2-7: Paleoclimate; Ice Core and Lake Sediment Records

Unit Objectives

To review the record of past climate changes as revealed through proxy data (e.g., non-meteorological information such as tree rings and ice cores) in order to give perspective to present and future climate changes.
To compare the simulations of past climates by use of global climate models with actual data on climate change.

Preparation for Online and Class Discussion

Read the summary information.
Class images
Related Class images
Print for offline review.
Take the summary information quiz. Quizzes are available from your portfolio.

Additional Related Reading. Although you are not ultimately responsible for content listed in this section, we encourage you to fully explore the links in order to provide a better scope on the upcoming class discussion.

	How records from the past climates support the case for global warming. (From the United Nations Environment Programme, UNEP)
	From NOAA: Drought history and predictions
	From NOAA: Paleoclimatology Program
	Houghton, J. T., L. G. Meira Filho, B. A. Callander N. Harris, A. Kattenberg, and K. Maskell, 1996: Climate Change 1995. The Science of Climate Change. Cambridge University Press, 413-419.
	Houghton, J. T., G. J. Jenkins, and J. J. Ephraums, 1990: Climate Change, The IPCC Scientific Assessment. Cambridge University Press. p. 124-127.

Online and Class Discussion

A major component of the course is participation in the online dialog. Your comments in the online dialog may be:

Social Comments
Knowledge-building Comments
Ethical Comments

The following may be used as discussion statments for the online dialog:

Unit Problem to Ponder
Unit exam questions from previous years
Unit discussions from previous years

Unit Wrap-up Materials

Group Discussion Summary:

Summary prepared by: Trevor Dickerson, Mark Kochen, Kyle Tackett and Brian Vote
Group 7 Summary
Understanding past climates can be helpful in understanding and determining present and future climates. Past climates can be divided into two periods: Pre-instrumental records and instrumental records. Instrumental records of sufficient spatial coverage to represent global observations started in the mid to late 1800's. Pre-instrumental records are only ancecdotal evidence such as glacier termini, memorable floods and droughts. Reconstruction of climates are called paleoclimates. The data used for the reconstruction are called proxy data. Some examples of proxy data are: tree rings, Pack rat middens, glacier termini, and archeological information. There are uncertainties that go along with using proxy data.
The Pliocene Optimum (3.3 -4.3 million years ago), the Eemian Optimum (125 - 130 years ago) and The Mid-Holocene period (5,000 - 6,000 years ago) are warm periods that are useful in understanding climates.
Figure 1 graph 1 shows temperature changes over last million years. The variations on the time scales are due to Milankovitch effects (variations of the Earth's orbital motion about the sun). Graph 2 of figure 1 shows last 11,000 years it is notable that an increase in CO2 was not apparent as in older periods. The "Little Ice Age" is included in this which might be due to a minimum in solar activity.
The National Oceanic and Atmospheric Administration (NOAA) has a lot of information on the paleoclimate period. Measurements of O18 in the layer structutr of coral is one such proxy data the NOAA website contains.
Geothermal observations from boreholes on several continents show evidence of globsal warming. Data from bore holes under 20 m are omitted due to the annual variability of the ground. Comparison of boreholes and instrumental records are in agreement of a global warming period. Other indicators are Measurement of glacier termini, which has retreated on all continents, and major droughts seen in tree rings also show a global warming trend over the last century.

Recommended Reading Materials

	Carbon dioxide Variations have a Key Role in Creating Ice Ages
	Temperature and CO2 concentration in the atmosphere over the past 400,000 years (from the Vostok ice core)
	Global Ice Volume, Deep Ocean Temperatures, and Climate Surprises
	Raymo, M. E., 1998: Glacial puzzles. Science 281, 1467-1468.
	Hall, M. J. Nicholas, and Paul J. Valdes, 1997: A GCM simulation of the climate 6000 years ago. J. Climate 10, 3-17.
	Houghton, J.T., G.J. Jenkins, J.J. Ephraums, eds, 1990: 1990 Intergovernment Panel on Climate Change, Cambridge University Press, 99-115.
	Oreskes, N., K. Shrader-Frechette, and K. Belitz, 1994: Verification, validation, and confirmation of numerical models in the earth sciences. Science 263: 641-645.

References

	Ganopolski, A., and S. Rahmstorf, 2001: Rapid changes of glacial climate simulated in a coupled climate model. Nature, 409 153-158.
	Blunier, T., and E. J. Brook, 2001: Timing of millennial-scale climate change in Anartica and Greenland during the last galcial period. Science 291, 109-112.
	Labeyrie, L., 2000: Glacial climate instability. Science 290, 1905-1907.
	Hughen, K. A., J. R. Southon, S. J. Lehman, and J. T. Overpoeck, 2000: Synchronous radiocarbon and climate shifts during the last deglaciation. Science 290, 1951-1954.
	Ivany, L. C., W. P. Patterson, and K. C. Lohmann, 2000: Cooler winters as a possible cause of mass extinctions at the Eocene/Oligocene boundary. Nature 407, 887-890.
	Braconnot, P., 2000: Paleoclimate Modeling Intercomparison Project (PMIP). Proceedings of the Third PMIP Workshop. World Meteorological Organization. 278 pp.
	NOAA Paleoclimatology Program
	Glaciology bibliography from the University of Tasmania
	Black, D. E., L. C. Peterson, J. T. Overpeck, A. Kaplan, M. N. Evans, and M. Kashgarian, 1999: Eight centuries of North Atlantic Ocean Atmosphere Variability. Science 286, 1709-1712.
	Steig, Eric J., 1999: Mid-Holocene climate change. Science 286, 1485-86.
	Katz, Miriam, E., Dorothy K. Pak, Gerald R. Dickens, and Kenneth G. Miller, 1999: The source and fate of massive carbon input during the latest paleocene thermal maximum. Science 286, 1531-1533.
	Derr, R. A., 1998: Warming's unpleasant surprise: Shivering in the greenhouse? Science 281, 183-184.
	J. A. McGowan, D. R. Cayan, and L. M. Dorman, 1998: Climate-ocean variability and ecosystem response in the northeast Pacific. Science 281, 210-217.
	Oppo, Delia, 1997: Millenial Climate Oscillations. Science 278, 1244-1245.
	Overpeck, J., K. Hughen, D. Hardy, R. Bradley, R. Case, M. Douglas, B. Finney, K. Gajewski, G. Jacoby, A. Jennings, SK. Lamoureux, A. Lasca, G. MacDonald, J. Moore, M. Retelle, S. Smith, A. Wolfe, G. Zienlinski, 1997: Artic environmental Change of the Last Four Centuries. Science 278, 1251-1256.
	Bond, Gerard, William Showers, Maziet Cheesby, Rusty Lotti, Peter Almasi, Peter deMenocal, Paul Priore, Heidi Cullen, Irka Hajdas, Georges Bonani, 1997: A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates. Science 278, 1257-1266.
	Lange, Carina B., Arndt Schimmelmann, Memorie Yasuda, and Wolfgang H. Berger, 1996: Marine varves off southern California. Scripps Institution of Oceanography- Reference Series, September 24, University of California, San Diego, 54 pp.