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Stuttgart Energy and Climate Congress

October 2004

Global Climate Change: A Survey of the Science and Policy Implications
D. Warner North and Stephen H. Schneider

Presentation at the Conference on Global Climate Alteration and Energy Policy
Sponsored by the Ministerium fur Umwelt und Verkehr,
State of Baden-Wurttemberg,
Stuttgart, Germany, October 11, 2004

      It was a pleasure and privilege for Warner North to replace his Stanford University colleague Stephen Schneider on a few days' notice at the Stuttgart Conference. This written version of the material presented by Dr. North was prepared at the request of the conference organizers in the Ministerium fur Umwelt und Verkehr Baden-Wurttemberg. It combines Professor Schneider's visual aid materials prepared in advance for this conference with additional comments and references inserted by Professor North for the oral presentation at the conference. Because of space and graphics limitations in the printed Conference Summary, pictures and graphics used in the oral presentation are not included, but brief descriptions and references to websites are given in the text below.


          In the city of Stuttgart, a world-renowned center of automobile design and manufacturing, an American expert on energy and climate might appropriately open his presentation with the American "Hummer" H2 sport utility vehicle pictured in an advertisement, with a caption that this vehicle "does well at the (melting) Poles." This picture did indeed begin Professor Schneider's visual aid materials and Dr. North's presentation. It illustrates the concern for both recent scientific findings that polar ice is melting at an alarmingly rapid rate and the need for increased energy efficiency and reduced reliance on fossil fuels, policy issues for leaders in business and government in both of our countries.
          Article 2 of the United Nations Framework Convention on Climate Change (UNFCC) states that we must prevent dangerous levels of climate change from occurring. This implies a shift in energy policy:

      The ultimate objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.

    The UNFCCC further suggests that "Such a level should be achieved within a time frame sufficient:

    • to allow ecosystems to adapt naturally to climate change,
    • to ensure that food production is not threatened and
    • to enable economic development to proceed in a sustainable manner."
          What do these requirements mean for Germany, the United States, and other leading industrialized countries? We must consider the emerging knowledge from scientific research of the potential impact of increasing atmospheric concentrations of carbon dioxide (CO2), which results primarily from the burning of coal, oil, and natural gas (fossil fuels) for energy. While other greenhouse gases contribute to climate alteration, and some of the increase in atmospheric carbon dioxide comes from deforestation, it is our ongoing reliance on the combustion of fossil fuel that must be considered the primary candidate for multinational action under the terms of the UNFCC. However, at early phases of international mitigation actions, considering multiple gases may be the most cost-effective way to initiate abatement.
          A number of scientific reports summarize what is known and not known about the potential for increased levels of carbon dioxide and other greenhouse gases to alter the climate. Dr. North was involved in the peer review of two reports prepared by the United States Environmental Protection Agency (USEPA) to the US Congress fifteen years ago on the potential effects of climate alteration in the US and on mitigation strategies [1,2,3]. The reports of the Intergovernmental Panel on Climate Change (IPCC), in which Dr. Schneider has played a large role, follow a similar approach to the USEPA reports [4]. A European audience may find useful the reports on climate change and energy policy from the Unites States National Academy of Sciences [5,6,7].
          A report on climate change science [7] was prepared by the National Research Council in a three-week period in 2001 at the request of President George W. Bush's Administration. Like previous reports, it stresses the uncertainty regarding whether the warmer global average surface temperatures observed over the last few decades are due to natural fluctuations in the earth's climate, or, more likely, to increased levels of carbon dioxide and other greenhouse gases. The report goes on to stress that continued emissions of greenhouse gases are expected to alter climate, although the magnitude and the rate of such alteration remain uncertain. The report states:
      Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability. Human-induced warming and associated sea level rises are expected to continue through the 21st century. Secondary effects are suggested by computer model simulations and basic physical reasoning. These include increases in rainfall rates and increased susceptibility of semi-arid regions to drought. The impacts of these changes will be critically dependent on the magnitude of the warming and the rate with which it occurs.

    ([7], page 1, emphasis added.)

