SES4U
Grade 12 Earth & Space – University
Unit: Earth History
Reference: OERB
Paleoclimates & Climate Cycles
Paleoclimatology is the study of past climates. Past climatic events are preserved and recorded in
tree rings, skeletons of coral reefs, glaciers and ice caps, the sediments of lakes and oceans, and in
fossils.
How are Paleoclimates Measured?
Ice Cores
Ice cores are taken from ice sheets date back to over 800 000 years. Pollen found in the cores
help determine the amount of precipitation and the types of plants that existed there, and air
trapped in the snow is analyzed to determine the composition of the atmosphere.
Dendroclimatology
The measurement and analysis of tree rings can give valuable information about the temperature
and precipitation; however, tree ring data is limited to the last 4000 years.
Milankovitch Cycles
Periodic Cycles of Glaciation and warmer weather have caused swings in climatatic conditions.
Serbian Astronomer Milutin Milankovitch proposed a mechanism(cycle) for these climatic changes.
Cycle
Description
Diagram
Effect on Climate
The orbit of the
When orbit is circular the two
earth varies in its
hemisphere have similar seasons. When
eccentricity (the
more eccentric, there are large
shape of the orbit
variations (one hemisphere has extreme
is not constant)
seasons (hot & cold, other hemisphere is
Eccentricity
cool and warm)
Axial Tilt
(obliquity)
Precession
The earth has
seasons because
the earth is tilted
on its axis. Our
current tilt is
23.5°
The “wobble” of
earth on its axis
(like a spinning
top) (observed by
watching stars like
Polaris and
observing their
change in position)
@ max. tilt, more extreme seasons. @
min. titl, more moderate seasons.
Makes changes in axial tilt more
extreme
(Use animation on OERB. Additional gizmo on explore learning can be used for axial tilt)
SES4U
Grade 12 Earth & Space – University
Unit: Earth History
Reference: OERB
Discussion:
Climate change has been dramatic in the past and carbon dioxide levels were nearly 6 times greater
during the Cambrian period compared to the present. Is the climate change in the last century out
of the ordinary compared to the past 2000, 20 000, or 1 million years? Scientists have also
debated the cause (volcanic eruptions, Sun’s energy output, natural cycles, greenhouse gases) of the
global warming over the last century.
Should we be concerned about the current global warming trends? (Think about current organisms
being able to adapt, past climate changes, and causes of this climate change event.)