1. What Causes an Ice Age?

3. What changes the energy budget?
INCOMING ENERGY
solar output cycles
sunspots
Earth’s tilt
shape of Earth’s orbit
OUTGOING ENERGY
reflection from surface
reflection from clouds
absorption by ground
Greenhouse effect
water & air circulation

4. Solar Activity Cycles
Our sun goes through cycles of increased and decreased output every 11 years
Sunspots appear and disappear in response to the changing activity

5. Maunder Minimum
Edward Maunder noticed that in the 17th cent. there was a long time with no sunspots (1645 – 1715)
“Little Ice Age” The Little Ice Age was caused by the cooling effect of massive volcanic eruptions, and sustained by changes in Arctic ice cover, scientists conclude

6. Milankovic Cycles
Milutin Milankovic studied the shape of Earth’s orbit over time, and how that could affect the amount of sunlight that reaches us
Three variables
Eccentricity (degree of roundness)
Obliquity (how far the poles are tilted)
Precession (which way the poles point)

7. Eccentricity
Earth’s orbit is nearly circular, but not quite… therefore seasons are not equal quarters
Autumn
89.8 days
Summer
93.6 days
Winter
89.0 days
Spring
92.8 days

8. As the orbit gets more oval, the seasons become even more unequal

9. Obliquity
Earth’s tilt determines which regions get direct sunlight, and which get their light at a slant
Arctic / Antarctic Circle
Long periods of weak light in summer
Long periods of dark in winter
Current tilt = 23.5°
more tilt, ice caps and tundra expand
less tilt, ice caps and tundra retreat

10. Precession Like a spinning top, Earth’s axis slowly rotates
AD 2015: north star is Polaris
3000 BC: north star was a Draconis
12,000 BC: north star was Vega

11. Why do we care? Tilt determines what season it is TOWARD SUN = SUMMER
AWAY FROM SUN = WINTER
FALL
WINTER
SUMMER
SPRING
FALL
WINTER
SUMMER
SPRING

12. Summary:

13. Cycles overlap to make Earth really cold every 40,000 years or so, and super-cold every 400,000 years

14. Once solar energy gets here, what happens next?
Reflected by atmosphere
Reflected by ground surface
Absorbed by ground surface
Absorbed by atmosphere

15. Reflection from Ice or Clouds
If ice caps shrink they reflect less sunlight, and Earth warms up
If ice caps grow, they reflect more sunlight, and cool the Earth

16. Absorption by Atmospheric Gases
Some gases hold in the heat
Water Vapor
Carbon Dioxide
Nitrous Oxide
Methane
Trapped heat keeps our planet warm

17. Blue waters are very cold
Circulation Patterns
Global ocean currents carry heat from the equator to the poles
Orange & Yellow
If currents get out of balance, the poles get colder and colder
Blue waters are very cold

18. Global Wind Patterns
Polar, Tropical, and Temperate cells circulate the air
Rising air at 0° & 60° makes stormy LO pressure regions
Falling air at 30° N & S creates HI pressure and dry arid climates

19. the Jet Streams
Fast winds form at high altitude where air cells come together
Usually around 30 and 60 latitude, but they can drift north or south

20. When the jet stream is shifted by a storm, cold polar winds push farther south and warm tropical air comes farther north