 Section 0 of Understanding Climatic Change. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Warren Cotty, Gurnee, Illinois. Understanding Climatic Change, a program for action by the U.S. Committee for the Global Atmospheric Research Program. Section 0. Forward. The preface of the U.S. Committee for the Global Atmospheric Research Program document Plan for the U.S. participation in the Global Atmospheric Research Program begins. In late 1967, the International Council of Scientific Unions acting jointly with the World Meteorological Organization proposed a Global Atmospheric Research Program, GARP, to accomplish the objectives stated in UN Resolution 1721, XVI, and 1802, XVII, namely to advance the state of atmospheric sciences and technology so as to provide greater knowledge of basic physical forces affecting climate, to develop existing weather forecasting capabilities, and to develop an expanded program of atmospheric science research which will complement the program fostered by the World Meteorological Organization. Now, in 1974, a program to reach the weather forecasting objective of GARP is well underway. In this report, the U.S. Committee for the Global Atmospheric Research Program, USC, GARP, outlines a program to understand the basic physical forces affecting climate. There is ample evidence, summarized in Appendix A of this report, that climate does change and there is more than ample evidence from past history and even recent events that changes in climate can profoundly affect human activities and even life itself. Indeed, as a growing population places ever greater demands on food and fiber resources, man's sensitivity to variations in climate will increase. We have an urgent need for better information on global climate. Unfortunately, we do not have a good quantitative understanding of our climate machine and what determines its course. Without this fundamental understanding, it does not seem possible to predict climate, neither in its short-term variations nor in its larger, long-term changes. There are some who believe that important variations in climate can occur with changes in the controlling factors that are so small they are difficult to measure. With such barriers to be overcome, is there any assurance of success? We believe so. First, the two GARP objectives, dealing with weather and climate, are strongly related to each other. A better understanding of the physical processes that affect one means a better understanding of the processes that affect the other. The difference lies mainly in how the processes should be taken into account. Mathematical models fashioned to take into account long-term changes will have to have some characteristics that are different from those fashioned, mainly for short-term, weather changes. There has been significant progress in GARP's weather objective. Therefore, there already has been important progress in GARP's climate objective. Second, there has been a tremendous improvement in our ability to observe the global weather thanks to weather satellites. By the end of this decade, we will have the ability to observe the entire Earth with needed meteorological observations. An ability to obtain better weather observations is an ability to obtain better climate observations also. Important as this is, meteorological satellites also allow us to monitor those parameters that we now believe control the climate machine, the sun's output, the Earth's albedo, the distribution of clouds, the fields of ice and snow, and the temperatures of the upper layers of the ocean. These parameters control the average state of the weather and thus climate. Meteorological satellites are observing some of these parameters and could measure all of them. In some instances, the data are already being collected. These now need to be assembled to serve the needs of climate research. The feasibility of collecting data from ocean platforms has been established. A program to do it is needed. This report outlines the key requirements. Third, research into past climates has made significant advances. We now not only know what happened in the past far better than we did a decade or two ago, but these data will provide an important information base against which theories and numerical models of climate can be tested. Last, but far from least, there is a new generation of atmospheric scientists. Their tools are the computer, numerical models, and satellites, and they know how to use them well. The USC GARP believes that this is an adequate manpower base. We do not expect any breakthroughs, and progress could be slower than desired, but the program outlined in this document is a rational approach toward obtaining progress as rapidly as possible on this vital subject. The USC GARP further believes that neither the scientific community nor the nation can afford to be complacent with its present level of understanding on this important aspect of the Earth's physical environment. The natural forces determining the world's weather and climate are beyond our control, but having better insight into what nature might do should help the nation to plan for what it must do. This report was prepared by the committee's panel on climatic variation. On behalf of the USC GARP, I express full appreciation to its co-chairman, Yale Mintz and W. Lawrence Gates and all of its members for this important report. Werner E. Swalmy, chairman, U.S. Committee for the Global Atmospheric Research Program. Preface, the increasing realization that man's activities may be changing the climate and mounting evidence that the Earth's climates have undergone a long series of complex natural changes in the past have brought new interest and concern to the problem of climatic variation. The importance of the problem has also been underscored by new recognition of the continuing vulnerability of man's economic and social structure to climatic variations. Our response to these concerns is the proposal of a major new program of research designed to increase our understanding of climatic change and to lay the foundation for its prediction. The need for increased understanding of the physical basis of climate was recognized by the Panel on International Meteorological Cooperation of the Committee on Atmospheric Sciences in its report of 1966 which led to the development of the Global Atmospheric Research Program, GARP. This objective was embodied in the GARP plan as a second objective devoted to the study of the physical basis of climate to be undertaken along with the program's primary concern of improving and extending weather forecasts with the aid of numerical models. In March 1972, the United States Committee for GARP appointed the Panel on Climatic Variation to study the problem and to submit recommendations appropriate for climatic objectives of GARP's observational programs particularly the first GARP Global Experiment, FGGE, planned for 1978. The Panel's charge was subsequently enlarged to include recommendations for the design and implementation of a national climatic research program. In its initial deliberations, the work of the Panel seemed logically to fall into three categories depending on the time scale of climatic variation. First, the shorter period variations on the order of 10 to the minus 1 to 10 years which are documented by modern instrumental observations. Second, the variations of intermediate length of the order of 10 to 10 to the third years which are largely documented by historical and proxy data sources and third, the longer period variations of the order 10 to the third years and beyond for which documentation comes from paleoclimatic and geological records. Three subpanels were therefore formed and a report was issued in February 1973 by the subpanel concerned with monthly to decade old timescales W.L. Gates Chairman which is the basis of the main body of the present report. The deliberations of the subpanels concerned with decade old to millennial changes J.M. Mitchell Chairman and with millennial changes and beyond W.S. Broker Chairman were the basis of appendix A of this report. From the beginning of the Panel's work it was realized that it would be necessary to address a wide range of questions involving the use of climatic data from instrumental and proxy sources, the use of numerical simulation models and the conduct of research on the physical mechanisms of climatic change. It was also obvious in undertaking an assignment of this magnitude that the panel would not be able to refer to the large number of studies that have an important bearing on the problem of climatic variation. We have therefore generally cited only those works that were useful in framing our recommendations and in making a brief overview of present research, C.Chapter 5. Some of our recommendations have been made previously by other groups. C. for example, C. L. Wilson Chairman, 1971 Study of Man's Impact on Climate, SMIC, report Invertent Climate Modification, W.H. Matthews, W.W. Kellogg and G.D. Robinson Editors, Massachusetts Institute of Technology, Cambridge, Massachusetts And we are also aware that the problem of climatic change has been considered by several other groups and is of concern to other committees of GARP. In addition to the contributions of the Panel's members a number of consultants to the Panel also made valuable contributions J.E. Kutzbach and A.H. Ortt on the observational and statistical aspects of climatic change C.E. Leith on the question of climatic predictability and R.C.J. Somerville on the evaluation of numerical model performance A.R. Robinson of Harvard University also contributed material on the role of the oceans in climatic change Useful comments on various aspects of the Panel's work were also made by S.H. Schneider of the National Center for Atmospheric Research by E.W. Byerley, J.O. Fletcher and U. Raydock of the National Science Foundation by R.S. Linsen of Harvard University by R.J. Reed and R.G. Flegel of the University of Washington and by J. Smogorinski of the Geophysical Fluid Dynamics Laboratory The organization and preparation of the report as a whole was undertaken by W.L. Gates Appendix A, which is a survey of past climatic variations was prepared principally by J.E. Embry, W.S. Broker J.M. Mitchell Jr. and J.E. Katzbach The portions of this appendix, concerned with dendrochronology were prepared by H.C. Fritz and those concerned with glaciology by G.H. Stenton Unpublished data and figures used in this appendix were also kindly supplied by A.H. Ort C. Sansetta of Oregon State