as I was.10 The meeting soon concluded, with little more said by the NOAA
people.
After the meeting Nierenberg revealed to me that he had talked with Deputy
Secretary Edward Frieman of DOE, who felt that killing my program abruptly
would be unjustified. Slade had followed the secretary’s advice. After peer
review I was granted two years of DOE funding, in an amount equal to the total
previously supplied jointly by DOE, NOAA, and NSF.
My good fortune was shortlived. Ronald Reagan had become President of
the United States. His new administration almost immediately shook up the
DOE environmental program. Dr. Frieman was replaced. Slade soon after wastransferred to an inconsequential job. Slade’s replacement, Dr. Fred Koomanoff,
almost surely under instructions from above in DOE, substantially reduced theoverall funding for CO2 research and promptly informed me that, except forthe 1982 funds already granted, I would receive no more DOE funding. He
made clear his authority to make this decision, because DOE, with the supportof NOAA and NSF, had become the US government’s “lead agency” in CO2
research.
My atmospheric CO2 observing program was again in turmoil. I reapplied
to NSF for funding, this time to their atmospheric chemistry program, where
there was a director who did not heed the earlier “agreement” that I should nolonger seek any funds from NSF. He was nevertheless constrained by the now
well-established doctrine that routine measurements shouldn’t be funded by the
Atmospheric Sciences Division of NSF and was probably further constrained
because of DOE’s status as “lead agency” in CO2 research. Only about one
third of the previously anticipated annual DOE funding was awarded to me by
NSF for 1983.
To gain additional funding I had two arguments. First, our data and NOAA’s
did not agree closely. This wasn’t surprising: NOAA had adopted measuring
procedures substantially different from ours. I argued that our measurements,
especially at Mauna Loa Observatory, should therefore not be discontinued.
Second, the responsibility for primary calibrating of the WMO CO2 program
was still assigned to Scripps. NOAA kept urging that this responsibility betransferred to the US National Bureau of Standards (NBS), to provide a desirably “institutional setting,” but the CO2 experts of WMO were refusing tosupport NOAA’s request.
10 For many years prior to DOE’s setting up a CO program he and Slade had worked closely2
together on joint AEC–Weather Bureau projects.

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Late in 1982, NOAA agreed to fund my Mauna Loa research for one more
year. This funding, however, was for the expressed purpose of coming promptly
into mutual agreement on measurements, so that there would be no further needfor my program.

A Mandated “Convergence” Effort
Measurement agreement would not have been a problem for NOAA if they
had closely imitated the Scripps procedures. From the start, however, they hadplanned a program that would produce more data at lower unit cost. To collect
air they used small flasks more likely to cause contamination on storage thanour 5-liter flasks. At four principle stations extending from Alaska to the South
Pole they had adopted less laborious procedures for sampling the air and forcalibrating continuous measurements there. The isotopic analyses, farmed out
to a laboratory of the US Geological Survey, appeared to be far from satisfactory.
NOAA’s project to prepare their own standards by a volumetric technique had
not worked out. The problem of the carrier-gas effect was still not settled withrespect to the WMO worldwide program, and the willingness of NOAA fromtime to time to swap one type of analyzer with another, without demonstrablyadequate overlap, supported my argument that, for a while at least, my program
should be allowed to continue measuring CO2.
I was now in the uncomfortable position that my program’s survival depended, paradoxically, on a continued disagreement between our data and
NOAA’s. I felt insecure and evaded requests coming from NOAA to tell themour results informally before they told us theirs.
Nevertheless, NOAA and Scripps set about formally to bring about the “convergence” of results. The field exercise was carefully planned. Success wasachieved in December, 1983, but only after both instruments had been adjustedwith unusual care, and we had sequenced our reference gases and matched
our other procedures very closely. The exercise didn’t solve the convergenceproblem, however, because we couldn’t agree on whose procedures were bestfor future “routine” work. I could still claim that our procedures were notredundant with NOAA’s, and might be better.
I argued that Scripps should be allowed to continue measurements at Mauna
Loa simply for the long-term continuity provided. There was no guarantee thatNOAA’s program might not have problems in the future. The CO2 program, I
argued, was important enough that at one spot on the Earth two parallel sets ofmeasurements were justified.
In 1984, NOAA and DOE each agreed to pay part of the cost for Scripps
to continue our measurements at Mauna Loa for one more year to complete areport on the convergence, but Koomanoff refused to grant any more funds from
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about the ending of my observing program. There were still further discussions
brokered by the former NSF program manager, now working for NOAA, whoin 1979 had asked me to cease seeking support from NSF. Then the Oak Ridge
National Laboratory, operated for DOE, agreed to supervise funding for Mauna
Loa studies for two more years, relieving Koomanoff of having to change his
mind about direct DOE funding.
A new program manager from this laboratory in Tennessee appeared on thescene and proclaimed to me new rules of engagement. I was to write a proposal
in which I anticipated two discoveries per year arising out of the data. The
discoveries could not be associated with the results from any other atmospheric
CO2 study or location and were to be programmed with stated “milestones”
anticipating progressive stages in the discovery process. After objecting over
the telephone that such a procedure was impracticable, if not impossible, I
philosophically attempted to comply. Funding for two years was forthcoming
but was not renewed after that. I had evidently failed in this discovery process,or there was no further perceived need for discoveries from Scripps.
Again I faced a budget crisis. A complaint reached Admiral James Watkins,
secretary of DOE during President Bush’s administration, who soon after visited
my laboratory. I heard from a new program manager, who had replaced Fred
Koomanoff, that “my predicament had sensitized all levels of DOE.” My DOE
program was saved for the second time, and remained secure until 1994.
In June of 1994 I received a letter from DOE stating that “research presently
being supported on the topics of the global carbon cycle, and on the responseof vegetation to CO2 will be redirected towards focused efforts related to terrestrial carbon processes (TCP).”11 Existing grants related to CO2, carbon, andvegetation topics were not going to be renewed, specifically including my grant.
This action of DOE, however, was not directed at my research alone; DOE had
decided to cease being the lead US agency for CO2 research and was giving
grantees a year’s warning of the fact. DOE had thus come full turn since Alvin
Weinberg had started the CO2 effects program in DOE to demonstrate that
CO2 released by the burning of fossil fuel might have adverse consequences.
DOE was now seeking evidence that this release might have favorable consequences. The agency didn’t need to support broadly based carbon cycle research
anymore.
Among those who received similar letters I was particularly fortunate because I could claim with some justification that my research would benefit the
new TCP program. Although the latter was conceived mainly to carry out field
experiments to test whether rising CO2 will result in greater uptake of CO2
11 The letter explained this unexpected change of focus by stating that “it is the practice of theresearch program offices [of DOE] to periodically change program direction...through the normal
course of identifying research needs related to the Department of Energy (DOE) mission....”

