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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 7, JULY 1998

PROFESSIONAL PUBLICATIONS...
PALEOCLIMATOLOGY

Item #d98jul100

"Deep-Sea Coral Evidence for Rapid Change in Ventilation of the Deep North Atlantic 15,400 Years Ago," J.F. Adkins (Geochem. 62, Lamont-Doherty Earth Observ., Rte. 9W, Palisades NY 10964),Science, 280(5364), 725-728, May 1, 1998.

Isotopic analysis of coral samples shows that the deep ocean changed on decadal-centennial time scales during more rapid changes in the surface ocean and the atmosphere.

Item #d98jul101

Two related items in Science, 279(5355), Feb. 27, 1998:

"Sea Floor Records Reveal Interglacial Climate Cycles," R.A. Kerr, 1304-1305. New ocean sediment records described in the next paper show that the Earth's climate varies on regular cycles lasting from 1200 to 6000 years, in glacial and interglacial periods alike. This comment explains why the finding offers a mixed message of reassurance and warning about the future of our own climate.

"Abrupt Climate Events 500,000 to 340,000 Years Ago: Evidence from Subpolar North Atlantic Sediments," D.W. Oppo (Dept. Geol. & Geophys., Woods Hole Oceanog. Inst., Woods Hole MA 02543), J.F. McManus, J.L. Cullen, 1335-1341.

Item #d98jul102

"Timing of Abrupt Climate Change at the End of the Younger Dryas Interval from Thermally Fractionated Gases in Polar Ice," J.P. Severinghaus (Grad. Sch. Oceanog., Univ. Rhode Island, Narragansett RI 02882), T. Sowers et al.,Nature, 391(6663), 141-146, Jan. 8, 1998.

The fractionation of nitrogen and argon isotopes in Greenland ice indicates a rapid warming that coincides with the onset of a prominent rise in atmospheric methane concentration. This indicates that the warming was synchronous (within a few decades) over a region at least hemispheric in extent.

Item #d98jul103

Two related items in Science, 278(5342), Nov. 21, 1997:

"Carbon Dioxide and Vegetation," G.D. Farquhar (Biolog. Sci., Australian Natl. Univ., Canberra 2601, Australia; e-mail: farquhar@rsbs.anu.edu.au), 1411. Discusses the research implications of the following paper.

"Impact of Lower Atmospheric Carbon Dioxide on Tropical Mountain Ecosystems," F. A. Street-Perrott (Dept. Geog., Univ. Wales, Swansea SA2 8PP, UK), Y. Huang et al., 1422-1426. Carbon isotope samples taken over a range of altitudes in Africa show that carbon limitation due to lower ambient CO₂ had a significant impact on the distribution of forest on the tropical mountains, in addition to climate. Tree line elevation should not be used to infer paleotemperatures.

Item #d98jul104

"A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates," G. Bond (Lamont-Doherty Earth Observ., Rte. 9W, Palisades NY 10964; e-mail: gcb@lamont.ldgo.columbia.edu), W. Showers et al.,Science, 278(5341), 1257-1266, Nov. 14, 1997.

Evidence from North Atlantic deep sea cores reveals abrupt climatic shifts during the Holocene, the period since the last ice age conventionally thought to have been quiescent. These and similar but stronger fluctuations that occurred during the last ice age have a cyclicity of 1470 (plus or minus 500) years. The Little Ice age appears to be the most recent cold phase in the series of such cycles. However, whether the climatic amelioration since the Little Ice Age marks the onset of a warming phase of this natural cycle is unclear; brief warmings often punctuated the cold phases of the millenial-scale fluctuations.

Item #d98jul105

Two related items in Nature, 390(6656), Nov. 13, 1997:

"Sudden end of an Interglacial," S. Lehman (INSTAAR, Campus Box 450, Univ. Colorado, Boulder CO 80309; e-mail: lehmans@spot.colorado.edu), 117-119. Evidence in the following paper of sudden climate shifts only adds to the concern about the potential impact of increased greenhouse forcing on the oceans.

