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Ice Age Introduction
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What are Ice Ages?
Ice Ages are intervals of time when large areas of the surface of the globe are covered with ice sheets (large continental glaciers).
The term is used to describe time intervals on two very different scales. It describes long, generally cool intervals of Earth history (tens to hundreds of millions of years) during which glaciers waxed and waned. The term also describes shorter time periods (tens of thousands of years) during which glaciers were near their maximum extent. These shorter intervals are also known as "glaciations."
When did Ice Ages occur?
Many glacial advances and retreats have occurred during the last billion years of Earth history. These glaciations are not randomly distributed in time.Instead, they are concentrated into four time intervals. Large, important glaciations occurred during the late Proterozoic (between about800 and 600 million years ago), during the Pennsylvanian and Permian (between about 350 and 250 million years ago), and the late Neogene toQuaternary (the last 4 million years). Somewhat less extensive glaciations occurred during parts of the Ordovician and Silurian (between about 460 and 430 million years ago).
Why do Ice Ages occur?
Although scientists cannot answer this question with certainty, they know that a number of factors interact to produce conditions favoring the formation of ice sheets. Some of these factors include (following links are to Illinois State Museum):
1. changing continental positions
2. uplift of continental blocks
3. reduction of CO2 in the atmosphere
4. changes in the Earth's orbit
Long ice age intervals did not just suddenly occur. Instead, they seem to have been the culmination of even longer periods of worldwide climatic cooling. This cooling took place for tens of millions of years before the beginning of glaciation.
Once ice sheets start to grow, they could contribute to their own further development. This positive feedback occurs because ice sheets reflect more sunlight back into space than does earth not covered by ice. The reflected sunlight would otherwise warm the Earth's surface. Consequently, the presence of ice sheets may lead to more cooling and continued development of ice sheets.
Last & Previous Ice Ages
"An atlas of the ice age Earth. The following ecosystems maps, compiled by Jonathan Adams, are still under development and as-yet unpublished. Their presentation here is intended to provoke comment and criticism which can lead to them being improved. They are based on simple compilations of the available information in the literature, relying heavily on the conclusions given by review papers for each subregion. Dates are given in radiocarbon years; the actual chronology in terms of 'real' years is still being worked out in the literature." -[Jonathan Adams, Environmental Sciences Division, Oak Ridge National Laboratory]-
The time span of the last 130,000 years has seen the global climate system switch from warm interglacial to cold glacial conditions, and back again. This broad interglacial-glacial-interglacial climate oscillation has been recurring on a similar periodicity for about the last 900,000 years, though each individual cycle has had its own idiosyncrasies in terms of the timing and magnitude of changes.
An artist's conception of how much of the Midwestern United States might have looked approximately 16,000 years ago. A reconstruction which is based on the work of many different types of scientists who study various aspects of past environments. You can join Illinois State Museum and Northern Arizona University scientists as they visit a cave and study the paleontological remains contained in it.
Map showing the Earth has been in an Ice House Climate for the last 30 million years. When the Earth is in its "Ice House" climate mode, there is ice at the poles. The polar ice sheet expands and contacts because of variations in the Earth's orbit (Milankovitch cycles). The last expansion of the polar ice sheets took place about 18,000 years ago.
"During the last Ice Age, there were many large, interesting mammals, like the saber-toothed cats, giant ground sloths, mastodons, and mammoths. These animals have long since gone extinct and are known mostly from fossils, from frozen, mummified carcasses, and even from ancient cave drawings."
"The last Ice Age started about 70,000 years ago and ended about 10,000 years ago (during the Pleistocene epoch). The Earth was much colder than it is now; snow accumulated on much of the land, glaciers and ice sheets extended over large areas and the sea levels were lower. These phenomena changed the surface of the earth, forming lakes, changing the paths of rivers, eroding land, and depositing sand, gravel, and rocks along the glaciers' paths." -[EnchantedLearning.com]-
by Carla Helfferich
"Just as in an archaeological dig, deeper holes offer older evidence. The core samples of soupy sub-Pacific mud totalled more than four kilometers long, so they offered the researchers a glimpse of the far past. They found some interesting juxtapositions of debris in the layers near 2.6 million years old, about the time when the Pleistocene ice age began.