University A. McIntyre, J.D. Hayes and G. Kukla of the LeMont-Doherty Geological Observatory B.C. LeMarc of the University of Arizona J. Kennet of the University of Rhode Island and T. Kellogg, N.G. Kip, R.K. Matthews and T. Webb of Brown University Appendix B, which presents a comparative review of selected climate stimulation capabilities of global general circulation models was prepared principally by W.L. Gates, K. Brian and W.M. Washington. Valuable comments and contributions of unpublished material were also made by S. Monobi, R.C. J. Somerville, Y. Mintz and R.C. Alexander of the Rand Corporation This report makes no claim to completeness and many important matters are not touched upon. For example, we have not considered the questions of instrumental design and logistical support necessary to carry out the observational programs that we have recommended, nor have we dealt with the training and educational activities necessary to supply the additional scientific manpower. Although we have presented some thoughts on possible organizational arrangements for the conduct of the necessary research and have made some preliminary cost estimates, such questions were regarded as being outside the scope of the panel's immediate objectives and responsibility. The principal purpose of this report is to recommend a comprehensive research program which we feel is necessary to increase significantly our understanding of climatic variation and the panel will consider its efforts to have been successful if the report serves as a useful planning document to this end. In making its recommendations, the panel is aware of what has been called the problem of don't know, i.e. those who are called on to implement the program may not know that we don't know the answers to the central questions. The presentation of this report at least makes it clear that we don't know and thereby reduces the exponent to unity. The successful execution of the program should remove at least part of the remaining don't know. In short, we have attempted to describe here what should be done and recognize that what can be done and then what actually will be done remain to be determined. We wish to acknowledge the valuable advice and assistance of John R. Severs of the National Research Council and of Werner E. Swomey of the University of Wisconsin throughout the preparation of this report. We are also indebted to Viv Picklesimmer of the Rand Corporation for her efficient handling of many of the details of the panel's work and the preparation of the TypeScript. W. Lawrence Gates, Yale Mints, co-chairman, panel on climatic variation. End of section 0, recording by Warren Cotty, Gurney, Illinois. Section 1 of Understanding Climatic Change. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, visit LibriVox.org. Understanding Climatic Change, a program for action by the U.S. Committee for the Global Atmospheric Research Program. Section 1, Introduction. Climatic Change has been a subject of intellectual interest for many years. However, there are now more compelling reasons for its study. The growing awareness that our economic and social stability is profoundly influenced by climate and mayans' activities themselves may be capable of influencing the climate in possibly undesirable ways. The climates of the Earth have always been changing and they will doubtless continue to do so in the future. How large these future changes will be and where and how rapidly they will occur, we do not know. A major climatic change would force economic and social adjustments on a worldwide scale because the global patterns of food production that have evolved are implicitly dependent on the climate of the present century. It is not primarily the advance of a major ice sheet over our farms and cities that we must fear, devastating as this would be. For such changes take thousands of years to evolve. Rather, it is persistent changes of the temperature and rainfall in areas committed to agricultural use, changes in the frost content of Canadian and Siberian soils, and changes of ocean temperature and changes of high nutrient production, for example, that are of more immediate concern. We know from experience that the world's food production is highly dependent on the occurrence of favorable weather conditions in the breadbasket areas during the growing seasons. Because world grain reserves are but a few percent of annual consumption, an unfavorable crop here, such as occurred in Ukraine in 1972, has immediate international consequences. The current drought in parts of Asia and in Central Africa is producing severe hardship and has already caused the migration of millions of people. As the world's population grows and as the economic development of newer nations rises, the demand for food, water, and energy will steadily increase, while our ability to meet these needs will remain subject to the vagaries of climate. Most of the world's land suitable for agriculture or grazing has already been put to use and many of the world's fisheries are being exploited at rates near those of natural replenishment. As we approach full utilization of the water, land, and air which supply our food and receive our waste, we are becoming increasingly dependent on the stability of the present seemingly normal climate. Our vulnerability to climatic change is seen to be all the more serious when we recognize that our present climate is in fact highly abnormal and may already be producing climatic changes as a result of our own activities. This dependence of the nation's welfare as well as that of the international community as a whole should serve as a warning signal that we simply cannot afford to be unprepared for either a natural or a man-made climatic catastrophe. Reducing this climatic dependency will require coordinated management of the nation's resources on the one hand and a thorough knowledge of the climate's behavior on the other. It is therefore essential that we acquire a far greater understanding of climate and climatic change than we now possess. This knowledge will permit a rational response to climatic variations including the systematic assessment beforehand of man-made influences upon the climate and will make possible an orderly economic and social adjustment to changes in climate. Limits of our present knowledge Although we have considerable knowledge of the broad characteristics of climate we have relatively little knowledge of the major processes of climatic change. To acquire this knowledge it will be necessary to use all the research tools at our disposal. We must also study each component of the climatic system which includes not only the atmosphere but the world's oceans, the ice masses and the exposed land surface itself. Only in this way can we expect to make significant advances in our understanding of the elusive and complex processes of climatic change. Need for data Observations are essential to the development of an understanding of climatic change. Without them our theories will remain theories and the potential uses of our models will remain untapped. Our observational records must be extended in both space and time so that we can adequately document specific events that have occurred in the past and so that we can monitor the climatically important physical processes that are now going on around us. Much of the present climatic data are of limited availability and need to be put into forms that permit the systematic determination of appropriate climatic statistics and the assessment of the practical consequences of climatic variation. It is especially important that climatic data be organized and assembled to permit their use in conjunction with dynamical climate models. The oceans in particular exerted powerful influence on the Earth's climates yet we have inadequate oceanographic observations on the space and time scales needed for climatic studies. The important heat, moisture and momentum changes that occur at the sea surface and the corresponding transports that occur within the ocean are not at all well known. Recent observations from the mid-ocean dynamics experiment mode reveal energetic oceanic mesoscale motions at subsurface levels and our ignorance becomes even greater than we thought it was. The present international network of conventional meteorological observations has grown largely in response to the need for weather forecasts while most oceanographic data have been collected from ships widely separated in space and time. For the proposed research program these data must be supplemented by truly global observations of the large scale geophysical boundary conditions and of the physical processes that are important in climatic change. It is here that satellite observations are expected to play a key role as they offer an unparalleled opportunity to monitor a growing list of variables such as cloudiness, temperature and the extent of ice and snow. Other climatically important valuables will require special monitoring programs on either a global or regional basis. It is essential, moreover, that the relevant data be collected on a long-term basis in order to acquire the necessary statistics of climate. Need for understanding Our knowledge of the mechanisms of climatic change is at least as fragmentary as our data. Not only are the basic scientific questions largely unanswered but in many cases we do not yet know enough to pose the key questions. What are the most important causes of climatic variation and which are the most important or most sensitive of the many processes involved in the interaction of the air, sea, ice and land components of the climatic system. Although there is evidence of a strong coupling between the atmosphere and the ocean for example we cannot yet say that we understand much about its consequences for climatic change. There are also indications in paleoclimatic data that the Earth's climates may be significantly influenced by the long-term astronomical variations of the Sun's radiation received at the top of the atmosphere but here again we do not yet understand the processes that may be involved. There is no doubt that the Earth's climates have changed greatly in the past and will likely change in the future but will we be able to recognize the first phases of a truly significant climatic change when it does occur? Like the familiar events of daily weather from which the climate is derived climatic changes occur on a variety of space scales. These range from the change of local climate resulting from the removal of a forest