"Variability of the North Atlantic Thermohaline Circulation During the Last Interglacial Period," J.F. Adkins (Dept. Earth Sci., Mass. Inst. Technol., Cambridge MA 02139), E.A. Boyl et al., 154-158. High-resolution ocean sediment records from the Bermuda Rise indicate that the last interglacial, like the present one, was relatively stable, but it began and ended with abrupt changes in deep-water flow on a time scale of less than 400 years.

Item #d98jul106

"The Holocene-Younger Dryas Transition Recorded at Summit, Greenland," K.C. Taylor (Desert Res. Inst., Univ. Nevada, Reno NV 89506), P.A. Mayewski et al.,Science, 278, 825-827, Oct. 31, 1997.

High-resolution analyses of ice cores shows that the transition occurred over a 40-year period, mostly in a series of steps with duration of about five years. Changes in atmospheric water vapor are likely to have played a large role in the climate transition.

Item #d98jul107

Two related items in Nature, 388(6645), Aug. 28, 1997:

"Influence of CO₂ Emission Rates on the Stability of the Thermohaline Circulation," T.F. Stocker (Phys. Inst., Univ. Bern, Switz.; e-mail: stocker@climate.unibe.ch), A. Schmittner, 862-865. The thermohaline circulation of the North Atlantic Ocean, which has a large influence on climate and CO₂ uptake, is sensitive to the level of atmospheric CO₂. This study uses a simple coupled atmosphere-ocean model to show that the circulation also depends on the rate of change of CO₂. A modeled increase to 750 parts per million by volume over the next 100 years, corresponding roughly to today's growth rate, leads to a permanent shutdown of the thermohaline circulation. But if CO₂ increases more slowly, the circulation merely slows down. This sensitivity to the rate of change of CO₂ has potentially important implications for the choice of future CO₂-emission scenarios.

"Risk of Sea-Change in the Atlantic," S. Rahmstorf (Potsdam Inst. for Clim. Impact Res. [PIK], POB 60 12 03, D-14412 Potsdam, Ger.; e-mail: rahmstorf@pik-potsdam.de), 825-826. A research comment on the previous article, which serves as a reminder that swift action is needed to reduce the risk of unwelcome climatic surprises.

Item #d98jul108

"A Warm Future in the Past," W.R. Howard (Coop Res. Ctr. Antarctic, Univ. Tasmania, GPO Box 252-80, Hobart, Tasmania 7001, Australia),Nature, 388(6641), 418-419, July 31, 1997.

A period 423,000 to 362,000 years ago called stage 11 is a useful analog for today's climate, because the Earth's orbital geometry was similar to today's. This article discusses a recent symposium at the Spring 1997 AGU meeting on that period, which may provide insight into the response of the natural carbon cycle to future climate change.

Item #d98jul109

"The International Tree-Ring Data Bank: An Enhanced Global Database Serving the Global Scientific Community," H.D. Grissino-Mayer (Lab. Tree-Ring Res., Univ. Arizona, Tucson AZ 85721), H.C. Fritts,The Holocene, 7(2), 235-238, June 1997.

The data bank was created in 1974 and is housed in Boulder, Colorado. It holds 3275 tree-ring chronologies and 2804 tree-ring measurement data sets from over 1500 sites, contributed by 139 researchers worldwide. The data are freely available to all scientists. Future efforts will focus on increasing the worldwide coverage.

Item #d98jul110

"Younger Dryas Research and Its Implications for Understanding Abrupt Climate Change," D.E. Anderson (Sch. Geog., Univ. Oxford, Mansfield Rd., Oxford OX1 3TB, UK),Prog. Phys. Geog., 21(2), 230-249, June 1997.

Reviews studies on the Younger Dryas, the final phase of cold, glacial conditions preceding the Holocene, and on the North Atlantic thermohaline circulation (THC). The sensitivity of the THC to changes in freshwater flux is still unknown, and this poses problems for predicting future responses. With predicted increases in freshwater input to the North Atlantic resulting from increased CO₂, a future shift in the THC is a possibility; further research on this sensitivity is imperative.