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Sunday, October 10th 2010, 6:18 PM UTC
Co2sceptic (Site Admin)
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In the ICECAP section on solar cycles, we explain why the sun is a driver for climate changes over time.

Historically, the sun undergoes changes on periods of 11, 22, 80, 180 years and longer. When the sun is more active it is brighter and warmer and when it is warmer, we are warmer. This direct effect is relatively small varying only 0.1% during the 11 year cycle and maybe 0.4% for the longer term.

However, there are accompanying effects from other solar changes that appear to magnify these irradiance cycles. An active sun is accompanied by increased ultraviolet radiation. Though the brightness/irradiance on the 11 year scale may only increase 0.1%, the ultraviolet changes by several percent especially at the lower wavelengths (X-rays) where factor of two changes may take place.

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Labitzke has shown a variance of the heights and temperatures in higher levels in low and middle latitudes with the 11 year cycle correlated well with solar flux (which itself correlates well with UV). Shindell (NASA GISS) in 1999 in an excellent paper showed results from a global climate model which included a parameterization of stratospheric chemistry, how UV induced stratospheric ozone changes may amplify observed irradiance effects and have them penetrate into the troposphere, in effect confirming Labitzke’s findings.

Also an active sun leads to less cosmic rays and a reduction in the amount of low level (water droplet) cloudiness. Low clouds have a cooling effect by reflecting energy back to space.This was first proposed by Svensmark (1997), Bago and Butler (Astronomy and Geophysics 2000), and Yu and Tinsley (AGU 2002). Recently Svensmark was able to replicate water cloud droplet nucleation in a laboratory (Royal Society Proceedings A 2006). Shaviv (2005) estimated that the combination of cosmic ray cloud effects and brightness related increases in irradiance since 1900 could account for 77% of the changes in global temperatures.

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