Ice age
An ice age is a period when for a long time the temperature of Earth's climate is very low. This leads to an expansion of the continental ice sheets, polar ice sheets and mountain glaciers.
'Ice age' is a term used in palaeoclimatology for the period of extensive ice sheets in the recent Pleistocene period. We now know that ice ages have happened a number of times in the past, the greatest and longest of which took place in the Proterozoic era, before multi-cellular eukaryotes evolved.[1][2]
During ice ages the sea level drops as water is held in the great ice sheets at the poles. How much it drops depends on several factors, such as the length of time that a cold period lasts.
Stages
Within an ice age, there are stages. The longer cold stages are called glacials or glacial periods. The shorter warm periods are called interglacials. The last glacial ended about 11,000 years ago when the present interglacial started. The Greenland and Antarctic ice sheets still exist. The last two million years have been the Pleistocene ice age. During glacials, large and thick ice sheets cover much of the North American and Eurasian continents.
Many glacial periods that have occurred during the last few million years are initially at 40,000-year frequency, but more recently ice ages have occurred at 100,000-year frequency.
This data comes from a time when human beings had no effect on the climate, or virtually none. Therefore, it is technically correct to say that humans had no effect on global climate in the Earth's history. However, in recent centuries they have burned much fossil fuel, and this has partly been responsible for the present temperature rise.
Ice Age Media
An artist's impression of ice age Earth at glacial maximum.
The Antarctic ice sheet. Ice sheets expand during an ice age.
Haukalivatnet lake (50 meters above sea level) where Jens Esmark in 1823 discovered similarities to moraines near existing glaciers in the high mountains.
Timeline of glaciations, shown in blue.
Ice age map of northern Germany and its northern neighbours. Red: maximum limit of Weichselian glacial; yellow: Saale glacial at maximum (Drenthe stage); blue: Elster glacial maximum glaciation.
Sediment records showing the fluctuating sequences of glacials and interglacials during the last several million years.
Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials
Past and future of daily average insolation at top of the atmosphere on the day of the summer solstice, at 65 N latitude.
Northern hemisphere glaciation during the last ice ages. The setup of 3 to 4 kilometer thick ice sheets caused a sea level lowering of about 120 m.
Related pages
References
- ↑ Imbrie J. & Imbri, K.P. 1979. Ice ages: solving the mystery. Short Hills NJ: Enslow. ISBN 978-0-89490-015-0
- ↑ Alley R.B. 2000. The two-mile time machine: ice cores, abrupt climate change, and our future. Princeton University Press. ISBN 0-691-10296-1
Other websites
- Cracking the Ice Age from PBS
- Climate patterns