Sea-Tac

Glacial evidence

In what way is a glacier like a water reservoir (other than they are both water)?

Advancing/Retreating If a glacier has a positive budget, we say that it is advancing If a glacier has a negative budget, we say that the it is retreating

Winter= snowfall Summer = summer melting Net is winter- summer If the Net is positive, it means? If the Net is negative, it means? Is the South Cascade Glacier advancing or retreating?

Atom/Molecule What is an atom? What is a molecule?

Carbon 6 C C

Link to ice core oxygen isotope data Link to deep sea oxygen-isotope data

Seasons vs. climate change Seasons –Temperature variation annually Climate change

Seasons vs. climate change Seasons –Temperature variation annually Climate change –Longer term variation in temperature

Seasons vs. climate change Seasons –Temperature variation annually –Less effect at the equator; greater effect at the poles Climate change –Longer term variation in temperature –Less effect at the equator; greater effect at the poles

Seasons vs. climate change Seasons –Temperature variation annually –Less effect at the equator; greater effect at the poles –Caused by the tilt of the earth’s axis Climate change –Longer term variation in temperature –Less effect at the equator; greater effect at the poles

Seasons vs. climate change Seasons –Temperature variation annually –Less effect at the equator; greater effect at the poles –Caused by the tilt of the earth’s axis Climate change –Longer term variation in temperature –Less effect at the equator; greater effect at the poles –Caused by multiple factors: variations in Earth’s orbit, “greenhouse effect, albedo, plate tectonics, ocean circulation

Multin Milankovitch Serbian astrophysist

Basic principles What happens to the intensity of light as we increase the distance to the sun?

Basic principles What happens to the intensity of light as we increase the distance to the sun? What happens when the angle of sunlight striking the Earth is less perpendicular?

Earth’s Orbit is not circular Aphelion- the point in the planet’s orbit farthest from the sun. Perihelion- the point in the planet’s orbit closest to the sun.

Present day orbit Closest to the sun during northern hemisphere winter Farthest from the sun during the northern hemisphere summer

Other basic ideas: Glaciations tend to happen when the winters are longer than the summers. The Earth’s orbit varies in distance from the sun. What would happen if we were farthest from the sun in the northern hemisphere winter?

Other basic ideas:  We are more likely to have glaciations if the winters are more intense, even if the summers are more intense.

Milankovitch cycles- Eccentricity Earth’s orbit changes from nearly circular to more elliptical. The present difference in light intensity between summer and winter is about 6%. During very elliptical orbit, can be as much as 30% different. Cycle is ~95,000 years

Milankovitch cycles- Eccentricity Predicted variations in eccentricity through time

Milankovitch cycles-Obliquity If the axis of the Earth is more vertical to the plane of the ecliptic, are there seasons? Earth varies from 21.8 deg to 24.4 deg over 41,000 years

Milankovitch cycles- Obliquity Predicted obliquity through time

Milankovitch cycles-Precession One cycle of precession occurs about every 21,700 years

Milankovitch cycles- Precession Predicted precession cycles through time

Milankovitch cycles What happens when we combine all of these cycles together?