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by plants and soil and thereby reduce the prospect of greenhouse warming, it
could benefit from global data gathered in my program, simultaneously withdata from the TCP field studies. My program has thus survived to the present.

Struggling with the Standardization Issue
Still greater than my frustration with the attempt of US agencies to restrict
my atmospheric CO2 research for the sake of a doctrine was their determination to institutionalize international calibration of standards, even if to do somight compromise the entire worldwide atmospheric CO2 program of WMO.
In March, 1977, less than two years after Scripps was approved by WMO as a“central laboratory” to maintain worldwide standards, DOE sponsored a conference on global effects of CO2 from fossil fuels, including a special panel
to address future needs of CO2 standards (12). I was not informed. The panel
found that the Scripps standards were “unsatisfactory” and proposed that the
National Bureau of Standards (NBS) issue new standards in which the “total
uncertainty” in any sample “will not exceed 0.1% relative.”12
I was dismayed by this administrative decree because our Scripps manometricstandards were demonstrably more precise than that, and their absolute uncertainty should be hardly greater than the imprecision as soon as the carrier-gas
effect was fully resolved for the WMO CO2 program. For a while the calibrating matter remained quiet, however, as NBS responded to DOE’s request. Our
UNEP funding ceased, however, and we proceeded only very slowly to carryout our calibrational obligations to WMO.
Four years went by. Then in 1981, at a WMO CO2 Experts meeting in Geneva,
Switzerland, an NBS representative claimed that the requested standards goalof 0.1% “uncertainty” had been met. As I reminded the CO2 Experts, they had
previously set a goal of 0.1 ppm or better, whereas the NBS goal was equivalent
to relaxing their goal to 0.3 ppm. The director of the NOAA CO2 program,
who had chaired the DOE standards panel, and was now chairing this meeting,thereupon sought their concurrence to so relax the goal. I argued strongly toretain the previously agreed upon goal. The director was unsuccessful (60).
After the meeting, NOAA nevertheless pressed NBS to make CO2 standards,
without stressing the need for higher precision.
DOE now asked NBS to predict when their standards would be ready. Sensing
WMO’s need for higher precision, NBS pleaded to be given three more years.
DOE responded by providing funding for a convergence of NBS standards
with our standards, constrained by a timetable to assure compliance in three
years. Adequate funds, under NBS supervision, were passed on to Scripps tocarry out our part of the convergence effort. Early on, NBS had decided not to
12 This wording cleverly left ambiguous the distinction between imprecision and absoluteinaccuracy.

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attempt to develop manometric calibrating, in favor of two other approaches.
One was simply to improve a gravimetric technique they had already used toachieve 0.1% uncertainty. The other was an untried isotopic dilution method.
Near the end of the three years, it became evident that they would probably failin both attempts. I learned from dedicated personnel at the working level in
NBS that considerable pressure was then placed on them to meet the originalcontract schedule, irrespective of problems being encountered and a funding
cut imposed by DOE in the third year.
In November, 1985, the WMO Experts met at NBS headquarters to decide
whether to accept the NBS standards. Shortly before the meeting, the DOE
office of Koomanoff, calling attention to the 1977 DOE conference, sent atelegram to all relevant US agencies asking them to concur in a DOE decision
that, because NBS had achieved the uncertainty of 0.1% recommended in 1977,
the agency should now assume responsibility for providing standards for theinternational “CO2 measurement community.” Astoundingly, the agencies wererequested to concur with the DOE statement prior to the WMO meeting.13
The CO2 Experts, notwithstanding this telegram, rejected the NBS standards.
NBS, without prospects of further DOE funding, dug into their own resources toremedy the situation. When they failed again at their next meeting in 1987, theembarrassment caused the principal staff personnel involved to be transferred
to other duties or to leave the agency. NBS gave up their attempt to replace the
Scripps standards.
The NBS failed to provide reliable standards because they could not find a satisfactory substitute for manometric calibrations. Ironically this occurred mainly
because of their “institutional setting.” They consistently rejected “manometry,” as they called it, because this technique was useful only for trace gasesthat could be trapped from air at low temperature. The manometric technique
was not generally applicable to their agency mission.14
Who should prepare international CO2 standards was finally resolved by aspecial panel of the National Academy of Sciences, set up after the 1987 WMO
13 The telegram dated 28 October, 1603Z, stated in part: THE 1977 CONFERENCE
ON GLOBAL EFFECTS OF CO2 FROM FOSSIL FUELS...RECOMMENDED THAT THE
NATIONAL BUREAU OF STANDARDS DEVELOP STABLE STANDARD REFERENCE
MATERIALS FOR MEASURING ATMOSPHERIC CO2 [WITH RELATIVE UNCERTAINTY
OF 0.1% OR BETTER]. THIS TASK HAS NOW BEEN ACCOMPLISHED. I AM THEREFORE PROVIDING YOU WITH A STATEMENT OF THE USA CO2 PROGRAM WHICH ESTABLISHED WITH NBS THE INSTITUTIONAL RESPONSIBILITY FOR PROVIDING CO2
STANDARD REFERENCE MATERIALS TO THE CO2 MEASUREMENT COMMUNITY.
YOUR CONCURRENCE IS REQUESTED BY 31 OCTOBER, PRIOR TO WMO EXPERTS
MEETING IN CALIFORNIA, NOV. 4–8, 1985.
14 I had previously met with NBS personnel on my own initiative to urge their use of our manometric procedures. As I learned later, a formal report was written by NBS personnel rejecting
manometry.

