Understanding Climatic Change A Program for Action (1975) / Chapter Skim
Currently Skimming:

APPENDIX A SURVEY OF PAST CLIMATES
Pages 127-194

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 127...
... For example, northern hemisphere winter temperatures from the midfifteenth to the midnineteenth centuries were significantly lower than they are today. The late nineteenth century represented a period of transition between this cold interval -- sometimes known as the Little Ice Age -- and the thermal maximum of the 1940's.
From page 128...
... (a) An etching made about 1850, showing the extent of the glacier during the waning phase of the Little Ice Age.
From page 129...
... This objective can be achieved only by studying the workings of the global climate machine over a time span adequate to record a representative range of conditions in nature's own laboratory, and for this the record of past climates is indispensable. From the evidence discussed below and summarized in Figure A.2 we conclude that a satisfactory perspective of the history of climate can be achieved only by the analysis of observations spanning the entire time range of climatic variation, say, from 10-' to 10° years.
From page 130...
... (d) Generalized northern hemisphere air-temperature trends during the last 100,000 years, based on midlatitude sea-surface temperature and pollen records and on worldwide sea-level records (see Figure A.13)
From page 131...
... Records from well-dated tree rings, annually layered (or varved) lake sediments, and ice cores resemble the historical data in that values can be associated with individual years and may be calibrated with modern data to extend the climatic record for many centuries, and in certain favored sites for as long as 8000 to 10,000 years.
From page 132...
... suon $1319e|3 uTeJUNOU JO 1Ud)
From page 133...
... SpueISI 91Uv390 YyMolZ Jao QUINOA 99]
From page 134...
... Tree-ring records go back several thousand years at a number of widely distributed continental sites, pollen records have the potential of providing synoptic coverage over the continents for the past 12,000 years or so, and a nearly complete record of the fluctuating margins of the continental ice sheets is available for about the last 40,000 years. Planktonic and benthic fossils from deep-sea cores can in principle provide nearly global coverage of the ocean going back tens of millions of years, although sampling difficulties have thus far limited our access to sediments deposited during the last several hundred thousand years.
From page 135...
... If, for example, the fluctuations in the volume and extent of the polar ice caps are to be studied, a time interval of order 100,000 years (the maximum residence time of water in the ice caps) is required.
From page 136...
... And only since about 1950 does the surface observational network begin to approach adequate coverage over the continents; large portions of the oceans, particularly in the southern hemisphere, remain inadequately observed. For the climate of the free atmosphere, the international radiosonde network permits reliable analyses for the midlatitudes of the northern hemisphere only since the 1950's, and less than adequate coverage exists over the rest of the globe.
From page 137...
... APPENDIX A 137 FIGURE A.3 Growth of the network of surface pressure observations and of the area that can be covered by reliable 10-year average isobars (Lamb, 1969)
From page 138...
... Identification of Natural Climatic Records A number of different monitoring techniques that can provide data for paleoclimatic inference are summarized in Table A.1 and are based on observations of fossil pollen, ancient soil types, lake deposits, marine shore lines, deep-sea sediments, tree rings, and ice sheets and mountain glaciers. The techniques that are emphasized here are those that in general yield more or less continuous time series.
From page 139...
... The oxygen isotope ratio '* O/1%O as it is preserved in different materials is used in three separate paleoclimatic monitoring techniques.
From page 140...
... Such deposits include sediments left by melting glaciers on land; sediments accumulating in peat bogs, lakes, and on the ocean bottom; soil layers; layers accumulating in polar ice caps; and the annual layers of wood formed in growing trees. Ideally, a recording site selected for paleoclimatic work should yield long, continuous, and evenly spaced time series.
From page 141...
... Their relatively uniform but low deposition rates, however, generally limit the chronological detail obtainable. Cores taken in the continental ice sheets provide a detailed and generally continuous record for many thousands of years, although their interpretation is handicapped by the lack of fully adequate models of the ice flow with its characteristic velocity -- temperature feedback.
From page 142...
... Together, these techniques have provided a reasonably satisfactory chronology of the past 200,000 years with a dating accuracy of about +10 percent. Our chronology for older climatic records is based on the well-known K/Ar technique, applied to terrestrial lava flows and ash beds.
