Within the ice ages more
temperate and more severe periods occur.The colder periods are called
GLACIAL PERIODS, the warmer periods INTERGLACIALS,
such as the Eemian Stage.
Glacials are characterized by cooler and drier climates over
most of the Earth and large land and sea ice masses extending outward from the
poles.Mountain glaciers in otherwise
unglaciated areas extend to lower elevations due to a lower snow line. Sea
levels drop due to the removal of large volumes of water above sea level in the
icecaps.There is evidence that ocean
circulation patterns are disrupted by glaciations, also known as abrupt climate
change.The Earth has been in an
interglacial period known as the Holocene for more than 11,000 years.It was conventional wisdom that the typical
interglacial period lasts about 12,000 years, however there has been some
controversy regarding this.For example,
an article in Nature argues that the current interglacial might be most
analogous to a previous interglacial that lasted 28,000 years.Predicted changes in orbital forcing suggest
that the glacial period would begin at least 50,000 years from now, even in
absence of human-made global warming.Moreover, anthropogenic forcing from increased greenhouse gases might
outweigh orbital forcing for as long as intensive use of fossil fuels
continues.At a meeting of the American
Geophysical Union on December 17, 2008, scientists detailed evidence in support
of the controversial idea that the introduction of large-scale rice agriculture
in Asia, coupled with extensive deforestation in Europe
began to alter world climate by pumping significant amounts of greenhouse gases
into the atmosphere over the last 1,000 years.In turn, a warmer atmosphere heated the oceans making them much less
efficient storehouses of carbon dioxide and reinforcing global warming,
possible forestalling the onset of a new glacial age.
