Earth 2

Monday, January 1st, 1999
Announcements: The second earth test will be held the Thursday after Spring Break...I think it's on March 18. Another homework assignment was also given.

Lecture notes:

Today's lecture deals with what the world was like tens of thousands of years ago.

Glacial-Interglacial Cycles

• These are the ice-ages--the time periods during which ice caps were present
• This occurred during the Pleistocene time period, which was about 1.9 million years ago
• The extent of the ice which existed was determined by the moraines

• The deep sea core plays a big part in the glacial-interglacial cycles
• The CaCO3 has oxygen molecules with different isotopes because it has a varied number of neurons, causing the oxygen to act differently
• The lighter the oxygen (O16), the easier it is to evaporate. The heavier the oxygen (O18), the more likely it is to see precipitation
• By the time snow falls on an ice cap, it is very enriched in O16, which is stored on land as ice

• The last major ice age was about 21,000 years ago
• Ice ages occur about every 20,000 , 40,000 , and 100,000 years
• There's a rhythm to the occurance of ice ages--ice advances and then retracts
• There is a slow build up to the ice age, then there is a very rapid fall
   

What causes the Increase and Retract Rhythm?

1) Volcanism--volcanoes must go off every 1-2 years to put enough dust into the stratosphere. Timing is very problematic with this method

2) Magnetic Reversals--This does not work or make sense, it will change the solar flux. The last one occurred 700,000 years ago

3) Solar Variability--Maybe the sun's variable is a star. Does it flicker? This can be checked by the reflection of other stars off the planets

• Possible to be variable by +/- %'s
• But, why would this flicker occur every 20,000 , 40,000 , and 100,000 years?

4) Galactic Arm--The solar system sort of wiggles through the system, brought on by going through the dust, gas, and other materials of each arm

5) Greenhouse Gases--The dust on the snow gets more concentrated as the snow melts, creating a dark ring. This annual banding shows us that there are 180 parts per million (ppm) CO2 in our atmosphere

• Prior to the Industrial Revolution there were 280 ppm
• The level of CO2 is always less during Ice Ages, however, it does not explain the ice age

6) Surge of Ice Caps--the earth's climate is perfectly situated to hace ice caps grow, get bigger, and surge...thus causing the earth to become unstable and the ice melts quicker

• There is no forcing mechanism causing the ice age--it's an internal characteristic

7) Earth's Orbit--it has a rhythm. Milutin Milankovitch noted this, but nobody believed him because the first core sample was not taken from the Deep Sea until 1949. The only thing they could go by were the moraines, which indicated that there were only 4 ice ages. However, Milankovitch was proved correct whenever deep sea cores were taken

Orbital Elements Explanations

1) Eccentricity--how out of shape is earth's orbit around the sun?

• The earth's orbit is not a circle because the large planet's motion around the sun has sufficient gravitational pull which regulates the orbit of the earth
• Every 100,000 years, earth's orbit goes from mroe elliptical to more circular, changing the distance from the earth to the sun
• On average, earth gets the same amount of solar energy no matter what shape the orbit is, it just receives the energy at different times

2) Obliquity "Tilt"--This refers to the tilt of the earth's axis relative to the plane it is rotating on. This explains why we have seasons, solstices, equinoxes, and the tropic of capricorn and cancer.

• Because of interaction with other planets, the tilt can change between 22-25 degrees
• The greater the tilt, the more energy received in the summer, the less received in the winter

3) Procession of the Equinoxes--The sun and moon provide torque on the bulge of the earth, making it fatter at the equator because of it's rotation.

• The earth's position throught he ellipse slowly progresses, making the planet closer to the sun during the winter (it's closest when tilted away from the sun and farther when tilted toward the sun). This reverses every 19,000 years

Example: ORBIT

• ellipse
• high tilt--24.5 degrees
• Therefore, earth would be closest to the sun in the summer
•  
• circular
• low tilt
• Therefore, there would be weak seasons...not much change in the amount of energy received

Feedbacks

1) Ice Rhythm Observation

2) Mechanism--Timing Matches

3) Climate Model

• 20,000 and 40,000 year rhythm...no 100,000 years rhythm
• Add CO2 to ice bubbles...the wiggles become bigger (occurrung every 20K-40K)

Ice-Lithosphere Feedback

When the ice cap begins to flow, it advance over large areas. The weight of the ice becomes enormous and after thousands of years it starts to depress the continent underneath it. The ice cap then sinks with the lithosphere and the are above the snowline becomes smaller until the mass balances and therefore the ice cap would melt faster than it accumulates

Evidence

1) Significant climate change on the time scale of tens of thousands of years is seen in geologic records

2) Relatively small changes occur in earth's orbit are strong enough to initiate ice ages. This indicates that the earth is very sensitive

3) CO2 plays a part in what it takes to explain the ice ages

4) There must be other feedback in earth's system that can amplify/change earth's signals

HMWK:

Make a study guide listing what each component of the Energy Balance Equation does. Take the terms and list the mechanisms that may alter climate.