Global Warming: The Scientific Consensus

Testimony before the Senate Foreign Relations Committee
Subcommittee on International Economic Policy, Export and Trade Promotion

June 26, 1997

Professor Alan Robock

Department of Meteorology
University of Maryland
College Park, Maryland 20742


    First I would like to introduce myself. I earned a Ph.D. in Meteorology at the Massachusetts Institute of Technology in 1977. Since then I have been on the faculty of the Department of Meteorology of the University of Maryland, where I am now a Professor and the State Climatologist of Maryland. My research involves many aspects of climate change, including the greenhouse effect, impacts of climate change and satellite observations. I have published more than 125 articles on my research, more than half of these in the peer-reviewed literature. I conduct both observational analyses and climate model simulations.

    I have published papers on the creation of regional climate change scenarios for impact analysis and on the effects of climate change on corn production in Venezuela. I recently published a paper (Vinnikov, Konstantin Ya., Alan Robock, Ronald J. Stouffer, and Syukuro Manabe, 1996: Vertical patterns of free and forced climate variations. Geophys. Res. Lett., 23, 1801-1804) which showed that the cooling of the stratosphere which has been observed during the past 30 years has a very small chance of having happened due to natural climate fluctuations, and is most likely a signal of human impacts on the climate.

    I am a contributing author to 4 of the 11 chapters of the most recent IPCC 1995 Working Group I report, including Chapter 8, "Detection of Climate Change and Attribution of Causes." The work I did in contributing information to these chapters, and in reviewing these and other chapters, was done as a volunteer, at night and in my spare time, with no compensation. I currently have grants from the National Science Foundation, the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the US Department of Energy (DOE) that support my scientific research. I have no private financing of my research or publications.

    I am a member of the American Meteorological Society, the American Geophysical Union, and the American Association for the Advancement of Science (AAAS). I serve on the Scientific Advisory Board of the National Institute for Global Environmental Change, Great Plains Regional Center, at the University of Nebraska in Lincoln, and have since its inception in 1992. This center is funded by DOE. I am the Associate Editor for Meteorology of Reviews of Geophysics. I serve on the International Climate Commission of the International Association for Meteorology and Atmospheric Science (IAMAS) and the American Meteorological Society Committee on Climate Variations. I was awarded a AAAS Congressional Science Fellowship in 1986, and served as Legislative Assistant to Congressman Bill Green (R-NY) and as a Research Fellow with the Environmental and Energy Study Conference from September, 1986, through August, 1987, where I authored the report The Greenhouse Effect: Global Warming Raises Fundamental Issues. During the 1994-95 academic year I was a Visiting Research Scientist at Princeton University in the Atmospheric and Oceanic Sciences Program, conducting climate research at NOAA's Geophysical Fluid Dynamics Laboratory.

Scientific Consensus on Global Warming

    I agree with the conclusions of the 1995 IPCC Working Group I report that "the balance of evidence suggests that there is a discernible human influence on global climate." Note that this is the balance of evidence, NOT unambiguous proof. The report points out that "our ability to quantify the human influence on global climate is currently limited because the expected signal is still emerging from the noise of natural variability, and because there are uncertainties in key factors. These include the magnitude and patterns of long term variability…." [Both these quotes are from p. 5 of the Summary for Policymakers.] I agree with this part of the assessment, too.

    What is the evidence we use? The evidence which supports a human influence on climate includes observations that the concentrations of "greenhouse gases" which are produced by human activity, especially carbon dioxide, are increasing and that these gases warm the surface by enhancing the natural greenhouse effect. These facts are undisputed. But these gases are not the only cause of climate change. When the most recent climate models include the effects of greenhouse gases, aerosols (particles in the atmosphere), volcanic eruptions, solar variations, and El Niño in their calculations, they produce simulations of climate change of the past 100 years that agree quite well with the past surface temperature record. In addition, stratospheric temperatures are decreasing, sea level is rising, and glaciers are melting, all in agreement with these theoretical calculations.

