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)
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.
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.
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.
An ice 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 and 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 in an interglacial period - the holocene, of the ice age that began 2.6 million years ago at the start of the Pleistocene epoch, because the Greenland, Arctic, and Antarctic ice sheets still exist.