1. Climate Change: Ice Ages Naturally Occuring, Long Term
Ice Age: Colder than usual & glaciers cover larger portion of Earth’s surface as they advance fr. poles.
When:
4 major ice ages in last 2 million years
Last one ended 10, 000 yrs ago
Scientific American: Hot Planet, Cold Comfort Planet

2. Icehouse vs. Greenhouse
LOW
18O:16O
HIGH 18O:16O
Icehouse vs. Greenhouse
ICE HOUSE = Ice poles
GREEN HOUSE= NO ice poles

3. Causes of Ice Ages
1. Milankovitch Cycles = Changes in incoming solar radiation due to variations in Earth’s orbit, tilt, or wobble.
A. Change in shape of E’s orbit
(How elliptical or circular our orbit is. Varies from 0 – 6% elliptical; Now: 1.7% elliptical)
Cycle: years
More elliptical = more variation in climate = ice age
B. Changes in Tilt
Ranges from 22 – 24.5 degrees (Now 23.5 degrees)
More Tilt = more seasonal variation = ice age
Cycle: yrs
C. Changes in Wobble (direction of axis). N. Pole pointed toward or away from sun? Cycle: 23, 000 years

4. Causes of Ice Ages continued
2. Volcanic Activity
Dust & ash can cause cooling in short term by blocking solar radiation (ice age)
Volcanic gases cause warming over long term (b/c they are greenhouse gases)

5. 3. Changes in Solar Radiation (solar cycles)
Any change in the sun’s pattern of sun-spot activity can cause climate change.
A prolonged stop of sunspot activity correlates with COOLING.
A prolonged period of excessive sunspots correlates with a WARMING.

6. Lull in sunspot activity = “Little Ice Age” in Northern Europe
Thames River during the Little Ice Age in the Maunder Minimum. Ice parties were common on the Thames each winter.

7. 5. Causes of Ice Ages: Mt. Building & Plate Tectonics
Changes in continental arrangements can change ocean currents or air flow  can change climate
Mt. Building = Uplift of new land  more chemical weathering of newly exposed rock  removes CO2 from air  cooling
55 Ma: Uplift of the Himalayas

8. Cause of Ice Ages: Change in ocean circulation
Change in ocean circulation patterns  change climate.
Ocean currents can be changed by changes in water temperature or salinity.
Scientific American: Hot Planet, Cold Comfort Planet

9. Ancient Ice Age: Snow Ball Earth
Ice covered Earth ~ 2.4 bya (end of Precambrian Time)
Global temps: ~ - 74 F
6. Biology Driven Ice Age = Snowball Earth
Weaker sun (30% weaker) + Arrival of photosynthesizing bacteria (removing CO2 from atmosphere) = ICE
ICE has high albedo --> more solar radiation reflected --> less energy absorbed --> MORE ICE
Volcanic GHG eventually warm planet up