 Section 4 of Understanding Climatic Change. 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 4. Past climatic variations and the projection of future climates. It is universally accepted that global climate has undergone significant variations on a wide variety of time scales. And we have every reason to expect that such variations will continue in the future. The development of an ability to forecast these future variations, even on time scales as short as one or two decades, is an important and challenging task. Study of the instrumental, historical, and paleoclimatic records not only offers a basis for projection into the future, but furnishes insight into the regional effects of global climatic changes. This chapter attempts to summarize our knowledge of past climatic variations and to give some indication of the future research that must be carried out on critical aspects of this subject. Further details of the record of past climates are given in Appendix A. Importance of Studies of Past Climates. In order to understand fully the physical basis of climate and climatic variation, we must examine the Earth's atmosphere, ocean, ice system under as wide a range of conditions as possible. Most of our notions of how the climatic system works and the tuning of our empirical and dynamical models are based on observations of today's climate. In order that these ideas and models may be useful in the projection of future climates, it is necessary that they be calibrated under as wide a range of conditions as possible. The only documented evidence we have of climates under boundary conditions significantly different from today's comes from the paleoclimatic record. It is here that paleoclimatology, in conjunction with climatic modeling, can make an especially valuable contribution to the resolution of the problem of climatic variation. Modern instrumental data suggests that the atmosphere, at least, may be capable of assuming quite different circulation patterns, even with relatively constant boundary conditions, and that the resulting variability of climate is strongly dependent on geographical location. Although the database is much less complete for the oceans, persistent anomalies of sea surface temperature appear to be related to atmospheric circulation regimes over time scales of months and seasons, and the oceans may show other longer period variations of which we are now unaware. In general, the record of past climate indicates that the longer the available record, the more extreme are the apparent climatic variations. An immediate consequence of this red noise characteristic is that the largest climatic changes are not revealed by the relatively short record of instrumental observation, but must instead be sought through paleoclimatic studies. The record of past climates also contains important information on the range of climatic variability, the mean recurrence interval of rare climatic events, and the tendency for systematic time-wise behavior or periodicity. Such climatic characteristics are in general shown poorly, if at all, by the available instrumental records. Record of Instrumentally Observed Climatic Changes Our knowledge of instrumentally recorded climatic variations is largely confined to the record of the past two centuries or so, and it is only in the last 100 years that synoptic coverage has permitted the analysis of the geographical patterns of climate change over large portions of the globe. It is only during the past 25 years or so that systematic observations of the free atmosphere, mainly in the northern hemisphere, have been made, and that regular measurements of the ocean surface waters have been available in even limited regions. Enough data have been gathered, however, to permit the following summary. A striking feature of the instrumental record is the behavior of temperature worldwide. As shown by Mitchell, 1970, the average surface air temperature in the northern hemisphere increased from the 1880s until about 1940, and has been decreasing thereafter. Star and Oort, 1973, have reported that, during the period 1958 through 1963, the hemisphere's mass-weighted mean temperature decreased by about 0.6 degrees centigrade. In that period, the polar and subtropical arid regions experienced the greatest cooling. The cause of this variation is not known, although clearly this trend cannot continue indefinitely. It may represent a portion of a longer period climatic oscillation, although statistical analysis of available records has failed to establish any significant periodic variation between the quasi-biennial cycle and periods of the order of 100 years. The corresponding patterns of precipitation, cloudiness, and snow cover have not been adequately determined, and it would be of great interest to examine the simultaneous variations of oceanic heat storage and imbalances of the planetary radiation budget once the necessary satellite observations become available. For the earlier instrumental period, there are scattered records of temperature, rainfall, and ice extent, which clearly show individual years and decades of anomalous character. The only apparent trend is a gradual warming in the European area since the so-called little ice age of the 16th to 19th centuries. Historical and Paleoclimatic Record Two sources of data are available to extend the record of climate into the pre-instrumental era, historical sources, such as written records, and qualitative observations, which give rise to what may be called historical climatic data, and various natural paleoclimatic recorders, which give rise to what may be called proxy climatic data. Nature of the Evidence The historical record contains much information relating to climate and climatic variation over the past several hundred to several thousand years, and this information should be located, catalogued, and evaluated. Historical data on crop yields, droughts, and winter severity from manuscripts, explorations, and other sources sometimes provide the only available information on the general character of the climate of the historical past. Such information is especially useful in conjunction with selected tree ring, ice core, and lake sediment data in diagnostic studies of the higher frequency climatic variability on the time scales of years, decades, and centuries. For earlier periods, the paleoclimatic record becomes increasingly fragmentary and ultimately nil for the oldest geological periods, but for the past million years and especially for the past 100,000 years, the paleoclimatic record is relatively continuous and can be made to yield quantitative estimates of the values of a number of significant climatic parameters. Each record, however, must first be calibrated or processed to provide an estimate of the climate. The elevation of an ancient coral reef, for example, is a record of a previous sea level, but before it can be used for paleoclimatic purposes, the effect of local crustal movements must be removed. The taxonomic composition of fossil assemblages in marine sediments and the width of tree rings, for example, are known to reflect the joint influence of several ecological factors. Here, multivariate statistical techniques can be used to obtain estimates of selected paleoclimatic parameters such as temperature and precipitation. In order to be useful, a proxy data source must also have a stratigraphic character, that is, the ambient values of a climatically sensitive parameter must be preserved within the layers of a slowly accumulating natural deposit or material. Such sources include the sediments left by melting glaciers on land, sediments in peat bogs, lakes, and on the ocean bottom, the layers in soil and polar ice caps, and the annual layers of wood formed in growing trees. Since no proxy source yields as long and continuous a record as would be desired, and the quality of data varies considerably from site to site, a coherent picture of past climate requires the