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Sea-Tac Average Sea-Tac Temperatures as a function of time 55.00 Temperature (deg F) 54.00 53.00 52.00 51.00 50.00 49.00 48.00 47.00 1940 1950 1960 1970 1980 Years 1990 2000 2010 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 wintersummer • 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 12.01 • 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 • 1879-1958 • 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?