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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 11, NUMBER 9, SEPTEMBER 1998

PROFESSIONAL PUBLICATIONS...
OF GENERAL INTEREST

Item #d98sep3

“Contribution of Hurricanes to Local and Global Estimates of Air-sea Exchange of CO₂,” N. R. Bates, A. H. Knap, and A. F. Michaels, Nature 395, 58-61 (Sept. 3, 1998).

The Sargasso Sea was sampled before and after hurricane Felix in 1995. Measurements of surface seawater temperature showed a cooling of about 4°C that lasted 2 to 3 weeks. At the same time, the seawater partial pressure of CO₂ decreased by almost 60 matm. From these figures, an increase of almost 55% was estimated in the summertime efflux of CO₂ into the atmosphere over this part of the Sargasso Sea. Extrapolating this rate to all hurricanes led to an estimate that those storms contribute 0.04 to 0.51 Pg C to the atmosphere per year. Such effluxes would exert an important influence on ocean-atmosphere CO₂ exchange and on the annual variability of CO₂ fluxes over the subtropical oceans.

Item #d98sep4

“Global Variations in Droughts and Floods: 1900-1995,” A. Dai, K. E. Trenberth, and T. R. Karl,Geophysical Research Letters 25 (17), 3367-3370 (Sept. 1, 1998).

Regions of the Earth experiencing unusually wet or dry conditions have increased during the past 30 years. The overall trend is small. Increases were found in drought-affected areas in Africa and Asia and in both extremely wet and extremely dry areas in Europe and the United States. These changes were particularly noticeable in regions affected by El Niño. These findings are in accord with predictions of climate researchers, who say that global warming could promote drought in some areas and extreme wetness in others.

Item #d98sep5

“Key Issues in Global Change,” K. Y. Kondratyev (nansen@sovam.com),Tiempo No. 28, http://www.cru.uea.ac.uk/tiempo/floor0/recent/issue28/index.htm (June 1998); this article also appeared as “Key Issues of Global Change at the End of the Second Millennium,” European Geophysical Society Newsletter No. 63 (June 1997).

Kondratyev lays out five principles that, he believes, should underlie all global-change research: (1) The Earth is a unique planet in the solar system in that life exists on it in the form of biota. (2) Homo sapiens is one of the species of the biota; if that species’ principal aim were not to support the global biosphere, it would be impossible to develop sustainment. (3) Simple approximations indicate that a stable biosphere can be guaranteed only if not more than 1% of the biospheric resources are used; at present, this number is close to 10%. (4) Parity in the use of existing resources by the developed and the developing countries must be established through relevant international agreements. (5) More efforts are necessary to develop clean and efficient technologies, minimize the use of energy and raw materials, and reduce the global population.

Item #d98sep6

“A Neoproterozoic Snowball Earth,” P. F. Hoffman (hoffman@eps.harvard.edu), G. P. Halverson, and D. P. Schrag, Science 281, 1342-1346 (Aug. 28, 1998).

Studies of carbon-isotope anomalies in Neoproterozoic carbonate rocks in glacial deposits in Namibia were combined with estimates of thermal subsidence history. The results suggested a multimillion-year-long collapse of biological productivity in the surface ocean. An explanation of such a collapse is proffered in the form of a global glaciation (i.e., a snowball Earth). The postulated snowball is expected to have ended relatively abruptly under the influence of a massive greenhouse effect produced by atmospheric carbon dioxide concentrations about 350 times those seen today. Such CO₂ levels are attributed to volcanic outgassing. These high CO₂ concentrations are expected to have rapidly warmed the Earth to extreme greenhouse conditions. Absorption of the atmospheric carbon dioxide by the ocean would then have resulted in the rapid precipitation of calcium carbonate producing the cap carbonate rocks that are observed globally today.

Item #d98sep7

“Asynchrony of Antarctic and Greenland Climate Change During the Last Glacial Period,” T. Blunier et al., Nature 394, 739-743 (Aug. 20, 1998).

Rapid temperature oscillations of about 15° C called Dansgaard-Oeschger events occurred in Greenland about every 3000 years during the last glaciation. Examination of the Antarctic temperature record for the same general period indicates analogous warming/ cooling events. Ice cores from central Greenland (GRIP) and west Antarctica (Byrd) were compared in detail to determine whether these temperature variations occurred simultaneously in the two hemispheres or led in one hemisphere or the other. Variation in the isotopic distribution of oxygen in the ice cores was used to determine the temperature records for each site. Correlation of the cores from the two sites was made possible by maintaining consistency between their respective 10Be peaks and methane data. The results indicated that two Greenland warming events that occurred 36 thousand and 45 thousand years ago lagged behind their Antarctic counterparts (of much lower magnitude) by more than a thousand years. Moreover, on the average, Greenland climate changes lagged behind Antarctic changes by 1 to 2.5 thousand years during the period 47,000 to 23,000 BP. Thus, the ocean must be the connecting medium because an atmospheric link would produce a quicker connection.

Item #d98sep8

“A 3000-Year Climatic Record from Biogenic Silica Oxygen Isotopes in an Equatorial High-Altitude Lake,” M. Rietti-Shati, A. Shemesh, and W. Karlen,Science 281, 980-982 (Aug.14, 1998). Biogenic opal was collected from a glacial lake on Mount Kenya in East Africa. The oxygen isotopes of those opal samples were analyzed to provide a record of the temperature when the opal was formed, which ranged from 1200 to 4200 years ago. The temperature record shows long-term variations, but it also shows short-term fluctuations with durations on order of centuries. The long-term variations are attributed to changes in lake temperature, and the short-term fluctuations to changes in the temperature of the glacial meltwater entering the lake. Specifically, the data indicate the occurrence of a period that was warmer than the current climate in Equatorial East Africa from 2300 to 1500 years before the present. Other temperature records from Africa and other continents indicate a similar warm period at that time.