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Causes & Evidence: Ice Age…or Glacial?

Midnight sun Baffin Bay, Greenland: image – Cody Whitelaw

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Home > Climate wiki > What causes climate change? > Ice Age or Glacial?

What’s in a name: Ice Age or Glacial? And why do we care? 

Fig 1. What the Arctic looks like during the different Geological Periods and Epochs. We are currently in an Ice Age and Interglacial (centre figure).
Fig 1. What the Arctic looks like during the different Geological Periods and Epochs. We are currently in an Ice Age and Interglacial (centre figure).

Summary

  • An Ice Age is a geological Period that lasts millions of years. Today, we’re living in the Quaternary Period, an ice age that began 2.58 million years ago
    when ice sheets formed over the Arctic and Antarctica, and mountain chains around the world including New Zealand’s Southern Alps.
  • A Glacial is a very cold stretch of time (a geological Epoch) during an Ice Age, when the ice sheets spread out from the poles and down from (and in many places over the top) of the mountains. It can last thousands or millions of years. The last Glacial was the Pleistocene Epoch (2.58 million to 11,700 years ago).
  • An Interglacial is a geological Epoch when most ice sheets retreat back to the poles (today, that’s Greenland and Antarctica) and some high mountain areas. We have now left the Holocene Epoch, an interglacial (11,700 years ago – around 1950; the exact date is yet to be decided).
  • Ice sheets vs glaciers: ice sheets form when glaciers join together and cover large areas of land, sometimes entire continents. An ice sheet is generally defined as an area of ice covering at least 50,0002 km.
  • As Greenland and Antarctica still have much larger ice sheets than 50,0002 km., we’re still in an Ice Age.
  • Because human activities are causing global climate change, which is melting the Greenland and Antarctic ice caps and triggering mass species extinctions, the Epoch we are now living in is to be called the Anthropocene, however the exact date is yet to be decided.

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Home > Climate wiki > What causes climate change? > Ice Age or Glacial?

Fig 1. What the Arctic looks like during the different Geological Periods and Epochs. We are currently in an Ice Age and Interglacial (centre figure).
Fig 1. What the Arctic looks like during the different Geological Periods and Epochs. We are currently in an Ice Age and Interglacial (centre figure).

Summary

  • An Ice Age is a geological Period that lasts millions of years. Today, we’re living in the Quaternary Period, an ice age that began 2.58 million years ago
    when ice sheets formed over the Arctic and Antarctica, and mountain chains around the world including New Zealand’s Southern Alps.
  • A Glacial is a very cold stretch of time (a geological Epoch) during an Ice Age, when the ice sheets spread out from the poles and down from (and in many places over the top) of the mountains. It can last thousands or millions of years. The last Glacial was the Pleistocene Epoch (2.58 million to 11,700 years ago).
  • An Interglacial is a geological Epoch when most ice sheets retreat back to the poles (today, that’s Greenland and Antarctica) and some high mountain areas. We have now left the Holocene Epoch, an interglacial (11,700 years ago – around 1950; the exact date is yet to be decided).
  • Ice sheets vs glaciers: ice sheets form when glaciers join together and cover large areas of land, sometimes entire continents. An ice sheet is generally defined as an area of ice covering at least 50,0002 km.
  • As Greenland and Antarctica still have much larger ice sheets than 50,0002 km., we’re still in an Ice Age.
  • Because human activities are causing global climate change, which is melting the Greenland and Antarctic ice caps and triggering mass species extinctions, the Epoch we are now living in is to be called the Anthropocene, however the exact date is yet to be decided.

Think of it this way; comparatively speaking in Geological time, Ice Ages are like ‘hours’, Glacials are like ‘minutes’, and Stadials are like ‘seconds’.

Interstadials and Stadials including the Last Glacial Maximum

These are smaller geological units of time that describe in more detail the differences in global temperatures and the extent of ice sheets and glaciers during a Glacial (Fig. 2).

  • Stadials: during the last glacial epoch, the Pleistocene, there were shorter periods when it was extremely cold and the ice sheets spread much further. The last of these stadials, from ~33,000 to 19,000 years ago is often referred to as the Last Glacial Maximum (LGM); it was the coldest, and the ice sheets were the most widespread during the Pleistocene. The end of the LGM was ~14,500 years ago when the West Antarctic ice sheets collapsed and sea levels abruptly rose. This paved the way for the arrival of the Holocene epoch, which began about 2,000 later.
  • Interstadials: between the super cold Stadials, ice sheets covered the continents but itwas slightly warmer, so the ice sheets retreated a little. But not nearly as much as during interglacials.
Fig. 2: The difference between Periods, Epochs, and Stadials. By convention, the terms 'Before Present (BP)' or 'Years Ago (YA)' is the year 1950. A new epoch, the Anthropocene, has been proposed to describe how humans have changed the planet so much that it shows up in the geological record. As there still are ice sheets on Earth, this proposed Epoch is still in the Quaternary Period Ice Age. The exact starting date is yet to be settled.
Fig. 2: The difference between Periods, Epochs, and Stadials. By convention, the terms ‘Before Present (BP)’ or ‘Years Ago (YA)’ is the year 1950. A new epoch, the Anthropocene, has been proposed to describe how humans have changed the planet so much that it shows up in the geological record. As there still are ice sheets on Earth, this proposed Epoch is still in the Quaternary Period Ice Age. The exact starting date is yet to be settled.

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