The paper adds to many other peer-reviewed papers describing solar amplification mechanisms by which tiny 0.1% changes of total solar irradiance can be amplified to produce large effects on climate. According to this paper, 0.1% changes in solar irradiation over solar cycles are amplified by a factor of 18 to 24 times at the surface of the South Pole, dependent upon wavelength. As noted by Dr. Roy Spencer, a mere 1-2% change in global cloud cover [such as the 1.8% - 2.4% found by this paper] can alone account for global warming - or global cooling.
|The current solar cycle is the weakest in 100-200 years.
Atmos. Chem. Phys., 11, 1177-1189, 2011
Full paper available here:
Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, USA
Abstract. This research examines a 17-year database of UV-A (320–400 nm) and visible (400–600 nm) solar irradiance obtained by a scanning spectroradiometer located at the South Pole. The goal is to define the variability in solar irradiance reaching the polar surface, with emphasis on the influence of cloudiness and on identifying systematic trends and possible links to the solar cycle. To eliminate changes associated with the varying solar elevation, the analysis focuses on data averaged over 30–35 day periods centered on each year's austral summer solstice. The long-term average effect of South Polar clouds is a small attenuation, with the mean measured irradiances being about 5–6% less than the clear-sky values, although at any specific time clouds may reduce or enhance the signal that reaches the sensor. The instantaneous fractional attenuation or enhancement is wavelength dependent, where the percent deviation from the clear-sky irradiance at 400–600 nm is typically 2.5 times that at 320–340 nm. When averaged over the period near each year's summer solstice, significant correlations appear between [ground level] irradiances at all wavelengths and the solar cycle as measured by the 10.7 cm solar radio flux. An approximate 1.8 ± 1.0% decrease in ground-level irradiance occurs from solar maximum to solar minimum for the wavelength band 320–400 nm. The corresponding decrease for 400–600 nm is 2.4 ± 1.9%. The best-estimate declines appear too large to originate in the sun. If the correlations have a geophysical origin, they suggest a small variation in atmospheric attenuation [clouds] with the solar cycle over the period of observation, with the greatest attenuation [more clouds] occurring at solar minimum.