Ice ages
During the last 2.6 million years or so in the Quaternary period, ice ages, also called glacial ages, were times of extreme cooling of the Earth's climate where ice sheets and other types of glacier expanded to cover large areas of land. Between ice ages there were warmer interglacial periods and we are now living during such a time.
There have been many ice ages during the last 2.6 million years but when people talk about the Ice Age, they are often referring to the most recent glacial period, which peaked about 21,000 years ago and ended about 11,500 years ago.
What causes ice ages is not completely understood. The composition of the atmosphere, changes in the position of our planet around the Sun, and changes in ocean currents are some of the important factors that control the climate.
Image: A reconstruction of the Anglian ice sheet in Precambrian North London (credit: The Natural History Museum, London)
Introduction
Ice ages
TV clips (3)
play
The ice age cycle
Iain Stewart explains how the rise of farming may have prevented an ice age.
Professor Iain Stewart describes a new theory that the rise of farming about 11,000 years ago released enough greenhouse gases into the atmosphere to prevent the onset of another ice age.
play
The current ice age
We are living in an age of ice.
Dr Iain Stewart explains that we are living during a relatively warm period of an ice age.
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Volcanoes defeat Snowball Earth
Volcanoes may have saved an ice-bound Earth.
Dr Iain Stewart describes Snowball Earth, a period of dramatic cooling that may have started 700 million years ago. He explains how the carbon dioxide from volcanoes may have rescued our planet from an icy fate.
Ice ages
An ice age, or more precisely, a glacial age, is a period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual pulses of cold climate are termed "glacial periods" (or alternatively "glacials" or "glaciations" or colloquially as "ice age"), and intermittent warm periods are called "interglacials". Glaciologically, ice age implies the presence of extensive ice sheets in the northern and southern hemispheres. By this definition, we are still in the ice age that began at the start of the Pleistocene epoch, because the Greenland and Antarctic ice sheets still exist.
More colloquially, "the Ice Age" refers to the most recent glacial period that peaked approximately 20,000 years ago, in which extensive ice sheets lay over large parts of the North American and Eurasian continents. This article will use the term ice age in the former, glaciological, sense: glacials for colder periods during ice ages and interglacials for the warmer periods.
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