A Paucity of Evidence, pt. 4 - Cyclical variances in global temperatures also complicate things for those who would make the case for anthropogenic global warming. Generally speaking, long-term trends in temperature are not unusual, as the earth is always either warming or cooling. The existence of temperature cycles is reflected in data from the IPCC which suggest that the fluctuations in average global temperatures observed during the period between 1400 and 1500 A.D. were nearly as great as that recorded between 1900 and 2000 A.D. Global temperature variability has also been extensively detailed in a paper authored by researchers at the Harvard-Smithsonian Center for Astrophysics entitled, “Reconstructing Climatic and Environmental Changes of the Past 1000 Years: A Reappraisal,” published in Energy & Environment, Volume 14, Numbers 2-3, 1 May 2003, pp. 233-296.

The study authors examined the climactic history of the earth over the past 1000 years by reviewing changes in glaciers, corals, stalagmites and fossils, as well as investigations of cores drilled out of sediments lying at the bottom of bodies of water. The paper’s abstract states that currently available evidence, “establishes the reality of both the Little Ice Age (1300 to 1900 A.D.) and the Medieval Warm Period (800 to 1300 A.D.) as climatic anomalies with world-wide imprints.” The abstract goes on to say, “many records reveal that the 20th century is likely not the warmest nor a uniquely extreme climatic period of the last millennium.”

Temperature variability has also been detected on Mars, suggesting that global temperatures may be mediated by factors other than man-made greenhouse gases. Since arriving at Mars in 1997, NASA’s Mars Global Surveyor (MGS) has enabled scientists to observe changes in the size and thickness of the polar ice caps on the Red Planet that go beyond the seasonal changes in the ice caps that have been previously documented. The ice caps themselves seem to be comprised of a thin surface layer of frozen CO2 and a thicker layer of frozen water.

The spacecraft has observed a gradual evaporation of the carbon dioxide ice in one of Mars’ polar caps, pointing to a slowly changing Mars climate. At this point, scientists are unsure as to whether the shrinking of the polar caps is related to increased solar activity or if there is some other explanation. As Michael Malin, principal investigator for the MGS Mars Orbiter Camera put it “Why is Mars warmer today that it was in the past, we really have no way of knowing why.”

What we do know as it pertains to the Sun’s impact on global temperature is that there are and have been measurable changes in sunspot activity throughout various periods of time. The Sun normally has an 11-year cycle of increasing and decreasing numbers of sunspots (although the cycle has been as short as 8 years and as long as 15.) This sunspot cycle is part of an approximately 22-year solar magnetic cycle, and is monitored and measured by the number of sunspots seen at any given time, as sunspots reflect the overall activity near the surface of the Sun.

But above and beyond these normal fluctuations, there is evidence that the Sun’s radiation has increased since the late 1970s. This evidence comes from research authored by Richard Willson, a Columbia University researcher also affiliated with NASA’s Goddard Institute for Space Studies, and published in the March 4, 2003 issue of Geophysical Research Letters. Dr. Willson’s paper, entitled, “Secular total solar irradiance trend during solar cycles 21–23,” analyzed data from six satellites orbiting Earth at different times over 24 years to conclude that the Total Solar Irradiance (as measured by the amount of solar energy that falls upon a square meter outside the Earth’s atmosphere) has increased by .05 percent per decade.

Similar findings have been observed by scientists at Duke University. According to work done by Nicola Scafetta and Bruce West, both professors in the university’s physics department, “the sun may have minimally contributed about 10 to 30 percent of the 1980-2002 global surface warming.” Using a 22 year period allowed Drs. Scafetta and West to control for short term factors that may temporarily cool the atmosphere, such as changes in ocean current and volcanic eruptions. Their research built upon the work done by Dr. Willson, and was published in the September 28, 2005 issue of Geophysical Research Letters.

Dr. Willson’s research has been corroborated by a study done by a team of Swiss and German researchers and led by Dr. Sami Solanki, Director of the Max Planck Institute for Solar System Research in Gottingen, Germany. When Dr. Solanki was interviewed for the July 18, 2004 edition of the U.K. Telegraph, he is quoted as saying “The Sun has been at its strongest over the past 60 years and now may be affecting global temperatures.”