for example to regional or global anomalies resulting from shifts of the pattern of the large-scale circulation of weather, variations of climate take place relatively slowly and we may think in terms of yearly decadal and millennial climatic changes but the system is complex and the search for order in the climatic record has only begun. Even the barest outline of a theory of climate must address the key question of the predictability of climatic change. This question is closely tied to the limited predictability of the weather itself and to the predictability of the various external boundary conditions and internal transfer processes that characterize the climatic system. Although there is evidence of regularity on some timescales the climatic record includes many seemingly irregular variations of large amplitude. How do we separate the genuine climatic signal from what may be unpredictable noise and to what extent are the noise controlled? These are important questions and ones to which there are no ready answers. The determination of the climate's predictability will require the further development and application of both theory and dynamical models along with a greatly expanded database. The answers when they are found will determine the limit to which we can hope to predict future climatic variations. Special attention must be paid to the fundamental role of the world's oceans in controlling the climate. The oceans not only are the primary source of the water in the atmosphere and on the land, but they constitute a vast reservoir of thermal energy. The timing and location of the exchange of this energy with the overlying air has a profound effect on the more rapidly varying atmospheric circulation. When the dynamics of this ocean-atmosphere interaction are better known we may find that the ocean plays a more important role than the atmosphere in climatic changes. Need for assessment We should add to these limits of our present knowledge the lack of comprehensive assessment of the impacts of climatic variation on human affairs. No one doubts that there are such impacts. For the specter of drought and the consequences of persistently severe winter weather are all too familiar in many parts of the world. Even so, we must admit that we cannot now adequately answer the question what is the change of climate worth? A farmer may know what knowledge of the climatic conditions of the next growing season would be worth to him but the answer in terms of national and international resource planning is more elusive. This lack of assessment is brought into sharper focus when we attempt to discern the economic and social consequences of possible alternate future climates. Future efforts and resources Research approaches Our future efforts must be guided by the realization that climatic changes in any one part of the world are manifestations of changes in the global climatic system since our fundamental goal is to increase our understanding of climatic variations to the point where we may predict and possibly even control them, we must subject our ideas to quantitative tests wherever possible. The recent development of satellite-based observing systems, the coming new generation of high-speed computers and the emergence of models suitable for climatic simulation combine to make such an undertaking feasible at this time. The importance of climatic variations requires, moreover, that we use all methods of inquiry that are likely to yield useful information and that we do so at the earliest possible time. The principal approaches to the problem that are available to us are shown in Figure 1.1 and we recognize the importance of maintaining a balance of effort among them. These same approaches form the elements of the climatic research program recommended in this report and broadly cover what we believe to be the needed efforts for observation, analysis, modeling and theory. The successful execution of the program will require contributions from the physical sciences of meteorology, oceanography, glaciology, hydrology, astronomy, geology and paleontology, and from the biological and social sciences of ecology, geography, archaeology, history, economics, and sociology. A program of this sort calls for a long-term commitment from the scientific research community from the sponsoring government agencies and from the public. Figure 1.1 shows the interdependence of the major components of the climatic research program and a number of key questions. At the center is climatic data analysis, what has happened in the past. Around this are six interdependent components, monitoring what is going on, empirical studies, how does the system work, future climates, how and when is the climate going to change, climatic impacts, what does it all mean to man, theoretical studies, how much do we really understand, and numerical models, what is shown by climatic simulations. The question of priorities. The various components of the recommended climatic research program fully described in Chapter 6 are to a great extent interdependent. Data are needed to check the coupled general circulation models and to calibrate the simpler models. The models are needed to test hypotheses and to project future climates. Monitoring is needed to check the projections and all are needed to assess the consequences. The question of priorities then becomes a matter of the priority of questions and there appear to be no a priori easy guidelines to relative importance. Our priorities are reflected in those actions and activities that we recommend be implemented at once and in those subsequent activities for which planning should begin as soon as possible. While anticipating that much further planning will be necessary to implement the complete program, we urge that the essential interdependence of the various efforts be recognized and that all aspects of the problem be given support as parts of a coherent research program. Purposes and contents of this report. Broadly speaking, the purposes of this report are two fold. First to advise the United States Government through the National Research Council's United States Committee for GARP on the urgent need for a coherent national research program on the problem of climatic variation and second, to advise on the steps necessary to address the same problem in the international scene. As noted previously, our response to the government is the recommendation of a broadly based national climatic research program, NCRP whose goal is the resolution of the problem of climatic variation. This program is presented in detail in Chapter 6 and its adoption is the first of our major national recommendations, summarized in Chapter 2. In view of the possibly great impacts of future climatic variation on the nation's welfare, we believe that it is our responsibility to call for a national commitment to this effort. We accordingly urge strongly that resources to carry out such a program be made available at the earliest possible time including provision for the necessary observations, computers and research facilities. Our further response to the appropriate international bodies is the proposal of a coordinated international climatic research program ICRP, which we believe to be a suitable mechanism for the pursuit of the climatic aspects of GARP. As discussed in Chapter 6, we review this as a new program of considerably greater breadth than the present GARP activities, but one for which the GARP is a necessary prelude. The US national program NCRP would form an integral part of the ICRP as would the national programs of other countries. In addition we recommend a number of supporting programs whose observational requirements may impact on the first GARP global experiment scheduled for 1978 through 1979. The remainder of this report consists of one, a summary of our principal conclusions and recommendations, Chapter 2. Two, a discussion of the physical basis of climate and climatic change, Chapter 3. Three, a summary of past climatic variations as drawn from the instrumental and paleo-climatic record, Chapter 4. Four, a brief review of the scope of present research on climatic variation, Chapter 5. And five, the proposed climatic research program, Chapter 6. Two technical appendices prepared specially for this report present further details of the record and interpretation of past climates, Appendix A, and a brief comparative review of the ability of present atmospheric and oceanic general circulation models to simulate selected climatic variables, Appendix B. And of Introduction, Section 1. Section 2 of Understanding Climatic Change This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org Recording by Tom Geller, Rotterdam, The Netherlands. www.omgler.com Understanding Climatic Change, a program for action by the U.S. Committee for the Global Atmospheric Research Program, Section 2. Summary of principal conclusions and recommendations The principal conclusions and recommendations that have resulted from the deliberations of this panel, which are expanded upon elsewhere in this report, may be summarized as follows. 1. To meet present and future national needs and to further the national contribution to GARP, we strongly recommend the immediate adoption and development of a coherent National Climatic Research Program, NCRP, with appropriate international coordination. The major sub-programs of the NCRP are summarized in recommendations 2, 3 and 4. 