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Climate Science: Investigating Climatic and Environmental Processes
Glacial and interglacial Scale (<105 Years)
Milutin Milankovitch's Major Cycles
Forcing Cycles

Sea Level Changes
100,000 Years of local pollen zonesDue to variations in the Earth's orbital process, the planet has experienced a series of Ice Ages over the past 2.6 million years. The most recent cycle culminated in the Last Glacial Maximum (or LGM) some 18,000 years ago, the world-- especially the northern hemisphere-- was a very different place than it is today. Ice covered large areas-- nearly 32% of the Earth's land area, sea level was about 120 meters lower than it is today, and many large, non-extinct mammals such as mammoths roamed the northern lands (Ruddiman, 2001).

The Ice Ages which have dominated the Earth's environment for around the past two million years are thought to be caused primarily by orbital fluctuations that, while changing the sunlight received by only a few percent, have major impact on climate systems. These orbital forces include the 22,000 year cycle of precession, 100,000 and 400,000 cycles of eccentricity, and 41,000-year cycles of Earth's obliquity or axial tilt. Scientists are still researching exactly what mechanisms trigger the flux and flow of Ice Ages.

Image during Last Glacial Maximum of Northern Hemisphere based on CLIMAP which was undertaken in the 1980s.


Milutin Milankovitch's
Major Cycles

Image of Milutin Milankovitch

Building on the research of James Croll, the Serbian mathematician Milutin Milankovitch, began in the 1910s to embark on a series of astronomical calculations that demonstrated how Earth's orbital variations play a role in Ice Ages and other climate variations. His theories continue to be controversial.

For more on Milankovitch and other pioneers of climate research, see the Ice Age Slideset from NOAA's Paleoclimatology Program.

Image of turning globe


Milankovitch cycles, such as precession of the equinoxes (23,000 years), obliquity (41,000 years) and eccentricity (100,000 and 400,000 year periods) influence climate change at larger time scales.

How Measured
Marine sediments, geomorphic features, loess, speleothems and astronomical observations and calculations provide the means of reconstructing past climate variability at 100,000 year and longer time scales.

Sea Level Changes

The figure below shows the relative temperature over the past million years and highlights how sea level has changed over the past 140,000 years.
Global Climate History

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