assembly of data from different periods and with different sampling intervals. Such characteristics of the principal proxy data sources are summarized in Table A1 of Appendix A. After proxy data have been processed and stratigraphically screened, an absolute chronology must be established in order to date specific features in the climatic record. The most accurate dating technique is that used in tree ring analysis, where dates accurate to within a single year may be determined over the past several thousand years under favorable conditions. Annually layered lake sediments and the younger ice cores also have a potential dating accuracy to within several years over the past few millennia. For suitable materials, Carbon 14 dating methods extend the absolute time scale to about 40,000 years, with an accuracy of about 5% of the material's true age. Beyond the range of Carbon 14 dating, the analysis of the daughter products of uranium decay make possible the reconstruction of the climatic chronology of the past million years. For even older records, our chronology is based primarily on potassium argon radiometric dating as applied to terrestrial lava and ash beds. Stratigraphic levels dated by this method are then correlated with undated sedimentary sequences by the use of paleomagnetic reversals and characteristic floral and faunal boundaries. Summary of Paleoclimatic History From the overview of the geological time scale, we live in an unusual epoch. Today the polar regions have large ice caps, whereas during most of the Earth's history, the poles have been ice free. As shown in Figure A-15 of Appendix A, only two other epochs of extensive continental glaciation have been recorded. One during late pre-Cambrian time, approximately 600 million years ago, and one during Permocarbonyphorus time, approximately 300 million years ago. During the era that followed the Permocarbonyphorus Ice Age, the Earth's climates returned to a generally warmer, non-glacial regime. Before the end of the Mesozoic Era, approximately 65 million years ago, climates were substantially warmer than today. At that time, the configuration of the continents and shallow ocean ridges served to block a circumpolar ocean current in the southern hemisphere. This barrier was formed by South America and Antarctica, which lay in approximately their present latitudinal positions and by Australia, then a northeastward extension of Antarctica. About 50 million years ago, the Antarctic-Australian passage opened as Australia moved northeastward and as the Indian Ocean widened and deepened. By about 30 million years ago, the Antarctic-circumpolar current system was established, an event that may have decisively influenced the subsequent climatic history of the Earth. About 55 million years ago, global climate began a long cooling trend known as the Cenozoic climate decline, C-figure A-15. Approximately 35 million years ago, there is evidence from the marine record that the waters around the Antarctic continent underwent substantial cooling. And there is further evidence that about 25 million years ago, glacial ice occurred along the edge of the Antarctic continent in some locations. During early Miocene time, approximately 20 million years ago, there is evidence that the low and middle latitudes were somewhat warmer. There is widespread evidence of further cooling about 10 million years ago, including the growth of mountain glaciers in the northern hemisphere and substantial growth of the Antarctic ice sheet. This time may be taken as the beginning of the present glacial age. Evidence from marine sediments and from continental glacial features indicates that about 5 million years ago, the already substantial ice sheets on Antarctica underwent rapid growth and even temporarily exceeded their present volume. Three million years ago, continental ice sheets appeared for the first time in the northern hemisphere, occupying lands adjacent to the North Atlantic Ocean, and during at least the last one million years, the ice cover on the Arctic Ocean was never significantly less than it is today. Once the polar ice caps formed, they began a long and complex series of fluctuations in size. Although the earlier record is still not clear, the last million years has witnessed fluctuations in the northern hemisphere ice sheets with a dominant period on the order of 100,000 years. See figure A2. These fluctuations may have occurred in parallel with substantial changes in the volume of the West Antarctic ice sheet. By comparison, however, changes in the volume of the ice sheet in East Antarctica were quite small and were probably not synchronous with glaciers in the northern hemisphere. The major climatic events during the past 150,000 years were the occurrence of two glacial maxima of roughly equal intensity, one about 135,000 years ago and the other between 14,000 and 22,000 years ago. Both were characterized by widespread glaciation and generally colder climates and were abruptly terminated by warm interglacial intervals that lasted on the order of 10,000 years. The penultimate interglacial reached its peak about 124,000 years ago, while the present interglacial, known as the Holocene, evidently had its thermal maximum about 6,000 years ago. Between 22,000 and 14,000 years ago, the northern hemisphere ice sheets attained their maximum extent, see figure A24. The eastern part of the Laurentide ice sheet, which covered portions of eastern North America and the Scandinavian ice sheet, which covered parts of northern Europe, both attained their maximum between 22,000 and 18,000 years ago. Several thousand years before the maximum of the Cordillarin ice sheet, about 14,000 years ago, deglaciation began rather abruptly and the Cordillarin sheet melted rapidly and was gone by 10,000 years ago. The interval of deglaciation 14,000 to 7,000 years ago was marked in many places by significant secondary fluctuations about every 2,000 to 3,000 years. In general, the period about 7,000 to 5,000 years ago was warmer than today, although the records of mountain glaciers, tree lines, and tree rings reveal that the past 7,000 years was punctuated in many parts of the world by colder intervals about every 2,500 years, with the most recent occurring about 300 years ago. For the last 1,000 years, the proxy records generally confirm the scattered observations in historical records. The cold period identified above is seen to have consisted of two periods of maximum cold, one in the 15th century and another in the late 17th century. The entire interval, from about 1430 to 1850, has long been referred to as the Little Ice Age and was characterized in Europe and North America by markedly colder climates than today's. Inference of future climates from past behavior. Notwithstanding the limitations of our present insight into the physical basis of climate, we are not altogether powerless to make certain inferences about future climate. Beginning with the most conservative approach, we may use the climatic normal as a reference for future planning. In this approach, it is tacitly assumed that the future climate will mirror the recently observed past climate in terms of its statistical properties. Depending on the sensitivity of the climate-related application and on the degree to which the climate is subject to change over a period of years, following that for which the normal is defined, this kind of inference can be anything from highly useful to downright misleading. Of the various other approaches to the inference of future climate, in which the attempt is made to capture more predictive information than is embodied in the normal, the most popular have been those based on the supposition that climate varies in cycles. Since the development of modern techniques of time series analysis, in particular those involving the determination of the variance or power spectrum, it has become clear that almost all alleged climatic cycles are either one, artifacts of