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meeting at the urgent request of Roger Revelle. With NBS out of the picture,
Dr. Pieter Tans of NOAA proposed to prepare manometric standards. The CO2
Experts agreed, and NOAA set about developing procedures. In 1995 WMO
granted NOAA full responsibility for preparing standards and operating theCentral CO2 Laboratory. As I write, the prospect is favorable that NOAA will
be able to maintain precise, stable standards for the WMO program, provided
that decision-makers in the US government don’t someday find standardization
an easy target for funding cuts, an ever present threat to a government agency
carrying out an activity with almost invisible benefits.

SCIENCE IN SPITE OF POLITICS
Why Go On?
Through the long years of my disagreement with government agencies onwhether or not I should be measuring atmospheric CO2, many people wondered
why I tried so hard to stay involved. I will now attempt to explain, although insome respects I’m not really sure.
First, my enthusiasm to study atmospheric CO2 never slackened; it depended,however, on acquiring data that truly reflected nature. The international CO2
monitoring program of WMO, although originally organized by scientists, wassoon mainly under the control of meteorological agencies. After agency managers began to assert that the acquisition of CO2 data, like the acquisition of
weather data, was to be regarded as routine rather than a pursuit of basic science,
I wondered what might happen to data quality over time. I hadn’t forgotten that
the CO2 measurements published in Tellus before I began my studies had been
terribly wrong but were generally regarded as valid until new data proved themwrong. I wanted to remain directly involved in CO2 data gathering to be able
to judge the quality of such data on my own terms.
Moreover, those recruited to inaugurate NOAA’s CO2 program set about removing what I felt to be safeguards in the procedures that I had adopted toassure valid data. Then these newcomers gave out an impression that measuring atmospheric CO2 was relatively problem-free, whereas I had had difficulty
sustaining high-quality measurements over long periods. To add to my apprehensions, the official in NOAA most responsible for opposing my program had
a reputation for after-the-fact apologies when data under his supervision had
turned out to be less than satisfactory.
The most compelling reason for my wishing to stay involved was that thedata gathered in my program became more and more fascinating as the records
lengthened. They didn’t appear to be subject to the law of diminishing returns.
To complete this biographical essay I will touch on some of the scientificfindings that led me to feel this way.

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More Discoveries from Time-Series Data
Following Bert Bolin’s and my analysis of a global “snapshot” of atmospheric
CO2 in 1963 (8), my interest turned to the ever lengthening time-series of
CO2 observations at Mauna Loa Observatory and the South Pole. As I havealready explained, these records by 1972 were long enough to see evidence that
CO2 varied on a decadal time scale in a manner that couldn’t be explained byemissions from fossil fuel combustion. I wanted to acquire the most trustworthy
data possible, for as long as possible, to study such subtle effects. I was dismayed
when advised that NSF funding for my CO2 measuring activities would be cut
drastically because they had become routine.
In 1982, during the darkest days of my funding problems, William Nierenberg, the director of the Scripps Institution of Oceanography, found me a new,nongovernmental source of funding: the Electric Power Research Institute(EPRI). The original intention was to support combined CO2 and climate studies by three Scripps investigators, but on the basis of peer review, EPRI awarded
the entire agreed-upon sum to my program. With this incredible windfall to
pay costs, I invited Dr. Martin Heimann, who had just completed his doctoral
thesis in Switzerland, to work with me. He was hired for two years with aprogrammer to assist him. Also, a data analyst, Mr. Timothy Whorf, and amodeler, Dr. Stephen Piper, didn’t have to be laid off.
With the generous collaboration of Dr. Inez Fung of the Goddard Institute ofSpace Sciences, who had pioneered three-dimensional modeling of atmosphericCO2, we were able, in less than a year, to simulate how prescribed oceanicand terrestrial processes specifically affected atmospheric CO2 at each of ourobserving stations (24). By the fall of 1985, we had identified the major sources
and sinks of atmospheric CO2 likely to be causing the variations seen in ourdata (29). Four years later, this work, which without EPRI support would
probably never have been completed, resulted in four articles totalling nearly
200 pages, setting forth virtually all that we knew at the time from measurements
of atmospheric CO2 (25, 26, 41, 42).
Meanwhile, in 1983 we experienced a partial breakthrough in understanding
the relationship of El Niño events to atmospheric CO2, discovered nearly ten
years earlier by Bacastow. While in Europe attending a meeting, I learned that
Drs. Chris Folland and David Parker of the British Meteorological Office inBracknell, England had assembled a global time-series of sea-surface temperature. I visited Bracknell the next week to compare our respective data sets. We
saw closely matching interannual patterns in CO2 and temperature, as thoughboth were influenced by El Niño events.
The El Niño phenomenon was just beginning to attract widespread attention. Indeed, a major event was in progress. Back at Scripps, Bacastow andI soon saw an unmistakable response to that new event, first in temperature,P1: PSA/spd

