Climate Change & The Data
A Brief History of Climate Change Studies
The modern science of climatology owes much to the work of field geologists of the 19th Century. These geologists provided evidence “in the rock” that showed northern regions of the Earth were covered repeatedly by continent-sized ice sheets. Yet, fossil evidence also showed extended periods of tropical climate in many of the same locations. These were startling discoveries in their day and caused major speculation over the causes of these natural climate changes.
In the early 20th Century, Swedish scientists came to study fossilized pollens and further identified cyclical trends to what became known as the Ice Ages. Further studies by physicists and others pointed to cyclical variations in the elliptical orbit of the Earth around the sun coupled with variations in the Earth’s rotational axis. These came to be known as the Milankovitch cycles, named for the Serbian engineer who first calculated them. The cycles, however, did not closely match the better data emerging about the various Ice Ages. Most significantly, radiocarbon dating during the 1950s was applied to all manner of geological samples. Long cores of clay extracted from deep seabeds were examined with these new methods and provided the first high-quality record of Ice Age temperatures and conditions.
By the 1960s, ancient ice cores from the Greenland shelf yielded valuable information to confirm the cyclical nature of the Ice Ages at roughly 40,000-year intervals, influenced if not governed by the Milankovitch cycles. But the best evidence remained seabed cores, which eventually pointed to cycles 20,000 to 40,000 years apart with major cycles perhaps every 100,000 years. When graphed, the temperatures showed a characteristic “sawtooth” appearance caused by seemingly random fluctuations.
By the mid-1970s, with good information about past Ice Ages, climatologists looked to the future. Most predicted a general cooling trend, perhaps over a couple thousand years, as Earth moved toward another natural Ice Age cycle.
But ice cores taken from Antarctica late in the 20th Century raised other possibilities. One fly in the ointment proved to be atmospheric carbon dioxide levels. In the Antarctic ice core record, atmospheric CO2 levels over the past 750,000 years had cycled between about 180 and 280 parts per million. Frustratingly, the levels of CO2 seemed to rise or fall a few centuries after a rise or fall in temperature. Climatologists knew this area of study warranted more attention, especially since current CO2 levels had now climbed above 370 and seemed on an upward path. The historical influence of so-called “feedback” responses from plant growth, ocean currents, and a myriad of other considerations had been underestimated. After nearly a century of Ice Age research, a tidy explanation of past and future climates seemed as elusive as ever.
The role that carbon dioxide plays in climate had been studied over the same period of time that the geologists, physicists, and others had spent researching the Ice Ages. The naturalist and philosopher John Tyndall had turned his attention to CO2 in the mid-19th Century. Rudimentary calculations in his time indicated that a chunk of rock so far away from the sun ought to be a lot colder than it actually is on the surface of the Earth. Taken by theories surrounding the Ice Ages, Tyndall launched an effort to explain the phenomenon. He designed experiments to examine whether gases could absorb heat rays. By the mid 1850s, he showed that water vapor exhibits these properties, as does carbon dioxide. The former is common in the Earth’s atmosphere, Tyndall knew, and rightly pointed out water vapor’s heat trapping properties. Carbon dioxide comprises only a few parts per ten thousand in the Earth atmosphere, however, and its role was left to Tyndall’s successors.
The Swede Svante Arrhenius also had an interest in Ice Age theory. In 1896, he laboriously computed that if the amount of atmospheric CO2 were cut in half, European temperatures would drop roughly 7-9°F – Ice Age levels. He and a colleague, Arvid Hogbom, next looked at the CO2 levels being emitted by European industry of the time and found, to their surprise, that the levels were roughly the same as those being emitted through background natural biological processes. When Arrhenius calculated a doubling of atmospheric CO2, he estimated it would raise the Earth’s temperature approximately 9°F. A popular book by Arrhenius was published in 1908 and first raised the possibility in the public mind that burning fossil fuels might contribute to global warming.
The interest in the theory proved short-lived, however. Most scientists at the outset of the 20th Century believed that water vapor levels in the atmosphere override any influences that carbon dioxide might have. Further, many scientists of the time felt the Earth automatically regulates itself. The prevailing theory was that oceans and land mass would absorb any excess gases that might come into the atmosphere. The study of atmospheric CO2 would languish, but not be totally forgotten.
During the early and middle of the century, scientists came to realize that the atmosphere was more complex than the single band of gases previously speculated. Meteorologists came to recognize this at about the time that decades of weather data pointed to an apparent warming trend in northern Europe. English engineer Guy Callendar studied meteorology as a hobby and had an interest in Ice Age theories. He took note of the rising temperatures and coupled them with emerging carbon dioxide measurements, speculating on a cause-effect relationship.
A problem of the day for Callendar and others was unreliable data on carbon dioxide. Measurements were easily influenced by “background noise,” both natural and human caused. Two breakthroughs changed the measurement debate. The first was the development of isolated monitoring stations. The second breakthrough was the development of measurements using the radioactive isotope carbon-14. In 1955, the chemist Hans Seuss reported the detection of atmospheric carbon from fossil fuel sources. Atmospheric carbon dioxide has been closely monitored since 1958.
Working through the Scripps Institute of Oceanography near San Diego, geochemist Dave Keeling recognized a need for base measurements of atmospheric CO2. The year 1957 marked the International Geophysical Year and two internationally known scientists from Scripps, Roger Revelle and Hans Suess, argued that funding should be made available to measure CO2 in the ocean and air simultaneously at various points around the globe. They selected Keeling, then a graduate student, for the work. Keeling lobbied for and got gas infrared spectrophotometers that penned a precise and continuous record on a strip chart. He also got use of a National Weather Observatory on Mauna Loa in Hawaii and located another station in Antarctica. The now-famous “Keeling Curve” is the steadily rising levels of atmospheric CO2 measured primarily from the volcano mountain top of Mauna Loa.
In the decades following World War II, meteorologists became more involved in climate studies, which had been largely the domain of geologists and physicists. Worldwide, military aviation fostered great interest in weather forecasting and research. In the midst of the Cold War, detailed models were developed to map global movement of radioactive fallout should a nuclear exchange break out between the major powers. Later, NASA and space exploration agencies would fund much of the atmospheric studies. A better understanding of the Earth’s atmosphere emerged in the latter half of the century and modeling grew more sophisticated. A more integrated and cooperative scientific approach to climate research was also initiated during this era. Oceanographers and hydrologists, physicists, geologists and earth scientists, meteorologists, and others coalesced around climate issues and began sharing data. A 1965 symposium in Boulder, Colorado was convened ostensibly to share research on climate changes during the glacial periods, but participants readily exchanged arguments about future climate changes as well.
The multidisciplinary scientific evidence from the last decades of the century strongly pointed to a global warming trend due to human-caused contributions of CO2 in the atmosphere. The scientists working in the field began to raise awareness of the work, first among fellow scientists and also to the public. The New York Times featured a detailed front-page article about climate change for the first time in 1981. The move from scientific circles to the broader public was underway.
Concerned scientists also hooked up with governments and in 1988 the International Panel on Climate Change (IPCC) was formed to coordinate, peer-review, and disseminate research. Its second report in 1995 stated unequivocally that the world is getting warmer, adding that the causes were at least in part influenced by human activities. In 1997, 2,600 scientists signed a letter urging the United States to take a lead role in addressing the issue of climate change. The language and evidence from the scientific community has only grown stronger over the ensuing decades.
For a more complete account of the history behind climatology and links to its scientific development, go to the online version of The Discovery of Global Warming, by Spencer Weart. The National Oceanic and Atmospheric Administration (NOAA) offers paleoclimatology timelines.
