http://www.bom.gov.au/info/climate/change/gallery/22.shtml

Gif image courtesy of:
http://vathena.arc.nasa.gov/curric/land/global/climchng.html

Glacial retreat in North America

Other Pertinent Sites on Ice Ages

http://www.pbs.org/wgbh/nova/ice/

http://members.cox.net/quaternary/

Alden's EC Website: Snowball Earth

Julie's EC Website: Ice Age 101

Denver Museum of Nature & Science: Ice Age

The Ice Ages

http://www.acs.ohio-state.edu/researchnews/archive/caperobr.htm
http://www.pbs.org/edens/patagonia/glaciares.htm
http://www.bellacoolaair.com/tours.html

Ice Age?

What is an ice age? Usually one thinks of woolly mammoths and saber-toothed-tigers roaming vast glaciers that covered the entire globe. Movies from Disney and Hollywood have lead many people to believe that the Ice Age occurred once a long time ago and blanketed the earth in a huge sheet of ice. Indeed such a time existed but the dazzling ice of Hollywood was only a small portion of earth’s climate during the late Pleistocene Epoch. In fact, in the last 150,000 years the earth’s temperature has fluctuated between glaciations and what could be called an Ice Age and milder temperatures. (Adams, 2004) In practically a one 30,000th of the total time that the earth has existed the temperature has swung between what humans consider to be most extreme of environments and climates that are similar to those we experience today. (See temperature graph)

Instead glaciers blanketed much of the northern and southern hemispheres. These massive blocks of snow and ice (metamorphic ice in most cases) spanned hundreds of miles and were often many miles thick. They did not however cover the entire globe, as some would leave their audiences to believe. In North America the glaciers hardly extended past Indiana during the final glaciation period roughly 20,000 years ago. (Maasch, 1997) The animation to the right shows the recession of glaciers in North America from the end of the last Ice Age. You can see starting around 18,000 years ago many of the 48 states are visible. Likewise, as you will see in the maps below ice did not actually cover most of our modern day continents. Global climate and environmental conditions were markedly altered, but as for a world that was covered completely in ice…that was only Hollywood.

To learn more about how the glaciers affected climates in North America click on the link to the left, just below the picture of a retreating glacier. It has left behind a deep trench as well as a glacial melt lake all in a matter of 30 or 40 years.

What Causes Ice Ages?

In what are called Wilson cycles the continents that comprise the surface of the earth move and collide with one another. Mountains are created, basins are formed, oceans are widened and continents are smashed into one. Thus is nature of the tectonic processes. Cycles have been observed within all these changes and it is generally accepted that there is a 100,000 year cycle to the warming and cooling of the earth’s surface. Theorists have deduced that the cycles may be linked to the movement of polar ice sheets, or what is quickly becoming the popular theory is that it has more to do with the carbon cycle. (Shakelton. 2000) Thus the amount of CO2 in the earth’s atmosphere may be a critical factor to inducing climate change such as Ice Ages.

Carbon has a powerful say in the global climate through its ability to produce a greenhouse effect when present in the upper atmosphere as CO2. Most life that relies on relatively warm temperatures above freezing rely on CO2’s ability to trap the suns heat. This happens because water vapor, carbon dioxide, methane and other gasses present in the upper atmosphere absorb the long wavelength radiation waves from the sun. Solar radiation is short wavelength waves and these pass through and then leave earth, but the gasses trap the heat radiation and help warm the earth.

http://www.nrcan.gc.ca/cfs-scf/science/brochure_carbon_budget/global_e.html

Carbon levels can change easily though a variety of geologic processes. Metamorphic degassing will release large amounts of carbon directly into the atmosphere when a volcano erupts. Or perhaps it never makes it to the surface as a gas and is instead weathered from organic carbon or silicates to be released. Take the Eocene where there was a seemingly warm spell 55 m.y.a. and then a quick decline, which is attributed to an orogeny that exposed many more silicates to be weathered and so was carbon removed from the atmosphere. The Himalayan orogeny is also thought to have contributed to global cooling in such a similar way. (Alley, 1997)