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and then in atmospheric CO2, as both rose anomalously. We couldn’t, however, account for the anomalous CO2 rise by any simple mechanism such aschanges in the temperature-dependent solubility of CO2 in surface ocean water,
because the observed CO2 rise was too large. Soon, however, we had a tentative
answer.
In spite of funding constraints, my program had gradually added more CO2
sampling sites. This expansion was possible mainly because of the generosityof technical personnel in NOAA, who collected air samples in flasks on ourbehalf at stations in their growing network. Also, by 1985, with Mook in the
Netherlands providing isotopic data at almost no cost to us, we were obtaining
isotopic data for all of our sites.
We now discerned patterns related to El Niño events in the 13C/12C isotopic
ratio of atmospheric CO2, as well as in its concentration (41). This was a surprise because these isotopic variations must mainly reflect CO2 exchanges withvegetation on land. Oceanic exchange of CO2 with the air does not cause significant isotopic fractionation, whereas, as I had learned at first hand during myyears at Caltech, vegetation on land does. The dominant cause of an anomalous
rise in CO2 concentration during El Niño events appeared to be a release of CO2
to the air by vegetation and soils.15
Ironically, these discoveries were coming at about the same time that the
program manager for our Mauna Loa studies was demanding that I anticipate
two discoveries per year in advance of receiving funding. What if we could
temporarily keep our isotopic discoveries confidential, and later propose to discover them, complete with milestones? Then I remembered that the anticipateddiscoveries to get funding must arise exclusively from Mauna Loa data. These
broader discoveries didn’t count.
It was time to take a further look at variations in the atmospheric CO2 records
on the decadal time scale. The gradual slowdown in the rate of rise of CO2
at Mauna Loa and the South Pole in the mid-1960s, and the subsequent more
rapid rise in the early 1970s, had been followed by two more such slowdowns
and rises. With our records now 30 years long, these fluctuations looked likea repeating decadal oscillation. Was the cause oceanic or terrestrial? Did El
Niño events in some way contribute? Our quest to find out led us, however,well beyond our original focus, because once again we found a surprising
relationship between CO2 and temperature.
As the first step in this quest, my associate Mr. Tim Whorf and I removed fromconsideration, as Bacastow had done earlier, the pervasive upward curvature in
our CO2 records. This feature, best seen in our long CO2 records at Mauna Loa
15 We couldn’t be sure that our data were correct, however. The US Geological Survey had notprovided any useful isotopic data. The only other data besides ours, from Australia, showed no El
Niño signal.

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Figure 10 Anomaly in the concentration of atmospheric CO2 for data of Mauna Loa Observatory
and the South Pole combined. The solid curve is a spline fit to monthly averages of the data (thelatter plotted as dots) to show El Niño patterns. The arrows denote the time of El Niño events,
ranked S, strong; M, moderate; W, weak; and VW, very weak. The event in 1979 is doubtful, andis not ranked. (Source: Ref. 41)

and the South Pole, captures the worldwide rate of rise in CO2, a rise reflecting
the relentless increase in rate of emissions of CO2 from the combustion of fossil
fuels. We estimated that 57% of these emissions accounted for the global risein atmospheric CO2 from 1958 to 1989 (41). By subtracting this fraction monthby month from the average of the Mauna Loa and South Pole CO2 records after
seasonal adjustment, we obtained an “anomaly” plot. Expressed by a spline
curve, this plot beautifully revealed El Niño patterns, except for a very weak
event in 1964, a year when we had no data (Figure 10). A stiffer spline curve
fit to the same data showed a decadal pattern (solid curve in Figure 11). An
even stiffer spline curve showed a hint of a yet longer-term trend, evidenced by

Figure 11 Interannual variability in the anomaly in atmospheric CO2, shown by curves of varying
stiffness. The solid curve is a spline fit to the monthly data of Figure 10, to show decadal variability.
The dashed curve is stiffer. The dotted curve is looser; it is the same as the solid curve in Figure
10 but plotted on an expanded scale. (Source: Ref. 41)

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a downward bowing near the middle of the anomaly record (dashed curve in
Figure 11). Amazingly, global temperatures showed all of the same patterns:
El Niño and decadal signals, and a bowed shape (Figure 12).
More recently, with our records extended through 1994, we further noticed
that the amplitude of the seasonal cycle of atmospheric CO2 at Mauna Loa
showed a similarly timed decadal signal, especially after 1975 (44). A longerterm increase, possibly related to fertilization of plants caused by rising CO2(41, 50), overlaid this signal, but the signal itself showed greatest amplitudes
during times of unusual warmth near 1980 and 1990 (Figure 13), suggesting a
positive response of plant growth to warming (44). Also, the seasonal decline in
CO2 concentration in the spring came earlier than usual during these warm years,
indicating an earlier growing season by as much as 7 days, confirmed by satellite
data on the Earth’s greenness (49). We saw even greater amplitude increases (upto 40%) and similar evidence of earlier plant growth at our two more northernsites.
An increase evidently also occurred in the north-south gradients in atmospheric CO2 and its carbon-13 isotopic ratio. These increases in gradient,
especially evident in the late 1980s, demonstrated that a net loss of carbon
to the atmosphere had occurred in the northern regions in spite of increased
plant growth, presumably because the ground and soil also warmed, releasing
more than the usual amount of CO2 from decaying plant detritus residing inlitter and soils (54). Thus both uptake and release of CO2 on land at higher
latitudes appear to have responded strongly to warming, the releases more sothan uptakes. Although we originally looked to the oceans as the likely leading
cause of temperature-driven signals observed in CO2, our data now pointed toterrestrial vegetation and soils as more important.

