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Solar Variability and Earth's Climate
Beer, J., Vonmoos, M. and Muscheler, R. 2006. Solar variability over the past several millennia. Space Science Reviews 125: 67-79.

What was done
The authors review the current state of knowledge relative to solar variability and its possible effects on earth's climate.

What was learned
There are two types of variability related to the flux of solar radiation incident on the earth. The first type, according to Beer et al., "is due to changes in the orbital parameters of the earth's position relative to the sun induced by the other planets," which arises from gravitational perturbations that "induce changes with characteristic time scales in the eccentricity (~100,000 years), the obliquity (angle between the equator and the orbital plane, ~40,000 years) and the precession of the earth's axis (~20,000 years)." The second type of variability in earth-incident solar radiation is due to variability within the sun itself; and it is this subject that occupies the bulk of their review.

Direct observations of total solar irradiance above the earth's atmosphere have only been made over the past quarter century, while observations of sunspots have been made and recorded for approximately four centuries. In between the time scales of these two types of measurements fall neutron count rates and aurora counts. Therefore, 10Be and other cosmogenic radionuclides (such as 14C) stored in ice and sediment cores and tree rings currently provide our only means of inferring solar irradiance variability on a millennial time scale; and as reported by Beer et al., who have studied the subject in depth, these cosmogenic nuclides "clearly reveal that the sun varies significantly on millennial time scales and most likely plays an important role in climate change," especially within this particular time domain.

What it means
In reference to their 10Be-based derivation of a 9,000-year record of solar modulation, Beer et al. note that its "comparison with paleoclimatic data provides strong evidence [our italics] for a causal relationship between solar variability and climate change." And so it does, as may be verified by perusing the many items we have archived under the headings of Solar Effects (Millennial-Scale Cycles and Centennial-Scale Cycles) in our Subject Index.

Reviewed 16 May 2007