At four of the sites near the northwest edge of their voyage, the scientists encountered a high number of layers of volcanic ash. They believe volcanoes on the Kamchatka Peninsula were the ultimate source of these layers; some ash also occurs in layers earlier in the record---but only a tenth as often as it does beginning about 50,000 years before the great ice sheets covered the land...." -[Alaska Science Forum]-
"There have been several ice ages in the history of the Earth. What is commonly called the ice age is actually the most recent (Quaternary) which began about two million years ago, and was characterized by cold (glacial), and relatively warm (interglacial) phases.
Four major continental glaciations are recorded in North America. The last (Wisconsin) began about 70,000 years ago, and ended 10,000 years ago. At the peak of the last glaciation, approximately 97% of Canada was covered by ice...." -[ nature.ca ]-
"El Nino-like climate patterns occurred in the New England region during the last ice age, 17,500 to 13,500 years ago, according to a new study. This is the first time scientists have been able to document evidence of El Nino activity during that time period."
"Our evidence suggests that the El Nio phenomenon is more robust than we previously imagined," says Michael Mann, assistant professor of environmental sciences, and one of the study's authors. The findings appear in the May 12 issue of the journal Science. -[Copyright 2000 by the Rector and Visitors of the University of Virginia]-
"The ice age climate had a stronger effect on the habitats in the high northern and southern latitudes than in equatorial zones. Shown here are the differences between the annual mean near-ground air temperatures for present-day climate and for the climate during the last ice age approximately 18,000 years ago, computed with the Hamburg atmosphere-climate model. Inputs for this computation included the surface temperatures for the world ocean, reconstructed from ocean cores, the carbon dioxide content of the air, derived from ice core data, and the slightly modified solar radiation at that time.The mean temperatures during the last ice age were about 4 degree C lower than today."
"The following letter to the Editor, makes a point that Mike Reagan frequently makes: Our weather experts don't seem to be able to accurately predict the weather a few hours hence - and we are going to let them determine our economic policy because of their notions of global warming? As the letter writer points out - the earth's been warming since the last ice age - some 15,000 years ago. Don't know if we had much to do with it one way or another...." -[Victor H. Abadie III, Geologist, Montara, Calif.]-
Next Ice Age
"The notion that we're due another ice age is still occasionally peddled as a reason not to worry about global warming. But just about all the predictions made today are very different to those when this idea was hatched 30 years ago..." -[PHILIP BALL]-
"Over the past two decades, we have heard about greenhouse gases and the idea that our planet is gradually warming. Id like to throw a curveball into that thinkingspecifically the gradually warming part.
Global warming could actually lead to a big chill in some parts of the world. If the atmosphere continues to warm, it could soon trigger a dramatic and abrupt cooling throughout the North Atlantic regionwhere, not incidentally, some 60 percent of the worlds economy is based...." -[Dr. Robert B. Gagosian, President and Director of Woods Hole Oceanographic Institution]-
"Next week, next month, next year, it's not a question of if, only when. One day you'll wake up -- or you won't wake up, rather -- buried beneath nine stories of snow. It's all part of a dependable, predictable cycle, a natural cycle that returns like clockwork every 11,500 years. . . . And since the last ice age ended almost exactly 11,500 years ago . . ."
Just paranoia or is there truth to the above....you be the judge. There are several links on this page including info on the book "Not by Fire but by Ice".
Amidst several decades of media flurry and hype several critical factors about the 'greenhouse effect' and 'global warming' have been left out of the forecasts:
1) There was no C02 buildup in the 1990s.
2) According NASA satellite data and several Antarctic studies recently released, the Earth has been cooling for the last 18 years, the western ice sheet is growing, and the interior valleys have been getting colder for the last 30 years. -[Will Hart]-
There is considerable evidence that the Little Ice Age consisted of two main cold stages of about a century's length (Bradley
& Jones, 1992). These occurred in the seventeenth an nineteenth centuries, with relative warmth arising in the sixteenth and eighteenth centuries. Glaciers advanced in Europe, Asia and North America, whilst sea ice in the North Atlantic expanded with detrimental effects for the colonies of Greenland and Iceland (Lamb, 1982).