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New Paper: Solar irradiance at Earth surface varies up to 24 times more than expected
Monday, February 14th 2011, 11:09 PM UTC
Co2sceptic (Site Admin)
A new peer-reviewed paper published in the journal Atmospheric Chemistry and Physics finds that measurements of solar irradiance at ground level at the South Pole show variations of up to 24 times more than would be expected over the course of a solar cycle. While satellite measurements find that total solar irradiance only varies 0.1% from a solar minimum to solar maximum, the ground-level measurements analyzed by the authors show a change of 1.8 ± 1.0% in the UV-A (320–400 nm) spectrum and 2.4 ± 1.9% in the visible (400–600 nm) spectrum over the course of a solar cycle.

Regressions based on all 17 solstice periods indicate approximate 1.8% and 2.4% decreases in ground-level irradiance for the wavelength regions 320–400 nm and 400–600 nm, respectively, from solar maximum to solar minimum. The associated uncertainty ranges are approximately 0.8–2.7% for the UV-A and 0.5%–4.3% for the visible.

Changes in extraterrestrial irradiance over the solar cycle surely contribute a portion of the variability deduced at the polar surface for the 320–400 nm region, although the magnitude of this contribution is uncertain. However, the inferred solar cycle dependence in the 400–600 nm visible band is too large to be of extraterrestrial origin unless one adopts values at the lowest end of the error range.



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The UV-A and visible portions are the most energetic and significant portions of the solar spectrum heating the Earth. While the authors are uncertain of the origin of this variability at the surface, they note that it is "too large to be of extraterrestrial origin." Climate models assume that the solar irradiance reaching the Earth's surface only varies 0.1% over solar cycles in accordance with satellite measurements, but as shown by this paper, that may be an incorrect assumption. Another recent study has shown that solar UV activity has increased almost 50% over the past 400 years. The antiquated assumption in climate science that the effect of the Sun upon the Earth's climate is a constant (they even call it "the solar constant") is in dire need of reassessment. The IPCC, however, is only mandated to assess anthropogenic climate change and only pays lip service to the role of the Sun.

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