The CHAIRMAN. Thank you very much, Dr. Baliunas. STATEMENT OF DR. V. (RAM) RAMANATHAN, SCRIPPS INSTITUTE OF OCEANOGRAPHY Dr. RAMANATHAN. Honorable Chairman, and honorable members of the committee, I consider it a great privilege to participate in this important hearing. My written testimony focuses on the science of greenhouse effect on global warming. The CHAIRMAN. It will be entered into the record. Dr. RAMANATHAN. Thank you, Mr. Chairman. I must confess one thing I would like to add there is that I am what you would call a classical basket case two-handed scientist, so you must bear with me. The CHAIRMAN. The record will note. [Laughter.] Dr. RAMANATHAN. When I present both sides of the issue I would really directly like to go to the issue which was raised here, which is, is the theory wrong, and I believe the question should be more, not if the theory is wrong, but the issue is, have we exaggerated the effect, number 1, and second is what else are we changing which may have compensated for some of the greenhouse effect? So for this issue, it is my personal opinion it is best to separate the problem into two subcomponents. The first one is the greenhouse effect, and the second is the global warming that results from the greenhouse effect. In order to understand the greenhouse effect, let us ask, or take a metaphor, which is how does a blanket keep us warm on a cold night? The blanket simply reduces the loss of the body heat to the colder environment. Likewise, there are certain gases in the atmosphere that surround the planet like a blanket and reduce the heat loss from the planet which would otherwise escape to space. A second point, there is a large natural greenhouse effect provided by water vapor, the dominant greenhouse effect, carbon dioxide, and clouds. This is an observed fact, and we know from cyclic measurements that these greenhouse constituents reduces the heat escaping into space by about 40 percent. We know this figure. A second point, the human activities are simply adding to this large natural greenhouse effect. In other words, this blanket is porous. It is a leaky blanket, and we are simply making the blanket less porous by adding the gases. So in other words, a logical deduction from the observations and all of the physical laws we know, we can say with quite a degree of confidence a buildup of the greenhouse gases would enhance the greenhouse effect. The second question, then, is how would the planet respond? Again, we can say with a fair degree of confidence that the planet will warm if the enhanced greenhouse effect is not offset by other compensating human activities. This is the on the one hand, on the other hand business, just like a thicker blanket or a less porous blanket would keep us warmer in our bedroom if other factors are not altered. So far, we are fairly secure in our knowledge, in our understanding, and in our deductions how we make the statement an enhancement of the greenhouse effect will cause a global warming, but this is rather academic knowledge. As policymakers, you want to know how large is the warming, how soon is it going to descend on us, and what are the regional consequences? It is in answering these quantitative questions that we slip from facts and sound physical principles to model predictions that are, in my personal view, yet to be defined. There is now at least a threefold range in the model predictions. I must also say the models have made impressive improvement in their simulations, and they have tried their best to close the gap, but in the last 5 years new issues have come up with have increased uncertainties, and that is one of the reasons you would see when you go from 1990 IPCC to 1995, the warming projections have come down not because of any serious errors in the models but because of the new issues, and I would like to give you one example of that. Recent findings have increased on uncertainty even more. These studies have pointed out human activities may be modified. Several other climate-forcing factors, particularly I would note here a potentially large cooling effect due to aerosols, what we call aerosols. These are not to be confused with the chlorofluorocarbons. These are particles in the atmosphere which get cooked in the atmosphere because of sulphur compounds biomass burning and others. There is other climate-forcing factors like decrease of stratospheric ozone, which is also causing a slight cooling in the models, et cetera, so we are changing other factors which might be compensating for some of the greenhouse effect, but not all of it. Lastly, I would like to conclude with another important example, just to point out how the science is moving rapidly, and all we can hope for is a snapshot of a moving target. Recently, six independent studies in the United States, Germany, and Switzerland have identified a large and systematic discrepancy between climate model simulations and observations. In these studies, the model atmosphere absorbs significantly less solar radiation than indicated by observations. Remember, the solar radiation is one of the fundamental driving forces of climate. The cause of this absorption is still mysterious, and there is also a magnitude, and where it is occurring is being actively