statistical sampling, two, associated with such small fractions of the total variance that they are virtually useless for prediction purposes, or three, a combination of both. Other approaches, developed to a high degree of sophistication in recent years, include several kinds of non-linear regression analysis, in which no assumption need be made about the periodic behavior of the climatic time series, which appropriately degenerate to a prediction of the normal in cases where the series possess no systematic temporal behavior. The full potential of such approaches is not yet clear but appears promising, at least in certain situations. Natural Climatic Variations Regardless of the approach taken to infer future climates, the view that climatic variation is a strictly random process in time can no longer be supported. It has been well established, for example, that many atmospheric variables are serially correlated on timescales of weeks, months, and even years. For the most part, such correlations derive from persistence and resemble the behavior of a low-order Markov process. Unfortunately, non-randomness of this kind does not lend itself to long-range statistical prediction. In addition to persistence, long-term trends have a tendency to show up in great number and variety in climatological time series. See Appendix A. Many such trends are now understood to originate from what are called inhomogeneities in the series, as, for example, effects of station relocations, changes in observing procedures, or local microclimatic disturbances irrelevant to large-scale climate. Even after statistical removal of such effects, many real trends nonetheless remain and may be recognized as part of a longer-term oscillation of climate. We must, moreover, recognize that the climatic record may also reflect various natural environmental disturbances, such as volcanic eruptions and perhaps changes in the sun's energy output, which are themselves only poorly predictable, if at all. Clearly, a climatic prediction based on the linear extrapolation into the future of a record containing such effects would be highly unrealistic. The behavior of longer climatic series is seemingly periodic, or quasi-periodic, especially those series that extend into the geological past, as reconstructed from various proxy data sources. It is a fundamental problem of paleoclimatology to determine whether this behavior is really what it seems or whether it is an illusion created by the characteristic loss of high-frequency information due to the limited resolving power of most proxy climatic indicators. Illumination of this question would be of great importance to the determination of the basic causes of the interglacial climatic succession and to the assessment of where the Earth stands today in relation to this sequence. Spectrum analysis of the time series of a wide variety of climatic indices have consistently displayed a red-noise character, see, for example, Gilman et al., 1963. That is, the spectra show a gradual increase of variance per unit frequency as one proceeds from high frequencies toward low frequencies. The lack of spectral gaps provides empirical confirmation of the lack of any obvious optimal averaging interval for defining climatic statistics. Most spectra of climatic indices are also consistent in displaying some form of quasi-biannual oscillation. See, for example, Breyer 1968, Engel et al., 1969, or Wagner 1971. This fluctuation is most obvious in the wind data of the tropical stratosphere, but also has been shown to be a real, if minor, feature of the climate at the Earth's surface as well. Time series of some of the longer instrumental records show some suggestion of very low frequency fluctuations, periods of about 80 years and longer, but the data sets are not long enough to establish the physical nature and historical continuity of such oscillations. While numerous investigators have reported spectral peaks corresponding to almost all intermediate periods, the lack of consistency between the various studies suggests that no example of quasi-cyclic climatic behavior with wavelengths between those on the order of 100 years and the quasi-biannual oscillation have been unequivocally demonstrated on a global scale. Further discussion of these questions is given in Appendix A, page 127, FF, Man's Impact on Climate. While the natural variations of climate have been larger than those that may have been induced by human activities during the past century, the rapidity with which human impacts threatened to grow in the future and increasingly to disturb the natural course of events is a matter of concern. These impacts include man's changes of the atmospheric composition and his direct interference with factors controlling the all-important heat balance. Carbon dioxide and aerosols. The relative roles of changing carbon dioxide and particle loading as factors in climatic change have been assessed by Mitchell, 1973 A, 1973 B, who noted that these variable atmospheric constituents are not necessarily external parameters of the climatic system but may also be internal variables. For example, the changing capacity of the surface layers of the oceans to absorb CO2, the variable atmospheric loading of wind-blown dust and the interaction of CO2 with the biosphere. The atmospheric CO2 concentrations recorded at Mauna Loa, Hawaii, and other locations show a study increase in the annual average, amounting to about a 4% rise in total CO2 between 1958 and 1972, keeling at all 1974. The present day CO2 excess relative to the year 1850 is estimated at 13%. A comparison with estimates of the fossil CO2 input to the atmosphere from human activities indicates that between 50 and 75% of the latter has stayed in the atmosphere with the remainder entering the ocean and the biosphere. The CO2 excess is conservatively projected to increase to 15% by 1980 to 22% by 1990 and to 32% by 2000 AD. The corresponding changes of mean atmospheric temperature due to CO2, as calculated by Minabi, 1971, on the assumption of a constant relative humidity and fixed cloudiness, are about 0.3 degrees centigrade per 10% change of CO2 and appear capable of accounting for only a fraction of the observed warming of the Earth between 1880 and 1940. They could, however, conceivably aggregate to a further warming of about 0.5 degrees centigrade between now and the end of the century. The total global atmospheric loading by small particles, those less than 5 micrometers in diameter, is less well monitored than is CO2 content, but it is estimated to be at present about 4 times 10 to the 7th tons, of which perhaps as much as 1 times 10 to the 7th tons is derived both directly and indirectly from human activities. If the anthropogenic fraction should grow in the future at the not unrealistic rate of 4% per year, the total particulate loading of the atmosphere would increase about 60% above its present day level by the end of this century. The present day anthropogenic particulate loading is estimated to exceed the average stratospheric loading by volcanic dust during the past 120 years, but to equal only perhaps one-fifth of the stratospheric loading that followed the 1883 eruption of Krakatoa. The impact of such particle loading on the mean atmospheric temperature cannot be reliably determined from present information. Recent studies indicate that the role of atmospheric aerosols in the heat budget depends critically on the aerosols absorptivity as well as on their scattering properties and vertical distribution. The net thermal impact of aerosols on the lower atmosphere, below cloud level, probably depends on the evaporable water content of the surface in addition to the surface albedo. Aerosols may also affect the structure and distribution of clouds and thereby produce effects that are more important than their direct radiative interaction. Hobbes et al. 1974, Mitchell 1974. Of the two forms of pollution, the carbon dioxide increase is