          We shall now try to summarize the important uncertainties surrounding climate change in quantitative terms, using a set of emissions scenarios developed by the IPCC [4]. These emissions scenarios are projections of world population, socio-economic development, and technology and process choices, which determine the emissions of carbon dioxide and other greenhouse gases from the present through the year 2100. We shall focus on the A1 scenario, which is a scenario of very rapid world economic growth, with a world population that peaks at the middle of the 21st century. We shall compare three possibilities for technological change in the energy sector of the world economy: the A1FI "fossil intensive" pathway, the A1B "balanced" pathway, and the A1T, an advanced "technology" pathway in which fossil fuel use is greatly reduced. Under the A1FI scenario, CO2 emissions peak at about 30 gigatons (GT) of carbon annually and atmospheric carbon dioxide levels are projected to reach nearly 1000 parts per million (ppm) by 2100. Under the A1T scenario, annual CO2 emissions peak at about 12 GT, and atmospheric CO2 levels have not reached 600 ppm by 2100. In the "balanced" A1B scenario, the concentration of CO2 is projected to reach about 700 ppm by 2100. Even the "best" A1T, doubles CO2 concentrations by 2100, but at least they are stabilized, whereas A1FI triples concentrations by 2100 and would represent a quadrupling or more in the 22nd century.
          What difference does it make to earth's climate whether atmospheric CO2 levels reach 1000 ppm or stay below 600 ppm? We should recognize that the impact on climate of such large changes in CO2 and other greenhouse gases is highly uncertain. The atmospheric concentration of CO2 is now at about 370 ppm, an increase from 280 ppm prior to the industrial revolution in Europe and North America. We have reached levels at which most climate scientists believe that increased greenhouse gas concentrations are contributing to global warming at a level that can be distinguished from natural fluctuations in climate.
          The earth's climate does fluctuate on a time scale of centuries, and such past fluctuations have become an area of intense study [8,9,10,11,12]. From cores taken from Arctic and Antarctic ice, scientists can infer temperature levels and atmospheric levels of CO2 going back through the repeated cycles of glaciation of the past 500,000 years. A look at ice core data for the last 10,000 years (roughly since the last ice age receded and humans developed agriculture) indicates that temperature fluctuations over this period (which are not believed to be more than plus or minus a degree or two Celsius) have still been large enough to have significant impacts on European agriculture and history [8]. Within the past 1,000 years, European climate has warmed, cooled, and then warmed again, as measured from records of how often major rivers froze and where wine grapes could be effectively cultivated [9]. Scientists are in the process of refining quantitative estimates of these past fluctuations, but differences remain in how to interpret the data [10,11,12]. However, what seems clear to most scientists is that continued high levels of CO2 and other greenhouse gas emissions could result in climate changes over the next 50 to 100 years that are far greater than those that have occurred in the past ten thousand years of earth's history, during which human civilization emerged.
          We will sketch the process of developing a quantitative description of the uncertainty in future climate change, including the impact of changing emissions of greenhouse gases over the 21st century. To do this, we shall use a simplified measure of climate, the temperature averaged over the entire world and over the seasonal changes through a year (global average surface temperature). Past climate shifts since the ice age ended may have been of the order of one or two degrees Celsius on this scale. Projections of changes in the 21st century range up to about ten degrees Celsius. One widely used probability assessment [13] for the temperature changes resulting from a doubling of the atmospheric loading of CO2 (called climate sensitivity) estimates that there is a 10% probability that the global average temperature would increase by less than 1.1 degrees, and a 10% probability that the increase would be 6.8 degrees or more for a doubling of CO2 [13]. The most likely range of change is in the neighborhood of 2 degrees Celsius for a doubling of CO2. In [13] there is a 50% probability that the temperature increase will be less than 2 degrees Celsius, and a 50% probability the temperature increase will exceed 2o C. There is a small probability (5%) of an increase exceeding 10o C for CO2 doubling - a truly catastrophic prospect.
          Do climate scientists and other experts agree on such probabilities? As might be expected, the judgments of climate experts differ. Of 16 American experts asked in a study [14] published ten years ago, only one seemed certain that the change in global average temperature from a doubling of CO2 from pre-industrial levels would be small, within the range of historical variation over the past millennium. The others were in general agreement that the change could be much larger. The important insight from this survey is that most scientists think the range of uncertainty on the extent of climate change is very large.
          We will now look at the impact of reducing fossil fuel use by comparing the range of uncertainty in temperature changes for the scenario of continued intensive fossil use to 2100, A1FI, versus the phasing out of fossil fuels, as assumed in A1T. Let us take the 90th percentile estimate of climate sensitivity from [13] of 6.8o C warming from a doubling of atmospheric CO2. Under the fossil phase-out emissions scenario A1T, the 90th percentile estimate gives us temperature increases of 2.5o C by 2025, more than 5o C by 2050, and more than 8o C by 2100. At the median (50%) climate sensitivity, the projected temperature increases are about 1o C by 2025, 2o C by 2050, and 3o C by 2100. The 10th percentile estimate gives a rise of less than 1o C by 2050 and only about 1.5o C by 2100. Now let us compare these numbers to the numbers projected for A1FI. With the 90th percentile estimate of climate sensitivity, the predicted changes in global temperature are about the same as they are in A1T for 2025, and 2050, but they reach 13o C in 2100, compared to 8o C for A1T. The median and 10% estimates for 2025 and 2050 are also similar to those obtained under A1T, but by 2100, they deviate dramatically from A1T: 4.5o C for the median (versus 3o C for A1T) and 2.3o for the 10th percentile estimate (versus 1.5o C for A1T).
          The inference to take away from these numbers is that climate change could be moderate, or it could be quite large. If we were to examine all 40 of the scenarios developed by IPCC for its 2000 report, we would see a wide range of projections for global temperature increase, from a small change on the order of 1o C by 2100 to at least 5o C, or even 10o C! The larger the change that actually occurs, the larger and more complex will be the impacts, and the more difficult it would be for societies or natural systems to adapt. These impacts could include increased frequency and severity of floods, droughts, and extreme storms, as well and regional and global alteration in temperature patterns. Most climate models suggest the warming may be most apparent in the high latitudes of the Arctic and Antarctic regions. Melting of polar ice, changes in sea levels, and alteration of ocean currents such as the northeastern warm water flow in the Atlantic may occur, especially for warming beyond several degrees. Extensive climate alteration will have large impacts on agriculture and natural ecosystems, leading to changes in the areas suitable for many important food crops, and potential extinction of some species from the rapid alteration of habitat. Many case studies are being done to look at potential impacts in specific areas. Professor Schneider and colleagues have recently carried out one such assessment for California [15]. Many other such assessments are being carried out by scientists throughout the world. But at this time no one can predict accurately how large the climate impacts will be as continued emissions of CO2 and other greenhouse gases alter the composition of the atmosphere. Research and continuing observation of the earth's climate should allow better understanding to be achieved in coming decades, but given the complexity of the earth's atmosphere and oceans, such better understanding may not come easily or quickly.
          The United States government has an interagency climate research activity, the U.S. Climate Change Science Program, whose findings are similar to those of other groups of scientists. In a recent report, the group states:
      Climate variability and change can profoundly influence social and natural environments throughout the world, with consequent impacts on natural resources and industry that can be large and far-reaching. Recent advances in climate science are providing information for decision makers and resource managers to better anticipate and plan for potential impacts of climate variability and change. Further advances will serve the nation by providing improved knowledge to enable more scientifically informed decisions across a broad array of climate-sensitive sectors.

