The IPCC gang have essentially dismissed the influence of solar activity - "solar forcing"- on global warming, assigning a 5 times greater effect to mostly-man-made greenhouse gases. Solar ultra-violet, visible, and infrared radiation are the primary factors for the earth's climate, including global average temperatures, and these energy sources appear to be quite constant. However, many scientists have observed correlations between the solar magnetic activity, which is reflected in the sunspot frequency, and climate parameters at the earth. Sunspots have been recorded through several hundreds of years, which make it possible to compare their variable frequency to climate variations to the extent that reliable climatological records exist. Arguably, sunspot data (and sunspot proxies-see below) may be considerably more objective than tree-ring data given the influences of precipitation, altitude, CO2, missing data, clouds, latitude, and other "extraneous" factors. One of the most striking comparisons of sunspot activity to climate was published by E. Friis-Christensen and K. Lassen, Length of the solar cycle: An indicator of solar activity closely associated with climate, Science, 254, 698-700, 1991. In their work, the average temperature in the northern hemisphere was compared to the average solar activity defined from the interval between successive sunspot maxima, concluding "70-90 years oscillations in global mean temperature are correlated with corresponding oscillations in solar activity. Whereas the solar influence is obvious in the data from the last four centuries, signatures of human activity are not yet distinguishable in the observations. " An HTML version of this work is available here
and shows a striking correlation between sunspot cycle length and temperature using an 11 year moving average (Fig. 4).
Sunspot cycles vary in length from about 9 to 14 years. Some peaks are high, others low. The valleys are usually brief, lasting only a couple of years, but sometimes they stretch out much longer. In the 17th century the sun plunged into a 70-year period of spotlessness known as the Maunder Minimum that still baffles scientists. The Maunder Minimum coincided with the middle — and coldest part — of the Little Ice Age, during which Europe and North America, and perhaps much of the rest of the world, were subjected to bitterly cold winters. The postulated reason why decreased solar activity (correlated with decreased sun spots) leads to global cooling is that there is reduced solar wind, which decreases the geomagnetic shield of the earth from cosmic rays, resulting in increased galactic cosmic ray flux to the earth, which cause formation of more low-level clouds and more snow, which in turn cause more albedo effect (more heat reflected), and therefore colder climate.
Above: Yearly-averaged sunspot numbers from 1610 to 2008. Researchers believe upcoming Solar Cycle 24 will be similar to the cycle that peaked in 1928, marked by a red arrow.
Right now, the solar cycle is in a valley--the deepest of the past century. In 2008 and 2009, the sun set modern age records for low sunspot counts, weak solar wind, and low solar irradiance. The sun has gone more than two years without a significant solar flare. Take a look at the widget above right - zero sunspots- for far longer than the next solar cycle had been predicted to start. Might this be part of the reason for the "travesty" (quoting a climategate email
) of global cooling over the past decade?