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Spencer R. Weart - The Discovery of Global Warming
Chapter 1 - How could climate change?
p. 9: Early interest in climate change was driven by the desire to understand what caused the ice ages. During the 1800s and early 1900s scientists came to believe that the forces at work on Earth were uniform and that climate was inherently stable.
p. 3: In 1859, the British scientist John Tyndall demonstrated in a laboratory that certain gases such as methane and carbon dioxide (CO2) were opaque to infrared radiation. Such gasses in the atmosphere could control climate by trapping heat escaping from the Earth's surface.
p. 5: In 1896, a Swedish scientist named Svante Arrhenius suggested that if the amount of CO2 in the atmosphere were increased, this would raise the temperature a bit and the warmer air would hold more moisture. Since water vapor is a potent greenhouse gas, the additional humidity would greatly enhance the warming. Arrhenius believed that positive feedback might amplify to the effects of greenhouse gases on climate.
p. 11: In the 1800s and early 1900s, many explanations of the ice ages were put forward, including volcanic activity, ocean currents, variations in solar energy, and changes in the tilt of the Earth's axis. None were well accepted.
p. 15: In the 1920s, the Russian geochemist Vladimir Vernadsky argued that the volume of materials produced by man and other living creatures was approaching geological proportions and that living organisms constituted a force for reshaping the planet comparable to any physical force.
p. 2: In 1938, Guy Stewart Callendar (a steam engineer not a meteorologist) argued before the Royal Meteorological Society in London that weather statistics showed that climate was warming and that human industry, through the emission of CO2, was the cause. Callendar's assertion was generally dismissed (p. 19).
Chapter 2 - Discovering a possibility
p. 23: In 1956, Gilbert Plass used digital computers to calculate that CO2 added to the upper atmosphere by human activity could raise the average global temperature 1.1 degree C per century. Previously, scientists had argued (based on sea-level observations) that CO2 and water already blocked all the radiation that could be blocked.
p. 27: In 1957, Hans Suess and Roger Revelle tried to determine how quickly fossil carbon (released by burning fossil fuels) would be absorbed by the oceans. They concluded that the oceans would not absorb CO2 as quickly as previously thought.
p. 34: Climate studies received a boost during the International Geophysical Year (IGY) of 1957-58. The Cold War governments that funded IGY studies expected that the new knowledge would have civilian and military applications. Climate change ranked low on the list of IGY priorities.
p. 36: During the IGY, Charles David Keeling established precise CO2 measuring stations atop Mauna Loa in Hawaii and in Antarctica. In 1960, with two years of Antarctic data in hand, Keeling reported that the baseline CO2 level had risen. The rate of rise was approximately what would be expected if the oceans were not swallowing up most industrial emissions. With a brief interruption in 1964, Keeling has continued accumulating data ever since. His record of inexorably rising CO2 levels raised the possibility that human emission of greenhouse gases might warm the Earth.
Chapter 3 - A delicate system
p. 39: In 1965, the National Center for Atmospheric Research (NCAR) in Colorado hosted a conference on "Causes of Climate Change." This conference heralded a new way of looking at the future of climate. Climate was now viewed as a complex and precariously balanced system.
p. 57: Following World War II, the mathematician John von Neumann began to advocate using computers for numerical weather prediction. The goal was not only to predict daily weather changes but to calculate the general circulation of the atmosphere. The network of weather balloon observations established during and after the war made it possible to check the results of early computer models.
p. 62: In 1963 Edward Lorenz showed how tiny differences in the initial conditions of a computer model could lead to vast differences in outcome. Scientist came to accept that climatic changes must be attributed to a complex of causes. A holistic approach was required. "A plausible model for climate change could not be constructed, let alone checked against data, without information about a great many different kinds of things (p. 64)."
Chapter 4 - A visible threat
p. 66: During the early 1960s, scientist became concerned about the effect of aerosols--microscopic airborne particles--on the atmosphere. Scarcely anyone was studying how aerosols might influence global climate. Simple physics theory suggested that they should scatter incoming sunlight, cooling the Earth.
p. 69: The first Earth Day in 1970 marked the emergence of environmentalism into full public view. Technology was viewed with increasing skepticism due to its possible unintended consequences. These concerns contributed to the cancellation of the U.S. development program for supersonic transport (SST) airplanes in 1971.
p. 76: In 1973, Nicholas Shackelton developed a new method to analyze deep sea cores. His research showed that there had been dozens of ice ages in the past, at intervals corresponding with orbital variations of the Earth. Since these variations were small, Shackelton and others reasoned that feedbacks must be amplifying the changes to affect global climate.
