The History of Climate Change and Climate Science William Moomaw The Fletcher School of Law and Diplomacy, Tufts University Introduction The one constant of climate is that it changes. The pattern of these changes has been the subject of speculation and study for perhaps as long as human history. What is new is the study of how human actions have altered the climate in the past and continue to do so at an accelerating rate. These studies are accompanied by attempts to write future climate history by projecting current knowledge about the climate system onto alternative scenarios of future human activity. The history of climate change is both an accounting of what has happened to the climate prior to and during human existence, as well as the process by which natural and anthropogenic climate change have been studied and described. First, it is important to identify the relationship between weather and climate. Weather is the daily set of meteorological conditions that we experience locally. Local climate is the 40 year average of climate variables, regional and global climate is the 40-year average of the weather variables for a region or spatially averaged for the planet as a whole. Even though there are variations from mean values for temperature or precipitation, these longterm averages convey a sense of place and dictate appropriate agriculture, buildings and even cultural characteristics of entire societies. The variations can also be averaged to arrive at a normal range of weather conditions such as the frequency of heat waves or droughts. The Planetary Mechanics Theory of Ice Ages There is evidence that the Mesozoic era 100 million years ago was significantly warmer than it is today. For the past million years, it appears that the earth has been subject to several alternating ice ages and interglacial warming periods like our current Holocene that began about 10,000 years ago. The timing of the ice ages and relatively short intermediate warm periods occur with a frequency of approximately 100,000 years. The realization that there has been at least one past ice age developed gradually in the 19th century. The German born Swiss geologist, Jean de Charpentier studied glaciers and developed the argument in the 1830s for extensive past glaciers to explain the polished bedrock and the appearance of large boulders many kilometers from their place of origin. This contrasted with the traditional view that these marks were evidence of the great biblical flood and supported the model of slow geological processes advocated by Charles Lyell, the Scottish developer of “Uniformitarianism” a theory rejecting the abrupt changes described in the Bible. Louis Agassiz, a Swiss born scientist added additional evidence with his Origins of Ice Ages in 1840. Agassiz was also a great paleontologist, but unlike Lyell never accepted Darwinian Evolution even after moving to America and becoming the foremost scientist there. By the 1860s, the existence of a past ice age was generally accepted in Europe and North America, but the American environmentalist, John Muir still met skepticism in his first published paper in 1871 when he proposed that Yosemite Valley in California had been formed by glaciers like those he had seen in Alaska. Attempts to unravel the mystery of the ice ages in the 19th and early 20th centuries shifted to planetary mechanics. The first to recognize that the earth’s eccentric orbital motion might be related to ice ages appears to have been the French mathematician, Joseph Adhemar who proposed it in his book, Revolutions de la mer in 1842. James Croll, a janitor at the Andersonian College and Museum in Scotland, while browsing in the library after hours, came across Adhemar’s book and the updated calculations of the earth’s orbit by the French astronomer Urbain LeVerrier. Having taught himself physics, Croll developed a mathematical theory that the eccentricities in the earth’s orbit would alter the amount of sunlight hitting the earth’s surface. He was also apparently the first to recognize the role of large ice sheets in reflecting sunlight back to space, and the importance of ocean currents, but erroneously concluded that the last ice age had ended 80,000 years earlier, and that ice ages alternated in the Northern and Southern hemispheres.
