Pleistocene Climate Change

10 Key excerpts on "Pleistocene Climate Change"

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  Climate, Environment, and Society in the Pacific during the Last Millennium

  • Patrick D. Nunn(Author)
  • 2007(Publication Date)
  • Elsevier Science

    (Publisher)

  40 Developments in Earth and Environmental Sciences affairs. In addition to environmental changes associated with climate and sea-level changes - the only types considered in detail here- volcanic eruptions and earthquakes were the main sources of extraneous change to have affected humans during the Holocene (Nunn, 1999). Within the Pacific Basin, a good example comes from the fringes of the Atacama Desert of northern Chile, the late Pleistocene and Holocene human occupation of which was marked by a cultural hiatus - the Silencio Arqueologico - between 9,500 and 4,500 BP (N6~ez et al., 2002). Climate change is regarded as the main explanation, the earlier time of occupation (ll,800-9,000BP) being wetter and marked by an abundance of vegetation and animals for hunting, the focus towards the end of this period being on seasonal migration between upland lakes (now dry) and lowland wetlands. The area was abandoned as the lakes dried up and wetlands were reduced in number and area. The hiatus ended as wetter conditions resumed, and people resettled shallow lake borders. It was seen above how agriculture may have developed in East Asia and elsewhere as a result of increasing climate variability during the late Pleistocene and earliest Holocene, particularly the Younger Dryas. Yet for most of the early Holocene (12,000-6,000BP) rising temperatures generally ensured enhanced opportunities for human existence, exemplified in the Pacific Basin by the deve- lopment by 7,000 BP in East Asia of towns such as Hemudu that prospered from rice agriculture (Zhao, 1998), and by the spread 7,200-6,000 BP of settlement into areas of this region that had earlier been desert (Feng et al., 1993). In montane environments of Andean South America, climate (particularly precipitation) was the dominant cause of Holocene changes in settlement pattern and, more broadly, human lifestyles (Rigsby et al., 2003).

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  Climate Change

  A Multidisciplinary Approach

  • William James Burroughs(Author)
  • 2007(Publication Date)
  • Cambridge University Press

    (Publisher)

  Indeed, as implied in Section 8.1 there may well have been vast periods of geological time when the climate was far more benign than in recent millennia. Here, however, it helps to distinguish between inter-preting the impact of long-term climate change on many earth sciences, and the more immediate issues of understanding how current climatic fluctua-tions may now influence our lives. 9.1 Geological consequences In examining the geological record, there is the fundamental issue of whether it is possible to unravel the climatic factors from other causes of geological change. Clearly, climatic events like the waxing and waning of ice sheets, the desiccation of continental interiors or the drying up of oceans had major impacts on the geology of the large parts of the Earth. The real question is: were they ‘cause’ or ‘effect’? If they were the result of more basic processes in the Earth’s geological history linked principally to plate tectonics and changed levels of volcanism then their import in understanding climate change is less profound than if they played a significant part in driving the pace and direction of the underlying geolo-gical changes. This boils down to two issues. First, do shifts in the climate exert a significant feedback on tectonic activity (e.g. volcanism) by, say, changing the load on the Earth’s crust due to the build-up and collapse of polar ice sheets, or changing sea levels? Secondly, if the climate can exert influence on tectonic activity, is it affected by extraterrestrial effects (e.g. the Earth’s orbital parameters, fluctuations in the Sun’s output, or even the motion of the solar system through the galaxy)? As yet, there is no agreement on whether climate change exerts a significant effect on tectonic activity. There is, however, sufficient evidence to suggest that there are various ways in which the climate might create, or help relieve, the stresses in the Earth’s crust.

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  Global Environmental Change

  A Natural and Cultural Environmental History

  • Antoinette Mannion(Author)
  • 2014(Publication Date)
  • Routledge

    (Publisher)

  BP . There is abundant evidence for the replacement of deciduous forests by such vegetation communities as heathlands, moorlands and peatlands though many of these changes were initiated by human activity rather than by climatic change. Indeed, separating those changes due to climatic stimuli and those due to human activity is at best difficult and often impossible. Moreover, some changes during the progression of an interglacial cycle, as proposed by Iversen (1958) do not have to be driven by climatic change. This is particularly so for the oligocratic phase; Iversen proposed that soil deterioration due to progressive leaching and consequent nutrient impoverishment could initiate retrogressive vegetational development.

