Understanding Climatic Change A Program for Action (1975) / Chapter Skim
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PAST CLIMATIC VARIATIONS AND THE PROJECTION OF FUTURE CLIMATES
Pages 35-45

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From page 35...
... 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 further research that must be carried out on critical aspects of this subject.
From page 36...
... 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.
From page 37...
... 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.
From page 38...
... 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.
From page 39...
... 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 1 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.
From page 40...
... 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 in
From page 41...
... 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 time scales of weeks, months, and even years.
From page 42...
... 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-biennial oscillation (see, for example, Brier, 1968; Angell et al., 1969; or Wagner, 1971)
From page 43...
... Carbon Dioxide and Aerosols The relative roles of changing carbon dioxide and particle loading as factors in climatic change have been assessed by Mitchell (1973a, 1973b) , 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 CO., the variable atmospheric loading of wind-blown dust, and the interaction of CO, with the biosphere.
From page 44...
... 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.
From page 45...
... 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.


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