Ice Age Orbital Theory Flashcards
What causes long-term climatic change?
Hypotheses fall into three main categories
(1) Geographical changes in the Earth’s
surface
(2) Changes in the atmosphere
(3) Changes in solar radiation receipt
Seasons are caused by…
the tilted axis of the Earth
The axis of the earth always points…
in the same direction as Earth orbits the sun
In Northern hemisphere summer, Earth’s axis points towards…
the sun
….and away from the sun in Northern hemisphere
winter
Summer solstice =
Hemisphere tilted directly towards the sun…produces the longest day of the year
Equinox =
the direction of axis side on to the sun
– (produces equal length of night and day)
Aphelion =
Earth at most distant part of elliptical orbit
Perihelion =
Earth closest to the sun
There are three main long-term changes in
the Earth’s orbit called:
- Eccentricity - c. 100 k yrs (circularity)
- Obliquity - c. 42 k yrs (tilt of axis)
- Precession - c. 21 k yrs (‘wobble of axis)
Eccentricity is the weakest effect yet the ice
ages occur every 100,000 years
Precession is caused by…
a ‘wobble’ in the Earth’s axis
The ‘wobble’ takes an average of c. 21,000 years to complete
…this results in a progressive change in the direction in which the axis points
Problems with the astronomical theory of climate change
• Doesn’t explain long-term Tertiary cooling
• Stage 11 problem
• Main pacing of the ice ages has shifted from 41ka
(early Quaternary ) to 100ka.
– Shift occurred after c.900ka.
– Glaciations also intensified
• Shifts in period and intensity of the ice ages can’t be
solely orbital in origin
The 100 kyr problem
Once an ice age has begun a number of feedback
processes can act to deepen the glacial activity,
regardless of solar radiation inputs:
(1) Albedo = more reflection of sunlight
(2) Reduced sea level = larger land area for ice
(3) Sea area small (moderates temps)
(4) Ice sheet height increases height of land
(5) CO2 reduced in the atmosphere