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It remained for a Serbian mathematician, Milutin Milankovitch to build on Croll’s
insights and develop a robust mathematical model that gave a quantitative prediction of the frequency of ice ages. Milankovitch, a professor at the university of Belgrade, began his work in 1912 and completed it while in prison during WW II. His insight about the different reflecting properties of oceans and land masses, , plus his use of improved orbital calculations by Ludwig Pilgrim, provided what he thought was a final solution to the theory of ice ages. He eventually published a full accounting in 1941 just in time for the Second World War to divert attention from it. In 1970, American chemical oceanographers Wally Broecker and Jan van Donk published evidence from deep seabed sediments that confirmed the predicted 100,000-year Milankovitch cycle, and cast further doubt on the heat trapping theory of climate. Throughout the 19th and early 20th century the planetary mechanics theory of ice ages developed through communication among individual continental scientists and mathematicians in France and Switzerland and geologists and physicists in England and Scotland. Their work was refined into an elegant predictive theory by a lone Serbian mathematician. In the 20th century the scale of the research expanded, and recently multinational teams worked on massive efforts to extract deep ice cores to go back in time. These teams were assembled with deliberate political as well as scientific goals whether it was to maintain cooperation during cold war tensions, or to cement relationships within a new and fragile European Union. It would take an additional strand of atmospheric research to create a scientifically robust explanation of the onset of the ice ages. Atmospheric Composition and Climate – An alternative theory Having narrowly escaped the guillotine during the French Revolution, the French mathematical physicist, Jean Baptiste Joseph Fourier, published a paper in 1827 in which he posited that the earth did not lose its absorbed solar heat back to space because, clouds and (unknown) gases in the atmosphere absorbed that radiant heat and reradiated it back to the earth’s surface. He likened this to a glass bell jar trapping heat, and this process eventually came to be known as “The Greenhouse Effect.” Throughout the 19th century there was intense intellectual competition among leading physical scientists to study heat and electromagnetic radiation, and their work contributed to an understanding of how gases trap radiant heat from the earth and return it to the surface. John Tyndall an Irish born Professor of Natural Philosophy demonstrated that the bulk of the atmosphere made up of oxygen and nitrogen had no effect on the radiant heat from the earth, but that water vapor, carbon dioxide and ozone did. He correctly identified water vapor as the most important heat trapping gas, and also postulated the urban heat island effect, and contributed to the theory of the motion of glaciers. The latter part of the 19th century saw a lively dialogue about the nature of the heat balance of the earth. The American founder of aviation, Samuel P. Langley, a solar physicist, invented the bolometer to accurately measure the incoming energy from the sun in 1878. In 1884 he published a paper in Professional Papers of the Signal Service and in 1890 a study of the radiant properties of the atmosphere free moon that quantified the infrared portion of the solar spectrum. Combing these data with Tyndall’s quantitative measurements of radiant heat absorption in earth’s atmosphere, allowed the calculation of the thermal heat balance of the earth. This task fell to Svante Arrhenius, a Swedish chemist whose chemical rate equation is still in use today, and who won the chemistry Nobel Prize in 1903 for his doctoral research on the electrical conductivity of charged ions in water despite its having received the lowest passing grade. Arrhenius was convinced that it was the concentration of carbon dioxide, water vapor, ozone and other trace gases that determined just how much heat was retained by earth’s atmosphere. He conducted painstaking calculations, and published his landmark paper “On the Influence of Carbonic Acid In the Air on the Temperature of the Ground” in 1896 in the British journal Philosophical Magazine. He correctly predicted that warming would be greater in winter, and at higher latitudes, and estimated that if carbon dioxide were doubled, global temperatures would increase by 5-6 oC. Arrhenius believed it might be possible to avoid entering another ice age by adding carbon dioxide to the atmosphere by burning more coal, and indeed this would be essential if the world were to avoid catastrophic descent into the next ice age. The Swedish physicist Knut Ångström in 1900 quantitatively measured the absorption of infrared radiation by carbon dioxide, and strongly criticized Arrhenius for overestimating its absorption intensity. Current best estimates suggest that a doubling of carbon dioxide would increase global average