From page 143...
... Their importance stems from the fact that the principal magnetic reversal boundaries, which have occurred irregularly about every 400,000 years, are recorded in both marine and continental sedimentary sequences. Regularities in Climatic Series On the assumption that climatic changes are more than just random fluctuations, paleoclimatologists have long sought evidence of regularities in proxy records of the earth's climatic history.
From page 144...
... . This ratio reflects fluctuations in global ice-volume.
From page 145...
... In view of the relatively short memory of the atmosphere, it seems likely that this is provided by the oceans on time scales of years to centuries and by the world's major ice sheets on longer times scales. An initial estimate of the variance spectrum of temperature has been made from the fluctuations on time scales from 1 to 10,000 years by Kutzbach and Bryson (1974)
From page 147...
... "(716 ‘uoshig pue Yoseqz}yny Wo) eBuer Aouenbesj-a2e/pewezU]
From page 148...
... . ‘The geographic patterns of temperature change during these overall warming and cooling epochs show considerable variability, with the largest changes concentrated in the polar regions of the northern hemisphere.
From page 149...
... The Last 1000 Years To obtain an indication of the climate in the northern hemisphere for the last 1000 years, Lamb (1969) has compiled manuscript references on the character of European weather and has developed an index of winter severity, as shown in Figure A.2(b)
From page 150...
... 150 UNDERSTANDING CLIMATIC CHANGE 1790-1829 ; -- 1800-1839 | -- 1810-1849 r -- Trough Ridge Trough 1820-1859 | -- 1830-1869 |[ -- 1840-1879 | -- 1850-1889 / -- 1860-1899 [ -- 1870-1909 | -- 1860-1919 }- -- 1890-1929 | -- 1900-1939 | -- 1910-1949 - -- 1920-1959 1 | 1 l 60°w 50 40 30 20 10 0 10 20°E a 1780-1819 [ 1800-1839 | -- 1820-1859 |- -- Trough Ridge 1840-1879 | -- 1860-1899 [ -- 1880-1919 - -- 1900-1939 [ -- 1920-1959 [- | | | L | | | | 70°wW 60 50 40 30 20 10 0 10°E FIGURE A.7_ Forty-year running means of the longitudes of the semipermanent surface pressure troughs and ridges In the North Atlantic (Lamb, 1969)
From page 151...
... The period from about 1430 to 1850 is commonly known as the Little Ice Age, and some records indicate that this period had cold maxima in the fifteenth and seventeenth centuries. From such evidence we infer that the atmospheric circulation may have been more meridional than at present and characterized in western Europe and western North America by short, wet summers and long, severe winters.
From page 152...
... . The last 5000 years is characterized by generally declining temperatures and a trend toward more extensive mountain glaciation (but not ice sheets)
From page 153...
... the curves of ice accumulation and decline are not identical for the various ice sheets. The Laurentide ice sheet (which covered parts of eastern North America)
From page 154...
... The climatic instability suggested by these fluctuations in the margins of the northern hemisphere's major ice sheets is corroborated by the records from fossil pollen, deep-sea cores, ice cores, and sea-level variations, as shown in Figure A.12, and by lacustrine records in western North America and Africa. By 8500 years ago the ice conditions in Europe had reached essentially their present
From page 155...
... state, and in North America the ice sheets had shrunk to about their present extent by about 7000 years ago. How widespread and synchronous these fluctuations were is not yet known, but evidence is growing that there were several periods of widespread cooling and glacial expansion in the regions bordering the Atlantic Ocean [see Figure A.2(c)
From page 156...
... is generally ascribed to the melting of northern hemisphere continental ice sheets. Details of the sea-level curve, however, do not correspond to the chronology of deglaciation just described: while the continental ice sheets had essentially disappeared by about 7000 years ago, the worldwide stand of sea level has reached its maximum only during the last few thousand years or is still slowly rising
From page 157...
