Chapter 16 – Rapid Climate Change During the Holocene
16.1 Introduction to the Holocene
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The last 10,000 of the Pleistocene are commonly referred to as the Holocene
Epoch, or simply, the “Recent”
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Ice core studies indicate that natural climate change during the Holocene has often been quite abrupt and rapid o Such climate change is now understood to occur at sub-Milankovitch time scales (over time spans less than a few thousand years down to durations as short as decades of less
16.2 Beginning of the Holocene
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Sea-Level Rise o The Holocene is marked by sea-level rise, augmented in some localities by isostatic rebound o Rapid sea-level rise may occur catastrophically for various reasons, such as collapse of the Antarctic ice sheets
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Younger Dryas o The Holocane actually began twice; as the world began to warm, it suddenly turned cold again during the Younger Dryas interval o Named for a cold-tolerant flowering plant represented by abundant pollen in sediments from about 13,000 years ago, the interval lasted roughly 1000 years o It have had a rapid onset, with much of the initial cooling in as little as a decade o The cooing may have been caused by a freshwater layer preventing the formation and sinking of North Atlantic Deep Water, which increased ocean productivity and the drawdown of CO
2
16.3 Rapid Climate Change on Millennial Time Scales
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Rapid Climate Change Involving the Oceans o Evidence shows that meltwater pulses like the Younger Dryas occurred repeatedly during the Holocene o These are indicated by layers of ice-rafted debris called Heinrich events, which occur every 1500 years o Ice-rafting events also occurred before the Holocene, so other factors may be involved, such as changes in solar radiation
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Rapid Climate Change on Land o Speleothems (cave-deposited travertine) provide records of changes in temperature and precipitation reflecting shifts in air masses over land o The oxygen isotope record from speleothems corresponds to welldocumented changes in vegetation; these in turn reflect changes in precipitation
16.4 Rapid Climate Change on Centennial Time Scales
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Newly emerging evidence indicates that climate fluctuates significantly on centennial (century) time scales o There is a growing realization that the sun may be involved o Sunspots appear to be related to gigantic magnetic storms on the sun’s surface; they have an 11-year-long activity cycle
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o Longer cycles of sunspot minima may occur during prolonged intervals of harsher climate, such as the “Little Ice Age” (1850-1880 A.D.)
16.5 Rapid Climate Change on Interdecadal to Multidecadal Time Scales
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Rapid climate change on interdecadal to multidecadal scales represent attempts by
Earth’s systems to redistribute heat by atmospheric and oceanic currents o The resulting fluctuation of the convection cells associated with these changes has led to these phenomena being referred to as “oscillations” o These oscillations and other ocean-atmospheric phenomena are linked by long-distance teleconnections o The oscillations and teleconnections may be influenced by changes in soar radiation and anthropogenic activities, although this is complex and remains poorly understood o The El Niño-Southern Oscillation (ENSO) is one of the best understood oscillations; La Niñas, in which conditions reverse themselves, sometimes follow El Niño events
16.6 Climatic Modes and Climatic Irreversibility
 Given the complexity of the systems involved in regulating Earth’s climate, it is difficult to predict the exact mode that Earth’s climate will occupy in the immediate future o Climate scientists state that anthropogenic production of carbon dioxide has caused some of the warming during the 20 th
century o Anthropogenic warming may dominate climate during the next few centuries or longer o Carbon dioxide may accumulate in Earth’s atmosphere with relatively little effect until a threshold is crossed and climate suddenly shifts into an entirely new mode
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