2. To perform the needed analysis of selected climatic data, including that from conventional instruments and satellites, historical records and paleoclimatic data sources, we recommend the establishment of a Climatic Data Analysis Program, CDAP, as a sub-program of the NCRP. This program's functions would be to facilitate and coordinate the preparation and maintenance of a comprehensive climatic data inventory, the development of selected climatic data banks, and the preparation of suitable data analyses, both on current and paleoclimatic data. To carry out these functions, we recommend the development of new climatic data analysis facilities with access to suitable computing and data processing and display equipment as components of a national network for climatic data analysis. We envisage these facilities as working closely with the various specialized climatic data depositories and as an essential mechanism for the successful execution of the CDAP and of related components of the overall national program. In response to immediate practical needs, we recommend the initiation and continued support of empirical and statistical studies of the impacts of climatic change on man's food, water, and energy supplies. Support should also be given to studies of the broader social and economic consequences of climatic variations. Three, to acquire the needed data on the important boundary conditions and physical processes of climate, we recommend the development of a global climatic index monitoring program, CIMP, as a second sub-program of the NCRP. This program's functions would include the monitoring and collection on appropriate climatic time and space scales of data on the components of the global heat balance, including the solar constant, the ocean surface temperature and the thermal structure of the surface mixed layer, the extent of ice and snow cover and other land surface characteristics, the atmospheric composition and turbidity, anthropogenic processes, and, if possible, ocean current transports and components of the hydrological cycle. This program will require a number of new observational schemes in the atmosphere, in the ocean and on land, and will rely heavily on environmental satellites. We anticipate that such data will also have important uses on a real-time basis, and that the CIMP could serve as a national watchdog for climatic change. Four, to accelerate research on climatic variation and to support the needed development of climatic modeling on a broad front, we recommend the establishment of a climatic modeling and applications program, CMAP, as a third sub-program of the NCRP. In this program, emphasis should be given to the development of couple of global climate models, CGCMs, of the combined atmospheric and oceanic general circulation, and to the improvement of the model's treatment of clouds, mesoscale processes, and boundary layer phenomena. Attention should also be given to the processes of air-sea interaction, and to treatment of the ocean surface layer, sea ice, and the oceanic mesoscale phenomena. We note the importance of extended model integrations to determine the annual and inter-annual variability of simulated climates, and urge that appropriate studies be made of the sensitivity of simulated climates to physical and numerical uncertainties in the model's formulation. To provide the basis for the needed further modeling of climatic variation, we recommend the development and support of a wide variety of statistical dynamical and other parameterized climate models. We note the importance of calibration in such models, and urge that appropriate schemes be developed to permit extended climatic simulations which include oceanic and cryospheric variables. To provide the needed further insight into the mechanics of climatic variation, we recommend the application of climatic models in support of empirical and diagnostic studies, with particular attention to the roles of climatic feedback processes in the coupled ocean-atmosphere system, to the questions of climatic predictability and transitivity, and to the climatic effects of changes in the geophysical boundary conditions. To provide the needed reconstruction of past climates and to develop a broader calibration of climate models, we recommend the initiation and support of systematic efforts to reconstruct selected events and periods in the climatic history of the Earth. This should include the application of the CGCMs to simulate selected equilibrium paleoclimates and the use of statistical dynamical or other parameterized climate models to infer the time-dependent evolution of the coupled atmosphere-hydrosphere-cryosphere climatic system. To further the needed application of climatic models, we recommend the systematic exploration with suitable climate models of a variety of possible future climates due either to natural or man-made causes. These should include determination of the likely effects of changes in solar radiation, land surface character, cloudiness, pollution and ice extent. We urge that efforts be made to extract consistent physical hypotheses from such experiments and that the necessary statistical controls be developed. To lay the basis for the needed assessment of the possibilities of long-range or climatic forecasting, we further recommend the application of climate models of all types in experimental integrations using observed initial and boundary conditions. Appropriate climatic statistics should be drawn from such integrations and compared with observation in so far as possible in order to establish the model's usefulness as long-range forecast tools. Initial emphasis should be given to the time periods of seasons to decades for which there is presently the greatest practical need for scientifically-based information. To assist in the performance of the needed research or climatic modeling and applications, we recommend that efforts be made to identify or form a number of cooperative research associations or climatic research consortia which we view as natural and useful coordinating mechanisms for the effective performance and long-range stability of the NCRP. We further recommend that the period prior to 1980 be used to develop additional scientific and technical manpower through the establishment and support of fellowships in appropriate areas of climatic research. 5. In order to further the aims of the international GARP efforts directed to the problem of climate and climatic variation, we recommend the adoption and development of an international climatic research program, ICRP. By the very nature of climate, the U.S. national program is considered an integral part of the ICRP along with the climatic research programs of other nations. In view of the differences of the observational time scales and of the variables in weather forecasting and climatic studies and in view of the latter's broadly interdisciplinary character, we visualize such a program being the logical successor to GARP in matters relating to climate. Recognizing that the elements of the NCRP recommended above could equally well apply to an international program, we suggest that they be considered by the appropriate international organizations. To help provide the observational framework needed for climatic research, we recommend the designation of the period 1980 to 2000 as International Climatic Decades ICD. During this period, efforts should be made to secure broad international cooperation in the collection, analysis and exchange of all available climatic data, including conventional observations and special datasets of particular climatic interest, such as during droughts and following volcanic eruptions. During the ICD, we also recommend the initiation and support of regional climatic studies in order to describe and model local climatic anomalies of special interest. We further recommend development of appropriate national and international training programs and educational activities in order to promote the participation of all nations in climatic research. Six, to provide the global paleoclimatic data needed for the reconstruction of past climates, we recommend the development of an international paleoclimatic data network, IPDN, as a sub-program of the ICRP. This program should aim to assist each nation in the cooperative identification, extraction, analysis, monitoring and exchange of its unique paleoclimatic records, such as those from tree rings, soil types, fossil pollen, and data on sea and lake levels. End of section 2 Recording by Tom Geller, Rotterdam, the Netherlands T-O-M-G-E-L-L-E-R dot com Section 3 of understanding climatic change. This is a LibreVox recording. All LibreVox recordings are in the public domain. For more information or to volunteer, visit LibreVox.org. Recording by Warren Coddy, Gurney, Illinois Understanding Climatic Change A program for action by the U.S. Committee for the Global Atmospheric Research Program Section 3 Physical Basis of Climate and Climatic Change Climatic System The term climate usually brings to mind an average regime of weather. The climatic system, however, consists of those properties and processes that are responsible for the climate and its variations and are illustrated in Figure 3.1. The properties of the climatic system may be broadly classified as thermal properties which include the temperature of the air, water, ice, and land, kinetic properties which include the wind and ocean currents together with the associated vertical motions and the motion of ice masses, aqueous properties which includes the air's moisture or humidity, the cloudiness and cloud water content, groundwater, lake levels, and the water content of snow and of land and sea ice, and static properties which include the pressure and density of the atmosphere and ocean, the composition of the dry air, the oceanic salinity, and the geometric boundaries and physical constants of the system. These variables are interconnected by the various physical processes occurring in the system such as precipitation and evaporation, radiation, and the transfer of heat and momentum by advection, convection, and turbulence. Components of the system. In general terms, the complete climatic system consists of five physical components, the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere as follows. The atmosphere which comprises the Earth's gaseous envelope is the most variable part of the system and has a characteristic response or thermal adjustment time of the order of a month. By this we mean that the atmosphere, by transferring heat vertically and horizontally, will adjust itself to an imposed temperature change in about a month's time. This is also approximately the time it would take for the atmosphere's kinetic energy to be dissipated by friction if there were no processes acting to replenish this energy. The hydrosphere which comprises the liquid water distributed over the surface of the Earth includes the oceans, lakes, rivers, and the water beneath the Earth's surface, such as groundwater and subterranean water. Of these the world's oceans are the most important for climatic variations. The ocean absorbs most of the solar radiation that reaches the Earth's surface and the oceanic temperature structure represents an enormous reservoir of energy due to the relatively large mass and specific heat of the ocean's water. The upper layers of the ocean interact with the overlying atmosphere on timescales of months to years while the deeper ocean waters have thermal adjustment times of the order of centuries. The cryosphere which comprises the world's ice masses and snow deposits includes the continental ice