    It is these same models that we use for projections of future climate, and they say that the global average temperature will rise by 2 to 6°F by the end of the next century. Even for the smallest increase projected, "the average rate of warming would probably be greater than any seen in the last 10,000 years." [p. 6 of the IPCC Summary for Policymakers.] The IPCC goes on to say, "actual annual to decadal changes would include considerable natural variability. Regional temperature changes could differ substantially from the global mean value." This means that at any one location on the globe, the probability of high temperatures will increase, but it will not be warmer on each and every day.

    Of the projected consequences of global warming to society, I see the threat of midlatitude drought, and resulting crop failures in the breadbaskets of the world, as a significant potential danger. The food supply of a planet that will have many more mouths to feed is threatened. It is difficult to quantify this threat. While IPCC studies show possible large increases and decreases in crop productivity in different regions of the world, with no net large changes in current production, much more work is need in this area.

    Other potential impacts on humans include stronger and more violent storms, coastal flooding and erosion, forest declines, spreading of deserts, more intense droughts and floods, spread of tropical diseases, poorer winter skiing and snowboarding, increased human mortality and illness from heat, and increased economic and geographical dislocations. The distribution of impacts is not uniform around the world. Ironically, while the developed nations of the world produce the majority of greenhouse gases, it appears that developing countries will be more severely affected. However, quantified estimates of total damage to society are currently quite uncertain.

What Should We Do?

    Here I give you my professional opinion based on my scientific and political knowledge. We need to take measures as insurance against possible serious consequences. Policy responses will have to made in an environment of uncertainty, but not in an environment of ignorance.

    Our response to the threat of global warming at this time should be one of adaptation, improved knowledge, and mitigation. "No regrets" responses should be strongly pursued. I will briefly comment on each of these.

    Adaptation. No matter what our response, the planet will warm. The most we can hope to achieve is to slow the rate of warming in the next century. Therefore, in the case of each threat to society listed above, all the threats not mentioned, and the threats that will appear that we are not smart enough to imagine now, we will have to adapt to minimize the negative impacts. This adaptation will require much better information and technological innovations. This represents a significant business opportunity in the United States to develop the necessary devices and products and to market them to the world.

    Improved knowledge. We need better data, better models, better computers, and more trained scientists and engineers to address the problems presented by global warming. Investing in the nation's scientific research establishment is a very inexpensive and very rewarding allocation of the nation's resources. We have to know where and when temperature, precipitation, storm, and sea level changes will take place. We need to know the biological response of agricultural and natural ecosystems to the changed climate. Only then can we gauge the impacts of our actions, and help to adapt precisely to the changes.

    Mitigation. If climate change is slowed down and more gradual, society will have more time to learn to live in this new world. This means stopping the global growth in the emission of carbon dioxide, and slowly reducing it. The only way to do this is to include burning less coal and oil in the response. Any combination of conservation, energy efficiency, energy tax, and public transportation enhancements will result in less gasoline being burned and less coal being burned.

    "No regrets" policies. Reduced usage of energy will have many positive benefits to society, while exacting small costs, even if projected global warming turns out to have been exaggerated (which is just as likely as that the warming turns out to have been underestimated). We would have cleaner air, less acid rain, greater visibility in the atmosphere, cooler central regions of cities, more trees, and less dependence on foreign oil supplies (currently about half of our usage). There are many proposals along this line that will not reduce American living standards, and our productivity will increase in the long run as we use energy more efficiently.

    Legislative response. In light of the above discussion, I cannot support the Byrd/Hagel Senate Resolution 98 which seeks to limit current US participation in a climate treaty unless developing countries are also included now. The United States agreed in Berlin in 1995 that the current round of negotiations will only commit industrialized nations to emissions targets, and that the developing countries will produce commitments in the subsequent round of talks. There is no reason to change this now. The latest scientific research supports this position.

    The fact is that each US citizen currently produces more than 5 times the greenhouse gas emission as the average person on earth. Once industrialized countries set an example, as we have in so many other social, moral, and environmental issues, the developing world will accept its responsibility to restrict greenhouse gas emissions as already agreed in the next few years.

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