Shackleton (2000) attributes oxygen isotopic composition in deep-sea sediment a significant indicator of the cyclic nature of the ice ages. The sediment record has a clear cycle every 100,000 years that corresponds with the “ice-age rhythm.” Deep-water temperature, Delta 18O signals of ice volume (how much ice there was) atmospheric carbon dioxide and orbital eccentricity were all on the same 100,000-year cycle. The ice volume actually lags 100 years behind these variables since it is much more a consequence, and needs time to adjust to the changes.

Impacts

Glaciers have tremendous effects on global climate systems. They store vast amounts of water in either glacier ice or lakes that are in contact with the glaciers. Due to the nature of glacial melting patters this water can be released very quickly. If this water is suddenly (on a geologic time scale) re-introduced into earth’s hydrological systems, sea levels change and global oceanic circulation is effected as well. These all have direct consequences on earth’s climate.

Modern theories have suggested that many of the current glaciers that exist today and hold a significant portion of earth’s surface water are melting. Many studies have been conducted on the West Antarctic ice Sheet, which was formed a few million years ago. The West Antarctic Ice Sheet has managed to remain much longer than many of the other glaciers that inhabited the earth during past ice ages, and up until recently it scientists believed that the glacier was melting. Contrary to the popular belief that the earth’s climate is getting warmer everywhere and that the ice caps are melting, new work by Joughin and Tulaczyk has shown that indeed the ice sheet is actually thickening. (Alley, 2002)

The Ice Age Today

Even today we are feeling the impacts of glaciers, and not just in the glacial till that rests in our backyards. Studies have shown that the sudden departure of the glaciers has caused the plates on which they rested to rebound upwards, much like a buoy in the ocean. One of the largest earthquakes that was no where near an active fault was in New Madrid. Geophysicists hypothesized that the earthquake was a response to the weight that was lifted much like a piece of plastic responds when severe weight is lifted from it. On the other hand places like Scandinavia have experienced different geological reactions. Their coast has been reported to have risen more than three feet in the last 100 years. (Harish, 2001)

Literature Cited

Adams, Jonathan. (2004) “Global land environments since the last interglacial.” http://members.cox.net/quaternary/ (Visited on 04/05/04)

Alley, Richard B. (2002) “On Thickening Ice?” Science, Vol. 295 Issue 5554, p451. GeoREF Accessed 04/11/04

Bard, Edouard. (1999) “Ice Age Temperatures and Geochemistry” Science, Vol. 284 Issue 5417, p1133. GeoREF Accessed 04/12/04

Harish, Nir. (2001) “Ground Control.” Sciences, Vol. 41 Issue 2, p8. GeoREF Accessed 04/12/04

Kerr, Richard A. (1999) “The Little Ice Age--Only the Latest Big Chill.” Science, Vol. 284 Issue 5423, p2069. GeoREF Accessed 04/11/04

Maasch, Kirk. (1997) “Big Chill.” http://www.pbs.org/wgbh/nova/ice/ (Visited on 04/14/04)

Shackleton, Nicholas J. (2000) “The 100,000-Year Ice-Age Cycle Identified and Found to Lag Temperature, Carbon Dioxide, and Orbital Eccentricity.” Science, Vol. 289 Issue 5486, p1897. GeoREF Accessed 04/12/04

Tyson, P.D.; Karlen, W.; Holmgren, K.; Heiss, G.A. (2000) “The Little Ice Age and medieval warming in South Africa.” South African Journal of Science, Vol. 96 Issue 3, p121. GeoREF Accessed 04/10/04

Author: Nathan Henderson (hendena@earlham.edu)
Creation/revision date: April 19, 2004

Link to other Student Webpages for 2004 Earlham Physical Geology

Copyright © 2004 Earlham College. Revised April 19, 2004">April 19, 2004 . Send corrections or comments to parkero@earlham.edu