sheets, mountain glaciers, sea ice, surface snow cover and lake and river ice. The changes of snow cover on the land are mainly seasonal and are closely tied to the atmospheric circulation. The glaciers and ice sheets which represent the bulk of the ocean's freshwater storage respond much more slowly. Because of their great mass these systems develop a dynamics of their own and they show significant changes in volume and extent over periods ranging from hundreds to millions of years. Such variations are, of course closely related to the global hydrologic balance and to variations of sea level. Sea appendix A The lithosphere which consists of the land masses over the surface of the earth includes the mountains and ocean basins together with the surface rock, sediments and soil. These features change over the longest timescales of all the components of the climatic system ranging up to the age of the earth itself. The processes of continental drift and sea floor spreading which have resulted in mountain building changes in the shapes and depths of the oceans occur over tens and hundreds of millions of years. These events are not generally regarded as representing the same kind of interaction with other components of the system as the variations described above. We note, however, that there may be a significant relationship between the occurrence of major glacial periods and the times when continental land masses occupied positions near the rotational poles of the earth. Sea appendix A The processes of isostatic adjustment and the accumulation of deep ocean sediments also represent significant changes of the lithosphere and as such may be viewed as earth, ice, ocean interactions. The introduction of volcanic debris into the atmosphere and its subsequent dispersal may also be cited as an example of earth-air interaction. The biosphere includes the plant cover on land and in the ocean and the animals of the air, sea, and land including man himself. Although their response characteristics differ widely these biological elements are sensitive to climate and in turn may influence climatic changes. It is from the biosphere that we obtain most of the data of climate. Sea appendix A Natural changes in surface vegetation occur over periods ranging from decades to thousands of years in response to changes in temperature and precipitation and in turn alter the surface albedo and roughness, evaporation and ground hydrology. Changes in animal populations also reflect climatic variations through the availability of food and habitat. The anthropogenic changes due to agriculture and animal husbandry are not known but may well be appreciable in altering at least regional climates. Physical processes of climate The climate at any particular time represents in some sense the average of the various elements of weather along with the state of the other components of the system. Physical processes responsible for climate as distinct from climatic change are therefore basically the same as those responsible for weather. These processes are expressed in quantitative fashion by the dynamical equation of motion, the thermodynamic energy equation and the equations of mass and water substance continuity as applied to the atmosphere and ocean. Sea appendix B A process of primary importance for the circulation of the atmosphere and ocean is the rate at which heat is added to the system, the ultimate source of which is the sun's radiation. The atmosphere and ocean respond to this heating by developing winds and currents which serve to transport heat from regions where it is received in abundance such as in the equatorial and tropical areas where relatively little radiation is received such as the polar regions of the earth. In this way, the atmosphere and ocean maintain the overall global balance of heat. A great deal of this heat is transported by the disturbances responsible for much of our weather in middle and high latitudes and similar disturbances may occur in the ocean. These eddies of the general circulation also participate in the transports necessary to maintain the global balances of momentum, mass and the total quantity of water substance. While this simple view is a fair summary of our basic understanding of the general circulation, it is not without shortcomings. For example, it does not consider the basically different circulation regime in the low latitudes or the role of convective phenomena and it does not consider important variations of the circulation with height. It might also be noted that for other combinations of the planetary size and rotation rate, atmospheric composition and meridional heating gradient such as occur on other planets an altogether different circulation regime and hence climate could result. Although the equations referred to above are fundamental in that they form the basis of our ability to simulate numerically the climate with dynamical models, they are not in themselves particularly revealing as far as the more subtle physical processes of climate are concerned to say nothing of the processes of climatic change. The heating rate is itself highly dependent on the distribution of the temperature and moisture in the atmosphere and does much to the release of the latent heat of condensation during the formation of clouds and to the subsequent influence of the clouds on the solar and terrestrial radiation. These processes together with others that contribute to the overall heat balance of the atmosphere are shown in figure 3.2 in which data derived from recent satellite observations have been incorporated. See for example Vonderhaar and Swammy 1971. Here the presence of clouds, water vapor and CO2 is seen to account for over 90% of the long wave radiation leaving the Earth-ocean atmosphere system. This effect of blocking of the radiation emitted by the Earth's surface commonly referred to as the greenhouse effect permits a somewhat higher surface temperature than would otherwise be the case. It is interesting that this important effect is achieved by gases in the atmosphere that exist in near trace amounts. We see from figure 3.2 that the role played by clouds is an important one. The reflection and emission from clouds accounts for about 46% of the total radiation leaving the atmosphere and in terms of the short wave radiation alone, clouds account for two thirds of the planetary albedo. The largest single heat source in the atmosphere is that supplied by the release of the latent heat of condensation and this is particularly important in the lower latitudes. There is also an appreciable supply of sensible heat from the oceans especially in the middle and higher latitudes. It is therefore clear that water substance in either vapor or droplet form plays a dominant role in the atmospheric heat balance when we recall that the oceans themselves absorb most of the solar radiation reaching the surface and that the presence of ice and snow also affect the heat balance. The climatic dominance of global water substance becomes overwhelming even if ice is not taken into account. Definitions It is useful at this point to introduce a number of definitions related to climate and climatic change. In what may be called the common definition climate is the average of the various weather elements usually taken over a particular 30 year period. A more useful definition is what we shall call the practical definition which introduces the concept of a climatic state. This and related definitions are as follows. Climatic state is defined as the average together with the variability and other statistics of the complete set of atmospheric, hydrospheric and cryospheric variables over a specified period of time in a specified domain of the earth atmosphere system. The time interval is understood to be considerably longer than the lifespan of individual synoptic weather systems of the order of several days and longer than the critical time limit over which the behavior of the atmosphere can be locally predicted of the order of several weeks. We may thus speak, for example, of monthly, seasonal, yearly, or decadal climatic states. Climatic variation This is defined as the difference between climatic states of the same kind as between two January's or between two decades. We may thus speak, for example, of monthly, seasonal, yearly, or decadal climatic variations in a precise way. The phrase climatic change is used in a more general fashion but is generally synonymous with this definition. Climatic anomaly This we defined as the deviation of a particular climatic state from the average relatively large number of climatic states of the same kind. We may thus speak, for example, of the climatic anomaly represented by a particular January or by a particular year. Climatic variability This we defined as the variance among a number of climatic states of the same kind. We may thus speak, for example, of monthly, seasonal, yearly, or decadal climatic variability. Although it may be confusing, this definition of climatic variability includes the variance of the variability of the individual climatic states. The foregoing definitions are useful for two reasons. First, the concept of climatic state preserves the essence of what is usually connoted by climate while circumventing troublesome problems of statistical activity. Second, climatic states represent definite realizations or samples of climate rather than the climate, per se, and are comparable with the climates simulated by numerical general circulation experiments. There are many other definitions in existence to distinguish particular statistical characteristics of climate and climatic change, such as climatic fluctuations, oscillations, periods, cycles, trends, and rhythms. The above definitions are generally adequate for our purposes, although we shall later consider another definition of climate related to the climatic system. We shall also subsequently introduce the concepts of climatic noise and climatic predictability, except when otherwise indicated, the use of the word climate in this report is to be considered an abbreviation for climatic state. It should be noted that we have included the oceans in the definition of a climatic state as well as information on other aspects of the physical environment. The ensemble of statistics required to completely describe a climatic state is presently available for only a few regions and for limited periods of time. The climatic data analysis and monitoring programs recommended in Chapter 6 are intended to fill in as much of the gap as