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Six Centuries of Climate Along the Southern Norwegian Continental Margin
Berstad, I.M., Sejrup, H.P., Klitgaard-Kristensen, D. and Haflidason, H. 2003. Variability in temperature and geometry of the Norwegian Current over the past 600 yr; stable isotope and grain size evidence from the Norwegian margin. Journal of Quaternary Science 18: 591-602.

What was done
Working with a marine sediment core retrieved from the southern Norwegian continental margin, the authors established its chronology over the past 600 years by means of 210Pb measurements and 14C dates, while they reconstructed sea surface temperatures (SSTs) from 18O data derived from the remains of the planktonic foraminifera species Neogloboquadrina pachyderma (summer temperatures) and Globigerina bulloides (spring temperatures).

What was learned
Berstad et al. say their data "suggest that the summer water temperatures in the NC [Norwegian Current] were 1-2C colder than at present most of the time between ca. AD 1400 and 1920." They also report that their data "suggest that the spring water temperature along the southern Norwegian continental margin was 1-3C colder than at present most of the time between AD 1400 and 1700." They additionally note that "the cold interval between ca. AD 1400 and 1700/1920 is coincident to the Little Ice Age (LIA)," and within this interval they report that the two coldest periods were coincident with "the solar minima of 'Maunder' and 'Sporer'." Last of all, they indicate that "the youngest 70 yr of the proxy record show the warmest temperature of the entire record, and are coincident to the 'Modern maximum' in solar irradiation."

What it means
The degree of Little Ice Age coldness derived by the authors is much more akin to that of the reconstructed temperature history of Esper et al. (2002) than it is to the temperature history of Mann et al. (1999), the latter of which gives no indication of the existence of either the Little Ice Age or the earlier Medieval Warm Period. In addition, the authors' work depicts a clear connection between the cold temperatures of the Little Ice Age and the reduced solar activity of the concomitant Maunder and Sporer solar minima, as well as between the warm temperatures of the most recent 70 years and the enhanced solar activity of the concomitant Modern solar maximum, which they clearly imply is a causative connection, as is also implied by the recent sunspot number reconstruction of Usoskin et al. (2003). Hence, the work of Berstad et al. adds to the ever-accumulating mountain of evidence that argues strongly against a human-induced cause of 20th-century warming.

In discussing the implications of their findings for the thermohaline circulation (THC) of the ocean and its role in facilitating global climate change, Berstad et al. forthrightly express their opinion that the Little Ice Age was of global extent, which is something else that is vociferously denied by climate alarmists who revere the temperature history of Mann et al. Berstad et al. note, for example, that "the evidence of the LIA as a global event, as documented in changes in the atmospheric circulation in the Southern (Kreutz et al., 1997) and Northern Hemisphere (O'Brian et al., 1995), suggests that large-scale changes in ocean and atmospheric circulation were involved," additionally stating that "the findings of increased deep-water formation in the Southern Ocean during the LIA by Broecker (1999, 2001) and Broecker et al. (1999) further support this interpretation of variability in the THC." Hence, they deal yet another blow to the temperature reconstruction of Mann et al.

In summation, the work of Berstad et al. suggests that the Little Ice Age was (1) real, (2) really cold, and (3) solar-induced, while they report corroborating evidence for its global extent. In addition, their work suggests that the Modern Warm Period is (1) real, (2) the warmest period of the past six centuries, and (3) solar-induced. CO2 figures nowhere in the mix.

Broecker, W.S. 1999. Was a change in thermohaline circulation responsible for the Little Ice Age? Proceedings of the National Academy of Science of the United States of America Online 4: 1339-1342.

Broecker, W.S. 2001. Was the Medieval Warm Period global? Science 291: 1497-1499.

Broecker, W.S., Sutherland, S. and Peng, T.H. 1999. A possible 20th-century slowdown of Southern Ocean deep water formation. Science 286: 1132-1135.

Esper, J., Cook, E.R. and Schweingruber, F.H. 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science 295: 2250-2253.

Kreutz, K.J., Mayewski, P.A., Meeker, M.S., Twickler, M.S., Whitlow, S.I. and Pittalwala, I.I. 1997. Bipolar changes in atmospheric circulation during the Little Ice Age. Science 277: 1294-1296.

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.

O'Brian, S.R., Mayewski, P.A., Meeker, I.D., Meese, D.A., Twickler, M.S. and Whitlow, S.I. 1995. Complexity of Holocene climate as reconstructed from a Greenland ice core. Science 270: 1962-1964.

Usoskin, I.G., Solanki, S.K., Schussler, M., Mursula, K. and Alanko, K. 2003. Millennium-scale sunspot number reconstruction: Evidence for an unusually active sun since the 1940s. Physical Review Letters 91: 10.1103/PhysRevLett.91.211101.

Reviewed 21 January 2004