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Lecture 14: The LGM (Last Glacial Maximum)

Lecture 14: The LGM (Last Glacial Maximum). Part III: Deglacial and Millennial Climate Changes. (Chapter 12). Last Glacial Maximum. Big signal. 21,000. Much more data, with 14 C dating. Mammals of the Last Glacial Maximum (21,000 years ago). Cave painting of LGM era in Southern France.

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Lecture 14: The LGM (Last Glacial Maximum)

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  1. Lecture 14: The LGM (Last Glacial Maximum) Part III: Deglacial and Millennial Climate Changes (Chapter 12)

  2. Last Glacial Maximum Big signal 21,000 Much more data, with 14C dating

  3. Mammals of the Last Glacial Maximum (21,000 years ago)

  4. Cave painting of LGM era in Southern France

  5. Climate forcing since LGM CO2 sensitivity Obital similar Ice Sheet (NH)

  6. CLIMAP: Reconstruction of LGM Climate Colder ! LGM August SST LGM- present August SST

  7. LGM SST Changes, Data uncertainty CLIMAP 81: El Nino-like Prell 85: La Nina-like Broccoli, A., 2000

  8. How large is the Ice Sheet at LGM? More Ice! Why the greatest ice sheet not over Siberia?

  9. LGM reconstruction of North America Ice Sheet East-west asymmetry, why?

  10. Sea Level Change LGM IPCC/AR4 2007

  11. LGM Coastlines

  12. Ice sheet contribution to sea level Which value should be used for isotope balance?

  13. LGM desert and sand (expanded) Sand dunes today Sand dunes LGM

  14. LGM desert and dust Drier and windier! 10 times more dust LGM desert dust LGM loess deposits

  15. Projected Precipitation Changes (%) in response to Future CO2 (AR4) Rich get richer and poor get poorer!

  16. Climate forcing at LGM CO2 sensitivity Obital similar Ice Sheet (NH)

  17. Implication to future projectioin? Sand dunes today LGM

  18. Ice Age climate deposits Winds lift and transport dust downstream and around the world Colder/drier loss of vegetation cover, stronger wind. weight grinding Freezing-thaw Water/rain rework Ice sheet moraines boulder, cobble sand loess (silt-size) dust (clay-size)

  19. LGM ice rafting Freshwater melting..

  20. Model/Data Comparison

  21. How to compare model climate with data (vegetation)? Biome models Now: Interactive climate-ecosystem model

  22. Vegetation and Climate Pollen distributions and climate Wetness indicator Cold spiece Warm spiece

  23. Pollen percentage and climate

  24. Pollen history in a lake core Wetness minimum in mid-Holocene? Decrease cooling Iincreasing warming

  25. Modern/LGM spruce pollen Data/model LGM spruce pollen

  26. Why wetter in the southwest at LGM ?

  27. Simulated LGM Climate Alaska, warmer Cold, drier Split of jet, snow storm, cold, wetter

  28. Model/data mismatch Too much warm-adapted trees, Cooler Mississippi outflow at LGM may help the cooling in the observation.

  29. Vegetation in Europe Modern LGM Cold and dry, out flow from Scandinavia ice sheet and North Atlantic

  30. LGM northern Asia Colder and drier Stronger Aleutian High, stronger winter monsoon flow, reduced moisture source from N. Atlantic Closing of Bering Strait….

  31. LGM climate in the Southern Hemisphere Why global synchronous cooling? CO2 LGM sea ice expansion around Antarctic

  32. Why synchronous global cooling? CO2

  33. LGM tropical cooling: Important for Testing Climate Sensitivity Evidence for small cooling: Ocean, 1-2oC Not much difference of plankton assemblages (Pacific and Indian Oceans) Similar estimates: Alkenone method and CLIMAP modern analogue

  34. The problem of tropical cooling: mismatch between SST and mountain snowline Evidence of large cooling: Land, DT > 4 - 6 C Mountain snowline

  35. Freezing level

  36. 1910 Recession of the Grinnell Glacier “Glacier National Park” 1997 Source: D. Fagre, USGS, 2004

  37. Tibetan Plateau: Trends in surface air temperature with elevation: 1961-90 3rd polar amplification? Source: Liu and Chen, 2000

  38. Biosphere “hotspots” identified by Conservation International Much of the American Cordillera has high biodiversity but is under threat from climate change and land use pressures

  39. Projected change in annual mean temperature with 2x CO2 C Source:Bradley et al., 2004: GRL

  40. Clues to Tropical cooling discrepancy? • High altitude more sensitive to climate change (lapse rate change) • Plant physiology effect (trees are less efficient in photosynthesis under a lower CO2 environment)

  41. Response of North Atlantic thermohaline present LGM

  42. LGM model-data comparison: SST 21 ka – 0ka

  43. AMOC model-data comparison Proxy CCSM3 Salinity AMOC Δ 13C 0ka 21ka

  44. AMOC model-model comparison?? Observation AMOC in Models (PMIP2) Δ 13C CCSM HadCM MIROC ECBILT_CLIO 0ka 21ka Otto-Bliesner et al., 2007, GRL

  45. Future Projection of AMOC in IPCC IPCC, 2001, TAR IPCC, 2007, AR4 Is it consistent with LGM evidence?

  46. Water Age

  47. LGM Wind, or Buoyance? SO brine injection  AABW Obs: Δ13C CCSM: Salinity AMOC Ideal Age Holocene ~1000 yrs LGM 21ka ~500 yrs Other PMIP2s failed

  48. Reference for reading • Shin S., Z. Liu, B. Otto-Bliesner, E. Brady, J. Kutzbach, 2002: Southern Ocean sea-ice control of the glacial North Atlantic thermohaline circulation. Geophys. Res. Lett., 30, DOI:10.1029/2002GL015513 • Liu, Z., S. Shin, R. Webb, W. Lewis and B. Otto-Bliesner, 2005: Atmospheric CO2 forcing on glacial thermohaline and climate. Geophys. Re. Lett, 32, L02706, doi:10.1029/2004GL021929

  49. End of Lecture 13

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