debated within the community, but if these findings are confirmed, they are bound to have a large impact on the model simulation of climate. It is unknown how it will change the climate predictions. So with that, I would like to conclude with again an opinion now, is that we have to accelerate the pace of research if we are going to come to grips with uncertainties and help the policymakers. Thank you. [The prepared statement of Dr. Ramanathan follows:] PREPARED STATEMENT OF DR. V. (RAM) RAMANATHAN, SCRIPPS INSTITUTE OF OCEANOGRAPHY Honorable Chairman and Honorable Members of the Senate Energy and Natural Resources Committee, I respectfully submit the testimony below, in response to your letter of September 9, 1996, in which you raise the following important and fundamental issue: Whether or not there is sufficient scientific certainty about the question of anthropogenic climate change to justify urgent actions to limit green house gas emissions, and where there are areas of uncertainty that merit further emphasis and scientific study. My testimony takes into consideration the following statement (paraphrased from your letter) by the Under Secretary of State for global affairs, the Honorable Timothy E. Wirth: "Continued buildup of [greenhouse] gases will enhance the natural greenhouse effect and cause the global climate to change," and that "science calls upon us to take urgent action." My Background: I published my first paper in this field on the greenhouse effect of CFCs in 1974, followed by papers on the climatic effects of carbon dioxide, water vapor and ozone during the succeeding 10 years. A variety of climate models were employed in these studies. For the past 12 years, my work has focused on the role of clouds in climate and climate change using satellite radiation budget measurements, aircraft, ship and surface measurements. Caveat: In spite of working nearly 25 years on some very formidable and challenging problems, I have never faced an issue as difficult as the one raised in this testimony. As a scientist with very little training or preparation in such policy related issues of great economic consequences, I must restrict my statements below to the scientific issues. This is only natural, for the policy issues rarely arise during the conduct of science. However, conscientious attempts will be made to state the problem in a format that is not only scientifically rigorous, but also informative enough for a non-specialist to address the policy issue at hand. As another cautionary statement, I must add that the science of climate change has witnessed: on the one hand, many surprising discoveries that tend to decrease the uncertainties; and on the other hand, the development of unanticipated major gaps in our knowledge that lead to more skepticism. The statement below should be viewed as a personal (as opposed to a consensus view) snap-shot of the problem as it is understood today. The text begins with the facts, moves on to deductions based on sound physical principles, and concludes with model predictions, recent findings and the emerging uncertainties. The essence of the testimony is summarized first: • For scientific, as well as policy purposes, it is convenient to separate the problem into two sub-components: the greenhouse effect; and the global warming that results from the greenhouse effect. • The natural greenhouse effect is provided by water vapor, carbon dioxide, clouds and other trace gases and is an observed and observable fact. • A buildup of the greenhouse gases would enhance the greenhouse effect. • Fundamental physical principles such as global energy balance and Planck radiation law lead to the deduction that an enhancement of the greenhouse effect would lead to a global warming if it is not offset by competing natural variations or other compensating changes by human activities. The magnitude and timing of the warming are highly uncertain (about a four fold range in the predicted magnitude), for these estimates are based on climate models which require further refinement in the treatment of clouds, aerosols and ocean-atmosphere interactions. • The uncertainty is compounded by the recent findings that anthropogenic activities may be modifying several other climate forcing factors. Of these, the cooling effect due to tropospheric aerosols and the warming effect of tropospheric ozone require focused studies, because: (1) the magnitude of their effects are estimated to be large in the northern hemisphere continental regions; and (2) their radiative cooling effects are largely based on aerosol-model studies which require experimental verification. • Another area which requires further scientific study is the magnitude of atmospheric absorption of solar radiation in clear and cloudy regions. Six independent studies (documented in the text) conducted in the U.S., Germany and Switzerland have identified a large and systematic discrepancy between climate models and observations. The model atmosphere absorbs less solar radiation than indicated by observations. The cause of this excess absorption, its magnitude, as well as whether it is in clear or cloudy regions, are being debated actively in the open literature. The sources of uncertainty identified above are in addition