p. 78: Around the same time, scientists grew more willing to consider that climate might change dramatically in a period as short as a century. Most concerns were about the possibility of another ice age. In 1972, a group of scientists wrote a letter to President Richard Nixon calling on the government to support intensified studies (p. 81).
p. 85: Around 1968, Mikhail Budyko developed a simple model of climate change that showed that at critical points above and below current temperature conditions, global climate could change dramatically. Observations of Mars by the Mariner 9 spacecraft suggested that the climate of a planet could flip from one state to another as a result of relatively minor changes.
Chapter 5 - Public warnings
p. 91: By the mid-1970s, the majority of scientists felt that "the world's prolonged streak of exceptionally good climate has probably come to an end." The rise in dust pollution worked in the opposite direction of the rise in CO2 pollution, and nobody could yet say whether there would be cooling or warming. But most felt that man's effects on his climate were becoming dominant. A few scientists including Reid Bryson and Stephen Schneider began to write and speak about climate change for the general public. Many researchers felt uncomfortable engaging the public on this issue given the scientific uncertainties that remained (p. 93).
p. 95: In 1970, the National Oceanic and Atmospheric Administration (NOAA) was created. NOAA became one of the world's chief sources of funding for basic climate studies.
p. 96: A 1977 report by a committee of the National Academy of Sciences noted that the threat of climate changes was intimately connected with energy production. Government and industry officials were starting to realize that CO2 emissions had economic implications, and therefore political ones.
p. 97: A National Climate Act was passed by Congress in 1978 but it was weak and had little effect.
p. 106: During the 1970s, debates between biologists and physical scientists raised awareness of the potential of the biosphere to provide feedback that might influence global climate. But as yet, nobody was sure just how to balance the global carbon budget.
p. 109: In a discussion of general circulation models (GCMs) of the atmosphere, the author notes that by about 1970, computer models developed by the U.S. Weather Bureau were doing better at short-term weather predictions than the old rule-of-thumb forecasters. These efforts were aided by a steady increase in the use of satellites to collect data on the atmosphere.
p. 110: A group of researchers at NASA had been developing a weather model to study the atmospheres of planets. James Hansen assembled a team to reshape their equations into a climate model. This model was able to get a simulation much faster than general circulation models, enabling the group to investigate "what if" scenarios by varying parameters between one run and another.
p. 112: In 1967, a group including Syukuro Manabe at the U.S. Weather Bureau developed a special model to test what would happen if the level of CO2 in the atmosphere changed. They predicted that for a doubling of CO2 the global temperature would rise about 2 degrees C. Manabe updated the model and calculated in 1975 that the temperature increase would be around 3.5 degrees C.
p. 115: In 1977 a panel of the National Academy of Scientists declared they had "rather high confidence" that in the next century the Earth would warm by about 3 degrees C, plus or minus 50 percent. A World Climate Conference in 1979 concluded that there was a "clear possibility" that an increase in CO2 might result in significant long-term changes in global climate. By the early 1980s, the possibility of global warming had become prominent enough that it was included in public opinion polls for the first time.
Chapter 6 - The erratic beast
In this chapter, the author discusses other factors that might influence climate, including sunspots and cosmic rays (p. 125), trace chemicals like chlorofluorocarbons (CFCs), methane, and nitrates (p. 127), sulfate aerosols (p. 132), and ocean currents (p. 135).p. 120: In 1981, James Hansen's group predicted that "carbon dioxide warming should emerge from the noise level of natural climatic variability" by the year 2000. In 1986, British researchers concluded that the warmest three years in their 134-year record had all occurred in the 1980s. (On p. 182, the author writes that 1995, 1997, and 1998 each broke the record as the warmest year for the planet as a whole.)
p. 130: In 1980, better methods were developed for analyzing ice cores. Data from the Vostok core confirmed the emerging scientific consensus that CO2 played a central role in climate change. The findings suggested that powerful feedbacks occurred--global warming and natural emission of greenhouse gasses reinforced one another.
p. 139: In 1985 Wallace Broecker and colleagues concluded that the ocean heat conveyor belt in the North Atlantic could shut down. Other researchers found that the ocean-atmosphere system was delicately balanced and that a shutdown could be swift, with dramatic consequences.