  Polar and tropical ice cores, however, provide direct evidence for climatic change during the late Holocene. Reference has already been made, for example, to apparent discrepancies between last interglacial and Holocene records which suggest that the latter was a period of comparatively stable rather than unstable climate (Section 2.4 ). Nevertheless some, though minor climatic changes when compared with those of the glacial–interglacial transition, are reflected in ice-core data. There is evidence for a temperature decline of ca. 1 °C per century during the period 5 to 3 K years BP with an ensuing slightly warmer period between 2.5 and 1 K years BP . There is also evidence for a warm period, which is known as the medieval optimum, during the thirteenth century AD when temperatures were comparable with those of the period 6 to 5 K years BP (the so-called climatic optimum). There is increasing evidence from diverse regions to suggest this may have been a global event. Arctic ice cores also record a cold period centred on the fifteenth century AD , which has become known as the Little Ice Age. This is a time-transgressive event but does appear to have been global; during the three to four centuries when it occurred there was also at least one relatively warm period. Detailed analyses of Holocene climate and palaeoenvironments have been produced by Thompson et al. (1989) and Thompson et al. (1986, 1995) based on ice cores from Tibet and Peru respectively. Both record Little Ice Age cooling, which in the Quelccaya Ice Cap of Peru is dated to between AD 1500 and 1900 (Thompson et al. , 1986). Data from the Huascarán ice core (Thompson et al. , 1995) indicate that after the warmest phase of the Holocene, between 8.4 and 5.2 K years BP , climate cooled gradually with the Little Ice Age, dated as occurring between AD 1450 and 1750. In agreement with the Tibetan cores and other sources the last few decades have witnessed unprecedented warming. Similar recent warming has been identified in tree-ring sequences (e.g. Jones et al.

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  The Great Ice Age

  Climate Change and Life

  • J.A. Chapman, S.A. all at The Open University Drury, R.C.L. Wilson(Authors)
  • 2005(Publication Date)
  • Routledge

    (Publisher)

  Figure 1.1 ).

  If we compress Earth history into one year, with the planet forming at one minute past midnight on 1 January, then The Great Ice Age began at about 7 pm on 31 December. Why is this short period of geological time so important? Because studying it helps us understand our past and our future. It is a unique period of time in the Earth’s history for a number of reasons:

  • it is the only time when both poles were/are covered by ice sheets
  • it is characterised by repeated, and relatively regular, patterns of climate change over time scales ranging from hundreds of thousands (10) to less than 100 (102) years;
  • these changes can be studied to a much greater degree of resolution than for any other period of geological time;
  • humans evolved during this period of climatic change and occupied every continent, and virtually every type of environment, be it hot or cold, or wet or dry;
  • much of our natural heritage of landforms and wildlife is a relic of the last glacial period that ended some 20 thousand years ago;
  • the Great Ice Age is not over yet, so understanding the past may help us predict future climatic and ecological changes.

  The last point about predictions is worth exploring a little further in the context of forecasting the weather and longer term climatic trends. Daily changes in the weather are a familiar fact of life. Likewise, we expect seasonal changes in temperature and precipitation. We have made some progress in predicting the weather, but even with the aid of super computers, our ability to make accurate forecasts only extends to a week or two ahead. This is because weather systems exhibit chaotic behaviour. In contrast, seasonal changes are triggered by latitudinal variations in solar insolation caused by the fact that the Earth’s axis of rotation is inclined with respect to its orbital plane around the sun. This is a very simple model in which there is a broadly linear relationship between radiation received by each of the Earth’s hemispheres and seasonal changes in temperature.

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  Physical Geography

  • James Petersen, Dorothy Sack, Robert Gabler, , James Petersen, James Petersen, Dorothy Sack, Robert Gabler(Authors)
  • 2021(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Extremely cold Arctic and Antarctic waters are dense and tend to sink, whereas tropical waters are warmer and tend to flow near the surface. Salinity and temperature taken together bring about complex subsurface flows deep within the ocean basins that influence Earth’s climate. Changes in oceanic circulation have also contributed to climate change during the last 2.6 million years. 8-3d Changes in Landmasses The locations of Earth’s landmasses have a considerable impact on both climatic cooling and warming, and they affect changes in the oceans. One characteristic that glaciations during Earth’s earlier geologic history share with the Pleistocene is the presence of continents in a polar region. The rapid winter heat loss from extensive landmasses at high latitudes encourages snow and ice accumulation, which fosters the development of massive ice sheet glaciers. Huge glaciers store tremendous amounts of water as ice, and because the amount of water on Earth is fixed, as gla- ciers grow in size, sea level will lower, and vice versa. Geologic and topographic influences on climate include the formation, disappearance, or movement of landmasses that can alter oceanic and atmospheric circulation, or change the atmosphere’s composition. When volcanic eruptions formed the Isthmus of Panama, connecting North and South America, this new land area blocked a former seaway between the Atlantic and Pacific Oceans. This new connection between two continents had a major influence on ocean circulation and created the Gulf Stream current (● Fig. 8.25). Also, as the Hima- layas rose to form the world’s highest mountains their topo- graphic barrier affected regional winds and the Asian monsoon. Creation of the Isthmus of Panama, the Himalayan uplift, and other significant landmass changes immediately predate the onset of Pleistocene glaciations.

