Geoscience Reference
In-Depth Information
Table 26.1.
Summary of global and regional environmental and climatic changes
discussed in this volume from 250,000 years ago to present
I. 250-25 ka
(Interval includes two glacial-interglacial cycles, each
100 ka long)
High interglacial sea levels at
125 ka
Warmer interglacial sea surface temperatures, high rates of evaporation from the oceans,
and wetter climates in the intertropical zone
High lake levels in Africa and Australia at
210 and
130-110,
100-80,
65 and
40 ka
Low glacial sea levels at
150 ka; large ice caps over North America and north-west
Europe; glacier advances in South America
74 ka eruption of Toba volcano, possibly followed by several decades of intense global
cooling and several centuries of sustained reduction in precipitation in Asia and perhaps
Africa (controversial)
Prolonged wet phase at
125 ka; Sahara and peninsular Arabia studded in lakes, with
ITCZ displaced up to 500 km further north over North Africa during Northern
Hemisphere (NH) summer
Stronger summer monsoon in Asia during last two interglacial phases
Sapropel accumulation in East Mediterranean Sea at 217 ka (S8), 195 ka (S7), 172 ka
(S6), 124 ka (S5), 102 ka (S4), 81 ka (S3) and 55 ka (S2), broadly coincident with phases
of very high Nile discharge
II. 25-17 ka
(Interval includes the Last Glacial Maximum (LGM: 21
±
2 ka))
Maximum global ice volume and LGM sea levels
120 m lower than today
Small ice caps and more extensive mountain glaciers in Africa, South America, Australia
and Asia
Cooler sea surface temperatures and reduced evaporation from the oceans, with drier
conditions in the intertropical zone
Weaker summer monsoon in Asia, North Africa and northern Australia
Lakes low or dry in Africa, India, China and Australia during the LGM
Desert dunes active in Africa, Asia and Australia; widespread deposition of desert
dust/loess in China, India, South America, Australia and Europe
High lakes levels in drier parts of North America
III. 17-5 ka
Retreat of ice caps and mountain glaciers in both hemispheres and rapid sea level rise
from 17 ka onwards
Sea surface temperatures higher once more, with greater evaporation from the oceans and
wetter climates in the intertropical zone
Stronger summer monsoon in both hemispheres
High postglacial lake levels in Africa, Asia and Australia
Desert dunes vegetated and stable along desert margins; supply of desert dust/loess much
reduced
Stronger summer monsoon; ITCZ extends
500 km further north than today during the
NH summer
The Sahara is once more studded in sporadic lakes and supports a human population of
Mesolithic hunter-fisher-gatherers and later Neolithic pastoralists