Figure 12 Interannual variability in the global anomaly in air temperature, in ◦ C, shown as in
Figure 11, by spline curves of varying stiffness fit to monthly data (not shown). (Source: Ref. 41)

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Figure 13 Comparison of trends in the amplitude of the seasonal cycle of atmospheric CO2 andin temperature over land north of the tropics. Dots connected by dashed lines indicate the data.
The smooth curves are spline fits to show decadal variability. The upper plot shows annual averagetemperatures north of 30◦ N. The lower plot shows annual amplitudes for Mauna Loa Observatory,
relative to 1964. (Source: Ref. 44)

Linking CO2 Data to Global Climate
Our curiosity was now drawn towards what could be causing approximately
10-year fluctuations in temperature. Finding no clear explanation in the scientific literature, we began to search for a cause ourselves. Global temperature data
had recently become available from A.D. 1855 onward, giving us a much longer
record for studying decadal variability than afforded by atmospheric CO2 data.
To this long global temperature record we fit spline curves of three different stiffnesses, as we had in our analysis of temperature variability over the
40-year period of our CO2 record (Figure 14, upper plot, from Refs. 43 and45). We then subtracted the spline curve of intermediate stiffness from the mostflexible spline curve to create an approximately decadal “band-pass” curve(Figure 14, lower panel). Supporting our belief that the recent decadal fluctuations in CO2 and temperature might have some underlying cause, this curveP1: PSA/spd

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Figure 14 Trends in global temperature shown by spline curves fit to anomaly data. Upper plot:
curves (1 to 3) of decreasing stiffness to match as well as possible the curves of Figure 12, but extended back to A.D. 1855. Lower plot: approximately 10-year fluctuations revealed by subtracting
Curve 2 from Curve 3. Note the replacement of such fluctuations with 6-year fluctuations from1920 to 1940 during a time interval of global warming. Below the plot are shown time intervals ofstrong and weak tidal forcing on a centennial time scale. (Source: Ref. 43 and 45)

showed approximately 10-year temperature fluctuations during the nineteenth
century, as well as recently. But strangely, the curve showed approximately
6-year fluctuations in the 1920s and 1930s. A spectral analysis of the whole
record yielded oscillations in the band-pass region with periods of 6.0, 9.3,
and 10.3 years, phased such that when combined, they created nearly the same
pattern as the band-pass curve, supporting the latter as a reasonable portrayalof both the 6- and 10-year fluctuations (43).
There is a school of thought in meteorology (47, p. 72) that the circulationof the oceans and the atmosphere, and hence temperature, can change on neardecadal time scales solely as a result of their interacting with each other as adynamically coupled system. This view does not, however, preclude the possibility that external forces also influence temperature on similar time scales. We
found suggestions in the scientific literature of astronomical causes of decadal
variability in temperature linked to variations in the number of spots on the Sun
and the strength of the oceanic tides. We decided to examine these claims.
The interruption that we saw in decadal fluctuations in temperature, beginningin the 1920s, had already been noted by others (27) and was almost surely real.

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This was not an encouragement to finding a decadal connection of temperature
with the sunspot cycle, which showed no such interruption and anyway has anaverage periodicity slightly longer than the 10-year periodicity that we foundin the temperature data. We turned our attention to exploring a possible tidal
connection with temperature, encouraged by a relevant discussion in the same
treatise on climate where Bacastow had discovered the Southern Oscillation(46). Also, in an article by Loder & Garrett (48) we found mention of aplausible mechanism: that strong tides may cause vertical mixing of stratified
surface ocean water with cooler deeper water, sufficiently to cause appreciabletransient cooling at the sea surface.
Periodicities abound in the astronomical forcing of oceanic tides by the Sun
and the Moon, but to our surprise the only nearly decadal periodicities in tidal
forcing that we found were at 9.3 and 10.3 years, very close to the spectral
periods that we had found for temperature. Moreover, these two periodicities
reinforced each other near 1880 and 1970 but cancelled each other out near
1920, as did the spectral oscillations in temperature. Most surprising, a 6.0 year
tidal periodicity replaced the cancelled out decadal periodicity in the 1920s and1930s; it was phased such that, by causing periodic cooling, it might explain the
6-year fluctuations in temperature seen in our decadal spline curve from about
1920 to 1940. We had perhaps found a plausible tidal mechanism that could
explain all of the main features of our band-pass temperature curve. Encouragedby this success, we began to look for additional features of global temperaturethat might be explained by an hypothesis that strong tides cause cooling of
surface sea water.
We were now attracted to the El Niño time scale by work of a graduate
student at Columbia University, Ms. Ami Ffield (16). She gave us a preprintof an article that she and her supervisor had submitted to a journal proposingthat tidal action in the west Pacific Ocean might affect the timing of El Niñoevents. The paper, although afterwards rejected by referees, seemed to us to havemerit.16 We could, however, not find any convincing tidal relationship related
to global temperature to support her thesis, although we found hints of one.
Another feature to investigate as a test of our tidal hypothesis was a steplike upward trend in temperature seen in the stiffest spline of Figure 14 (anextension back to the 1850s of the bowshaped spline curve in Figure 12). Could
this step-like feature be related to the appearance and disappearance of decadal
tidal forcing? During times of this strong decadal forcing, from about 1870 to
1910, and again from about 1950 to 1980, the stiffest temperature spline showedno overall warming. In contrast, from about 1920 to 1940, when this strong
forcing gave way to weaker 6-year forcing, the stiffest spline shows pronounced
16 The idea is discussed in Ffield’s doctoral thesis (17).