possible with available data and to ensure that at least certain critical data are systematically gathered for an extended period of time in the future. Causes of Climatic Change While the above discussion may describe the process as responsible for the maintenance of climate, it is an accurate description of the processes involved in climatic change. Here we are on less secure ground and must consider a wide range of possible interactions among the elements of the climatic system. It is these interactions that are responsible for the complexity of climatic variation. Climatic boundary conditions If we view the gaseous, liquid and ice envelopes surrounding the earth as the internal climatic system, we may regard the underlying ground and the space surrounding the earth as the external system. The boundary conditions then consist of the configuration of the earth's crust and the state of the sun itself. Changes in these conditions can obviously alter the state of the climatic system, i.e. they can be causes of climatic variation. Each of the external processes illustrated in figure 3.1 may be used to develop a climatic theory on which basis one may attempt to explain certain features of the observed climatic changes. For example, changes of the distribution of solar radiation have been used since the time of Milankovic 1930 to explain the major interglacial cycles of the order of 10 to the fourth to 10 to the fifth years. Aside from the question of variations of the sun's radiative output, variations of the earth's orbital parameters produce changes in the intensity and geographical pattern of the seasonal and annual radiation received at the top of the atmosphere and in the length of the radiational seasons in each hemisphere. Those known with considerable accuracy have resulted in occasional variations of the seasonal insulation regime several times larger than those now experienced. These orbital elements eccentricity, obliquity and precession vary with periods averaging about 96,000 years, 41,000 years and 21,000 years respectively. These seasons themselves represent substantial climatic variations such astronomical theories of climatic change must be given careful consideration. The separate question of the climatic effects of possible changes in the sun's radiation i.e. changes of the so-called solar constant has a much less firm physical basis. Not only are the measured short period variations of solar output small, but the repeated search for climatic periodicities linked with the 11-year and 80-year sunspot cycles has not yielded statistically conclusive results. The question of still longer periods solar variations cannot be adequately examined with present data. Although over periods of the order of hundreds of millions of years the sun's radiation seems likely to have changed. The time range of this and other possible causative factors of climatic change is shown in figure 3.3. On time scales of tens of millions of years there are changes in the shapes of the ocean basins and the distribution of continents as a result of seafloor spreading and continental drift see figure 3.3. Over geological time these processes must have resulted in substantial changes of global climate. Just how much of the recorded paleoclimatic variations may eventually be accounted for by such effects however, is not known and applying climatic models to the systematic reconstruction of the Earth's climatic history prior to about 10 million years ago is an important component of the research program recommended in this report. See Chapter 6 In such climatic reconstructions the oceans must be simulated along with the atmosphere and eventually the ice masses must also be reproduced. Accompanying the migration of the land masses are the processes of mountain building, epirogeny, isostatic adjustment and sea level changes all of which must also be taken into account. Yet another external cause of climatic variation is the changes in the composition of the atmosphere resulting from the natural chemical evolution of the nitrogen, oxygen and carbon dioxide content in response to geological and biological processes as well as from the effluence of volcanic eruptions. On shorter time scales however it is probably the injection of dust particles into the atmosphere by volcanoes that has produced a more significant climatic effect by modifying the atmospheric radiation balance. See Figure 3.2 The progressive enrichment of the atmospheric CO2 content which has occurred during this century as a result of man's combustion of fossil fuels amounting to an increase of order 10% since the 1880s must also be considered an external cause of climatic variation. These considerations lead to the physical definition of climate as the equilibrium statistical state reached by the elements of the atmosphere, hydrosphere and cryosphere under a set of given and fixed external boundary conditions. There is of course the possibility that a true equilibrium may not be reached in a finite time due to the disparity of the times of the system's components but this is nevertheless a useful definition by progressively reducing the internal climatic system to include only the atmosphere and ocean in equilibrium with the land and ice distribution and then to include only the atmosphere itself in equilibrium with the ocean ice and land a hierarchy of climates may be defined which is useful for the analysis of climatic determinism climatic change processes and feedback mechanisms important as the above processes may be for the longer period variations of climate there are other factors that may also produce climatic change these involve changes in the large scale distribution of the effect of internal driving mechanisms for the atmosphere and ocean variations of the global ice distribution for example have a significant effect on the net heating of the atmosphere by virtue of the ice's effective control of the surface heat budget and thereby may change the meridional heating gradient that drives the atmospheric and oceanic circulation and equally significant change for the oceans at least may be introduced by widespread salinity variations as caused for example by the melting of ice the salinity of the ocean surface water is in turn closely related to the formation of relatively dense bottom water which by sinking and spreading fills the bulk of the world's ocean basins such processes may act as internal controls of the climatic system with time scales extending from fractions of a year to even thousands of years see figure 3.3 some of these processes display a coupling or mutual compensation among two or more elements of the internal climatic system such interactions or feedback mechanisms may act either to amplify the value or anomaly of one of the interacting elements positive feedback or to damp it negative feedback of the large number of degrees of freedom of the ocean atmosphere system for the moment considering the ice distribution to be fixed there are a large number of possible feedback mechanisms within the ocean within the atmosphere and between the ocean and the atmosphere the same degrees of freedom however invite a high risk of error in any qualitative analysis and in some cases equally plausible arguments of this sort lead to opposite conclusions some of the more prominent feedback effects operate among the shorter period processes of climatic change especially those concerning the radiation balance over land and the energy balance over the ocean for example a perturbation of the ocean surface temperature may modify the transfer of sensible heat to the overlying atmosphere and thereby affect the atmospheric circulation and cloudiness these changes may in turn affect the ocean surface temperatures through changes in radiation wind induced mixing advection and convergence and may subsequently affect the deep ocean temperatures through geostrophic adjustment to the convergence in the boundary layer these processes may result either in the enhancement or reduction of the initial anomaly of sea surface temperature a number of studies have shown positive feedback of this sort for several years time in the north pacific ocean the greenhouse effect in which the absorption of long wave radiation by water vapor produces a higher surface temperature is probably the best known example of a semi-permanent positive feedback process although other positive feedbacks of climatic importance may be noted one of these is the snow cover albedo temperature feedback in which an increase of snow extent increases the surface albedo and thereby lowers the surface temperature this in turn, all else being equal, further increases the extent of the snow cover an example of negative feedback is the coupling between cloudiness and surface temperature noted earlier in this scheme an initial increase of surface temperature serves to increase the evaporation which is followed by an increase of cloudiness this in turn reduces the solar radiation reaching the surface and thereby lowers the initial temperature anomaly here we have ignored the effects of long wave radiation and of advective processes both ocean and atmosphere what these examples serve to illustrate the uncertainty that must be attached to such arguments while there is much evidence to support the existence of feedback processes the key phrase in their qualitative use is all else being equal in a system as complex as climate this is usually not the case and an anomaly in one part of the system may be expected to set off a whole series of adjustments depending on the type, location and magnitude of the disturbance any positive feedback must, in any event be checked at some level by the intervention of other internal adjustment processes where the climate would exhibit a runaway behavior we do not adequately understand these adjustment mechanisms and their systematic quantitative by numerical climate models is an important task for the future in that research it will be essential to use coupled models of atmosphere and ocean and these must be calibrated with great care so as not to distort the feedback mechanisms themselves climatic noise climatic states have been defined in terms of finite time averages and as such are subject to fluctuations of statistical origin in addition to the changes of a physical nature already discussed since these statistical fluctuations arise from the day-to-day fluctuations in weather the auto-variation of the atmosphere identified in figure 3.3 they are unpredictable over time scales of climatological