National Academies Press: OpenBook

Effects of Past Global Change on Life (1995)

Chapter: SUMMARY OF TROPICAL CLIMATE EXTREMES

« Previous: MODEL-DERIVED TROPICAL TEMPERATURES
Suggested Citation:"SUMMARY OF TROPICAL CLIMATE EXTREMES." National Research Council. 1995. Effects of Past Global Change on Life. Washington, DC: The National Academies Press. doi: 10.17226/4762.
×
Page 112

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

TROPICAL CLIMATE STABILITY AND IMPLICATIONS FOR THE DISTRIBUTION OF LIFE 112 tropical temperatures too high for many organisms. Crowley (1991) calls attention to the issue of tropical temperatures during warm climates in general. As stated earlier, a wide variety of atmospheric GCMs (Washington and Meehl, 1984; Manabe and Bryan, 1985; Hansen et al., 1988; Schlesinger, 1989) predict increased tropical sea-surface temperatures for a doubling of carbon dioxide. Schlesinger and Mitchell (1987) illustrate results from models of the National Center for Atmospheric Research (NCAR), the NOAA Geophysical Fluid Dynamics Laboratory, and the Goddard Institute for Space Studies. In each, the doubling of carbon dioxide resulted in a 2 to 4°C increase in tropical sea-surface temperatures. In the geologic record, tropical warming may be the product of changes in carbon dioxide (e.g., as proposed by Berner et al., 1983; Berner, 1990), and by changes in geography. Barron and Washington (1985) specifically examine the warmth of the mid-Cretaceous utilizing a version of the NCAR Community Climate Model. The specification of Cretaceous geography without polar ice resulted in a 2 to 3°C increase in tropical sea-surface temperatures. However, the global warming was insufficient to explain most of the geologic observations at higher latitudes. The addition of four times the present-day atmospheric carbon dioxide concentration produced a climate with temperatures high enough to satisfy most geologic observations. In this case, tropical sea surface temperatures are more than 5°C higher than present-day values (Figure 6.2). Similar experiments with a full seasonal cycle using the GENESIS GCM also produced tropical temperature increases of 3 to 4°C for 4´ present day CO2 (Barron et al., 1993b). These model predictions for the mid-Cretaceous are within the interpretations proposed based on the oxygen isotopic data. Although still limited in scope, the results from comprehensive climate models supported by the oxygen isotopic data provide the best case for a working hypothesis on tropical temperature variation during Earth history. Figure 6.2 Cretaceous zonally averaged surface temperature (K) limits in comparison with Cretaceous modelderived surface temperatures for the geography and geography plus CO2 quadrupling experiments EVIDENCE FOR TROPICAL SALINITY DIFFERENCES Much of the discussion of tropical climates has centered on temperature analyses. However, salinity is also a major control on the distribution of organisms. Unfortunately, little or no information on salinity has been derived from either geochemical or biological paleoclimatic indices. Only recently (Barron and Peterson, 1989; 1990) have ocean GCM been utilized to derive ocean salinity maps for different periods in Earth history that provide a basis for examining the potential importance of salinity variations. Figure 6.3 illustrates salinity predictions for the mid-Cretaceous, Paleocene, Eocene, Miocene, and Present day continental geometries utilizing the ocean GCM. Substantial ranges in salinity are projected, largely as a result of changes in the area of the oceans within the subtropical arid zone, the restriction of the tropical and subtropical basins and the degree of warmth. In the Eocene and the mid-Cretaceous, salinity predictions for substantial areas of the subtropics exceed 38 parts per thousand (%o) and a range of several parts per thousand is evident within the tropics throughout the Cenozoic. The results from the ocean GCM studies are highly preliminary, but suggest that large salinity variations are also plausible in response to climate and geographic changes. The salinity variations projected are sufficient to influence the distribution of organisms. Interestingly, the high salinities for some time periods (e.g., the Eocene) would also serve to increase the isotopic temperature for the tropics by approximately 2°C (J. Zachos and L. Sloan, personal communication). SUMMARY OF TROPICAL CLIMATE EXTREMES In summary, a combination of model sensitivity studies and isotopic temperature analyses supports the conclusion that the tropics have been subjected to substantial climatic variation during Earth history. A temperature range of 3 to 5°C and a salinity range of several parts per thousand are reasonable hypotheses for variation within the tropics during the Mesozoic and Cenozoic. The case for warmer, and potentially more saline, tropical and subtropical oceans presents interesting prospects for biogeography and the response of tropical organisms to global warming. This case, perhaps exemplified by the mid-Cretaceous, is par

Next: CLIMATE TOLERANCES OF TROPICAL ORGANISMS »
Effects of Past Global Change on Life Get This Book
×
Buy Hardback | $65.00 Buy Ebook | $49.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

What can we expect as global change progresses? Will there be thresholds that trigger sudden shifts in environmental conditions—or that cause catastrophic destruction of life?

Effects of Past Global Change on Life explores what earth scientists are learning about the impact of large-scale environmental changes on ancient life—and how these findings may help us resolve today's environmental controversies.

Leading authorities discuss historical climate trends and what can be learned from the mass extinctions and other critical periods about the rise and fall of plant and animal species in response to global change. The volume develops a picture of how environmental change has closed some evolutionary doors while opening others—including profound effects on the early members of the human family.

An expert panel offers specific recommendations on expanding research and improving investigative tools—and targets historical periods and geological and biological patterns with the most promise of shedding light on future developments.

This readable and informative book will be of special interest to professionals in the earth sciences and the environmental community as well as concerned policymakers.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!