    [16], page 42. Emphasis added.

          This and many other assessments make clear that the large uncertainties in the scientific understanding should not be a basis for continuing inaction. Many scientists and energy experts in the United States concluded as early as 1991, in a report produced by the National Research Council, that steps should be taken to adapt energy policy to the threat posed by climate alteration:
      Despite the great uncertainties, greenhouse warming is a potential threat sufficient to justify action now. Some current actions could reduce the speed and magnitude of greenhouse warming; others could prepare people and natural systems of plants and animals for future adjustments to the conditions likely to accompany greenhouse warming.

    [5], page 72. Emphasis added.

          Policy makers need to inform themselves about current thinking on climate change, which has been developed through continuing scientific research. The opportunities and challenges of rapid industrialization in China, India, and other areas of the world need to be carefully assessed, because greater use of coal, oil, and gas by growing economies outside Europe and North America could more than offset gains from conservation, increased energy efficiency, and use of renewable energy sources in highly developed countries. Climate alteration is a global problem, and global strategies are needed to deal with it.
          Perhaps our most important message is that we need to make policy decisions about our energy future in the face of great uncertainty about what continued high emissions of CO2 imply for climate alteration over the next 50 to 100 years. It seems unlikely that the uncertainty will be resolved quickly -- decades of additional research may be needed. Further, changing the energy sector of the world economy from its present high reliance on fossil fuels to alternative energy sources and higher energy efficiencies will take many decades. The IPCC and many economists and other analysts have therefore adopted the viewpoint of decision making under uncertainty about emissions control, with a focus on the coming 50 to 100 years. One analysis of policy alternatives published in a leading journal since the Stuttgart Conference is an October 2004 article in Science magazine, "To Hedge or Not Against an Uncertain Climate Future" [17]. Leaders in the energy sector of the international business community are speaking out on the need to learn and to take appropriate action [18].
          Much more effort will be needed beyond the productive discussion that those present enjoyed in Stuttgart on October 11, 2004. Such effort will be needed in Germany, in the United States, and by leaders throughout the world. Some of us from the United States are pleased to see the Russian ratification of the Kyoto Protocol as a useful first step in international collective action. But far larger emission reductions will be needed to mitigate significant climate alteration if climate sensitivity turns out to be moderate or large, as opposed to very small. Kyoto does not remotely resemble a viable plan to control climate change over a century, though it is an important first step to create the international cooperative actions needed to fashion truly meaningful abatement strategies like those in the A1T scenario. If world governments deem it "dangerous" to allow a doubling of CO2, then even stronger actions will be needed than is represented by the A1T scenario. If the world opts for a "business as usual" scenario like A1FI, then massive climate changes will have a better than coin-flip (i.e., 50%) odds of occurring by the end of the century. Collectively, we need to continue to enhance the international efforts to provide improved scientific knowledge, and to encourage and enable timely and informed cooperative decisions to manage the future of our planet's climate. One plausible strategy may be to focus first on cost-effective efficiency investments and co-benefits (an example of the latter is replacing a highly polluting coal plant near a population center with a natural gas unit that will not only emit half the CO2 per unit energy, but also will greatly reduce health-damaging aerosols and other pollutants). A search for cost-effective "win-win" solutions has the best promise to advance the international dialogue seeking both fair and efficient solutions to the risks imposed by anthropogenic climate change.