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  Geomorphology

  • Mateo Gutierrez(Author)
  • 2012(Publication Date)
  • CRC Press

    (Publisher)

  20 CLIMATE CHANGE IN GLACIAL AND PERIGLACIAL REGIONS 1. Introduction 2. Paleoclimate data provided by drill cores of ice sheets and deep sea sediments 3. Fluctuations of quaternary ice sheets and resulting landforms 4. Retreat of cirque and valley glaciers 5. Glacio-isostasy and glacio-eustasy 6. Reconstruction of periglacial environments 7. Relict periglacial landforms 8. Fluvial systems in periglacial areas 9. Eolian activity in periglacial regions 10. Fluctuations in periglacial areas during the late Quaternary 11. Considerations of global climatic change in periglacial zones 20.1 Introduction Glacial and periglacial regions are morphoclimatic zones where cold conditions predominate. As Tricart (1967) states: “cold countries are those where the geomorphic activity of water is controlled by its existence in the solid state, either permanently or periodically.” Glaciers develop in areas where snow persists from year to year; as a result, it accumulates and turns into ice. Glacier limits are clear-cut; they outline ice accumulations. Periglacial zones are characterized by freezing and thawing but snow does not persist from year to year. Frozen soils (per- mafrost) may develop under the land surface. During glacial periods, 30% of the global land sur- face was covered by ice including extensive areas of North America and Eurasia. Antarctica also expanded during this time. Small ice caps formed and valley glaciers advanced con- siderably in mountainous areas. Today ice covers 10% of the land surface. Large advances and retreats of ice masses have sculpted extensive areas, eroding rock masses and depositing thick accumulations of glacial material (Fig. 20.1). Movements of glacial fronts are responses to climate change; thus they are a source of information for the study of climate change. In addition, ice sheets and glaciers play an important role in the general atmospheric circulation system.

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  Ecology of Climate Change

  The Importance of Biotic Interactions

  • Eric Post(Author)
  • 2013(Publication Date)
  • Princeton University Press

    (Publisher)

  46 CHAPTER 2 which species survived the transition, which species established at the site, and which species became extinct locally. This interpretation accords with the climate-equability model, according to which the distributions of species are determined to a greater extent by extremes in climatic seasonality than by cli- matic means (Graham and Grimm 1990). As well, it supports the notion that increasing climatic variability, especially over relatively short timescales, may represent a substantial disadvantage to species independently of the trend in average climatic conditions. SPATIAL, TEMPORAL, AND TAXONOMIC HETEROGENEITY IN PLEISTOCENE REDISTRIBUTIONS: LESSONS TO BE LEARNED Although extinctions have been the major focus of this chapter, there is also a great deal to be learned about the ecological consequences of rapid climate change for species assemblages by examining episodic and gradual redistribu- tions of species throughout the Pleistocene epoch, especially during the Late 0.22 (a) –0.55 –0.50 –0.45 –0.40 –0.35 0.18 0.14 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 0.10 Bray-Curtis Index Jaccard Index Calibrated years before present Figure 2.13. (a) Dynamics of small mammal faunal diversity at Popcorn Dome in the U.S. state of California from the Late Pleistocene onward, with time progressing from right to left along the x-axis. Both the Jacard (solid black line) and Bray-Curtis (dashed line) indices quantify similarity between adjacent sample sets, and thereby, in this example, turnover in richness and diversity of communities as differences from one sample to the next, with greater values indicating higher turnover. Index estimates are superimposed on a temperature index (gray line) derived from the North Greenland Ice Core Project (NGRIP) ice core data to illustrate changes in faunal diversity in association with warming that commenced approximately 12,000 years before the present. Adapated from Blois et al. (2010). (continued)

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  Applied Climatology

  Principles and Practice

  • Allen Perry, Dr Russell Thompson, Russell Thompson(Authors)
  • 2013(Publication Date)
  • Routledge

    (Publisher)