probably the more influential at the present time in changing temperatures near the Earth's surface, Mitchell 1973A. If both the CO2 and particulate inputs to the atmosphere grow at equal rates in the future, the widely differing atmospheric resident times of the two pollutants means that the particulate effect will grow in importance relative to that of CO2. Thermal pollution, clouds and surface changes. There are other possible impacts of human activities that should be considered in projecting future climates. One of these is the thermal pollution resulting from man's increasing use of energy and the inevitable discharge of waste heat into either the atmosphere or the ocean. Although it is not yet significant on the global scale, the projections of Butiko 1969 and others indicate that this heat source may become an appreciable fraction, one percent or more, of the effective solar radiation absorbed at the Earth's surface by the middle of the next century. And a future energy generation is concentrated into large nuclear power parks, the natural heat balance over considerable areas may be upset long before that time. Recent estimates by Hefeli 1974 indicate that by early in the next century the total energy use over the continents will approach 10% of the natural heat density of about 50W per square meter and that in local industrial areas the man-made energy density may become several hundred times larger. There is also the possibility that widespread artificial creation of clouds by aircraft exhaust and by other means may induce significant climatic variations although there is no firm evidence that this has yet occurred. Such effects could serve to increase the already prominent role played by natural clouds in the Earth's heat balance. See figure 3.2 Widespread changes of surface land character resulting from agricultural use and urbanization and the introduction of man-made sources of evaporable water may also have significant impacts on future climates. When the surface albedo and surface roughness are changed by the removal of vegetation, for example, the regional climatic anomalies introduced may have large scale effects depending on the location and scale of the changes. The creation of large lakes and reservoirs by the diversion of natural water courses may also have widespread climatic consequences. The list of man's possible future alterations of the Earth's surface can be considerably lengthened by the inclusion of more ambitious schemes such as the removal of ice cover in the polar regions and the diversion of ocean currents. Again, however, it is only through the use of adequately calibrated numerical models that we can hope to acquire the information necessary for a quantitative assessment of the climatic impacts. End of Section 4, Recording by Warren Coddy, Gurney, Illinois. Section 5 of Understanding Climatic Change. This is the LibriVox Recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Josh Kibbey. Understanding Climatic Change. A Program for Action by the U.S. Committee for the Global Atmospheric Research Program. Section 5, Scope of Present Research on Climatic Variation. The overview of the problem of climatic variation presented in the preceding chapters and in the technical appendixes contain only those references to the literature that were helpful in the illustration of a particular viewpoint or necessary to document a specific source of information. In the course of its deliberations, however, the panel found it necessary to survey present research on climatic variation as represented by the more recently published literature and by selected ongoing activities. In as much as this information may serve as a useful background to the panel's recommendations for a national and international program of climatic research, it is summarized here. Even this survey, in which emphasis is given to material published since 1970, must be considered incomplete and necessarily gives precedence to sources of information most readily available to the panel. Further useful references on various aspects of the problem of climatic variation are to be found in other recent publications. Committee on Polar Research, 1970, National Science Board, 1972, Wilson, 1970, 1971. Climatic Data Collection and Analysis Here the current status of efforts to assemble climatic data for both the atmosphere and ocean is summarized and the various observational field programs directed to the collection of specific data of climatic interest are described. Atmospheric Observations Climatological data banks are maintained by NOAA's National Climatic Center in CC and National Meteorological Center in MC and by the Military Operational Weather Services, particularly the Air Forces, Environmental Technical Application Center, ETEC, and the Navy's Fleet Numerical Weather Central, FNWC. Using data from these sources, atmospheric data sets specifically for climatic studies have been assembled by the National Center for Atmospheric Research, the Geophysical Fluid Dynamics Laboratory, MIT, and other institutions. Efforts to assemble the rapidly accumulating data from meteorological satellites have also been made by NOAA's National Environmental Satellite Service, NESS, and by the University of Wisconsin. Sustained efforts to assemble and systematically analyze such data for the use of the climatic research community are important tasks for the future. In addition to the standard compilations of climatological statistics prepared on a routine basis by governmental agencies, new summaries of upper-air data have been prepared, Crutcher and Miserve, 1970, Teljard et al. 1969. These have permitted the initial construction of the average monthly global distributions of the basic meteorological variables of pressure, temperature, and dew points at selected levels. The analysis of such data in terms of the various statistics of the global circulation is less advanced, although intensive studies of a five-year period in the Northern Hemisphere have recently been completed, Ort 1972, Ort and Rasmussen 1971, Starr and Ort 1973. These studies provide the most quantitative analyses of the annual climatic variations of the atmosphere yet made, and plans are underway for their extension to additional five-year periods. Studies of the spatial patterns of observed variability over longer time periods are almost entirely confined to surface variables in the Northern Hemisphere, Hellerman 1967, Kutzberg 1970, Wagner 1971. Such studies should be extended to other portions of the atmosphere and broaden to include other, less comprehensively observed climatic elements. An observational analysis of the tropical and equatorial circulation has been completed, Newell et al. 1972, and statistics for the stratospheric climate are becoming increasingly available, Newell 1972. Comprehensive data on the components of the global atmospheric energy balance are only beginning to be available, Newell et al. 1969, although many rely on older and indirect data for the unobserved elements of the heat balance at the Earth's surface. Budiko 1956-1963, Vovovich and Nochchenikov 1964, Muller 1951, Posey and Klap 1964. More recent direct observations from satellites, however, are providing valuable new insight into both the time and space variations of the overall radiation budget of the Earth, Wander Haar and Suomi 1971, and a promise to provide further data of climatic importance as newer and more versatile satellite observational capabilities develop. Chehing 1974, Kospar Working Group 6 1972, Raschke et al. 1973, Smith et al. 1973. Oceanic and Other Observations The observational database for the oceans is much less developed than that for the atmosphere, and oceanic climatic summaries are based largely on observations that are more widely scattered in both space and time. Even for the more traveled parts of the ocean, these data are sufficient only to indicate the average large scale features of the ocean structure and