temperatures by 2-4.5 oC. Ångström was right. Arrhenius had over-estimated the “Greenhouse Effect,” not the last time that charge would be leveled at scientists studying this phenomenon. Guy S. Callendar, a British steam engineer became interested in testing the theory of carbon dioxide driven climate change, and saw that by the 1930s carbon dioxide had increased by an estimated 10% from a poorly verified pre-industrial baseline. He collected data from his own home over many years, combined temperature records from many weather stations and examined modest number of available measurements of retreating glaciers. He found statistically significant increases in northern hemisphere temperatures, especially in northern latitudes (consistent with recent findings), and attributed this rise to the increase in carbon dioxide. His initial publication in 1938 was largely dismissed as the work of an amateur. Undeterred, he continued his research and established the basis for the current global system of temperature measurements. In 1957, Hans Suess and Roger Revelle of Scripps Institution of Oceanography in California published an initially confusing finding about the uptake of atmospheric carbon dioxide released to the atmosphere. Using the new science of radioactive carbon 14, they were able to show that the oceans rather quickly absorbed fossil fuel generated carbon dioxide, but nearly as quickly released much of it back to the atmosphere. They also included the observations of California Institute of Technology Professor Harrison Brown that carbon dioxide concentrations could increase significantly if fossil fuel combustion continued its rapid rise. In their own calculations, they greatly underestimated the future growth of carbon dioxide emissions or atmospheric concentrations. In concluding, the paper made the now famous statement that humans are conducting a large-scale geophysical experiment that cannot be reproduced. They also paid tribute to the ignored work of Callendar and called augmented global warming from fossil fuel carbon dioxide the “Callendar Effect.” Creating the New Synthetic Theory of Climate and Climate Change Bringing the planetary and atmospheric threads together required a new synthesis in the 20th century. The atmospheric heat trapping alone did not account for the periodicity of the ice ages. While accounting for their periodicity, the planetary mechanics seemed insufficient to account for the large drop in temperature required to bring about an ice age, or to explain the sudden large rise in temperature marking the start of an interglacial warming period. The connection between the two theories grew out of the increase in interest in the possibility suggested by Arrhenius that the addition of heat trapping gases to the atmosphere from industrial processes might be responsible for significant future warming, and the confirmation of ice age frequency that corresponded to the predicted Milankovitch cycle. Climate research remained the province of individual scientists publishing in journals in Western Europe and increasingly North America until after the middle of the 20th century when “Big Science” began to dominate the field. An independent and parallel analysis of climate during the mid to late 20th century was underway in the Soviet Union and later Russia. Realizing that the complexity of the climate system required the coordinated study by atmospheric scientists, oceanographers, terrestrial ecologists as well as meteorologists, glaciologists, solar physicists, and others from the physical and biological and even social scientists, an argument was made to include it in the agenda of the International Geophysical Year (IGY) in1957-58. IGY drew a total of 67 nations and 80,000 scientists to study the physical properties of the planet from solar radiation to earthquakes, glaciers, ocean currents, the Arctic and Antarctica, weather and climate. This effort to study physical process of the earth was proposed by the International Union of Scientific Unions (National Academies of Science) and organized jointly with the World Meteorological Organization (WMO). The latter is a UN organization founded in 1950 from the preexisting International meteorological organization that dated back to an 1873 Congress of Vienna. Its purpose is to encourage collaborative sharing of data about weather and later climate. IGY mobilized previously unavailable funding for research from governments and stimulated the design of collaborative projects across disciplines and Cold War boundaries. While there had been two “Polar years” in 1882-83 and 193233, IGY was the first integrated look at the climate system, the oceans and other global scale systems and an important shift from traditional individualistic research and analysis to the rise of larger groups of interdisciplinary scientists working together. Large scale
