How does rising atmospheric CO2 affect marine organisms?

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A 500-Year Temperature History of a Site on the North Coast of Sicily
Silenzi, S., Antonioli, F. and Chemello, R. 2004. A new marker for sea surface temperature trend during the last centuries in temperate areas: Vermetid reef. Global and Planetary Change 40: 105-114.

What was done
For a site on the northwest coast of Sicily near Capo Gallo promontory, the authors "present new data on sea climate trend fluctuations that could be interpreted as Sea Surface Temperature (SST) variations, recorded on Vermetid (Dendropoma petraeum) reefs, by means of [oxygen] isotopic analysis."

What was learned
The authors' data clearly depict the existence of the Little Ice Age (LIA), with a "temperature variation of about delta T = 1.99 0.37 C between the LIA and present day." Of this period, they write that "Watanabe et al. (2001) report that 'seawater temperature records from marine biogenic carbonate including coral and foraminifera all indicate that tropical ocean temperatures were lower by anywhere from 0.5 to 5 during LIA (Druffel, 1982; Glynn et al., 1983; Dunbar et al., 1994; Linsley et al., 1994; Keigwin, 1996; Winter et al., 2000) with the vast majority of studies indicating a 1-2C change'."

Following the LIA, the data of Silenzi et al. reveal what they call "the warming trend that characterized the last century." However, they note that "this rise in temperature ended around the years 1930-1940 AD, and was followed by a relatively cold period between the years 1940 and 1995." Their data also indicate that in the early to mid-1500s, SSTs were warmer than they are currently, as has also been found by Keigwin (1996) and, most recently, by McIntyre and McKitrick (2003).

What it means
The results of this study disagree with the Northern Hemispheric temperature history of Mann et al. (1998, 1999) in three major ways. First, they indicate that the Little Ice Age was significantly colder than what Mann et al. suggest. Second, they do not show any sign of the dramatic late-20th century warming claimed by Mann et al. Third, they indicate that temperatures in the early to mid-1500s were warmer than they are currently, whereas Mann et al. claim it is currently warmer than it has been at any time over the past millennium or two (Mann and Jones, 2003). Hence, this study takes its place as one of the many comprising the mountain of evidence that will one day result in the unequivocal rejection of the false temperature history of Mann et al.

Druffel, E.M. 1982. Banded corals: change in oceanic carbon-14 during the Little Ice Age. Science 218: 13-19.

Dunbar, R.B., Wellington, G.M., Colgan, M.W. and Peter, W. 1994. Eastern Pacific sea surface temperature since 1600 AD: the 18O record of climate variability in Galapagos corals. Paleoceanography 9: 291-315.

Glynn, P.W., Druffel, E.M. and Dunbar, R.B. 1983. A dead Central American coral reef tract: possible link with the Little Ice Age. Journal of Marine Research 41: 605-637.

Keigwin, L.D. 1996. The little ice age and medieval warm period in the Sargasso Sea. Science 274: 1504-1508.

Linsley, B.K., Dunbar, R.B., Wellington, G.M. and Mucciarone, D.A. 1994. A coral-based reconstruction of Intertropical Convergence Zone variability over Central America since 1707. Journal of Geophysical Research 99: 9977-9994.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1998. Global-scale temperature patterns and climate forcing over the past six centuries. Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.

Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.

McIntyre, S. and McKitrick, R. 2003. Corrections to the Mann et al. (1998) proxy data base and Northern Hemispheric average temperature series. Energy & Environment 14: 751-771.

Watanabe, T., Winter, A. and Oba, T. 2001. Seasonal changes in sea surface temperature and salinity during the Little Ice Age in the Caribbean Sea deduced from Mg/Ca and 18O/16O ratios in corals. Marine Geology 173: 21-35.

Winter, A., Ishioroshi, H., Watanabe, T., Oba, T. and Christy, J.R. 2000. A two-to-three degree cooling of Caribbean Sea surface temperatures during the Little Ice Age. Geophysical Research Letters 27: 3365-3358.

Reviewed 4 February 2004