Climatic and Environmental Processes Glacial
and interglacial Scale
Milutin Milankovitch's Major Cycles
Forcing Cycles Sea Level Changes Due
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
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.
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.
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.
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.
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.