multiple disciplinary national and international teams of scientists have come to dominate climate science. Just before the IGY began, C. David Keeling, who was a doctoral research student of Harrison Brown, signed on to work as a post-doctoral researcher with Roger Revelle at Scripps. He had developed a highly accurate way to measure the amount of carbon dioxide in the atmosphere. Keeling began his atmospheric measurements at two pure air sites, the South Pole research station in Antarctica and atop Mauna Loa volcano in Hawaii. Each of these sites was thousands of miles from contaminating industrial emissions. What resulted were the most important geophysical measurements in history. The monthly averages showed an annual oscillation that was higher in the Northern hemisphere winter, and lower in summer as the relative seasonal rates of plant respiration and photosynthesis affect the atmospheric concentrations. The average concentration for the first full year of 1959 was 316 ppm (parts per million), or just over 0.03%. Concentrations in October of 2007 reached 384 ppm. Measurements at the South Pole were slightly lower, but the oscillations because of the inverted seasons were exactly out of phase, and because of the lower biomass of plants in the southern hemisphere the annual oscillations were smaller. The prospect of predicting or modifying the weather to improve agriculture or as a weapon of warfare captured attention during the 1960s, and 70s. In preparation for the first global environmental conference in Stockholm, a report, Man’s Impact on the Global Environment, was released in 1970. It examined the atmospheric measurements of rising carbon dioxide made by Keeling, and found that it seemed to confirm that future global warming might be of concern. By the 1980s, new evidence began to provide an answer to the riddle of the ice ages. Drilling down 3km into the ice carries us back in time and allows the measurement of the concentrations of heat trapping gases in air bubbles trapped in the ice and isotope ratios that are a surrogate of temperature. The initial measurements involved large international teams of Russian, French and American scientists working at the Soviet Vostok, Antarctica site in an attempt at Cold War cooperation. The data from ice cores demonstrated the strong correlation between heat trapping carbon dioxide, methane and nitrous oxide in the atmosphere, and the temperature of the ice ages and interglacial periods. The data extended back 420,000 years and covered five cycles, each lasting approximately the Milankovitch periodicity of 100,000 years. This record was extended back 650,000 years and two more warming periods at a nearby site by the 17-nation European Project for Ice Coring in Antarctica. The rise and fall of temperature is strongly correlated with carbon dioxide, methane and nitrous oxide, all heat trapping greenhouse gases. This latter study confirmed that current carbon dioxide levels are 27% higher than at any time in this entire period. The earlier results were first published in the British journal Nature in 1985, and the latter work in the American journal Science in 2005. The carbon dioxide concentrations ranged from about 180 ppm during the depths of the ice ages to a maximum of 300ppm during the warmer interglacial periods. Today’s concentration of 384ppm exceeds any amount ever measured over the past 650,000 years by 27%. A careful analysis found that the carbon dioxide lags the temperature rise by about 800 years during the warming period. This is just about the time needed to begin releasing the vast amounts of carbon dioxide dissolved in the deep oceans. It therefore appears that the Milankovitch cycle triggers global warming when planetary orientation to the sun is optimal. This warming releases carbon dioxide from the ocean surface and eventually from the deep ocean trapping more heat and giving rise to the rapid acceleration of warming as an ice age abruptly ends within a single millennium. Additional carbon dioxide may be released from plant decay, and methane releases are accelerated from anaerobic decay and from deposits in melting permafrost. These same trapped air samples show an increase in atmospheric concentrations of methane rising abruptly starting in the 19th century from 715 ppm to 1774 ppm in 2005. Methane adds to the atmospheric heat trapping until the planetary alignment falls out of favor, and cooling sets in. The cooling allows more carbon dioxide to dissolve in the ocean and slows the rate of decomposition and methane release from soils. A new ice age will begin. Hence both the planetary cycle advocates and the greenhouse backers were partially correct, but it took both aspects to account for the observed periodicity of the climate system.