interest and are therefore appropriately defined as climatic noise the amplitude of this noise decreases approximately as the square root of the length of the time averaging interval but some remains at a finite time scale Leith 1973 Chirvin et al. 1974 a key problem of climatic variation on any time scale is therefore the determination of the climatic predictability which we may define as the ratio of the magnitude of the potentially predictable climatic change of physical origin to the magnitude of this unpredictable climatic noise role of the oceans in climatic change it has been noted that the oceans play a prominent role in the determination of climate through the processes at the air-sea interface that govern the exchanges of heat, moisture and momentum while these conditions are actually determined mutually by the atmosphere in the ocean they are likely dominated by the ocean on at least the longer climatic time scales it is the high thermal and mechanical oceanic inertia that requires that special consideration be given to the role of the ocean in climatic change physical processes in the ocean over half of the solar radiation reaching the earth's surface is absorbed by the sea this solar radiation along with the surface wind stress is the ultimate energy source for a variety of physical processes in the ocean whose climatic importance is essentially a function of their time scales the absorption of solar radiation is primarily responsible for the existence of a warm surface mixed layer of order 10 to the second meters deep found over most of the world's oceans this warm surface layer represents a large reservoir of heat and acts as a significant thermodynamic constraint on the atmospheric circulation the exchange of the ocean's heat with the atmosphere occurs over a wide range of time scales and largely determines the relative importance of other physical processes in the ocean for climatic change some of this heat is used for surface evaporation some is stored in the surface layer and some is moved downward into deeper water by various dynamical and thermodynamical processes the fluxes of latents and sensible heat into the atmosphere are commonly parameterized in atmospheric models as functions of the large scale surface wind speed and the vertical gradients of humidity in the air over the ocean surface these fluxes are actually accomplished by small scale turbulent processes in the surface boundary layer whose behavior is not adequately understood physical processes in the ocean such as vertical convective motions depending on the local vertical stratification of temperature and salinity and wind induced stirring also affect the depth of the structure of the mixed layer as shown for example by the simulations of daily variations of local mixed layer depth by Denman and Miyake 1973 other small scale processes such as salt fingering and internal waves also produce transports that may contribute significantly to the overall vertical mixing in the ocean therefore the dynamics of the ocean surface layer must be taken into account in even the simplest of climate models it is becoming apparent that the most energetic motion scale in the oceans is that of the mesoscale Eddie whose period is of the order of a few months and whose horizontal wavelength is of the order of several hundred kilometers the kinetic energy of these motions which is predominantly in the barotropic in first baroclinic vertical mode may be one or two orders of magnitude greater than that of the time averaged motions themselves in a general sense these slowly evolving Eddies are the counterpart of the larger scale transient cyclones and anti cyclones in the atmosphere in understanding of the physical processes responsible for the origin and behavior of these Eddies and their role in the oceanic general circulation is essential for further insight into the dynamics of the vast open ocean regions in addition to the surface interactions vertical mixing processes and mesoscale motions the study of the longer period variations of climate clearly requires consideration of the large scale dynamics of the complete oceanic circulation this includes the large scale pattern of wind driven and thermohaline currents and their associated horizontal and vertical transports of heat, momentum and salt of particular importance here is the study of the local dynamics of the intense boundary and equatorial currents and the relative roles of inertial and topographic influences the characteristic variations of these large scale processes are on time scales of the order of seasons and years in the near surface waters but may occur in progressively longer time scales in deeper water the longest oceanic adjustment time associated with the permanent ocean circulation is of the order 10 to the third years see figure 3.3 for climatic variations on these time scales therefore the entire water mass of the global ocean must be taken into account modeling the oceanic circulation the systematic examination of the various mechanisms and feedbacks by which the oceanic thermal structure and circulation are maintained on various time scales is largely a task for the future in this research it will be necessary to conduct intensive observational programs in order to gain greater understanding of the various oceanic physical processes themselves and to construct numerical models of the oceanic circulation in which these processes are correctly represented for climatic studies it is important that the heat and energy balances of the ocean be modeled correctly over the time and space scales of interest and this cannot now be said to have been achieved the classical ocean circulation models which were initiated in the late 1940s and further developed in the following decades do account for the gross features of the ocean circulation such as the major current systems and the large scale oceanic thermal structure see appendix B but even these features are physically and geometrically distorted by the consideration of only the larger scale relatively viscous motions the commonly used vertical thermal eddy diffusivity in such models is also questionable and may be in order of magnitude too high as indicated for example by recent studies on oceanic tritium concentrations this alone will produce a distortion of the processes responsible for deep water formation in such models but perhaps more important is the fact that numerical ocean models have not had a sufficiently fine horizontal resolution to portray the mesoscale eddies either in the open ocean or in the restricted regions of concentrated currents the accuracy with which the meandering and vortex shedding of boundary currents such as the Gulfstream or Corosio must be modeled or the resolution required for the transient behavior of the equatorial and Antarctic current systems depends on the extent to which these features are coupled to the semi-permanent or primary current systems themselves and on the time scales under consideration it is unlikely however that these features or the mesoscale eddies can be successfully modeled with constant eddy diffusion coefficients to study the role of the oceans in climatic change it is necessary to construct dynamically and energetically correct oceanic general circulation models and to couple them in appropriate versions to similarly accurate and compatible atmospheric models some experience with simplified coupled models of coarse resolution has already been gained as discussed in Dependix B further tests of coupled models are necessary in which the oceanic mesoscale eddies are resolved in order that we may understand their role in the oceanic heat balance and their relationship to the climatically important changes of sea surface temperature since computational limitations will likely preclude the resolution of these eddies throughout the world ocean their successful parameterization will become an important problem for future research of particular importance for climate studies is the construction of an accurate model of the oceanic surface mixed layer since all the physical processes in the ocean ultimately exert their influence on the atmosphere through the surface of the sea until the dynamics of this oceanic boundary layer are better understood our ability to model climatic variations on any timescale will remain seriously limited simulation and predictability of climatic variation climate modeling problem from the above remarks it is clear that the problem of modeling climatic variation is fundamentally one of constructing a hierarchy of coupled atmosphere ocean models each suited to the physical processes dominant on a particular timescale the attack on this problem is now in its infancy whether we consider changes of the external boundary conditions or changes of the internally controlled physical processes and feedback mechanisms we note from figure 3.3 the wide range of time intervals over which characteristic climatic events occur and that many of these involve interactions among the atmosphere, oceans, ice, and land because of the system's non-linearity we may expect a broad range of response in both space and time in the individual climatic variables this is just what the climatic record shows to study the relative contribution of individual physical processes to the overall equilibrium climatic state one approach is to test the sensitivity of the statistics generated by a climate model to perturbations in the parameters that influence that particular physical process in such a modeling program the effects of changes can first be tested in isolation from other interacting components of the system and then in concert with all known processes in a complete climatic model in this research we should not rely exclusively on the general circulation models GCMs but we should employ a variety of modeling approaches we note however that not only are the GCMs and the coupled GCMs in particular useful in the calibration of the simpler models but they are essential to the detailed diagnosis of the shorter period climatic states that are in approximate statistical equilibrium with slowly changing boundary conditions a fundamental approach to the problem of modeling climates and climatic variation must proceed through the consideration of dynamical models of the coupled components of the climatic system in minimum practical terms this means the joint atmosphere ocean system although for some purposes such as the behavior of ice sheets and glaciers the cryosphere must be included as well