In an age where global warming is on everyone's mind, could we still really be in an ice age or headed for another? After all, most of the ice melted and the woolly mammoths are gone, but there are some remnants in the ice sheets that cover Antarctica and Greenland and that border Alaska and the Yukon Territory. That mixed evidence makes sense if you remember that ice ages are made up of both icy periods (known as glacials), and intervening warm periods (interglacials). We're currently in an interglacial period. Historically, interglacial periods last approximately 10,000 years, which is about how long this one has lasted.
There was a "Little Ice Age" in the Northern Hemisphere from A.D. 1300 to A.D. 1850 [source: NASA]. In this period, Holland's canals routinely froze over. But this ice age is considered "little" because it lacked a global punch. There's no precise definition of an ice age, which makes it difficult to know when another glacial period has officially started. One scientist has suggested that to qualify as an ice age, ice sheets must cover 400,000 square miles (1,035,995 square km) and appear on nonpolar continents [source: Gosnell].
As we lack both a basic definition and the exact reason for why the Earth sometimes creates the conditions for an ice age, it'll be hard to predict when the next one will take place. Some scientists think that humans might have affected the Earth enough to stave off an ice age by burning fossil fuels [source: University of South Hampton]. Still, you might want to hang on to that warm winter coat.
To learn more, see the ice age links and stories below.
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- Barton, Miles, Nigel Bean, Stephen Dunleavy, Ian Gray, Adam White. "Prehistoric America: A Journey Through the Ice Age and Beyond." Yale University Press. 2002.
- Britt, Robert Roy. "Inside Sunspots: New View Solves Old Puzzle." Space.com. Nov. 6, 2001. (May 5, 2008)http://www.space.com/news/sunspot_inside_011106.html
- Chapman, Phil. "Sorry to ruin the fun, but an ice age cometh." The Australian. April 23, 2008. (May 2, 2008)http://www.theaustralian.news.com.au/story/0,25197,23583376-7583,00.html
- Erickson, Jon. "Ice Ages: Past and Future." Tab Books. 1990.
- Gosnell, Mariana. "Ice." Knopf. 2005.
- Imbrie, John and Katherine Palmer. "Ice Ages: Solving the Mystery." Harvard University Press. 1979.
- Kious, W. Jacquelyne and Robert I. Tilling. "This Dynamic Earth: The Story of Plate Tectonics." U.S. Department of the Interior/U.S. Geological Survey. 1996.
- Macdougall, Doug. "Frozen Earth: The Once and Future Story of Ice Ages." University of California Press. 2004.
- Morgan, Alan V. "Pleistocene Epoch." Microsoft Encarta Online Encyclopedia. 2007 (May 2, 2008)http://encarta.msn.com/encyclopedia_761573397/Pleistocene_Epoch.html
- Ray, Louis L. "The Great Ice Age." U.S. Department of the Interior/U.S. Geological Survey. 1992.http://pubs.usgs.gov/gip/ice_age/ice_age.pdf
- Skinner, Brian J. and Stephen C. Porter. "The Dynamic Earth: An Introduction to Physical Geology, Second Edition." John Wiley & Sons, Inc. 1992.
- Than, Ker. "Hungry humans killed off Ice Age mammals." MSNBC. Aug. 4, 2005. (May 2, 2008)http://www.msnbc.msn.com/id/8826636/
- "The Ice Age (Pleistocene Epoch)." United States Environmental Protection Agency, Gulf of Mexico Program. (April 30, 2008)http://www.epa.gov/gmpo/edresources/pleistocene.html
- University of South Hampton. "Next Ice Age Delayed by Rising Carbon Dioxide Levels." ScienceDaily. Aug. 30, 2007. (May 2, 2008)http://www.sciencedaily.com/releases/2007/08/070829193436.htm
- "What was the 'Little Ice Age'?" NASA Goddard Space Flight Center. Nov. 28, 2005. (May 2, 2008)http://www.gsfc.nasa.gov/scienceques2005/20051128.htm
- Yasuda, Memorie. "Ice Ages." Voyager. Spring 2004. (April 30, 2008)http://explorations.ucsd.edu/Archives/Volume_10/Number_4/Voyager_V10_n4.pdf