Chambers et al. (1999), for example, reviewed recent research findings in the areas of solar science and palaeoecology, concluding that the evidence indicated "a greater role for solar forcing in Holocene climate change than has previously been recognized."  They also identified a number of "multiplier effects" that can operate on solar rhythms in such a way that, in their words, "minor variations in solar activity can be reflected in more significant variations within the earth's atmosphere."

Van Geel et al. (1999) also reviewed the role of solar forcing upon climate change, finding that "there is mounting evidence suggesting that the variation in solar activity is a cause for millennial scale climate change."  Noting that "the climate system is far more sensitive to small variations in solar activity than generally believed," they concluded that this fact could mean that "the global temperature fluctuations during the last decades are partly, or completely, explained by small changes in solar radiation"

This type of thinking is confirmed by the work of Verschuren et al. (2000).  In a study of the decadal history of rainfall and drought in equatorial east Africa, they found that the three major droughts of the past 700 years "were broadly coeval with phases of high solar radiation, and the intervening periods of increased moisture were coeval with phases of low solar radiation."  Commenting on their subsequent conclusion that variations in solar radiative output "may have contributed to decade-scale rainfall variability in equatorial east Africa," Oldfield (2000) states that although this thinking is "not consistent with current views" - particularly those of the IPCC - he too agrees that the results of Verschuren et al. "provide strong evidence for a link between solar and climate variability."  Likewise, as a result of a high-resolution study of sediments in the southern Caribbean that were deposited over the past 825 years, Black et al. (1999) concluded that "small changes in solar output may influence Atlantic variability on centennial time scales."

In terms of more recent solar and climatic history, Lockwood et al. (1999) determined that, contemporaneously with the warming of the earth, the sun's total magnetic flux rose by a factor of 1.41 over the period 1964-1996 and by a factor of 2.3 since 1901.  Commenting on this finding, Parker (1999) noted the doubling of the magnetic field of the sun over the past century was accompanied by a doubling of the number of sunspots, and that one consequence of the latter phenomenon is a much more vigorous sun that is slightly brighter, which caused him to wonder "to what extent the solar brightening has contributed to the increase in atmospheric temperature and CO2."  Likewise, Broecker (1999) wonders if cycles in the solar wind might not have been responsible for the warming of the 1980s and 90s.

Other extraterrestrial phenomena have also been suggested to be playing significant roles in modulating earth's climate.  Feynman and Ruzmaikin (1999), for example, cite cosmic rays, noting that early in the past century, "the part of the troposphere open to cosmic rays of all energies was typically confined to a relatively small high-latitude region," but that "as the century progressed the size of this region increased by over 25%."  On the other hand, Deming (1999) points to changes in the influx of extraterrestrial volatile compounds, and Muller and MacDonald (1995, 1997) cite meteoroids and extraterrestrial dust.

In view of these many observations, and with respect to the hue and cry that has been raised about potential CO2-induced global warming in many governmental and political circles, Parker (1999) has warned that "it is essential to check to what extent the facts support these conclusions [about CO2 and global warming] before embarking on drastic, perilous and perhaps misguided plans for global action."  How true that statement is!

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.

Broecker, W.  1999.  Climate change prediction.  Science 283: 179.

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.

Deming, D.  1999.  On the possible influence of extraterrestrial volatiles on Earth's climate and the origin of the oceans.  Palaeogeography,Palaeoclimatology, Palaeoecology 146: 33-51.

Feynman, J. and Ruzmaikin, A.  1999.  Modulation of cosmic ray precipitation related to climate.  Geophysical Research Letters 26: 2057-2060.

Lockwood, M. Stamper, R. and Wild, M.N.  1999.  A doubling of the Sun's coronal magnetic field during the past 100 years.  Nature 399: 437-439.

Milankovitch, M.  1920.  Theorie Mathematique des Phenomenes Produits par la Radiation Solaire.  Gauthier-Villars, Paris, France.

Milankovitch, M.  1941.  Canon of Insolation and the Ice-Age Problem.  Royal Serbian Academy, Belgrade, Yugoslavia.

Muller, R.A. and MacDonald, G.J.  1995.  Glacial cycles and orbital inclination.  Nature 377: 107-108.

Muller, R.A. and MacDonald, G.J.  1997.  Spectrum of 100-kyr glacial cycle: Orbital inclination, not eccentricity.  Proceedings of the National Academy of Sciences, USA 94: 8329-8334.

Oldfield, F.  2000.  Out of Africa.  Nature 403: 370-371.

Parker, E.N.  1999.  Sunny side of global warming.  Nature 399: 416-417.

Van Geel, B., Raspopov,O.M., Renssen, H., van der Plicht, J., Dergachev, V.A. and Meijer, H.A.J.  1999.  The role of solar forcing upon climate change.  Quaternary Science Reviews 18: 331-338.

Verschuren, D., Laird, K.R. and Cumming, B.F.  2000.  Rainfall and drought in equatorial east Africa during the past 1,100 years.  Nature 403: 410-414.