circulation. Fuglister 1960, Hellermann 1967, Sverdrup et al. 1942, US Navy Hydrographic Office 1944. Updated compilations of surface stress, Hellermann 1967, and sea surface temperatures, Alexander and Mobley 1973, Washington and Teal 1970, have been made and summaries of the observed subsurface temperature structure have recently become available for selected oceans. Born et al. 1973, Robinson and Bauer 1971. Significant repositories of oceanic data useful for climatic purposes existed in number of institutions, although a comprehensive oceanic data inventory has not yet been prepared. The Navy's Fleet Numerical Weather Center, the Scripps Institution of Oceanography, the Woods Hole Oceanographic Institution, and the National Marine Fisheries Service, for example, all have specialized oceanographic data banks, as well as data from individual cruises and expeditions. Guides to the oceanic data services of the Environmental Data Service 1973 of NOAA are also available. An increasing amount of data on oceanic surface conditions is becoming available from satellite observations and other remote sensing techniques, Monk and Woods 1973, Shane Consolomance in 1972, and offer the promise of routine global monitoring of sea surface temperature and sea ice distribution. Satellite data collected by NESS also permit the determination of the snow and ice extent over land. This and other glaciological data are being accumulated by the US Geological Survey. The further extension of oceanographic sea ice and glaciological observations by satellites, buoys, and ships is under active consideration in connection with the FGCE, GARP 1972, STOMEL 1973, and is part of other large-scale programs as well, International Decade of Ocean Exploration 1973, International Glaciological Program for the Antarctic Peninsula 1973, CASR 1973, Mid-Ocean Dynamics Experiment 1 Scientific Council 1973, joined the US Poll-X Panel 1974. Observational Field Programs Many observational data of importance to climatic research have been acquired in special field programs. Some of these are also directly related to GARP itself, Amtech Study Group 1973, GARP, Joint Organizing Committee 1972-1973, Haliton 1974, Condray of 1973, such as the Complete Atmospheric Energetics Experiment, KNEX, the Air Mass Transformation Experiment, Amtechs, the GARP Atlantic Tropical Experiment, GATE, and the Arctic Ice Dynamics Joint Experiment, ADJECS. Others are part of the NSF's International Decade of Ocean Exploration, IDGE 1973 Program, Mid-Ocean Dynamics Experiment 1 Scientific Council 1973, such as the Geochemical Ocean Sanction Study, Geosex, the Mid-Ocean Dynamics Experiment, MODE, the North Pacific Experiment, NORPACS, and the Climate Long Range Investigation Mapping and Prediction Climap Project. Other field programs are aimed at the monitoring of atmospheric composition and aerosols, such as those of INCAR, the Environmental Protection Agency, and NOAA's Environmental Research Laboratories. Each of these programs is focused on physical processes of importance in particular geographical regions and is a valuable source of experience and information. There are also international programs of this sort in various stages of planning, such as the Polar Experiment, POLEX, Joint U.S. POLEX Panel 1974, the International Glaciological Program for the Antarctic Peninsula, IGPAP 1973, and the International Southern Ocean Studies, ISOS, programs, ISOS Planning Committee 1973. Cooperative programs such as these will be necessary for the comprehensive future monitoring, analysis, and modeling of climate and climatic variation. Studies of Climate from Historical Sources The record of past climates, as contained in various historical documents, writings, and archaeological material, has been increasingly recognized as an important source of information. Bryson and Julian 1963, Butzer 1971, Carpenter 1965, Lavroy-Leduri 1971, Lamb 1968-1972, Ludlem 1966-1968. These sources permit the study of historical climates over the past several thousand years. A systematic compilation of material of this sort is being undertaken by the climatic research unit of the University of East Anglia, Lamb 1973-B. Studies of Climate from Proxy Sources The assembly of paleoclimatic information from proxy data sources has attained new importance in recent years with the development of new methods of dating and of new techniques of quantitative climatic inference. In the following, the various efforts in this aspect of climatic research are briefly summarized. General Synthesis Two broad surveys of paleoclimatology have appeared in recent years, Funnel and Rital 1971, Schwartzbach 1961, along with textbooks, Flint 1971, Washburn 1973, and Symposia, Black et al. 1973, Turkey in 1971, which emphasized the glacial processes during the late Sinozoic period. Other recent paleoclimatological syntheses have been concerned with the broad range of quaternary studies, Wright and Frey 1965, with the relationships between Pleistocene geology and biology, Boitzer 1971, West 1968, and with more recent paleoclimatic fluctuations from a meteorological viewpoint, Lamb 1969. The review of the full range of paleoclimatic events on all timescales given in Appendix A of this report have been made possible by the recent application of improved dating methods to the stratigraphic record of ocean sediments and of lifted reefs. This synthesis illustrates the essential need for an accurate timescale and the interpretation of proxy climatic data. Chronology The methods of dendocrinology, Ferguson 1970, Lamarston Harlan 1973, the radiocarbon method, Olson 1970, Wendelind and Brice in 1974, and other isotopic dating methods have recently been used to infer the chronology of climate over the past several hundred thousand years. Brocker and Van Donk 1970, Matthews 1973, Miss Aleyah et al. 1969. Biostratigraphic and paleomagnetic correlations between the marine and continental records have provided a reasonably accurate chronology of the past 60 million years by the use of potassium argon and other isotopes. Bergeron 1971, 1972, Hayes et al. 1969, Kukla 1970, Rudemann 1971, Sincetta et al. 1973, Shackleton and Kennett 1974A 1974B, Shackleton and Oppdike 1973. Monitoring techniques Following the initial efforts to estimate paleo temperatures from isotopic time series, Emiliani 1955 and 1968, recent work has made it possible to separate the effects of temperature from those of ice volume change, Shackleton and Oppdike 1973. Multivariate statistical techniques have recently been developed that permit the quantitative estimation of climatic parameters from the concentration of fossil plankton and deep sea sediments, Embry and Kip 1971, Embry et al. 1973, Kip 1974, the growth record of tree rings, Fritz et al. 1971, and the continental distribution of fossil pollen, Web and Brice in 1972. These methods have since been applied to the reconstruction of paleo-ocean temperatures. Luz 1973, Vacantair et al. 1972A, Paisios et al. 1973, Sacks 1973, as well as to pressure and precipitation anomalies, Fritz 1972. Isotopic studies of cores taken in the polar ice caps provide measures of the air temperature at the time of ice formation, Dan Gard et al. 1971. Further refinements of such monitoring techniques will help to fill in the paleoclimatic record, especially when several independent methods are available for the same period. Proxy data records and their climatic inferences Proxy data come from a wide variety of sources. Potentially, any biological, chemical, or physical characteristic that responds to climate may provide proxy data useful in the reconstruction of past climates. One of the more prolific sources of long-term climatic information has been the extensive collection of deep-sea cores, obtained routinely over the years on various oceanographic expeditions and more recently from the deep-sea drilling project, Douglas and Savin 1973, Shackleton and Kennet 1974A, 1974B. Analysis of the fossil flora