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Lecture 15

Lecture 15. Defining climate, climate controls Climate classification Past climates Historical climate paleoclimate Data and mechanism for change. Climate, the collective state of the atmosphere for a given location and over a specified time interval.

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Lecture 15

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  1. Lecture 15 Defining climate, climate controls Climate classification Past climates Historical climate paleoclimate Data and mechanism for change

  2. Climate, the collective state of the atmosphere for a given location and over a specified time interval • Location, regional or global scale climate • Time • Averages and extremes of variables • Temperature • Precipitation • winds

  3. Climate controls • Latitude • Elevation • Topography • Proximity to large bodies of water • Prevailing atmospheric circulation

  4. Classifying the climate zones (ancient Greek)

  5. Classifying climate zones --- Koppen • A. Humid tropical • B. Dry • C. Humid middle-latitude, mild winters • D. Humid middle-latitude, severe winters • E. Polar • H. Highland Note that boundaries fluctuate from year to year

  6. Fluctuating boundaries of dry/humid

  7. Tropical humid climates (A)

  8. Dry climates (B)

  9. Dry climates (B), not tropical

  10. Moist subtropical to Mid-Latitude (C)Marine west coast climates

  11. Humid subtropical (C)

  12. Mediterranean climates (C)

  13. Severe midlatitude climates (D) (humid, continental)

  14. Subarctic (D)

  15. Polar climates (E)

  16. Past climates • Historical climate (past several K years) • Instrumental record (measurements) • Historical data (for example diaries, ship logs) • Paleoclimate, study of climate of the distant past • Use environmental records, such as • Tree rings • Pollen records • Air bubbles and dust in ice • Marine sediments • Fossil record

  17. Concentration of atm CO2 and CH4 from ice bubbles in the Vostok ice core 2083 m long ice core. Dated by counting the number of ice layers

  18. Ice cores • Dust in ice sheets can be caused by volcanoes • Or by dry windy conditions that lead to soil erosion • Colder periods in Earth’s history are usually much dustier • Did the dust block the sun or did the colder temperatures cause drier conditions?

  19. Past climates, the change mechanisms • Volcanic eruptions • Asteroid impacts • Solar variability • Variations in Earth’s orbit: Milankovitch cycles • Precession • Obliquity • Eccentricity • Plate tectonics

  20. Volcanic activity and climate change • Explosive eruptions emit huge quantities of gases and fine grained debris into the atmosphere • The greatest eruptions at low latitudes are powerful enough to inject the material into stratosphere where it will filter out a portion of the incoming solar radiation • Mount St Helens • El Chichon • Mount Pinatubo

  21. Solar variability • Variations in the amount of energy from the sun • Variations in number of sunspots follow an 11 year cycle • Maunder minimum– some believe that a reduction in output of the sun during this time cooled Earth • Little Ice Age, 1400--1850

  22. Yearly averaged sunspot numbers, 1610-2000

  23. Precession: Earth’s axis wobbles (like that of a spinning top) every 27K years

  24. Obliquity: the angle Earth’s axis makes with the plane of Earth’s orbit (41K years)

  25. Eccentricity: change in the shape of Earth’s orbit around the sun (100K years)

  26. Plate tectonics and climate change 300million years ago

  27. Ice age is a period global cooling that leads to the creation of vast ice sheets across land

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