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The Search for Trends in Total Solar Irradiance
Willson, R.C. and Mordvinov, A.V.  2003.  Secular total solar irradiance trend during solar cycles 21-23.  Geophysical Research Letters 30: 10.1029/2002GL 016038.

What was done
The authors analyzed total solar irradiance (TSI) data sets obtained from different satellite platforms over the period 1978-2002, attempting to resolve various small but important inconsistencies among them.

What was learned
In view of the many complexities involved in the enterprise, a general conclusion was that "construction of TSI composite databases will not be without its controversies for the foreseeable future."  (Sounds a lot like the CO2-climate debate, doesn't it?)  The "most interesting" specific result, in the estimation of the authors, was the confirmation of a +0.05%/decade trend between the minima separating solar cycles 21-22 and 22-23, which they say "appears to be significant."

What it means
The authors state that the finding of the 0.05%/decade minimum-to-minimum trend "means that TSI variability can be caused by unknown mechanisms other than the solar magnetic activity cycle," which means that "much longer time scales for TSI variations are therefore a possibility," which they say "has obvious implications for solar forcing of climate."  Specifically, it means there could well be as-yet-undiscovered long-term variations in total solar irradiance of a magnitude that could possibly explain centennial-scale climate variability, which Bond et al., 2001 have already demonstrated to be related to solar activity, as well as the millennial-scale climatic oscillation that pervades both glacial and interglacial periods for essentially as far back in time as the eye of proxy climate science can see (Oppo et al., 1998; Raymo et al., 1998).

Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G.  2001.  Persistent solar influence on North Atlantic climate during the Holocene.  Science 294: 2130-2136.

Oppo, D.W., McManus, J.F. and Cullen, J.L.  1998.  Abrupt climate events 500,000 to 340,000 years ago: Evidence from subpolar North Atlantic sediments.  Science 279: 1335-1338.

Raymo, M.E., Ganley, K., Carter, S., Oppo, D.W. and McManus, J.  1998.  Millennial-scale climate instability during the early Pleistocene epoch.  Nature 392: 699-702.

Reviewed 2 July 2003