Chapter 7 - Breaking into politics
p. 142: The author discusses the increased politicization of the climate change issue during the Reagan administration in the 1980s. In 1983 the National Academy of Scientists and the Environmental Protection Agency issued reports which, while agreeing that global warming may be coming, differred in the level of concern expressed. Journalists reported on the "controversy," a tale of contesting views that made a lively news story.
p. 151: The 1985 meteorological conference at Villach, Austria announced an international scientific consensus: "In the first half of the next century a rise of global mean temperature could occur which is greater than any in man's history."
p. 153: The author discusses the international agreement in 1979 to address acid rain and the 1987 agreement to restrict ozone-damaging chemicals (CFCs). In 1988, scientists at the Toronto conference for the first time called on the world's governments to set strict, specific targets for reducing greenhouse gas emissions. Congressional testimony by James Hansen during that hot summer helped make global warming a new environmental cause.
p. 158: In 1988 the World Meteorological Organization created the Intergovernmental Panel on Climate Change (IPCC) to coordinate international climate studies. The IPCC was created in response to conservatives and skeptics who distrusted the international panels of scientists who had been driving the issue up to this time. The IPCC was neither strictly scientific nor strictly political, but a unique hybrid. It operated in a democratic fashion, with vigorous debate, negotiation, consensus building, and votes in councils. The author notes: "Such a transnational scientific influence on policy matched dreams held by liberals since the nineteenth century. It awoke corresponding suspicions in the enemies of liberalism."
Chapter 8 - The discovery confirmed
The author cautions that this chapter, dealing with recent developments, is only a preliminary sketch and should not be considered "history."p. 162: The first IPCC report in 1990 concluded that the world had been warming but that much of this might possibly be attributed to natural processes. Another decade of work would be necessary before scientists could be confident that warming was caused by the greenhouse effect. "Under pressure from the industrial interests, as well as from the mandate to make only statements that virtually every knowledgeable scientist could endorse, the IPCC's consensus statements were highly qualified and cautious. This was not mainstream science so much as conservative, lowest-common-denominator science."
p. 166: The most outspoken critics of global warming predictions rarely published their work in peer-reviewed journals. The popular press often sought an artificial balance by pitting "pro" against "anti" scientists, neglecting the fact that there was a consensus view shared by most experts.
p. 170: The 1991 eruption of Mt Pinatubo in the Philippines provided a "natural experiment" to test the latest computer models. The models correctly predicted a temporary global cooling. The effects of aerosols were added to general circulation models (GCMs), improving their accuracy.
p. 172: Computer models predicted that greenhouse gases would cause a particular regional pattern of temperature change (a so-called "fingerprint") that was different from what might be caused by other factors. The observed pattern did resemble the GCM predictions. The 1995 IPCC report concluded that "there is a discernible human influence on global climate."
p. 174: The Kyoto protocol to cut greenhouse gas emissions was drafted in 1997. The U.S. Senate ignored the treaty.
p. 181: After discussing climate modeling problems, the author concludes that "by the start of the twenty-first century the modelers could confidently declare what was reasonably likely to happen." Doubling the CO2 level was most likely to raise average temperature around 3 degrees C.
p. 183: By the late 1990s the Northern Hemisphere spring was coming on average a week earlier than in the 1970s. Ice core studies indicated that climatic temperature swings could happen much faster than previously thought. Computer models suggested that a rapid flip-flop of the North Atlantic circulation could be one explanation. Further studies indicated that the relatively stable climate known throughout history "was a lucky anomaly" (p. 186).
p. 187: The 2001 IPCC report concluded that the world was rapidly getting warmer and that most of the recent warming was likely due to increased greenhouse gas concentrations. (On p. 196 the author explains that "likely" means a probability between 66 and 90 percent.) Scientists started to think about greenhouse gases tripling from pre-industrial levels, not doubling. Newly elected President George W. Bush rejected any U.S. regulation of CO2 emissions.
p. 188: The first major business group to get worried about global warming was the insurance industry, which endured huge losses in the 1990s due to storms and floods. Lacking government leadership, far-seeing people in a variety of fields began to make plans to reduce and adapt to greenhouse warming (p. 190).
Reflections
p. 198: "Faced with scientists who publish warnings, the public's natural response is to ask them for definitive guidance. When the scientists fail to say for certain what will happen, politicians habitually tell them to go back and do more research. That is all very well, but in the case of climate, waiting for a sure answer would mean waiting forever. When we are faced with a new disease or an armed invasion, we do not put off decisions until more research is done; we act using the best guidelines available."
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