    [1]. US Environmental Protection Agency, The Potential Effects of Global Climate Change in the United States, Report to Congress, Washington, D.C., US Government Printing Office, EPA-230-05-89-050, 1990.
    [2]. US Environmental Protection Agency, Policy Options for Stabilizing Global Climate, Report to Congress, Washington, D.C.: US Government Printing Office, 1991.
    [3]. D. Warner North, "EPA's Draft Reports to Congress on Global Warming: An Overview," unpublished summary of the review of [1] and [2] in draft form by the EPA Science Advisory Board, 1990. Available at www.northworks.net.
    [4]. Intergovernmental Panel on Climate Change, Special Report on Emissions Scenarios, 2000. Available at: http://www.grida.no/climate/ipcc/emission/index.htm.
    [5]. National Research Council, Policy Implications of Greenhouse Warming, Washington, D.C.: National Academy Press, 1991: Available at: http://books.nap.edu/catalog/1794.html.
    [6]. National Research Council, Confronting Climate Change: Strategies for Energy Research and Development, Washington, D.C.: National Academy Press, 1990: Available at: http://books.nap.edu/catalog/1600.html.
    [7]. National Research Council, Climate Change Science: An Analysis of Some Key Questions, Washington, D.C.: National Academy Press, 2001: http://books.nap.edu/catalog/10139.html.
    [8]. Brian M. Fagan, The Long Summer, New York: Basic Books, 2003.
    [9]. Brian M. Fagan, The Little Ice Age, New York: Basic Books, 2001.
    [10]. Michael E. Mann and Philip D. Jones, "Global surface temperatures over the past two millennia," Geophysical Research Letters, 30(15):l820-1823 (2003). http://stephenschneider.stanford.edu/Publications/PDF_Papers/Mann_Jones1.pdf .
    [11]. Hans von Storch et al., "Reconstructing Past Climate from Noisy Data," Science, 306:679-682, 22 October 2004.
    [12]. Timothy J. Osborn and Keith R. Briffa, "The Real Color of Climate Change," Science 306:621-622, 22 October 2004.
    [13]. N. G. Andronova and M. E. Schlesinger, "Objective Estimation of the Probability Density Function for Climate Sensitivity," Journal of Geophysical Research, 106:22605-612 (2001).
    [14]. M. Granger Morgan and David W. Keith, "Subjective Judgments by Climate Experts," Environmental Science and Technology, 29(10):468A-476A (1995).
    [15]. Stephen H. Schneider et al. (18 co-authors), "Emissions pathways, climate change, and impacts on California," Proceedings of the National Academy of Sciences, 101(34):12422-12427, August 24, 2004. http://www.pnas.org/cgi/contents/full/101/34/12422.
    [16]. Our Changing Planet: The U.S. Climate Change Science Program for Fiscal Years 2004 -2005, August 2004. http://www.usgcrp.gov/usgcrp/Library/ocp2004-5/default.htm.
    [17]. Gary Yohe, Natasha Andronova, and Michael Schlesinger, "To Hedge or Not Against an Uncertain Climate Future," Science 306:416-417, 15 October 2004.
    [18]. John Browne, "Beyond Kyoto," Foreign Affairs, 83(4):20-32, July/August 2004.

    The Authors

    D. Warner North is President and Principal Scientist at NorthWorks, Inc., 1002 Misty Lane, Belmont California 94002-3651, USA, and Consulting Professor in the Department of Management Science and Engineering at Stanford University, Stanford, California 94305, USA.
    E-mail: northworks@mindspring.com Web: http://www.northworks.net

    Stephen H. Schneider is Professor, Department of Biological Sciences, and Co-Director, Center for Environmental Science and Policy, Stanford University, Stanford California 94305, USA.
    Web: http://stephenschneider.edu

    Warner North presenting this paper at the Stuttgart Conference

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