For the 15,000 years preceding this time, world sea levels never rose more than two meters above that of the sea level circa 1999 AD. But now sea levels worldwide drop to 1999 AD levels and significantly below between 118,000 and 8000 BC. This means there are greater chances for landbridges connecting islands and continents, and considerably more land exposed along the coastlines of continents and islands, among other things. All this extra dry land offers places where human civilizations might spend centuries or even millennia building cities and nations, and migrating over to explore new territories-- only to have the sea take them away again in the centuries to follow (and possibily leaving some folks permanently stranded on places like islands afterwards). In 1998 AD archaeologists will be discovering many human works submerged this way during prehistoric times.
Another implication of the great ice sheets are 'ice bridges' essentially offering yet another means of connection between many land masses during this time that would otherwise be inaccessible due to surrounding seas. Note that the Earth's north pole will have little or no exposed land area by 1998 AD; and yet it will be covered by an ice sheet sufficient to support lengthy migrations of human and animal species across the region. Thus, technically there exist paths allowing exploration of the americas and other regions for ancient hominids as far back as two million years or more as of 1998 AD. Such access ways may be as forbidding as deserts, or as temporary as seasonal sea ice, but they are there none-the-less. Indeed, early humans could theoretically explore almost every continent on earth now requiring little more than their feet for locomotion, due to ice sheets and lowered sea levels exposing various land bridges. No boats or rafts are required for most excursions. And yet, any humans intelligent enough to use floating constructions may trod the last few percentage points of the Earth's dry surface remaining out of reach of their land locked peers as well.
Unfortunately, towards the end of this period, when the ice sheets are retreating and the ocean levels rising again, volcanic action tends to increase as the weight of the ice sheets themselves seemed to have restrained them earlier. And the huge cataracts of flood waters released from melting glaciers and overflowing of sea-sized inland lakes during this time also wreak havoc on many regions.
-- "Surprise: Geologists Find Glaciers Can Suppress Volcanic Eruptions", 12-8-98, University of North Carolina at Chapel Hill
-- "The big thaw" by Jeff Hecht, Boston, From New Scientist ["http://www.newscientist.com"], 17 April 1999
Sudden large climate changes worldwide occurred during the last Ice Age. Apparently there were six events where immense numbers of ice bergs were created in Canada, which then flowed into the Atlantic Ocean. These spurred global climate changes.
|-- SIX IMMENSE ARMADAS OF ICEBERGS INVADED THE NORTH ATLANTIC From Science Frontiers Digest of Scientific Anomalies ["http://www.knowledge.co.uk/frontiers/"] #98, MAR-APR 1995 by William R. Corliss, citing Wallace S. Broecker; "Massive Iceberg Discharges as Triggers for Global Climate Changes," Nature, 372:421, 1994|
Climates fluctuated substantially during the last Ice Age, between very cold and milder conditions. The frequency of these swings was on average once per 3,000 years. The warm ups are called interstadials. The northern and southern hemispheres often were not synchronized in the timing of their respective interstadials. Apparently these warm ups happened in the southern hemisphere roughly a thousand years ahead of the time they occurred in the northern.
Curiously, western Antarctica does show some synchrony with the interstadials of the north-- unlike the rest of the continent.
|-- Rhythm of the ice age: North versus south By R. Monastersky From Science News Online, Vol. 154, No. 8, August 22, 1998, p. 119. Science Service ["http://www.sciserv.org/"]|
Orbital insolation may be the main culprit behind Ice Ages. This involves the Earth's tilt on its axis, possible changes in solar output, and cyclic changes in Earth's orbit about the Sun.
One of the cycles involved here is periodic (once in 41,000 years) wobbles in the tilt of Earth's axis of one to three degrees from normal (in the range of 22 to 25 degrees from vertical). The shape of the Earth's orbit shifts between a rough circle and a slight ellipse every 100,000 to 400,000 years. Once every 22,000 years there's a change in which hemisphere faces the sun when the Earth's orbit puts it nearest Sol.
All these factors affect the Earth's climate.
The mid-point of the interglacial period which preceded the present one was around 133,000 BC.
|-- A Debate That Could Last An Iceage ["http://www.spacer.com/spacecast/news/iceage-00c.html"] by Kurt Sternlof, March 22, 2000 SpaceDaily, Columbia University|
The ice sheets of Europe and North America began melting around 12,000 BC and were gone by around 6000 BC. Sea levels rose by roughly 350 feet in only 6000 years.
The Ice Age is also known as the Pleistocene Epoch, which began around 2,000,000 BC and ended about 6000 BC. There were possibly ten separate cycles of cooling and rewarming during this period, in which the glaciers advanced then retreated again. Sea levels may also have declined and rose again in these cycles.
Four of the cycles were exceptionally harsh in the cooling stage. The most recent cooling stage may have begun around 56,000 BC- 48,000 BC.
During the cooling stages of the Pleistocene, the North American west was wetter than circa 2000 AD.
Prior to the Pleistocene there was another Ice Age on the super-continent of Gondwana, in the southern hemisphere. There were 60+ cooling/warming cycles in that period. This Ice Age began around the end of the Paleozoic.
There was maybe 250 million years between the end of the Gondwana Ice Age and the beginning of the Pleistocene, during which no large ice sheets existed on Earth, and the entire planet was considerably warmer and more humid than 2000 AD.
It may be that Earth circa 2000 AD is subject to various cycles of orbit and axis-tilting/rotation that may coincide every 500,000 years to possibly trigger a new Ice Age.
|-- GLG 111, Chapter 12: Glaciers and Glaciation ["http://www.muohio.edu/~schafesd/glg111-outlines/glg111-ch12-glaciers.htmlx"] GLG 111, The Dynamic Earth, Steven D. Schafersman in the Department of Geology at Miami University, August 27, 1998, email@example.com|