Chairman CALVERT. Thank you, Doctor. Dr. Prinn? TESTIMONY OF RONALD G. PRINN, TEPCO PROFESSOR OF ATMOSPHERIC CHEMISTRY AND DIRECTOR, CENTER FOR GLOBAL CHANGE SCIENCE, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MA Mr. PRINN. Honorable Chairman and members, current predictions of future climate are very uncertain. Forecasts of quite slow or quite rapid warming can both be defended as plausible, but this uncertainty is not a sound argument for waiting for more knowledge before taking some action. The long-lived greenhouse gases emitted today will last for decades or centuries in the atmosphere and scientists cannot presently rule out the rapid warming forecasts. However, our policy response needs to be carefully measured. To quote a metaphor from a recent MIT report, "It would be irresponsible to ignore such a risk, just as it would be irresponsible to do nothing when you smell smoke at home until and unless you see flames. It would also be irresponsible, of course, to call the fire department and hose down all your belongings at the slightest whiff of what might be smoke." The climate change debate is driven by forecasts of significant warming over the next century. The computer models we use to make these forecasts are remarkable in their complexity and are invaluable tools for scientific research. However, current climate models cannot simulate realistically natural climate variability, exemplified most obviously by the succession of ice ages and warm periods over the last quarter of a million years. There may even be fundamental limitations to our ability to predict climate due to chaotic processes such as we already see in weather predictions. As a result, our present ability to predict climate is inadequate to provide a sharp focus for policy making. Ongoing efforts need to be accelerated. But, we have become too dependent on just a few climate models located mainly at national laboratories and centers. The full intellectual strength of the Nation's universities needs to be brought into the area of such climate modeling. To shed more light on the current substantial uncertainty in forecasts, we've recently developed at MIT a coupled model of global economic development, climate processes, and ecosystems. Within this model, we've made some plausible but differing assumptions about future human activity and about fundamental climate processes to produce a family of seven forecasts. The graph shows the predictions for the change in global average surface temperature from its 1990 value. By the Year 2100, forecasted temperature changes as small as 2 degrees or as large as 9 degrees Fahrenheit can be defended. We do not know which of these paths we are heading along in the absence of regulation. If we're on the lowest warming path, the impacts are likely to be relatively small. If we're on the highest warming path, the impacts are likely to be very large and there are compelling reasons to take very significant action to avoid this path. How can we determine which path, absent regulations, that we are really on? One approach is to determine whether human activity has already begun to substantially change climate. In 1996, as we all know, the Intergovernmental Panel on Climate Change declared that, "The balance of evidence suggests a discernible human influence on climate." Human influence is indicated if the observed global patterns of climate change are consistent with those predicted by climate models which include the human influences, but are not consistent with the patterns predicted when the human influences are neglected. But the imperfections of current climate models make them both inadequate tools for defining natural variability and uncertain predictors of the climate response to human forcing. For these and other reasons, there were a few scientists who were skeptical about the balance of evidence statement from the beginning. But now there are a growing number of scientists expressing doubts. It may be a decade or more before the human effects can be discerned above the noise of natural variability. How can scientists help better in the evolving policy process? First, the search for a definitive signal of human influence should be one important goal. I refer again to the graph of predicted temperature changes. The shaded region at the bottom of the graph represents the uncertain range of natural variability, or noise. The greater the predicted warming, the sooner the signal of the human effects emerges from this noise. A detection, therefore, helps to calibrate both the climate response to changes in forcing and the needed policy response. Another calibration is provided by estimation of the climate changes avoided by enacting specific regulations. The MIT model is being used to examine one proposal in which the 20 rich OECD countries bring their emissions down to 20 percent below 1990 levels by the Year 2010. The predicted temperature changes are reduced by only 15 percent relative to the low policy forecast that I show in that graph. Only a 15 percent lowering of the amount of warming. If we are heading along one of the rapid warming roads, the needed emissions reductions to avoid this path will need to be substantially greater even than those proposed in the above policy. Indeed, very substantial reductions will require ultimate participation by all nations. The policy response can be further calibrated by quantifying the impacts of climate change. Here, there's a serious need to better understand and quantify these effects. Impacts on human health, agriculture, forestry, water supply and quality, and flood-prone settlements can be potentially avoided by adaption. Natural ecosystems may not be able to adapt. Accurate quantification of impacts is essential to define the appropriate balance between the cost of policies to lower greenhouse gas emissions and the impacts avoided by these policies. Is the science-policy interrelation adequate? The IPCC process, while it has its merits, is simply not structured to provide the required continuous up-to-date integrated assessment mechanism for policy. There will, for example, be very significant policy development under the Framework Convention on Climate Change prior to the IPCC Third Assessment which is not due to be published until the Year 2001. We cannot afford to let scientists be mere spectators to this policy development. If improved scientific understanding shows that we're definitely on