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

8. Tropical humid climates (A)

9. Dry climates (B)

10. Dry climates (B), not tropical

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

12. Humid subtropical (C)

13. Mediterranean climates (C)

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

15. Subarctic (D)

16. Polar climates (E)

17. 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

18. 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

19. 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?

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

21. 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

22. 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,

23. Yearly averaged sunspot numbers, 1610-2000

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

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

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

27. Plate tectonics and climate change
300million years ago

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