  All the existing long-term records indicative of climate change over the past few million years of the earth’s history indicate a pattern of global climate change broadly matching the solar orbital and precessional rhythms (see Chapter 10, The Quaternary period). The climatic trend is asymmetrical, changes from warm to cold being gradual with an order of magnitude of 100,000 years, in contrast to which the shifts from cold to warm ‘terminations’ (Broecker and van Donk, 1970) appear to be much more rapid. Both glacial and interglacial periods included shorter term, including some rapid, climate changes (Street-Perrott and Perrott, 1990) as the curves in Figure 8.4 show. In the tropical zone, including the sensitive subtropical savannas and desert margins, critical changes in erosion rate were controlled by precipitation changes under the influence of variations in the monsoonal circulation (Kutzbach, 1983). The current astronomically forced trend is towards climatic deterioration, with a decline in the summer insolation peak since about 9000 year BP and an expected mimimum in about another 5000 years’ time (Berger and Tricot, 1986). Against this trend are the effects of the recent anthropologically induced increase in the greenhouse gases (see Chapter 22, Global air pollution problems), the values for carbon dioxide and methane already exceeding the values for the last interglacial calculated from the Vostok ice core (Chapellaz et al., 1990). Although all the models (Chapter 4)designed to estimate the amount of global warming likely to eventuate from these opposing trends differ in important particulars (Street-Perrott and Roberts, 1994), there is quite broad agreement that some rise in oceanic temperatures will occur. Rising sea levels (see Chapter 7, Conclusions)and changes in coastal morphology, already documented for parts of the Holocene (Matthews, 1990), are the most likely immediate threat at the regional scale

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  Paleoclimate

  • Michael L. Bender(Author)
  • 2013(Publication Date)
  • Princeton University Press

    (Publisher)

  Albedo would decrease and the greenhouse effect would increase, thereby warm- ing the planet. The attribution of Plio-Pleistocene cooling to the onset of colder conditions in the tropics begs the ques- tion of why the tropics cooled during the Pliocene. One idea is that high-latitude cooling caused the thermocline in tropical waters to rise to shallower and shallower depths. The thermocline is the depth interval in which the temperature of subsurface waters cools from the warm surface value to lower temperatures characteris- tic of the intermediate and deep ocean. At first, surface waters would have continued to be warm, with cooler subsurface waters found closer and closer to the surface. Eventually, cooler waters would have come all the way to the surface when winds were favorable (i.e., during non El Niño times), as they do today (Fedorov et al. 2006). Alternatively, seafloor spreading and continental drift has changed the exact position of islands in the west- ern equatorial Pacific. New Guinea and Australia have drifted to the north, and the island of Halmahera has THE PLEISTOCENE ICE AGES 197 grown. These changes may have redirected cool North Pacific waters into the Indian Ocean, cooling that basin (Cane and Molnar 2001; Karas et al. 2009). Again this cooling would have contributed to the growth of ice sheets in boreal regions. Origin of Northern Hemisphere Glaciation The onset of glaciation in different Northern Hemi- sphere regions generally cannot be documented from field deposits (moraines, glacial outwash, etc.), because these “near field” deposits would have been eroded by subsequent glaciers. However, early glaciers that reached the coast, and calved into the ocean, did leave permanent records in the form of ice-rafted detritus accumulating in deep-sea sediments.

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  The Anthropocene as a Geological Time Unit

  A Guide to the Scientific Evidence and Current Debate

  • Jan Zalasiewicz, Colin N. Waters, Mark Williams, Colin P. Summerhayes(Authors)
  • 2019(Publication Date)
  • Cambridge University Press

    (Publisher)

  6 Climate Change and the Anthropocene CONTENTS 6.1 Climate 201 Colin P. Summerhayes 6.2 Ice 218 Colin P. Summerhayes 6.3 Sea Level 233 Alejandro Cearreta We describe here the rapidly increasing rises in the greenhouse gases carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O) and ozone (O 3 ) that have taken place since the beginning of the 19th century, rises that are linked with a currently small but growing rise in temperature, as well as a yet smaller but also growing rise in sea level accompanied by increasing loss of ice from land. Natural changes cannot explain the warming since the late 1800s, which has reached levels higher than in the Holocene and is approaching those of past peak interglacial times in the Quaternary. Sea-level rise lags the rise in warming, reflecting the slow absorption of heat needed before land ice melts, along with the slow penetration of heat into the ocean interior. Due to this lag, sea levels are still up to 4–9 m lower than they were at past peak interglacial times in the Quaternary and may require several hundred years to equilibrate with the rise in temperature – or less time, if ice melt proves to be rapid. Continued anthropogenic emissions will likely also lead in the short term to prolonged rises in temperature above those typical of Quaternary interglacial phases, and above those regarded as desirable limits by the UN Framework Convention on Climate Change, bringing a variety of impacts including greater extremes of heat, drought and flooding. 6.1 Climate Colin P. Summerhayes 6.1.1 Pre-Holocene Climate Developments Since the days of James Hutton, all geologists have known that the present is the key to understanding the past. Rather fewer recall that Hutton also pointed out that the past is a guide to what we may expect in the future, given much the same circumstances (Hutton 1795).

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