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Sunspot values from: http://spaceweather.com
While looking at some old copies of Life magazine in an antique store in the spring of 2008, I came across a very interesting article from August 1956 about the fear of global warming. It reviewed many possible causes for the phenomenon, including increased levels of CO2. There seems to be nothing new today that goes beyond this 1956 article.
The most interesting possible cause presented was the sunspot cycle. It described the 11-year cycle commonly referred to today. However, it also mentioned that both global weather variations and sunspots also follow a longer cycle where sunspots shut down completely for a few years at the end of this lengthy cycle. (The mean cycle length over the last 400-year sunspot history seems to be about 95 years). The article also suggested that, within this 95-year cycle, there are more sub-cycles: increased sunspot activity with some increased global warming followed by decreased sunspot activity with some global cooling.
The summer of 2008 was cool and moist and the summer of 2009 was, for the most part, even more so, especially in Eastern Canada. This is not that unexpected as the earth has actually been cooling since 2005—not warming as it did in the previous two decades—according to the Climatic Research Unit in the U.K. Sunspots have also been decreasing since the last maximum was reached in about 2003 and are now at their lowest level in 100 years. Careful measurements by several NASA spacecraft have also shown that the sun's brightness has dimmed by 0.02 percent at visible wavelengths and a whopping 6 percent at extreme UV wavelengths since the second last solar minimum of 1996-7. Radio telescopes are now recording the dimmest “radio sun” since 1955.
But global CO2 concentrations have continued to rise according to National Oceanic Atmospheric Administration’s measurement site at Mauna Loa in Hawaii. Thus, there appears to be a negative relationship between CO2 levels and global temperature and a positive correlation between sunspot numbers/sun strength and global cooling. If CO2 were actually the dominant cause of global warming and sunspots accounted for only 20 percent of recent global temperature increases, as the Intergovernmental Panel on Climate Change claims, global cooling should not have started in 2005 because mean monthly CO2 levels have not stopped rising.