... + 4.9 6 60 90 °o-44 oO O05Ff -O2+ -09-16 + ~ 0 0F -70 + -40 40+ oO 5 e w IST e ° +15 = e ws 30+ e > + 30 : 457 + 40 % 60 + » + 60 90 i" n Qo > o ° > > +105 S 120 Tt ° - ° "> > t120 135 + 368 -- _+- -- _+ -- _+ b t + -- -- -- 4 r ¢ + -- -- + 5 $ is4 =6 O 3% 60 90 -44 -38 -32 -28 O5 -02 -09 -6 -l00-70 -40 -10 FAUNAL INDEX % ARBORE AL ICE CORE %e SO® in SEA LEVEL T, POLLEN 80 (%ee) PLANKTON SHELL METERS FIGURE A.13 Climatic records of the last 135,000 years.
From page 158...
... . The Last 1,000,000 Years For at least the last 1,000,000 years the earth's climate has been characterized by an alternation of glacial and interglacial episodes, marked in the northern hemisphere by the waxing and waning of continental ice sheets and in both hemispheres by periods of rising and falling temperatures.
From page 159...
... FAUNAL INDEX (3) SO TYPE tnterpretetion: OECREASING GLOBAL "INCREASING CoCOs DECREASING SALINITY TEMPERATE CLMATE (CE VOLUME OfSSOLUTION -- _____ -- ~» -- _______ -- » -- -- -- -- -- = oe FIGURE A.14 Climatic records of the last 1,000,000 years.
From page 160...
... Indirect evidence from marine sediments indicates that about 5,000,000 years ago the already substantial ice sheets on Antarctica underwent rapid growth and quickly attained essentially their present volume (Shackleton and Kennett, 1974a, 1974b)
From page 162...
... Such continental ice sheets first appeared in the northern hemisphere about 3,000,000 years ago, occupying lands adjacent to the North Atlantic Ocean (Berggren, 1972b) , and during at least the last million years the ice cover on the Arctic Ocean was never less than it is today (Hunkins et al., 1971)
From page 163...
... Most studies have therefore focused primarily on local or regional climatic changes. Lamb and Johnson (1961, 1966)
From page 164...
... , : : ® ny 7 | . \ s FIGURE A.16_ The first eigenvector of northern hemisphere sea-level pressure, based on the individual mean January maps for 1899-1969 (Kutzbach, 1970)
From page 165...
... (a) December, northern hemisphere; (b)
From page 166...
... of monthiy mean surface air temperature in the northern hemisphere, 1900-1950 (Lamb, 1972)
From page 167...
... . It is likely that interhemispheric relationships of one sort or another are important for the understanding of climatic variations, and that our ability to describe them will require the availability of much more comprehensive data than now exist from the southern hemisphere, the equatorial region, and the oceanic and polar regions of the northern hemisphere.
From page 168...
... have reported an unmistakable downward trend of the mean air temperature in the northern hemisphere of 0.6°C over the five-year interval shown in Figure A.20. Diagnostic studies of this type represent great investments of time and effort but are essential steps toward the monitoring of climate and an assessment of the mechanisms of climatic variation.
From page 169...
... APPENDIX A 169 interannual variations of available potential energy, and Kung and Soong (1969) have described the fluctuations of the atmospheric kinetic energy budget.
From page 170...
... (a) Northern hemisphere; (b)
From page 171...
... 33 +- 4 * +17 as 4 1 36 + 18 as 37 + 38 + 19 + Ty T 20 + T 1969 1970 = -- Ss«971 1972 1973 FIGURE A.23 Twelve-month running means of snow and ice cover in the northern hemisphere (upper curve)
From page 172...
... Such modes of atmosphere -- ocean coupling may be important parts of climatic fluctuations and must be given further study. In summary, we may say that observational data at the earth's surface show that during the period 1900 to 1940 the northern hemisphere as a whole warmed, although some areas (mainly the Atlantic sector of the Arctic and northern Siberia)
From page 173...
... . Continental ice sheets, indicated by the dotted area, are B, Barents Sea; S, Scandinavian; G, Greeniand; L, Laurentide; C, Cordilieran.
From page 174...
... Note that large regions in eastern Siberia were unglaciated. Sea-Surface Temperature Patterns The north-south migration of polar waters in the North Atlantic in response to major cycles of glaciation is shown in Figure A.25.
From page 175...
... "BLUJUJL JUSLUIPESS a3JBUCGIeS LUN[D] 8 93e5/pul 9 0} T SJequuNU aYyL ‘OZe sueeX COO'SI JNoqe wnuwyjxXew 18/903 SB]
From page 176...