The possibility of multiple positive and some negative feedback loops began to be realized. Melting snow and ice increased the absorption of solar radiation by dark land and water, which is one reason that high latitudes warm more than the equator. Warmer temperatures evaporated more ocean water and the air could hold more of it because of the higher temperature. This in turn could trap more heat. Of course there are other factors that can affect the climate such as fluctuating solar intensity, volcanic eruptions, deforestation, dust storms, shifts in ocean currents, massive forest fires, and other phenomenon. These have been found to have only episodic, short- term influences on the climate. The advent of satellites and other remote sensing technology has greatly enhanced the ability to monitor the planet and its climate. A global network of over 7000 weather stations now sends daily high and low temperatures, precipitation and other weather data to central locations where they are combined with sea surface temperature measurements to provide daily and annual regional and global average temperatures. Buoys and ships monitor sea surface temperature and measure ocean currents. Satellites provide observations of sea ice breakups, glacial retreat, atmospheric opacity from dust and aerosol droplets, surface albedo or reflectivity, planetary thermal emissions, sea level confirm patterns of climate change. Initially, these observational satellites were derivative from military technology and were mostly launched by the United States and the Soviet Union. Increasingly European, Japanese and other nations are launching their own satellites to observe the Earth’s climate and other natural processes. Over 7000 surface based weather stations were first linked in 1992 by research agencies of the US government as the Global Historical Climatology Network. Each locality sends its data directly to a central global location as well as to its national weather agency. The Climatic Research Unit at the University of East Anglia in England has established an alternative sampling system. The historical data collected by these stations over the years have now been compiled to provide a continuous record dating back to the mid-19th century. As the global data accumulated, the pattern became clear. Following a brief rise from 1900 until 1940, temperatures leveled and actually dropped slightly for 30 years prompting statements that the warmth was about to enter a new ice age. Then temperatures began soaring up through 2007. Based on major databases in the United States and the United Kingdom, the average global temperature has increased by 0.71oC from 1906-2005. Eleven of the twelve warmest years have occurred between 1993 and 2005. Michael Mann and colleagues reported surrogate temperatures going back 1000 years, demonstrating that the recent rise in temperature is abrupt and greater than the fluctuations observed in prior centuries. Challenges to this work were found not to alter its ultimate message. The small temperature dip at mid-century has been shown to arise from reflected sunlight off of small droplets of sulfuric acid that are produced downwind from the combustion of sulfur laden oil and coal. Removing sulfur to reduce acid rain has uncovered the imbedded heat trapping capability of greenhouse gases. As predicted by theory, the moisture content of the atmosphere has increased with the temperature rise trapping yet more heat. Beginning in the 1980s, the other tool that began to make an impact on understanding of climate change was the introduction of super computers that could simulate the circulation and heat trapping by greenhouse gases, and couple the atmosphere to ocean currents, plants and soils as they absorb and release carbon dioxide. Independent modeling efforts were initiated in the United States, the United Kingdom, within the European Union, Russia, Japan and now China. While part of the impetus for these models originated from attempts to better predict weather or explain ocean currents, they soon outgrew that mission. In fact today, there is some skepticism among many meteorologists that climate change is happening because of human contributions of heat trapping gases into the atmosphere. They can usually find a micro explanation for an observed shift in weather patterns rather than attribute them to larger changes in the global climate system. With the advent of very powerful supercomputers it has become possible to incorporate a great deal of the physics, chemistry and biology of the planet as it relates to climate. These models have been verified in that they “can accurately predict the past.” They are increasingly being used to test future trajectories of heat trapping gases under different scenarios to see how atmospheric concentrations of greenhouse
