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Decadal-Scale Climate Cycles (Solar Influence) -- Summary
In their review of the relationship between solar activity and climate during the Holocene and portions of the last great ice age, Chambers et al. (1999) say there is "increasing evidence for solar-driven variations in earth-atmospheric processes, over a range of timescales."  In this summary, we highlight some of the recent scientific literature in support of a solar-influence on climate at decadal and multi-decadal time scales.

With a periodicity of 10 to 11 years, the Schwabe (Sunspot) Cycle is one of the more publicized decadal-scale solar cycles thought to exert a significant influence on earth's climate, the imprint of which has been postulated among proxy climate records across the globe (Chambers et al., 1999).  Other solar cycles of multi-decadal timescale include the approximate 22-year double sunspot, or Hale Cycle, and the approximate 78-year (72- to 83-year) Gleissberg Cycle.  Additionally, there may be other decadal cycles of solar origin of which we are not yet aware.  Dean et al. (2002), for example, reported finding significant decadal periodicities of 29, 32 and 42 years along with the approximate 10-year oscillation discussed above.

Rigozo et al. (2002) detected an 11-year cycle in tree-ring width data from Brazil over the period 1837-1996; and Black et al. (1999) reported finding a 12.5- to 13-year signal of climatic variability in the North Atlantic Ocean over the past 825 years.  Additionally, Dean et al. (2002) found an approximate 10-year cycle in a lake sediment core obtained from Elk Lake, Minnesota, USA, covering the past 1500 years.  Both Rigozo et al. and Dean et al. implicate the sun as the likely source of the approximately 11-year periodicity noted in their records.  Black et al. are less enthusiastic about this possibility, but they feel the sun is responsible for driving centennial-scale climate oscillations in their record.

In an analysis of tree-ring chronologies from northeastern Mongolia, Pederson et al. (2001) report "possible evidence for solar influences" on the regional hydrologic cycle.  For the period 1651-1995, they reconstructed annual precipitation and streamflow histories for this region, which upon subjection to spectral analysis revealed significant periodicities of 12 and 20-24 years that are believed to be solar-induced.

Nearby in China, Xu et al. (2002) examined plant cellulose ð18O variations in cores retrieved from peat deposits at the northeastern edge of the Qinghai-Tibetan Plateau (32 46'N, 102 30'E).  Power spectrum analyses of these data revealed multi-decadal periodicities of 79 and 88 years, "suggesting," in the words of the authors, "that the main driving force of Hongyuan climate change is from solar activities."

Neff et al. (2001) also provide evidence for a solar-induced influence on the hydrologic cycle.  For the period 9,600-6,100 years before present, they investigated the relationship between a 14C tree-ring record and a proxy record of monsoon rainfall intensity inferred from calcite 18O data obtained from a stalagmite in northern Oman.  Their investigation revealed an "extremely strong" correlation between the two data sets; and spectral analyses revealed statistically significant decadal and multi-decadal periodicities of 10.4, 26 and 89 years for the 14C tree-ring record, and 87 years for the 18O record.

Not far from Oman, Castagnoli et al. (2002) studied a 1400-year 13C record derived from the remains of the foraminifera Globigerinoides rubber, which were extracted from a sediment core located in the Gallipoli terrace of the Gulf of Taranto (3945'53"N, 1753'33"E).  Variations in the 13C of the symbiontic foraminifera reflect the effects of productivity varying with the ambient light level; and because the 13C time series can thus provide information on sea surface illumination at the time of planktonic foraminifera growth, it can be utilized as a proxy for solar radiation variability.  Similar to several of the studies referenced above, Castagnoli et al. found an approximate 11.3-year cycle in this record.  Furthermore, comparison of their data with historical aurora and sunspot time series revealed that the three records are "associable in phase" and "disclose a statistically significant imprint of the solar activity in a climate record."

Lastly, a possible multi-decadal scale solar influence on climate has been reported by Domack et al. (2001), who analyzed ocean sediment cores from the Palmer Deep, located on the inner continental shelf of the western Antarctic Peninsula, covering the past 13,000 years.  Spectral analysis of their data revealed very significant multi-decadal periodicities of 70 and 85 years, which they suggest are perhaps driven by solar variability.

In light of these several findings, it is safe to say that as more and more scientists dig into all parts of the planet to study its climatic history, they are unearthing more and more evidence for the global reality of a solar-forced, as opposed to an anthropogenically-forced, climate.

References
Black, D.E., Peterson, L.C., Overpeck, J.T., Kaplan, A., Evans, M.N. and Kashgarian, M.  1999.  Eight centuries of North Atlantic Ocean atmosphere variability.  Science 286: 1709-1713.

Castagnoli, G.C., Bonino, G., Taricco, C. and Bernasconi, S.M.  2002.  Solar radiation variability in the last 1400 years recorded in the carbon isotope ratio of a Mediterranean sea core.  Advances in Space Research 29: 1989-1994.

Chambers, F.M., Ogle, M.I. and Blackford, J.J.  1999.  Palaeoenvironmental evidence for solar forcing of Holocene climate: linkages to solar science.  Progress in Physical Geography 23: 181-204.

Dean, W., Anderson, R., Bradbury, J.P. and Anderson, D.  2002.  A 1500-year record of climatic and environmental change in Elk Lake, Minnesota I: Varve thickness and gray-scale density.  Journal of Paleolimnology 27: 287-299.

Domack, E., Leventer, A., Dunbar, R., Taylor, F., Brachfeld, S., Sjunneskog, C. and ODP Leg 178 Scientific Party.  2001.  Chronology of the Palmer Deep site, Antarctic Peninsula: A Holocene palaeoenvironmental reference for the circum-Antarctic.  The Holocene 11: 1-9.

Neff, U., Burns, S.J., Mangini, A., Mudelsee, M., Fleitmann, D and Matter, A.  2001.  Strong coherence between solar variability and the monsoon in Oman between 9 and 6 kyr ago.  Nature 411: 290-293.

Pederson, N., Jacoby, G.C., D'Arrigo, R.D., Cook, E.R. and Buckley, B.M.  2001.  Hydrometeorological reconstructions for northeastern Mongolia derived from tree rings: 1651-1995.  Journal of Climate 14: 872-881.

Rigozo, N.R., Nordemann, D.J.R., Echer, E., Zanandrea, A. and Gonzalez, W.D.  2002.  Solar variability effects studied by tree-ring data wavelet analysis.  Advances in Space Research 29: 1985-1988.

Xu, H., Hong, Y., Lin, Q., Hong, B., Jiang, H. and Zhu, Y. 2002. Temperature variations in the past 6000 years inferred from ð18O of peat cellulose from Hongyuan, China.  Chinese Science Bulletin 47: 1578-1584.