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Errors in Solar Activity and Terrestrial Climate Data
Damon, P.E. and Laut, P.  2004.  Pattern of strange errors plagues solar activity and terrestrial climatic data.  EOS, Transactions, American Geophysical Union 85: 370, 374.

What was done
The authors report what they describe as errors made by Friis-Christensen and Lassen (1991), Svensmark and Friis-Christensen (1997), Svensmark (1998) and Lassen and Friis-Christensen (2000) in their presentation of solar activity data, which they correlated with terrestrial temperature data in a number of papers that appeared to explain most of the temperature variability of the earth over the past 140 years as arising from solar variability.

What was learned
The Danish scientists' error, in the words of Damon and Laut, of "adding to a heavily smoothed ('filtered') curve, four additional points covering the period of global warming, which were only partially filtered or not filtered at all," led to an apparent dramatic increase in solar activity over the last quarter of the 20th century that closely matched the equally dramatic rise in temperature manifest by the Northern Hemispheric temperature reconstruction of Mann et al. (1998, 1999) over the same period.  With the acquisition of additional solar activity data in subsequent years, however, and with what Damon and Laut call the proper handling of the numbers, the late 20th-century dramatic increase in solar activity totally disappears.

What it means
The new result, to quote Damon and Laut, means that "the sensational agreement with the recent global warming, which drew worldwide attention, has totally disappeared."  In reality, however, it is only the agreement with the last quarter-century of the Mann et al. hockeystick temperature history that has disappeared; and this new disagreement is most welcome, for the Mann et al. temperature reconstruction is likely vastly in error over this stretch of time.  Indeed, our website is replete with numerous reviews of studies that have found the late 1930s and early 1940s to have been the warmest period of the past century; and these temperature reconstructions now take the place of the Mann et al. curve in displaying "sensational agreement" with the new-and-improved solar activity history produced by Damon and Laut, which also peaks in the late 1930s and early 1940s.  We applaud them for helping to bring this important new fact to the attention of the world.

Friis-Christensen, E. and Lassen, K.  1991.  Length of the solar cycle: An indicator of solar activity closely associated with climate.  Science 254: 698-700.

Lassen, K. and Friis-Christensen, E.  2000.  Reply to "Solar cycle lengths and climate: A reference revisited" by P. Laut and J. Gundermann.  Journal of Geophysical Research 105: 27,493-27,495.

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.

Svensmark, H.  1998.  Influence of cosmic rays on Earth's climate.  Physical Review Letters 22: 5027-5030.

Svensmark, H. and Friis-Christensen, E.  1997.  Variation of cosmic ray flux and global cloud coverage - A missing link in solar-climate relationships.  Journal of Atmospheric and Solar-Terrestrial Physics 59: 1225-1232.

Reviewed 13 October 2004