gases might increase, and how that might affect future temperatures and sea levels. Depending on emission scenario assumptions, future temperatures could rise between 1.5 oC and 3.5oC, which would create remarkable changes in natural and agricultural systems as well as affect human health. In 1983 and again in 1985, groups of climate and biological scientists from American and European universities and independent research centers issued reports on the likelihood that climate change could become a serious problem. In the summer of 1988, at a hearing before a U.S. Senate committee, atmospheric scientist James Hanson from NASA stated that he was 99% certain that climate change was already happening and that within a decade it would be obvious to the man on the street. This began an intense debate over the science of climate change. Climate Change Policy Also in 1988, the United Nations created the Intergovernmental Panel on Climate Change (IPCC) through the World Meteorological Organization and the United Nations Environmental Programme (UNEP). The organization was to produce a report every 5 to 6 years on the state of climate science, climate change impacts and adaptation and to identify mitigation options. Physical, natural and social scientists were to be appointed by governments. They were to base their report on existing peer reviewed scientific literature and were to avoid making prescriptive recommendations. The first report, which was hastily assembled under the chairmanship of the Swedish meteorologist Bert Bolin, was published in 1990, and concluded that it was likely that human release of carbon dioxide and other gases into the atmosphere was responsible for changing the climate. A second report, also chaired by Bolin in 1995, found stronger climate change evidence and the third report chaired by Robert Watson, an English born American chemist at The World Bank, reported in 2001 evidence of human induced climate change. The fourth assessment report issued in 2007 under the chairmanship of Rajindra Pachauri, an Indian engineer and economist, stated that it is highly likely with a 90% degree of confidence that observed climate change was due to human actions. The reports also evolve in providing more information on impacts and adaptation in the second, more economic analysis and mitigation options in the third, and mitigation and equity issues of climate change in the fourth report. The scale and scope of this critical review and assessment of climate change is unprecedented. A rotating body of IPCC participants consists of nearly 2000 scientists and other technical researchers who spend 3 years reviewing data, research articles and reports without pay while working in their jobs in academia, government, industry, non-governmental organizations and research institutes. In October 2007, they shared the Nobel Peace Prize with former U.S. vice president Al Gore. The IPCC reports influenced governments to negotiate and adopt the 1992 UN Framework Convention on Climate Change that called upon all nations to work to stabilize “greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.” The treaty quickly entered into force and as of 22 August 2007 has 192 nations as parties. In 1997 following the release of the second IPCC report, nations negotiated the Kyoto Protocol that called upon developed countries to reduce their emissions of carbon dioxide and several other heat trapping greenhouse gases by specified amounts during the period 2008-2012. It took until 2005 for enough nations to ratify this agreement. The United States and Australia were the only industrial nations to opt out of the system. As of 6 June 2007, 171 nations had ratified the Protocol. To date relatively little action has been taken to lower the release of heat trapping greenhouse gases. A key component of future climate history will be how effectively global action can be mobilized and the fossil fuel economy moderated to reduce dramatically the release of heat trapping greenhouse gases. So the synthesis between planetary mechanics and atmospheric heat trapping theories seems to provide an explanation for both the ice ages and recent warming. If left unchecked concentrations of carbon dioxide could double or triple pre-industrial levels during the 21st century, and raise temperatures as much as they increased coming out of the last ice age. While a few may question whether climate change is human caused, the discussion has moved on to what can be done to avoid excessive warming. The only possible remedial action is to reduce human contributions of heat trapping greenhouse gases to the atmosphere since
altering planetary mechanics clearly remains beyond our reach. The science continues to unfold. We await future climate historian!s accounts, and the inevitable next ice age. Further Reading Arrhenius, Svente, 1896. “On the Influence of carbonic Acid In the Air on the Temperature of the Ground,” Philosophical Magazine 41, 237-276. http://web.lemoyne.edu/~GIUNTA/Arrhenius.html Fleming, James R. The Callendar Effect: The Life and Times of James Stewart Callendar, American Meteorological Society, 2006. Fleming, James R. 1998. Historical Perspectives on Climate Change. New York: Oxford University Press. Imbrie, John, and Katherine Palmer Imbrie. 1986. Ice Ages: Solving the Mystery. Rev. Ed. Cambridge, MA: Harvard University Press. Somerville, R., et al. 2007. "Historical Overview of Climate Change Science." In Climate Change 2007: The Physical Basis of Climate Change. Contribution of Working Group I to the Fourth Assessment Report of the IPCC, edited by Susan Solomon et al., pp. 93127. Cambridge and New York: Cambridge University Press (online at www.ipcc.ch) Weart, Spencer R., 2003. The Discovery of Global Warming, Harvard University Press. Wilson, Caroll, 1970. Man’s Impact on the Global Environment, Report of the Study of Critical Environmental Problems (SCEP), MIT Press. UN Intergovernmental Panel on Climate Change (IPCC) Assessment Reports and Special Reports; Technical Papers; Methodology Reports; and Supporting Material (http://www.ipcc.ch/) Cross references: Stockholm conference, nature and life sciences, mathematics, scientific expeditions, scientific stations, environmentalism, air pollution, environmental diplomacy, UN system