efforts to assemble such models are just getting underway and their further development is given high priority in the research program recommended in chapter 6 predictability and the question of transitivity it is possible to regard climatic chains as a conventional initial boundary value problem in fluid dynamics if we define the climatic system consisting of the atmosphere hydrosphere and cryosphere in this deterministic view the behavior of the system is governed by the changes of the external boundary conditions see figure 3.1 over relatively short periods it is even possible to regard the land ice masses as part of the external conditions as well it is probably not possible however to remove the hydrosphere from the internal system and still talk meaningfully about climatic variation as the surface layers of the ocean interact with the atmosphere on the shortest time scales associated with climate see figure 3.3 decoupling of the ocean however is exactly what has so far been done in conventional atmospheric and oceanic general circulation models although preliminary efforts to consider the coupled system have been made see appendix B even with the atmosphere together with certain surface effects regarded as the sole component of the climatic system and with all external boundary conditions held fixed there is in spite of our physical expectations no assurance that there will be a climate in the sense that time series generated by the atmospheric changes will settle into a statistically steady state and no assurance that the climate if it exists is unique in the sense that the statistics are independent of the initial state it is therefore useful to define a random time series or the system generating such a series as transitive if its statistics and hence its climatic states are stable and independent of the initial conditions and as in transitive if not as shown by Lawrence 1968 nonlinear systems which are far simpler than the atmosphere sometimes display a tendency to fluctuate in an irregular manner between two or more internal states while the external boundary conditions remain completely unchanged this behavior is related to the system's transitivity and is illustrated in figure 3.4 let us assume that two different states of a climatic system are possible at a time t equals 0 such as a and b in figure 3.4 and let us consider that a is the climatic state that would normally be expected under the given constant boundary condition in a completely transitive system the climatic state b would approach the state a with the passage of time and eventually become indistinguishable from it this would correspond to a unique solution for the climate under fixed boundary conditions in a completely intransitive system on the other hand the climatic state b would remain unchanged and two possible solutions would exist there would in this case moreover be no way in which we could continue to identify the state a as the normal or correct solution as state b would presumably furnish an equally acceptable set of climatic statistics a third behavior however is perhaps the most interesting of all and is displayed by an almost intransitive system in this case the system in state b may behave for a while or intransitive and then at time t1 shift toward an alternative climatic state a where it might remain for a further period of time at time t2 the system might then return to the original climatic state b where it could remain or enter into further excursions the climate exhibited by such a system would thus consist of two or more quasi-stable states together with periods of transition between them for longer periods of time the system might have stable statistics but for shorter periods of time it would appear to be intransitive because the atmosphere is constantly subject to disturbances such as those arising from flow over rough terrain or from the occurrence of baroclinic instability one might think that it could not be an almost intransitive system and fail to show greater excursions of annual and decadal climatic states than it does this depends of course on the level of variability associated with individual climatic states and hence on the time interval we select to define the climatic state itself and on how close neighboring quasi-stable states might be what may appear to be a climatic transition on one time scale to become the natural noise level of a climatic state defined over a longer interval this is consistent with many of the climatic records presented in appendix A even so it might still be possible for the coupled ocean-atmosphere system or for the coupled ocean-atmosphere ice system to be almost intransitive one cannot help but be struck by the appearance of those proxy records that display repeated transitions between two states see figures A13 and A14 in particular this evidence suggests that the interglacial oscillations that have characterized the past million years of the Earth's climatic history may be the climatic transitions of an almost intransitive system another possible example of this phenomenon is the irregular and relatively gradual of the Earth's magnetic poles the search for further evidence of this sort in both the paleoclimatic record and in the climatic history generated by numerical models is an important task for future research as though the specter of almost intransitivity were not enough on the longer time scales of climatic variation it is equally important to recognize the various complication if it turns out that climatic evolution is influenced to a significant degree by environmental impacts originating outside the atmosphere ocean cryosphere system then the predictability of climate will be additionally constrained by the predictability of the environment in a larger sense this in turn could turn out to be the greatest stumbling block of all illustrated for example by the difficulty of predicting the timing and intensity of volcanic eruptions which inject radiation attenuating layers of dust into the upper atmosphere and by the difficulty of predicting the behavior of the sun itself which is the ultimate source of the energy driving the climatic system as noted earlier the predictability of climatic variation constrained by an inherent limitation in the detailed predictability of the atmosphere and ocean climatic noise as previously defined thus arises from the unavoidable uncertainty in the determination of the initial state and from the non-linear nature of the relevant dynamics as shown for example by Lawrence 1969 fluctuations in the weather for periods beyond a few weeks may therefore be treated in large part as though they were generated by an unpredictable random process the observed time series of many meteorological variables may be reasonably well modeled by a first order Markov process with a time tau lagged correlation given by r as a function of tau equals exponent the quantity minus v times the absolute value of tau is the constant decay rate v of the order of 0.3 per day the corresponding power spectrum as a function of frequency omega is given by p as a function of omega equals a divided by the quantity v squared plus omega squared where a is a constant as omega approaches zero for such a spectrum we have p as a function of omega approaching a divided by v squared which is a constant and the very low frequency end of the spectrum therefore appears white there is thus some contribution to climatic variations on all time scales no matter how long arising from the fluctuations of the weather while these considerations do not directly address the physical basis of climatic change they are nevertheless basic to our view of the predictability of climatic change what parts of climatic variations on various time scales are potentially predictable and what parts are just climatic noise in the power spectrum is there potentially predictable variability above the white low frequency end of the daily weather fluctuations or is it possible that some of the long term compensation processes such as those shown in figure 3.3 might depress the spectrum below its white extension to omega equals zero the 250 year record of monthly mean temperatures in central England compiled by Manley 1959 shows small lagged correlations significantly above that of weather out to about 6 months small but perhaps significant lagged correlations at 2 and 4 years and a generally white spectrum with some evidence of extra variability for periods of few decades and longer C.E. Leith N.C.A.R. Boulder, Colorado unpublished results the 6 month lagged correlation may well be a reflection of the role of North Atlantic sea surface temperature anomalies on the English climate and illustrates the somewhat longer periods of the auto variation of the coupled ocean atmosphere system over those of the atmosphere alone as indicated in figure 3.3 additional evidence of even longer period variability is found in the historical and paleoclimatic records Kotsbach and Bryson 1974 see figure A5 further studies of this kind should be made with statistical tests not only of the pessimistic null hypothesis that nothing is predictable but also of hypotheses that are framed more optimistically long range or climatic forecasting as our understanding of the physical basis of climatic variation grows we hope to be able to discern the predictable climatic change signal from the unpredictable climatic noise and to describe with some confidence the character of both past and likely future climates in view of the questions posed by the limited predictability however this discernment may be limited to those circumstances in which there is a relatively large change in the processes or boundary conditions of the climatic system the related problem of forecasting specific seasonal and annual climatic variations rests upon the same physical basis and may prove more difficult to solve to reach these goals will require the coordinated use of all our research tools whether they be observational numerical or theoretical the capstone of these efforts will be the emergence of an increasingly well-defined and tested theory of climatic variation whether the predictability of climatic change turns out to be lower than many would like to believe or to be limited to a finite range in the problem of weather forecasting the quest for understanding must be made our recommendations for the research that we believe to be a necessary part of this effort are presented in detail in Chapter 6 End of Section 3 Recording by Warren Cotty Gurney, Illinois