1. Causes of Natural Variability
Volcanoes and Ice Ages
Causes of Natural Variability
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2. Key Points Past Variations in Global Temperature Volcanoes
100 yrs Warming + Volcanoes
1000 yrs Medieval Optimum + Little Ice age
10,000 yrs Post glacial
1,0000,000 yrs Milankovitch Cycles
Volcanoes
Climate records from ice and sediment cores
Ice ages
Worldwide, most small glaciers are receding

3. El Nino Events and Global Temperature

4. The last 1,000 years
Note +/- 0.5 oC

5. South Western U.S. 1300 AD Why did these communities collapse?
Mesa Verde Cliff House

6. Since the end of the last ice age
Note range of +/- 1 oC since 10,000 BP

7. Last Glacial Maximum
xxx

8. Signs of Past Glaciation
xxx

9. A million years of ice ages and interglacials
Estimated global surface temperature from ocean sediments
Present temperature 15 oC

10. Key Points Past Variations in Global Temperature Volcanoes
Large volcanoes inject sulfate aerosols into stratosphere
Sulfate aerosols reflect sunlight back to space
Cool the earth, but only for a year
Climate records from ice and sediment cores
Ice ages
Worldwide, most small glaciers are receding

11. Mount Saint Helens
May 18, 1980
United States Geological Survey

12. Atmospheric Transmission
Interrupted by large volcanoes
Mount Pinetubo
El Chichon

13. Global temperature and volcanoes
Each event followed by a drop for 2-3 years

14. Key Points Past Variations in Global Temperature Volcanoes
Climate records from ice and sediment cores
O18 (temperature), CO2, sulfate, ...
Ice ages
Worldwide, most small glaciers are receding

15. Drilling Ice Cores in Peru
Annual layers in the Quelccaya Ice Cap
Distant view of ice cap
Lonnie Thompson

16. Inca Country
Peru

17. Equator
Peru
Lonnie Thompson &Ellen Mosely Thompson

18. Annual Signature in O18 Quelccaya - 1976 Core
Also measured are dust, and sulfate
CO2 , methane can also be measured from ice cores, though not from this one

19. Drilling Ice Cores in Greenland
xxx

20. Key Points Past Variations in Global Temperature Volcanoes
Climate records from ice and sediment cores
Ice ages
Last ice age ended 12,000 years ago
Changes over tens of thousands of years
Driven by Milankovitch cycles in Earth orbit
Recent evidence of abrupt transitions within 100 years
Worldwide, most small glaciers are receding

21. A million years of ice ages and interglacials
Estimated global surface temperature from ocean sediments
Present temperature 15 oC

22. Land Ice in the Northern Hemisphere (now vs 18,000 BP)

23. Alaskan Glacier
Photo Inge Bretherton

24. Greenland Ice Sheet
More great pictures (University of Cincinnati)

25. Key Points Past Variations in Global Temperature Volcanoes
Climate records from ice and sediment cores
Ice ages
Last ice age ended 12,000 years ago
Changes over tens of thousands of years
Driven by Milankovitch cycles in Earth orbit
Recent evidence of abrupt transitions within 100 years
Worldwide, most small glaciers are receding

26. Milankovitch Cycles
Small, predictable, changes in orbit of Earth around the sun
Departures from idealized elliptic orbit of Newton, Kepler
Precession: period 23,000 years
Tilt: period 41,000 years
Ellipticity: period 100,000 years
Calculated in 1920’s but then no evidence
Do not change total radiation reaching earth, only distribution among seasons

27. Elliptic Orbit (Newton)
Ellipticity exaggerated
For small sun, earth, orbit is fixed in space

28. Tilt Present tilt 23.5o Varies 22o - 24.5o every 41,000 years
No tilt, no seasons

29. Precession - 1 Earth’s axis of rotation moves in space
Because earth not quite spherical
like a spinning top
Earth now closest to sun in Northern winter was/ will be in Northern summer
Period 23,000 years
About 12,000 years ago Hudson Bay ice cap melted

30. Precession - 2

31. Incoming solar radiation
Tilt + precession + ellipticity
Varies with latitude
Direct effects largest for continents

32. Key Points Past Variations in Global Temperature Volcanoes
Climate records from ice and sediment cores
Ice ages
Worldwide, most small glaciers are receding

33. Evidence for Ice Cap Melting
Right
Clear annual trace
Left
Warmed and melted

34. Melting Glaciers
xxx

35. Key Points Past Variations in Global Temperature Volcanoes
Climate records from ice and sediment cores
Ice ages
Worldwide, most small glaciers are receding

36. Sources of Information
Horel & Geisler Chapter 4,5
Lonnie Thompson and Ellen Mosely-Thompson, Ohio State University
Thomas Lowell, University of Cincinnati