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warming. The coincidence of this warming trend with 6-year fluctuations intemperature was striking, as though both features were related to the weakertidal forcing (see Figure 14). Beginning in the late 1970s decadal fluctuations
have been accompanied by overall warming, in violation of our tidal hypothesis, but this warming could reflect an enhanced greenhouse effect beginningmeasurably to affect global temperature.
Two additional temperature features that we thought it worthwhile to investigate were the cool period in the Middle Ages called “the Little Ice Age” andthe preceding warm period extending back to the Roman era. Could these alternations of warm and cold climatic conditions be partially a result of tidal
cooling on centennial and millennial time scales?
To explore this possibility we have extended the time frame of our analysis
over several tens of thousands of years, an investigation still in progress. Looking both forward and backward, we have verified the existence of a pervasive
tidal periodicity of approximately 1800 years that we had tentatively identified
earlier (45). We have also found pervasive, approximately 90 and 180 year periodicities related to alternations between stronger decadal and weaker, shorter
period tidal forcing in which the maximal decadal forcing varied from century
to century. The maximal decadal forcing in the 1970s, though stronger thanthat of the 1880s, was not as strong as that in the 1790s. Still stronger forcing,with peaks near 1610 and 1430, was the greatest during the past two thousand
years. This maximal forcing on the millennial time scale, in support of our tidal
hypothesis, occurred during the Little Ice Age, while the lesser forcing in theprevious thousand years occurred during the warm Roman era.
What may happen in the future if our tidal hypothesis is correct? Our analysis
suggests that if tidal forcing actually contributes to the global heat balance, theworld faces the prospect of substantial and increasing natural warming added
to greenhouse warming for the next three centuries followed by only slightnatural cooling for three more centuries. Only after A.D. 2600 will tidal forcing
as strong as that of the 1970s recur.
As these speculations indicate, we have been led in unexpected directions
by our pursuit of time-series data on atmospheric CO2. The CO2 signals that
we measured were slight but persistent. We dared to believe that they might bereal, because we deemed our data to be precise enough, and sufficiently wellcalibrated, to show weak patterns, if they existed. Then we risked proposingthat temperature also varied decadally because it correlated with our CO2 data,
and we looked for and found a possible cause.
It was a fortunate circumstance that we received a substantial part of ourfunding from the National Science Foundation while engaged in this exploratory
study. NSF, as we knew, encourages exploratory research, because its mission is“basic science,” a mission of which we have, paradoxically, had great difficultyP1: PSA/spd

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KEELINGproving our monitoring of atmospheric CO2 to be a part. Of course, not all
activities ascribable to basic science turn out to be successful. If, however, ourtidal hypothesis of climate change should turn out to be correct, we would owe
our discovery to having repetitively measured atmospheric CO2.

Where Do We Stand?
It has been over 30 years since I speculated before the American PhilosophicalSociety that the world by the end of the 20th century might be in greater danger
from rising CO2 than it was in 1969. Where do we stand on this issue today? My
friend Bert Bolin, joined by others around the world, a few years ago started apolitical process drawing attention to possible dangers of rising CO2 and urging
that the use of fossil fuels be scaled back, or at least stabilized (6). Governments
worldwide have recently tried to initiate this stabilization process, meeting in
Kyoto, Japan, to agree on the wording of an international treaty to restrict fossilfuel use. I have not been a part of this political process, but I would like to
add here a few thoughts on whether rising CO2 and attending climate change,
especially possible global warming, should be viewed with concern.
Not everyone agrees that there is a global-warming problem. There are probably even some who doubt that atmospheric CO2 concentrations are rising.
Not long ago, while attending a scientific conference on climate, I encountereda meteorologist employed by a utility company who was examining a poster
showing a curve of rising atmospheric CO2 labeled “Mauna Loa Observatory.”
He was pointing out to the author of the poster that one should be cautious about
interpreting this curve because of a steady increase in local automobile traffic
near the observatory. I could not fault him for raising this concern, because I
was at the time protesting to NOAA a lack of control over this increasing traffic,
but he should have acknowledged that CO2 measurements at other sites, withno possibility of local contamination, corroborated that the rate of rise seen in
the Mauna Loa record was global.
There is greater justification to doubt that air temperatures are rising globally,
because many more reliable measurements than for CO2 must be averaged toprove that the apparent upward trend in the data is significant. I am convincedthat temperatures are rising significantly, not just from viewing temperature
data, such as that plotted in Figure 14, but also because the atmospheric CO2
record makes any other interpretation difficult. The increase in amplitude of
the seasonal cycle from the 1960s to a peak in 1990, about 20% for Mauna Loa,
as shown in Figure 13, and nearly 40% in our longest northern polar record(44), is almost surely too large and too well correlated with decadally varying
temperature, to be accounted for solely by plant growth gradually stimulated
by higher CO2 concentrations, or by other chemicals introduced into the environment by human activities, such as nitrogen compounds. The advance ofP1: PSA/spd