one of the rapid warming pathways shown in the graph, then very significant action to lower total long-term greenhouse gas emissions will become necessary. We need to take the steps now to make the political agreements and develop the technological capabilities to substantially lower emissions if and when the science shows that to be necessary. Honorable Chairman and members, let me end with an extension of the smoke and flame metaphor quoted at the beginning of my testimony. I believe we need to increase the accuracy of our smoke detectors, design the fire extinguishers with the needed power, and agree on the worldwide mechanisms for using these extinguishers, should the smoke detectors show that to be necessary. Thank you. [The prepared statement and attachments of Mr. Prinn follow:] Climate Change: State of the Science and Ronald G. Prinn Massachusetts Institute of Technology Testimony to the Subcommittee on Energy and Environment of the Committee on Science U.S. House of Representatives The Honorable Ken Calvert, Chairman Honorable Chairman and Members of the House Subcommittee on Energy and Environment, I respectfully submit the following testimony in response to your invitation of September 25, 1997. I have been on the faculty of the Massachusetts Institute of Technology since 1971. While I specialize in atmospheric science, in my capacity as Director of the MIT Center for Global Change Science and Co-Director of the MIT Joint Program on the Science and Policy of Global Change, I have also gained some appreciation of the various disciplines in the natural and social sciences involved in the climate debate, and carried out research aimed toward better understanding of interactions between the natural and human systems which affect climate. I want to address here a few specific points. First, I will briefly say something about the definition of climate, the reality of the greenhouse effect, and how reliable the forecasts of future climate are. Second, I will look at why the detection of the human influence on climate is so difficult, but also so important to both the science and policy of the issue. Third, I will address certain areas of the scientific research which I think are especially important for informing policymaking. Finally, I will argue that because the science is both uncertain and evolving, scientists should be in much closer contact with the policy development process than they are at present. I want to say right up front that current predictions of future climate are very uncertain: forecasts of quite slow or quite rapid warming can both be defended as plausible. But this uncertainty is not a sound argument for waiting for more knowledge before taking some action. The long-lived greenhouse gases emitted today will last for decades to centuries in the atmosphere and scientists cannot presently rule out the rapid warming forecasts. Our policy response needs to be carefully measured, however. To quote a metaphor from a recent report by my colleagues and me', "It would be irresponsible to ignore such a risk, just as it would be irresponsible to do nothing when you smell smoke at home until and unless you see flames. It would also be irresponsible, of course, to call the fire department and hose down all your belongings at the slightest whiff of what Climate and the Greenhouse Effect What do we mean by the word climate? Climate is usefully defined as the average of the weather we experience over a ten- or twenty-year time period. Long-term temperature and rainfall changes are typical measures of climate change, and these changes can be expressed at the local, regional, country, or global scale. When the global average temperature changes we call that global warming or cooling. What produces global warming or cooling? Fundamentally, it can be driven by any imbalance between the energy the Earth receives, largely as visible light, from the sun, and the energy it radiates back to space as invisible infrared radiation. The greenhouse effect is a warming influence caused by the presence in the air of gases and clouds which are very efficient absorbers and radiators of this infrared radiation. The greenhouse effect is opposed by substances at the surface (such as snow and desert sand) and in the atmosphere (such as clouds and aerosols) which efficiently reflect sunlight back into space and are thus a cooling influence. Easily the most important greenhouse gas is water vapor which typically remains for a week or so in the atmosphere. Water vapor and clouds are handled internally, although with significant uncertainty, in climate models. Concerns about global warming, however, revolve around less important but much longer-lived greenhouse gases, especially carbon dioxide. The concentrations of carbon dioxide and some other long-lived gases (methane, nitrous oxide, chlorofluorocarbons, lower atmospheric ozone) have increased substantially over the past two centuries due at least in part to human activity. When the concentration of a greenhouse gas increases (with no other changes occurring) it temporarily lowers the flow of infrared energy to space and increases the flow of infrared energy down toward the surface. The Earth is then temporarily receiving more energy, for example 1% more, than it radiates to space. This small imbalance, which is often called "radiative forcing", tends to raise temperatures at the surface and in the lower atmosphere. The rate of surface temperature rise is slowed significantly by the uptake of heat by the world's oceans. The greenhouse effect as quantified by this radiative forcing is real and the physics relatively well understood. What is much more uncertain, and the cause of much of the scientific debate, is the complex system that determines the response of our climate to this radiative forcing. Feedbacks in this system can either amplify or dampen the response in ways which are only partially understood at present. How Good Are The Climate Forecasts? Much of the climate change debate is driven by forecasts of significant warming over the next century. The computer models used to make these forecasts attempt to simulate the behavior of clouds, water vapor, ocean circulation, and many other essential climate processes on the regional and global scale. These models are remarkable in their complexity and are invaluable tools for scientific research. However, many critical small-scale features like clouds are not resolved |