... * Sdjdosiqns OY)
From page 177...
... At the beginning of this time, pine species occupied sites in the southeastern Appalachians, but as the ice retreated, the pine moved farther north and west to colonize newly uncovered areas. A relatively complete chronology of the retreat of the Laurentide ice sheet itself is given by radiocarbon dating (Bryson et al., 1969)
From page 178...
... Control points representing radiocarbon dated cores are indicated by the open circles. The approximate margins of the Laurentide ice sheet are indicated by the stippled pattern (after Bryson et al., 1969)
From page 179...
... SUMMARY OF THE CLIMATIC RECORD In this survey of past climates, the characteristic time and spatial structures of climatic variations have been discussed as though there were sufficient data to document large regions of the globe. This is true only for the more recent parts of the instrumental period, as there are large gaps in the presently available historical and proxy climatic records.
From page 181...
... At the last glacial maximum, extensive areas of the northern hemisphere were covered with continental ice sheets, sea level dropped about 85 m, and sea-surface temperatures in the North Atlantic fell by as much as 10°C. At northern midlatitude sites not far from the glacial margins (locations now occupied by major cities and extensive agricultural activity)
From page 182...
... In view of the limited resolving power of most climatic indicators, especially those for the relatively remote geological past, it is difficult to establish whether the apparent fluctuations are quasi-periodic or whether they more nearly represent what are basically random Markovian "red-noise" variations. In the case of the longer-period variations (of 100,000-year and 20,000-year periods)
From page 183...
... Potential Contribution of Sinusoidal Fluctuations of Various Time Scales to the Rate of Change of Present-Day Climate Estimates of the amplitudes of all the principal climatic fluctuations identified in this report are listed in Table A.3 (where they have been made consistent with the data presented in Figure A.2 and are expressed in terms of the total range of temperature between maxima and minima)
From page 184...
... "suolenjony Jo adeys [epiosnuis sauinssy » Ik/D. PSIO'O -- LS7O'0+ sWAs Tcloo -- 0STO';O+ aBVIIAV S¢ $0 OOT °9 £$00°0 -- §L00°0+ ysIH SL S‘0 00¢ 9 Z00'0+ .
From page 185...
... FIGURE A.30 Relative (maximum) rate of change of climate contributed by climatic fluctuations, as a function of characteristic wavelength.
From page 186...
... , for example, has shown that while the northern hemisphere average air temperatures rose only about 0.2°C during the period 1900 to 1940, there were many areas that deviated markedly from this hemispheric average trend. Parts of the eastern United States, for example, exhibited a 1.0°C rise in average temperature (5 times the hemispheric average)
From page 187...
... FIGURE A.31 Probability of onset of climatic transitions analogous to the changes between maxima and minima in climatic fluctuations of arbitrarily selected characteristic wavelengths (interior numbers, in years) , as a function of elapsed time after present.
From page 188...
... The paleoclimatic record presented here does not preclude the possibility that relatively sudden climatic changes could arise through interactions between fluctuations of different periods. One may still ask the question: When will the present interglacial end?
From page 189...
... The onset of this climatic de cline could be several thousand years in the future, although there is a finite probability that a serious worldwide cooling could_ befall the earth within the next hundred years. _ What is the nature of the climatic changes accompanying the end of a period of interglacial warmth?
From page 190...
... L., 1971: Glacial-eustatic and isostatic controls of sea level since the last glaciation, in The Late Cenozoic Glacial Ages, K Turekian, ed., Yale U.P., New Haven, Conn., pp.
From page 191...
... C Langway, Jr., 1971: Climatic record revealed by the Camp Century ice core, in The Late Cenozoic Glacial Ages, K
From page 192...
... G Kipp, 1971: A new micropaleontological method for quanti tative paleoclimatology: application to a late Pleistocene Caribbean core, in The Late Cenozoic Glacial Ages, K
From page 193...
... A Bryson, 1974: Variance spectrum of Holocene climatic fluctuations in the North Atlantic sector, Dept.
From page 194...
... H., 1971: An assessment of the role of volcanic dust in determining modern changes in the temperature of the Northern Hemisphere, PhD Thesis, Dept. of Meteorol., U


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.