Page 332 - Earth's Climate Past and Future

308 PART V • Historical and Future Climate Change

A simulation of the effect of this carbon sequestra- 6. What are the major characteristics of El Niño
tion on atmospheric CO concentrations is shown in years in comparison with years of normal
2
Figure 16–17. By this estimate, the combined effect of circulation?
the two pandemic-driven reforestation episodes may 7. How does the latitudinal distribution of proxy
explain a CO drop of at least 4 ppm. Although the
2 sites affect hemispheric temperature
likely temperature effect of a 4-ppm CO drop—
2 reconstructions?
0.05°C—seems trivial, it represents 25% of the esti-
mated northern hemisphere cooling of ~0.2°C between 8. What is the connection between sunspots and
1000–1200 and 1600–1800. If the global mean cooling solar radiation sent to Earth?
was only half as large (0.1°C), reforestation could 9. Over what length of time can large volcanic
account for half the total.
explosions alter climate?
10. How could disease have affected climate during
IN SUMMARY, the estimated cooling from 1000 years the last millennium?
ago into the Little Ice Age is small, and any or all of
several factors could have played an important
causal role. Far greater geographic coverage is Additional Resources
needed to define the global climatic response before
meaningful cause-and-effect conclusions can be Basic Reading
drawn. In contrast, no such ambiguity exists about Alverson, K. D., R. S. Bradley, and T. F. Pedersen.
the large, rapid and global warming since 1850. 2003. Paleoclimate, Global Change, and the Future.
Berlin: Springer.
Bradley, R. S., and P. D. Jones. 1992. Climate Since
A.D. 1500. London: Routledge.
Grove, J. M. 1988. The Little Ice Age. London: Methuen.
Key Terms www.igbp.net (International Geosphere-Biosphere
Progam)
Little Ice Age (p. 289) ENSO (p. 300)
www.pages-igbp.org (Past Global Changes Project)
medieval warm period La Niña (p. 301) www.ngdc.noaa.gov.paleo/global warming
(p. 290) sunspot cycle (p. 304) /paleolast.html
lichen (p. 290) faculae (p. 304)
dendroclimatology Maunder sunspot Advanced Reading
(p. 295) minimum (p. 304) Jacoby, G. C., and R. D’Arrigo. 1993. “Secular Trends
calibration interval Sporer sunspot minimum in High Northern Latitude Temperature
(p. 297) (p. 304) Reconstructions Based on Tree Rings.” Climatic
Change 15: 163–77.
El Niño (p. 300) sulfate aerosols (p. 305) Mann, M. E., R. S. Bradley, and M. K. Hughes. 1999.
Southern Oscillation “Northern Hemisphere Temperatures During the
(p. 300)
Past Millennium.” Geophysical Research Letters 26:
759–62.
North, G. A., et al. 2006. Surface Temperature
Review Questions Reconstructions for the Last 2000 Years. Washington,
DC: National Academy of Sciences.
1. What evidence indicates a cooler climate in Quinn, W. H., V. T. Neal, and S. E. Antunez de
Europe and nearby regions during the Little Ice Mayolo. 1987. “El Niño Occurrences over the Past
Age? Four and a Half Centuries.” Journal of Geophysical
Research 92: 14449–61.
2. What evidence from ice cores suggests that the
warming during the twentieth century reached Thompson, L. G., E. Mosley-Thompson, M. E.
levels unprecedented over the last 1000 years? Davis, P. N. Lin, T. Yao, M. Sdyurgerov, and M. Dai.
1993. “Recent Warming: Ice Core Evidence from
3. Why are the rings of environmentally stressed Tropical Ice Cores, with Emphasis on Central Asia.”
trees ideal for detecting climate signals? Global and Planetary Change 7: 145–55.
Wilson, R., A. Tudhope, P. Brohan, K. Briffa, T.
4. How could rising CO levels complicate
2 Osborn, and S. Tett. 2006. “Two-Hundred-Fifty
interpretations of changes recorded in tree rings?
Years of Reconstructed and Modeled Tropical
18
5. What factors influence δ O values recorded in Temperatures.” Journal of Geophysical Research 111:
corals and how? C10007, doi:10.1029/2005JC003188.