Glacial and interglacial periods
Also called: Ice age · Topic: Climate Change: Causes, Evidence and the Global Response · NCERT: Class 11, Ch 11 "World Climate and Climate Change"
Meaning
Glacial periods are cold phases when ice sheets spread over large areas. Interglacial periods are the warmer phases between them, when the ice retreats. The two have taken turns many times in Earth's history. Glacial landforms and lake sediments record them. During the Pleistocene epoch, ice ages came and went many times. NCERT says the last peak glaciation was about 18,000 years ago. Today the Last Glacial Maximum is dated about 26,000–19,000 years ago, with its peak near 21,000 years ago. These swings show that climate changes naturally, and they help scientists judge how unusual today's warming is.
Example
We are living in a warm interglacial today, the Holocene, which began about 11,700 years ago. Before that, ice sheets were much larger. By contrast, the Earth was warm for a long stretch 500–300 million years ago (the Cambrian, Ordovician and Silurian periods).
Don't confuse with
- Little Ice Age: a short, regional cool spell from 1550 to about 1850 inside the present interglacial. It was not a true glacial period.