and fauna in such cores, with chronology provided from their isotopic content and paleomagnetic stratigraphy, had been performed for all the principal oceans of the world, Miliani 1968, Gardner and Hayes 1974, Humkins et al. 1971, Embry et al. 1973, Kellogg 1974, Kennet and Huddleston 1972, Moore 1973, and provides a preliminary documentation over the temperature and large-scale displacements of the surface waters during the last few hundred thousand years. McIntyre et al. 1972B, Shackleton and Optike 1973. Other characteristics of the sediment cores, such as the presence of volcanic ash, rudiment and glover 1972, also indicate climatically important events as well as providing valuable core-dating horizons. For periods of particular interest, such as the glacial maximum of about 18,000 years ago, detailed reconstructions of seasonal sea surface temperature and salinity have been made for the North Atlantic, McIntyre et al. 1974, and more recently have been extended to the world ocean under the Climap program. The concentration of fossil pollen and the record of soil types in the relatively undisturbed continental sites is another source of proxy data on terrestrial paleoclimates. In recent years, pollen data have been analyzed from a number of continental areas. Bernabeau et al. 1974, Davis 1969, Hueser 1966, Hueser & Floor 1974, Livingston 1971, Swain 1973, Sukada 1968, Vanderhamen et al. 1971, and provide a preliminary documentation of the surface vegetational changes during the late Sinozoic and Quartinary periods. Leopold 1969, Wright 1971. Soil records have been studied less extensively, but provide corroborative evidence of surface climatic conditions. Frye and Willman 1973, Kukla 1970, Sorensen & Knox 1973. In many ways, analogous to the records from deep sea cores, proxy climatic data from ice cores have recently been obtained from sites in both Antarctica and Greenland, Dansgaard et al. 1969, 1971. Such ice core records provide a detailed history of atmospheric conditions over the ice during the last 100,000 years, Dansgaard et al. 1973, Johnson et al. 1972, Langway 1970. The drilling of deeper cores are planned, and their analysis in correlation with other proxy data will contribute significantly to the reconstruction of global climatic history. Further climatic inferences are obtained from proxy data on marine shorelines. By assembling data on dated terraces at selected continental and island sites, and with the necessary adjustments for eustatic changes in the Earth's crust, the record of sea level variations over the last 150,000 years is becoming established. Bloom 1971, Curry 1965, Matthews 1973, Messolea et al. 1969, Milliman & Emory 1968, Steinem et al. 1973, Walcott 1972, particularly as regards the timing of high stands. Closely related to the question of ice, soil, and sea level changes are the proxy data from glacial fluctuations themselves. Considerable attention has been given in recent years to the reconstruction of the glacial history of the most recent major ice age in North America. Andrews et al. 1972, Black et al. 1973, Draymonus & Carrow 1972, Fry & Willamon 1973, Patterson 1972, Porter 1971, Richmond 1972, as well as the relatively small but significant fluctuations in mountain glaciers over the past 10,000 years, Dinten & Carlin 1973. Although local glacial margins fluctuate primarily in response to the glacial's net mass accumulation, their overall pattern provides evidence of larger scale and longer period climatic responses. When these changes are combined with the more limited data on the glacial history of the Antarctic ice sheet, a number of worldwide relationships, and the major fluctuations of glacial extent begin to emerge. Dinten et al. 1971, Hughes 1973. In the post-glacial period, important proxy data on climatic variations over the continents also come from the records of tree rings and closed basin lakes. Both of these features respond directly to the hydrologic and thermal balances at the surface and when properly calibrated for local effects can provide a record of climate over thousands of years. With the introduction of new dating and analysis methods, the records of tree ring width variations from both living and fossil trees provide an annually integrated record of climatic changes, especially in arid regions. Ferguson 1970, Fritz 1971, 1972, LaMarche 1974, LaMarche & Harland 1973. The radiocarbon dating of debris in selected arid lakes provides further evidence of climatic variations, particularly as they affect the local water balance. Bruckner & Kaufman 1965, Butzer et al. 1972, Ferrand 1971. Institutional programs. Much of the present research on paleoclimates is performed in conjunction with other glaciological and geological programs, such as those of the U.S. Geological Survey, the Illinois Geological Survey, the Lamont-Doherty Geological Observatory of Columbia University, and the Army's Cold Regions Research and Engineering Laboratory. Other efforts are conducted within the larger oceanographic research laboratories, such as the Scripps Institution of Oceanography at the University of California, the Woods Hole Oceanographic Institution, the U.S. Naval Oceanographic Laboratory, and the Marine Research Laboratories of the University of Miami, the University of Rhode Island, and Oregon State University. In recent years, more specialized paleoclimat research efforts have been developed at a number of other universities, joining the long-established Laboratory of Tree Ring Research of the University of Arizona and the Institute for Polar Research at the Ohio State University. These include the Coordinary Research Centers at the University of Washington and the University of Maine, the Center for Climatic Research at the University of Wisconsin, the Institute of Arctic and Alpine Research at the University of Colorado, and the Paleoclimatic Research Programs in the Geology and Geophysics Departments of Brown University and Yale University. Notable among the many cooperative activities of these and other institutions are the NSF's IDGE programs, including the CLIMAP and NORPACS programs. Such cooperative programs have been instrumental in developing an effective collaboration among the paleoclimatic, oceanographic, and meteorological research communities and should be broadened in the future. Physical Mechanisms of Climatic Change Although the problem of climatic change has been the subject of speculation for over a century, recent research has concentrated on the study of specific physical processes and on the interactions among various components of the climatic physical system. Here, the more recent of such efforts are briefly surveyed together with a review of associated empirical, diagnostic, and theoretical studies. Physical Theories and Feedback Mechanisms A particular interest in the problem of climatic change is the question of the cause of the ice ages. Among the recent attempts to answer this question are hypotheses that focus upon the roles of sea ice, dawn and ewing 1968, and ice shelves, Wilson 1964, the carbon dioxide bounce, PLAS 1956, and the ocean salinity, Wei 1968. Other hypotheses emphasize the roles of variations of external boundary conditions, particularly the incoming solar radiation, Alexander 1974, Budiko 1969, Klapp 1970, Manabean-Wetherald 1967, and the volcanic dust-loading of the atmosphere, Lam 1970. It is generally believed that the astronomical variations of seasonal solar radiation play a role in longer period climatic changes, Lankovich 1930, Mitchell 1971B, Vernikar 1972. Although there was no agreement on the physical mechanisms evolved, recent studies have also been made of the long-standing question of possible short-term relationships between the climate and solar activity itself, Roberts 1973, Roberts and Olson 1973. Other hypotheses of climatic change reckon with the possibility that much of the observed variations of climate are essentially the result of the