1. Climate and the Seasons

2. What causes seasons?
The seasons are a result of the tilt of the Earth’s axis.
As the Earth travels through space around the Sun in a year the axis will face the sun differently.

3. What determines the temperature of Earth?
Temperatures on our planet are not determined by the distance of the Earth from the Sun. Rather it is the angle the Sun’s rays strike the Earth.

4. Altitude (Sun’s Apparent Path)
In Summer, the Sun is high in the sky and the rays hit the Earth at a steep angle (more direct).
In Winter, the Sun is low in the sky and the rays strike the Earth at a shallow angle (less direct).
Remember the flashlight experiment.

5. Seasons
The seasons don’t begin on one day and finish on another because our orbit around the Sun is continuous. It actually takes quite some time for the Earth to heat up or cool down, and that’s why the seasons change gradually.

6. What are Solstices?
Days when the direct sunlight reaches its farthest latitude north and south of equator.
Winter solstice is December 21
beginning of winter (the shortest day of the year). Has the lowest number of daylight hours.
Summer solstice is June 21
beginning of summer (the longest day of the year). Has the longest number of daylight hours.

7. What are Equinoxes?
Days when the Earth’s axis is tilted neither toward nor away from the Sun. Day and night are the same length of time. Direct sunlight is on the equator.
Vernal (spring) equinox on March 21-23
Autumnal (fall) equinox on September 21-23

9. When do you think the Earth is closest to the sun?
Perihelion = when Earth is closest to the sun
About Jan. 5th
Aphelion = when Earth is furthest from the sun
About July 5th
Our Winter
Our Summer
91,405,436 miles
94,511,989 miles

10. What changes in Earth’s orbit cause Earth’s climate to change?
Eccentricity
Obliquity (axial tilt)
Precession (wobble)

11. What is Eccentricity? Periodicity: 100,000 years
Eccentricity = the shape of the Earth's orbit around the Sun.
constantly changing
shape ranges between more and less elliptical on a cycle of about 100,000 years.
This changes the distance Sun's radiation (heat) must travel to reach Earth.
reducing or increasing the amount of radiation (heat) received at the Earth's surface during the year affects global climates.
Periodicity: 100,000 years

12. What is Obliquity (axial tilt)?
Earth’s axis is currently tilted 23.5 degrees
Earth's axis points in the same direction in space as we orbit around the Sun
Currently points towards Polaris (the North Star).
The tilt is the reason for the seasons because it changes where the direct sun’s rays hit on Earth.

13. How does Obliquity (axial tilt) Change?
The tilt of the axis changes slowly over time.
ranges from degrees.
Less tilt (20.5)= less variation from season to season.
Greater tilt (24.5) = more variation from season to season
Periodicity: 41,000 years
Remember your Styrofoam balls

15. What is Precession (wobble)?
Precession is the Earth's slow wobble as it spins on axis.
Like a top running down, and beginning to wobble back and forth on its axis.
Periodicity: 23,000 years
Evidence: Thubin used to be the North Star on old sailing maps
Changes the location of seasons in Earth’s orbit around the sun.

17. What are Milankovitch Cycles?
All three factors: Eccentricity of the orbit, Obliquity (axial tilt), and Precession (wobble) collectively are called Milankovitch cycles.
All three combined cause global climate changes.

18. The impact of Milankovitch Cycles
What happens when:
The Earth’s axis is tilted at it’s maximum tilt? (24.5 degrees for example)
The Earth’s eccentricity is at it’s maximum stretch? (large ellipse)
The Earth’s wobble (precession) is at it’s maximum? (pointed away)
Stop for a moment with your group and make a hypothesis about what would happen

19. The answer!
Glaciers form in the Northern Hemisphere!

20. Climates can Change
As we learned in the tree ring activity, the Earth has gone through periods when the climate was colder than today or it was warmer than today.
Look how far south did the glaciers extend?