CHAPTER 19 (Moran and Morgan, 1997)

Scientists from various disciplines have accumulated information that the earth's climate has not always been the same as at present. A picture of the past climatic record is being pieced together from the instrumental record that extends approximately 100 years into the past, with various biological and geological indicators of climate that can extend the record even farther back into the past.
From these records several important conclusions can be drawn concerning the earth's climate.   The present climate is relatively mild as compared with the climatic record for over the last million years; the earth's climate continually varies with the changes extending over a wide range of time scales, ranging from a few years to millennia; past changes in the climate have had an impact upon society.
   
STUDY NOTES
CHAPTER 19

Look at Table 19.1, noting that over the last 350 million years, several large- scale glaciations have occurred, separated by warm intervals. Realize that these dates are only approximate.

Figure 19.1 -- Notice how the continent-ocean arrangement has changed over the last 200 million years.  Such long-term changes may have changed the planetary climate.

Figure 19.3 -- Locate your home state or province on this map and see where it would have been with respect to the edge of the most recent glaciation, also known as the Wisconsin glaciation. 

Figures 19.4, 19.5 and 19.6 -- Take a look at the sequence of figures showing an air temperature reconstruction over the past 150,000 years focusing upon several different geological time intervals.  Each successive figure focuses upon a shorter time interval that is closer to the present.  Specifically, Figure 19.4 provides a time sequence of air temperature for the most recent 150,000 years, covering the present warm Interglacial, the most recent Wisconsin glaciation and the previous (Eemian) Interglacial. The bottom chart focuses upon the last 18,000 years from a time close to the maximum extent of the most recent Wisconsin glaciation to the present, focusing upon the current Interglacial.  Note that the some of the warmest temperatures occurred between approximately 7000 and 5000 years ago.
 
CHAPTER 19 (Moran and Morgan, 1997)
THE CLIMATE RECORD
	In this second chapter on climatology, we focus on the climatic record and the lessons of the climatic past.  The reliable instrument-based record extends back only 100 years or so and may not include the full range of climatic variability.  For information on earlier climatic regimes, scientists rely on a wide variety of climatic indicators.  Although the sources of error in climatic reconstruction are many and formidable, scientists have pieced together a generalized understanding of the climate of the past 2 million years.  Perhaps the most important conclusions to be drawn from analysis of this record are that climate varies over a wide range of time scales, past changes in climate have impacted society, and our present climate is anomalously mild when compared to the climate of the past 1 million years.
CHAPTER OBJECTIVES
After reading this chapter, the student should be able to:
describe some of the ways whereby climatologists are able to reconstruct past climates.
explain how continental drift and mountain building may have contributed to climatic shifts in the geologic past.
sketch the principal features of the climatic record over the past 2 million years.
distinguish between a glacial climate and an interglacial climate.
explain the significance of polar amplification for future climates.
describe the climatic significance of the Climatic Optimum and the Little lee Age.
identify the individuals and events responsible for establishment of a national weather observation network.
sketch the large-scale temperature trends over the past 100 years or so.
list the principal lessons of past climatic behavior.
describe results of efforts to isolate cycles in the climatic record.
19 The Climatic Record	450
The Climatic Past	451
Lessons of the Climatic Record	462
Conclusions	467
Special Topic: Reconstructing Past Climates	452
Special Topic: Climatic Change and the Norse Greenland Tragedy	464
Key Terms	467
Summary Statements	467
Review Questions	467
Questions for Critical Thinking	468
Selected Readings	468