natural, self-excited variability of the internal climatic system. Bryson 1974, Mitchell 1966, 1971B, Sawyer 1966. Of the many feedback processes involved in climate, Schneider and Dickinson 1974, the role of aerosols has recently received particular attention. Childek and Coakley 1974, Joseph et al. 1973, Mitchell 1971A 1974, Razul and Schneider 1971, Schneider 1971. Although our knowledge of the physical properties and the global distribution of aerosols is limited, these studies indicate that the climatic effects may be substantial. Razul and Schneider 1971, Yamamoto and Tanaka 1972. Several research programs on aerosols are underway, including the Global Atmospheric Aerosol Research Study, GARS, of INKAR, and the Soviet K-NEX program, Kondratiev 1973, previously noted. Attention has also been focused on the regulatory roles of cloudiness, Coak's 1971, Mitchell 1974, Schneider 1972, and Air-Sea Interaction, NAMI-S 1973, White and Barnett 1972, in the global climatic system. In both cases, however, an adequate quantitative understanding has not yet been achieved. Diagnostic and Empirical Studies Related to the search for physical climatic theories and mechanisms are many empirical and diagnostic studies of various aspects of climatic change. Particular attention has been given to the analysis of the large-scale variations of the atmospheric circulation that had been observed during the past few decades. Angle et al. 1969, Björknis 1969, Davis 1972, Nimeus 1970, Wall 1972, Wall and Lawson 1970, White and Walker 1973, and to their relationship to regional anomalies of temperature and rainfall. Landsberg 1973, Nameus 1972, B, Wind Stanley 1973, A, 1973, B. Satellite observations of the large-scale variations of surface albedo and seasonal snow cover have brought new attention to these features of the climatic system. Kukla and Kukla 1974, Wagner 1973, as well as necessitating a significant revision of the atmospheric radiative energy budget, London and Sazomore 1971, and the estimated oceanic energy transport, Wanderhaar and Ort 1973. Several recent diagnostic and empirical studies have also focused on aspects of the atmosphere-ocean interaction on seasonal, annual, and decadal timescales. Lamm and Radcliffe 1972, Nameus 1969, 1971, B, 1972, A, and have prompted new attention to their relevance to long-range forecasting. Radcliffe 1973, Radcliffe and Murray 1970. The larger-scale variations of ocean surface temperature and sea level have also been studied and have led to the identification of apparent teleconnexions with the atmospheric circulation. Nameus 1971, A, Werkey 1973, 1974. New studies of mesoscale oceanic features have been made, Bernstein 1974, and to provide further evidence of the dominance of this scale in the oceanic energy spectrum in agreement with the preliminary results of the mode program. Other oceanic studies have concentrated on the empirical evaluation of the turbulent fluxes of momentum, heat, and water vapor across the air-sea interface. Holland 1972, Paul Sinetal 1971, 1972. The difficulties of estimating the transport of even the strongest ocean currents or the heat balance over ice-covered seas with the present database have also received renewed emphasis. Fletcher 1972, Neyler and Richardson 1973, Reid and Nalyn 1971. Predictability and Related Theoretical Studies An important problem in climatic variation is the determination of the degree of predictability that is inherent in the natural system, as well as that which is achievable by simulation. A number of recent studies of simplified models have shown that multiple climatic solutions may exist under the same external conditions. Budiko 1972, Fegra 1972, Lorenz 1968, 1970, in a manner suggestive of certain features of the observed climatic record. There is also evidence from simplified models that the completely accurate specification of a climatic state is not achievable in any case because of the same kind of nonlinear error growth that limits the accuracy of weather prediction. Fleming 1972, Houghton 1972, Leith 1971, Lorenz 1969, Robinson 1971a. Analysis of selected climatic time series indicate only limited predictability on yearly and perhaps decadal timescales. Kutzbock and Bryson 1974, Leith 1973, Lorenz 1973, Vulles and Mullen 1971. While the general white noise character of higher frequency fluctuation had been confirmed in model simulations, Cherven et al. 1974. Further studies of climatic predictability are needed in order to identify both the intrinsic and practical limits of climatic prediction. Numerical Modeling of Climate and Climatic Variation The accurate portrayal of global climate is the scientific goal of much of the atmospheric and oceanic numerical modeling effort now underway. Smagarensky 1974. When such models are coupled, the direct numerical simulation of at least the shorter period climatic variations becomes a realistic possibility. The study of longer period climatic variations, however, may require the construction of increasingly parameterized models. Here, the more recent modeling research in both of these approaches is briefly reviewed. Atmospheric General Circulation Models and Related Studies Studies with Global Atmospheric General Circulation Models, GC-IMS, have focused on the simulation of seasonal climate, with emphasis on the analysis of the surface heat and hydrologic balances. Gates 1972. Holloway and Manabee 1971. Cuzahara in Washington 1971. Manabee 1969A 1969B. Manabee et al. 1972. Somerville et al. 1974. As described more fully in Appendix B, simulations of average January climate have now been achieved by several GC-IMS. Although additional global GC-IMS are under development, Corbietal 1972, only two at this writing have been integrated over time longer than one year, Manabee et al. 1972, 1974B, Mintz et al. 1972. Global atmospheric models have also recently been applied to the simulation of specific regional circulations, such as those in the tropics, Manabee et al. 1974. In such applications, the model's parameterization of processes in the surface boundary layer is of particular importance. Deirdorf 1972. Delsau et al. 1971. Sazamori 1970. Considerable recent interest has also been shown in the simulation of stratosphere climate with global GC-IMS. Cuzahara et al. 1973. Malmon and Manabee 1972. An overview of global atmospheric and oceanic GC-IMS is given in Appendix B. More detailed reviews of these and other models have recently been prepared, Robinson 1971B, Schneider and Kellogg 1973, while others are in preparation, Garp Joint Organizing Committee 1974, Schneider and Dickinson 1974. Statistical Dynamical Models and Parameterization Studies. Research on the development of dynamical climate models, in which the transfer properties of the large-scale eddies are statistically parameterized rather than resolved as in the GC-IMS, has accelerated in recent years, Wilson 1973. These models include those that address only the surface heat balance, Boudicot 1969, Fager 1972, Sellers 1969, 1973. Those that consider the time-dependent zonally-averaged motion, McCracken 1972, McCracken and Luther 1973, Salisman and Vernacar 1971, 1972, Wynne Nielsen 1972, Williams and Davies 1965, and those in which the statistical eddy fluxes are represented in terms of the large-scale motions themselves, Dwyer and Peterson 1973, Kuhar-Hara 1970, 1973. A key problem in such models is the correct parameterization of the heat and momentum transports by the large-scale eddies, while a completely adequate formulation has not yet been achieved, research is continuing by a variety of methods. Clapp 1970, Gavriline Monan 1970, Green 1970, Salisman 1973, Smith 1973, Stone 1973. Because of the generally longer time scales involved in the oceanic general circulation, relatively less attention has been given to the corresponding formulation of statistical dynamical ocean models. A dim 1970, Petticove and Fagelson 1973, Pike 1972. This problem, however, will assume greater