Adding the the recent spate of papers showing that - surprise - the Sun has much, much more to do with climate change than previously thought, the respected German Physics Journal Annalyn der Physik recently published a paper analyzing solar irradiance data from 1905 to 2008 which finds cosmic rays modulated by solar activity cause a large portion of atmospheric aerosols (clouds) with profound effects on climate [see the cosmic ray theory of Svensmark et al]. The paper concludes, "The contribution of the active sun, indirectly via cosmic rays, to global warming appears to be much stronger than the presently accepted [IPCC] upper limit of 1/3."
Strong signature of the active Sun in 100 years of terrestrial insolation data
Werner Weber, Institut fur Physik, TU Dortmund, Otto-Hahn-Straße 4, 44221 Dortmund, Germany
Abstract: Terrestrial solar irradiance data of the Smithsonian Astrophysical Observatory from 1905 to 1954 and of Mauna Loa Observatory from 1958 to 2008 are analyzed. The analysis shows that, with changing solar activity, the atmosphere modifies the solar irradiance on the percentage level, in all likelihood via cosmic ray intensity variations produced by the active sun. The analysis strongly suggests that cosmic rays cause a large part of the atmospheric aerosols. These aerosols show specific absorption and scattering properties due to an inner structure of hydrated ionic centers, most probably of O− and O+ produced by the cosmic rays.
Introduction: In recent years, it has become clear from satellite data  that the total solar irradiance (TSI) varies only in the range of 0.1 % with solar activity. At the top of the atmosphere (TOA), the average TSI is ≈ 1360 Watt per m2 of normal incidence, and the solar variations are of order 1–2 Watt/m2 or 0.25–0.5 W per m2 of earth’s surface. For comparison, the anthropogenic warming due to CO2 increase is assessed to ≈ 2 W/m2 . Thus, the IPCC estimates the solar contribution to climate change to at most 1/3 of the total .
On the other hand, there are observations of pre-industrial climate change. For example the ‘little ice age’ of the 17th century correlates well with times of specific solar inactivity known as the Maunder minimum  from 1640 to 1710 where none of the usual 11 year sunspot cycles have been observed. Other climate variations also appear to parallel the solar activity changes. A survey of such features and others is given by Kirkby .
The active sun reduces the cosmic ray intensities by 20 % and more at the height of a sunspot cycle . Most affected are cosmic rays of 1–10 GeV energy which is the dominant part of the spectrum. These cosmic rays deposit most of their energy at altitudes between 8 and 15 km (upper troposphere, lower stratosphere). Balloon measurements have shown that approximately 30 to 50 ions are produced per cm3 and sec, depending on latitude and solar activity . These numbers are consistent with results from cosmic ray simulation programs . Further, from mass spectroscopy it is known that at these altitudes ≈ 6000 ‘small ions’ per cm3 exist, with masses of up to 400 unit masses . In contrast, in the continental boundary layer, there exist ≈ 2000 ‘small ions’, mainly produced by natural radioactivity. Svensmark , in his much debated papers, has postulated that the ‘small ions’ strongly influence water droplet nucleation, and thus significantly modulate the cloud formation and thereby influence the albedo. By analyzing satellite data of cloud coverage during solar cycle 22, as measured by the ISCCP satellite program , he has suggested that lower troposphere clouds (3–5 km altitudes) are most affected by the variation of cosmic ray intensities, and thus by solar activity (see also ). Further arguments for the link between cosmic ray flux and climate variability have been given by Shaviv and Veizer in a study on paleo-temperatures .
Conclusion: In summary, the terrestrial insolation data of SAO and of Mauna Loa observatory appear to vary strongly with solar activity. Evidence was presented that this modulation is caused by the cosmic rays, which pro- duce ‘small ions’, most probably consisting of O+ and O− ion centers surrounded by two shells of water
molecules. After coalescence, the very stable hydrated centers persist in the atmosphere as neutral nanometer size droplets and should constitute a large part of the atmospheric aerosols. Due to their strong light absorption, and due to their inner structure, these droplets show their own diurnal dynamics and appear to last for years, if not decades, especially over the oceans. They also exhibit strong Rayleigh scattering, which in solar active times results in a significant blue shift of the insolation, much bigger than that of the active sun itself.
Thus it appears that the SAO and Mauna Loa data represent a key for a more detailed understanding of atmospheric processes. The contribution of the active sun, indirectly via cosmic rays, to global warming appears to be much stronger than the presently accepted upper limit of 1/3. However, to really confirm this view, it is necessary to study the properties of atmospheric small ions and droplets in great detail, along paths which e. g. have been laid by C.T.R. Wilson. F.E. Fowle of the SAO group had been aware of Wilson’s work and had suggested explanations of SAO results along those paths. However, modern research has not taken up these ideas, and the SAO data have fallen into oblivion. In this paper it was shown that this is not justified. Instead, the SAO data, the works of Langley, Abbot, Fowle, Aldrich and others represent a great American scientific heritage.