to those identified in earlier reports (e.g., IPCC reports) which include: cloud, water vapor and ocean feedback effects on climate change. Likewise, areas that require focused efforts (in addition to the aerosol and the solar absorption issues) include: development of coupled land-ocean-atmosphere models; development of long-term surface, in-situ and spaceborne observing systems; and documentation of present and past climate changes. With respect to the policy related question, I offer the following opinions. • We absolutely have to accelerate the pace of research, if we are going to come to grips with the scientific uncertainties soon enough to have answers that policymakers need. Science can help provide a basis for sound policy, but only if we do the research in a timely and thorough way. • I conclude with a view I share with many of my colleagues (e.g., see R. Somerville, The Forgiving Air: Understanding Environmental Change, Univ. of California Press, 1996): Some "actions," like promoting energy efficiency and energy conservation may be an attractive policy alternative, in view of such large uncertainties in the predicted anthropogenic climate changes. CHANGING CHEMICAL COMPOSITION OF THE AIR: A FACT Observations over the last two decades have documented, beyond a reasonable doubt, that the concentrations of several gases in the atmosphere are increasing substantially due to human activities. In addition, a compelling case can be made that the increase began more than a century ago. The pollutants that concern us the most are: carbon dioxide (CO2), methane, halocarbons (e.g., CFCs), and nitrous oxide. Collectively, these gases are known as the greenhouse gases, which surround the planet like a blanket. THE NATURAL GREENHOUSE EFFECT: A FACT Heat Balance: A major fraction of the incoming solar radiation is absorbed by the atmosphere and the surface, which heats the earth-atmosphere system. In turn, the surface and the atmosphere radiates this heat to space as heat (alternately known as infrared or simply IR) radiation. Thus the planet, as whole, heats by absorbing solar radiation and cools by giving off IR radiation to space. The Natural Greenhouse Effect: The important naturally occurring atmospheric constituents that contribute to the greenhouse effect are: water vapor, carbon dioxide and clouds, with smaller contributions from ozone, methane and nitrous oxide. These gases and clouds reduce the IR radiation emitted by the surface which would, otherwise, have escaped to space. The reduction in the planetary IR cooling (to space) is the so-called greenhouse effect. This reduction results from the fact that the atmospheric greenhouse gases and clouds absorb IR radiation emitted by the warmer surface, and emit it to space at the much colder atmospheric temperatures. The net effect is that the gases absorb more IR radiation (from the surface) than they emit to space. In other words, the gaseous blanket traps the heat energy of the planet. Evidence for the Greenhouse Effect: Radiation budget satellites routinely measure the outgoing IR radiation emitted by the planet to space. These data reveal that, globally, only about 60% of the IR energy emitted by the surface escapes to space. The remaining 40% is effectively absorbed by the atmospheric gases and clouds, thus reducing the IR cooling to space by about 40%; in energy units, the global natural greenhouse effect of the atmosphere is about 150 W m-2 Watts per square meter of the earth's surface; 1 Watt is 1 Joule of energy flow per second, with an uncertainty of about 10 W m-2. This number (150 W m-2) should be compared with the global absorbed solar radiation by the planet, which is about 235 W mG5-2. Clearly, the natural greenhouse effect is almost as important as the solar radiation in maintaining the climate. NASA Earth Radiation Budget Satellite data (Barkstrom, Bull. Am. Met. Soc., 1989) were used to derive the greenhouse effect of atmospheric gases over the ocean (Raval and Ramanathan, Nature, 1989). The data were shown to be in close agreement with that predicted by models. ANTHROPOGENIC ENHANCEMENT OF THE GREENHOUSE EFFECT: A LOGICAL EXTENSION OF OBSERVATIONS It naturally follows from the above data that the observed increase in greenhouse gases will further reduce the IR cooling to space, i.e., enhance the greenhouse effect. This reduction in IR cooling to space is usually referred to as the direct radiative forcing (e.g., see IPCC, 1990). During the last fifteen years, there have been numerous national and international attempts to estimate this enhancement of the greenhouse effect, culminating in the IPCC studies. Earlier studies initiated by the WMO (Ramanathan, Cicerone, Singh, and Kiehl, J. Geophys. Res., 1995; Ramanathan and 10 Co-authors, Rev. of Geophys., 1987) concluded that human activities have enhanced the greenhouse effect by about 1.8 W m-2 from the pre-industrial era to the year 1980, and that it is increasing by about 0.4 W m-2 for the decade of the 1980s. This is consistent with the most recent IPCC assessment (IPCC 1995): the direct radiative forcing of the long lived trace gases from the pre-industrial era to the year 1992 is 2.45 W m-2. Thus, there is no major discrepancy between the various studies |