importance with the increased development of coupled ocean atmosphere systems reviewed below. Ocean general circulation models. Although generally less advanced than their atmospheric counterparts, oceanic GCMs have recently been developed to the point where successful simulations of the seasonal variations of ocean temperature and currents have been achieved in both idealized basins, Brian 1969, Brian and Cox 1968, Haney 1974, and in selected ocean basins with realistic lateral geometry, Cox 1970, Galt 1973, Holland and Hirschman 1972, Hwang 1973. The numerical simulation of the complete world ocean circulation has only recently been achieved with bare-clinic models. Alexander 1974, Cox 1974, Tacano et al 1973. This shows significant improvement over earlier global simulations with homogenous wind-driven models, Brian and Cox 1972, Crowley 1968. As noted earlier, such models have not yet been able to resolve the energetic oceanic mesoscale eddies, although a number of experimental calculations to that end are underway. Recent studies have also shown the importance of improving the model's treatment of the oceanic surface-mixed layer, Bath 1972, Denman 1973, Denman and Miyake 1973, and Sea Ice, May Cut and Untersteiner 1971, and of Incorporating Bottom Topography, Holland 1973, Ruth 1972, and the Abyssal Water Circulation, Kuo and Veronis 1973. Coupled General Circulation Models Although preliminary numerical calculations with a model of the coupled atmosphere ocean circulation were performed several years ago, Manabee and Brian 1969, whether or not in Manabee 1972, it is only recently that a truly global coupled model has been achieved, Brian et al 1974, Manabee et al 1974a. These calculations underscore the importance of the ocean's participation in the processes of air-sea interaction and in the maintenance of large-scale climate. These and other such coupled models now under construction will lay the basis for the systematic exploration of the dynamics of the atmosphere ocean system and its role in climatic variation. The necessary calibration and testing of coupled GCMs will require a broad database and access to the fastest computers available. Applications of Climate Models The uses of climate models extend across a wide range of applications, including the reconstruction of past climates and the projection of future climates. Here, the more recent use of models for such studies is briefly reviewed, as distinguished from the research on model design and the calibration reviewed above. Simulation of Past Climates By assembling the boundary conditions appropriate to selected periods in the past, numerical models may be applied to the simulation of paleo-climates. The climate of the last ice age has recently received increased attention. Both through the application of pyramidorized and empirical models, Aliyah 1972, Lamb and Woodruff 1970, McCracken 1968, and through the use of atmospheric GCMs, Kraus 1973, Williams et al. in 1973. In the latter case, the specification of the distribution of glacial ice and sea surface temperature represents a strong thermal control over the simulated climate. In order to provide realistic information on the near equilibrium ice age climatic state, these conditions should be constructed on the basis of the appropriate proxy climatic records, while other portions of this same paleoclimatic database serve as verification. An initial effort of this sort is now underway as part of the Climap program. At the present time, the simulation of the time-dependent evolution of past climates over thousands of years can only be achieved with the more highly pyramidorized models. The design and calibration of such models of the air-sea ice system are largely tasks for the future. Climate Change Experiments and Sensitivity Studies Numerical climate models also permit the examination of the climatic consequences of a wide variety of possible changes in the physical system and its boundary conditions. Such studies, in fact, are a primary motivation for the development of the climatic models themselves. As previously noted, a number of experiments on the effect of solar radiation changes have been performed with simplified models. Budiko, 1969, Manabin-Wetherald, 1967, Schneider and Galchen, 1973, Sellers, 1969, 1973. And further studies of this kind with global models are underway. A number of recent experiments have been made with atmospheric GCMs on the effects of prescribed sea surface temperature anomalies on the large-scale atmospheric circulation. Houghton et al, 1973, Roundtree, 1972, Sparr, 1973, A, 1973, B. While others have been concerned with the climatic effects of thermal pollution, Washington, 1972, and of sea ice, Fletcher, 1972. Although these experiments indicate that the models display a response over several months' time to small changes in the components of the surface heat balance, their longer-term climatic response is not known. Such experiments serve to emphasize the need for extended model integrations, preferably with coupled models and underscore the importance of determining the model's sensitivity and the consequent noise levels in model-generated climatic statistics. The reduction of this climatic noise has an important bearing on the determination of the significance of climatic variations. Chirvin et al, 1974, Gates, 1974, Gilman et al, 1963, Leith, 1973. This question is also closely related to the problem of long-range or climatic prediction. Breyer, 1968, Kukla et al, 1972, Lamb, 1973, A. Studies of the mutual impacts of climate and man. Although the influence of man's activities on the local climate has long been recognized, renewed attention has been given in recent years to the possibility that man's increasingly extensive alteration of the environment may have an impact on the large-scale climate as well. Sawyer, 1971. Here, the more recent of such studies are briefly reviewed, along with studies of the parallel problem of climate's impact on man's activities themselves. Aside from the numerical simulations of anthropogenic climatic effects noted earlier, there have been a number of recent studies of the climatic consequences of atmospheric pollution. Bryson and Wynland, 1970, Mitchell, 1970, 1973, A, 1973, B, Newell, 1971, Yamamoto and Tanaka, 1972. And of the possible effects of man's interference with the surface heat balance, primarily through changes of the surface land character. Atwater, 1972, Budiko, 1972, A, Landsberg, 1970, Sawyer, 1971. Aside from local climatic effects, such as those due to urbanization, these studies have not yet established the existence of a large-scale anthropogenic climatic impact, Machata, 1973. Like their numerical simulation counterparts, such studies are made more difficult by the high level of natural climatic variability and by the lack of adequate observational data. A longer-range question receiving increased attention is the problem of disposing of the waste heat that accompanies man's production and consumption of energy. When projected into the next century, this effect poses potentially serious climatic consequences and may prove to be a limiting factor in the determination of acceptable levels of energy use. FL, 1973, Levin, 1974. These and other aspects of man's impact on the climate have been considered extensively in the SCEP and SMIC reports. Wilson, 1970, 1971. Recent attention is also focused on the effects of climatic variations on man's economic and social welfare. From a general awareness of these effects, Budiko, 1971, Johnson & Smith, 1965, Monder, 1970, Research has turned to the representation of climatic anomalies in terms of the associated agricultural and commercial impacts, Pitcock, 1972, and the development of a climatic impact indices, Bayer, 1973. Further studies are necessary in order to develop comprehensive climatic impact simulation models with both diagnostic and predictive capability. End of Scope of Present Research on Climatic Variation