Page 312 - Earth's Climate Past and Future

288 PART V • Historical and Future Climate Change

Key Terms

savanna hypothesis Black Sea flood
(p. 276) hypothesis (p. 282)
variability selection overkill hypothesis
hypothesis (p. 278) (p. 284)
Fertile Crescent (p. 280) early anthropogenic
diluvial hypothesis hypothesis (p. 285)
(p. 282)

Review Questions

1. What are the problems with the savanna
hypothesis of human evolution?

2. Why is it difficult to determine whether or not
climate affected human evolution?
3. Why is the climatic explanation of the large-
mammal extinctions 12,500 years ago suspect?
FIGURE 15-17 Is a glaciation overdue? Model simulations 4. Why are natural explanations for the CO and
with present insolation but with CO and CH concentrations 2
2 4 CH increases in recent millennia suspect?
lowered to the natural levels they reached during previous 4
interglaciations produce year-round snow cover (incipient
glaciation) in northern Eurasia and North America. (Adapted Additional Resources
from S. J. Vavrus, W. F. Ruddiman, and J. E. Kutzbach, “Climate
Model Test of the Early Anthropogenic Hypothesis Using a Faces of Earth (DVD set, 2007). Discovery
Coupled Atmosphere-Slab Ocean Model,” Quaternary Science Communications and American Geological Institute.
Reviews, in review.)
Basic Reading
Diamond, J. 1997. Guns, Germs and Steel. New York:
regions at high northern latitudes would retain snow Norton.
throughout the year (Figure 15–17). Because snow that Roberts, N. 1998. The Holocene. Oxford: Blackwell.
persists through the summer and remains in autumn Ruddiman, W. F. 2005. Plows, Plagues and Petroleum.
forms a base that can be added to during the following Princeton, NJ: Princeton University Press.
winter, simulating year-round snow cover is equivalent Ryan, W., and W. Pitman. 1998. Noah’s Flood. New
to simulating a state of incipient glaciation. Different York: Simon & Schuster.
models put year-round snow in different regions,
including the Arctic margins of Canada and Russia, Advanced Reading
Baffin Island northeast of the Canadian mainland, and Curtis, J. H., D. A. Hodell, and M. Brenner. 1996.
the northern Rockies. These model-to-model differ- “Climatic Variability on the Yucatán Peninsula
ences are the result of differences in the feedback (Mexico) During the Past 3500 Years, and
processes included, particularly vegetation/albedo feed- Implications for Maya Cultural Evolution.”
back and ocean dynamics. Quaternary Research 46: 37–47.
Despite the differences, all the simulations agree Martin, P. S., and R. G. Klein. 1984. Quaternary
that a new glaciation would be underway now if humans Extinctions. Tucson: University of Arizona Press.
had not interfered with the natural operation of the cli- Potts, R. 1997. Humanity’s Descent: The Consequences of
mate system. Each of the new ice caps scattered across Ecological Instability. New York: Avon.
the north would probably be relatively small in size, but Ruddiman, W. F. 2003. “The Anthropogenic
their aggregate area might be considerable, perhaps Greenhouse Era began thousands of Years Ago.”
equivalent to that of modern Greenland ice sheet. Climatic Change 61: 261–93.