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the growing season during recent unusually warm years also points to risingtemperature as being significant.
These arguments, and others that address the significance of recent temperature trends, are not easily explained to a nonscientific audience, however. For
example, my own attempts to explain my research to interviewers working forthe public media hardly ever produce in-depth reports. Through the press, radio, and television, the public receives little more than snips of information
on which to judge the significance of rising CO2 or temperature changes. The
tendency of the news media to seek out alternative sides to every issue without
evaluating pros and cons makes almost every aspect of the global-warming issue appear controversial. People in general are poorly informed, and many areprobably confused.
In Montana, for example, on land once owned by my grandfather, I have beensampling forest air with flasks in the manner of my early studies at Caltech. One
day last year a neighbor saw some of these 5-liter glass spheres lying about,curiously wrapped in adhesive tape for security against breakage, and asked
my wife what they were for. She said, trying to keep the explanation simple,
that I was carrying out a scientific study having to do with global warming. He
replied with some surprise, “Oh, I thought that problem had gone away.”
A recent two-page presentation of environmental issues, in this neighbor’s
local newspaper in commemoration of an annual national event called “Earth
Day,” would give him little reason to change his mind. On half of the first
page, above advertisements urging readers to buy compost, irrigation pipe,
vitamins, power mowers, and the like, was an article noting that the day was ananniversary of the birth of the great communist V. I. Lenin, and that an 80-yearold elm tree had recently been saved by pruning its roots out from under an
endangering sidewalk. The article was necessarily short because of the ample
space given over to a photograph of the elm tree. On the second page was amore substantial article on “Myths and Facts about the Environment.” Alongwith “myths” regarding wetlands, ozone depletion, and pesticides, was the“myth” that “the temperature of the planet has been rising at such an alarming
rate that the United States and other nations must act immediately to reducegreenhouse gas emissions.” Refuting the “myth” was the “fact” that reliabledata show either cooling or only insignificant warming. The article had been
provided to the local paper by a “national center” in Washington, DC, andprobably appeared widely in newspapers across the United States.
Should scientists attempt to help the public to understand better the significance of rising CO2 and the global warming issue? Understandably, many
do not wish to take a position regarding a possible peril associated with theseissues. Even to publish scientific findings that suggest a peril in rising CO2 ortemperature can be construed as taking a prejudicial position.

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KEELINGA safe approach is just to remain an interested observer of the unfolding
scientific evidence of man-made global change and its possible significanceto future human welfare. Without risk one can comment dispassionately onsociological, political, and religious perspectives of the global warming issue, for example, as an historian might, beginning with the first hints ofman-made global change and progressing toward the time, not yet arrived,
when there may be convincing proof of global warming. (Perhaps convincing
proof will be acknowledged to have arrived when a substantial number of US
Congressman are discovered to have secretly purchased real estate in northern
Canada.)I believe, however, that a more prudent attitude would be to heed the risein atmospheric CO2 concentration as serious unless proven to be benign. If
scientists would make clear to the public the wisdom of this cautious approach,people would demand to be better informed about what scientists already know.
The collective talent and wisdom of a species self-named Homo sapiens mightthen be better directed toward the issue of global warming.
The consumption of fossil fuel has increased globally nearly three-fold since
I began measuring CO2 and almost six-fold over my lifetime. In Southern
California it isn’t necessary to look at statistics to sense this enormous increase.
When my family and I first moved here over 40 years ago, we could stand on
a vantage point above the Pacific Ocean a few miles north of the city center of
San Diego and look eastward over an expanse of hills and distant mountains
accessed by only a few country roads and inhabited mainly by farmers andwildlife. Revisiting this vantage point at night many times since, I have watched
the number of lights steadily increase; lights from new homes, lights fromcommercial enterprises, lights from vehicles after an eight-lane highway wasbuilt just to the east 30 years ago. I have repeatedly asked myself how longthese increases can go on.
Almost all of these lights, and the activities they support, depend on fossil
fuel energy. It is to protect such activities that people oppose restrictions on
the use of fossil fuel and hope, and even assert, that greenhouse warming is amyth.
Realistically, the greatest myth is that natural resources and the ability of the
Earth’s habitable regions to absorb the impacts of human activities are limitless. Harrison Brown, who wrote about The Challenge of Man’s Future (10)while I was a postdoctoral fellow at Caltech, was quite sure that fossil fuel could
not be used at an ever faster rate indefinitely. He contemplated the fossil fuel era
from its early stages to its peak and thence to its inevitable decline (10, p. 169),showing this progression graphically with two plots (Figure 15) adapted froman article in 1947 by the farsighted petroleum geologist King Hubbert. The firstof these plots shows the fossil fuel era predicted to last about a thousand years;

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Figure 15 Rise and fall in the global rate of consumption of fossil fuel estimated for the entire
era of its use. (Source: Ref. 10)

the second shows how brief this era appears when viewed over ten thousand
years.
In historic perspective, the fossil fuel era will probably span less time thanelapsed from the beginning of the Roman Empire in the 1st century after Christ
to the fall of Constantinople to the Turks that removed the Empire’s last vestige
in the 15th century. Good times for fuel users will be over in less than half thattime. But we live today still in an early stage of this era, shown on the plots byP1: PSA/spd

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KEELINGthe termination of black areas under the curves of fossil fuel usage (the timing
updated from Brown’s graph).17 The curve is rising today almost as rapidly as
it ever will or can. In essence, those who oppose the restriction of fossil fueluse want this curve to continue to rise as depicted in these plots, checked onlyby the inevitable depletion of fuel reserves. Brown asserted, and I agree, thatfossil fuel use should be restricted as much as possible simply so that it lasts
as long as possible, whether or not adverse environmental consequences result
from using it rapidly. The likely danger of man-made global warming would
then be significantly reduced as well.
Meanwhile, what about at least monitoring what is happening to our environment to prepare for possible change? It has been over 40 years since Roger
Revelle and Hans Suess (56) pointed out that the burning of fossil fuels was alarge-scale geophysical experiment that “if adequately documented may yield afar-reaching insight into the processes determining weather and climate.” There
was no sense of peril then, just a keen interest in gaining knowledge. Now, four
decades later, there is a hint, perhaps more than a hint, of peril. Nevertheless, and despite the heightened political awareness of the greenhouse problem
indicated by the Kyoto meeting last winter, most governments have shown little
heightened interest in environmental monitoring.
Even now my own studies, especially those involving carbon in the oceans,
which I have not had space to write about here, are again in jeopardy. This time
the cutting back of support is not directed at a few academic persons competingwith government-based science, but reflects a generally declining support forsuch time-series studies.
Examples, such as my effort to maintain repetitive observations of carbon
dioxide, have evidently done little to increase enthusiam for time-series measurements in general. I cite one startling instance: measurements of temperature
itself. One might rationally expect that a major effort would now be under way
to improve “routine” measurements of air temperature worldwide. Such is not
the case. Until now, temperatures have been measured worldwide mainly toachieve short-term benefits, e.g. to forecast weather and aid agriculture. Management of these measurements is institutionalized within agencies that do not
adapt easily to a new need for long-range climate studies. Most shocking is thateven the existing weather-observational programs have recently been seriously
degraded over a wide area owing to budget cuts and unstable, indifferent, or
financially distressed governments.
17 As Brown stated: Consumption of the earth’s stores of fossil fuels has barely started; yetalready we can see the end. In a length of time which is extremely short when compared with thespan of human history, and insignificant when compared with the length of time during which man
has inhabited the earth, fossil fuels will have been discovered, utilized, and completely consumed.
The “age of fossil fuels” will be over, not to be repeated for perhaps another 100 million years(because it will take that long for nature to create a new fossil fuel resource).

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Perhaps my success in sustaining time-series measurements will eventuallyraise the general scientific regard for making repetitive but important environmental measurements. Also, I hope that there will always be opportunity for
individual scientists to pursue scientific leads not anticipated by committees
and agencies.

EPILOGUE
I have tried to be as objective as I could be in this narrative, but I apologize
if, in my recollections, I have unfairly recalled, or never properly understood,
activities recounted here. I hope that my text makes clear that I had a great
deal of help in trying to stay in carbon dioxide research. Much of this help
came from personnel below the management level in the agencies opposing myresearch. I also received crucial assistance from interveners, not all of whom I
have had space to mention. On a more personal note, I express my appreciation
to John Harte, who after suggesting that I write this narrative, helped me inthis understandably difficult task, given the necessity to criticize the actions ofothers, however well meaning their intentions may have been. I also appreciate reviews of my text by Robert Socolow, Devendra Lal, and Ralph Keeling.
Contributing to my research at the Scripps Institution of Oceanography, besides
those mentioned in the text, are David Moss, who as the project engineer for
32 years, assured that my program had the best possible instruments withinbudget, and Alane Bollenbacher and Peter Guenther, who carried out many ofthe measurements in the laboratory for 20 and 30 years, respectively. Also,John Chin of NOAA, recruited for work at Mauna Loa, who has taken careof our equipment at Mauna Loa Observatory ever since the budget crisis of
1963, and is probably more directly responsible than anyone else for creating the Mauna Loa CO2 curve that has been credited to me. I would like toclose by expressing my deep gratitude to Louise Keeling, my wife for almost
my entire career, whose patience, sympathy, love, and understanding gave memuch needed support in my pursuit of the carbon dioxide molecule in all of its
ramifications.
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by University of California - San Diego on 08/30/06. For personal use only.

CONTENTS
From Physics to Development Strategies, José Goldemberg

1

Rewards and Penalties of Monitoring the Earth, Charles D. Keeling25

Science and Nonscience Concerning Human-Caused Climate Warming, J.
D. Mahlman

83

Consumption of Materials in the United States, 1900-1995, Grecia
Matos, Lorie Wagner

107

Future Technologies for Energy-Efficient Iron and Steel Making, Jeroen
de Beer, Ernst Worrell, Kornelis Blok123

The O2 Balance of the Atmosphere: A Tool for Studying the Fate ofFossil Fuel CO2, Michael L. Bender, Mark Battle, Ralph F. Keeling

207

Mexican Electric End-Use Efficiency: Experiences to Date, RafaelFriedmann, Claudia Sheinbaum

225

Drinking Water in Developing Countries, Ashok Gadgil

253

Engineering-Economic Studies of Energy Technologies to Reduce
Greenhouse Gas Emissions: Opportunities and Challenges, Marilyn A.
Brown, Mark D. Levine, Joseph P. Romm, Arthur H. Rosenfeld, Jonathan
G. Koomey

287

Climate Change Mitigation in the Energy and Forestry Sectors ofDeveloping Countries, Jayant A. Sathaye, N. H. Ravindranath387

Toward a Productive Divorce: Separating DOE Cleanups from Transition
Assistance, M. Russell

439

Recycling Metals for the Environment, Iddo K. Wernick, Nickolas J.
Themelis

465

Environmentally Conscious Chemical Process Design, J. A. Cano-Ruiz,
G. J. McRae

499