File:Sunspot Numbers.png

From Global Warming Art


Changes in carbon-14 concentration in the atmosphere, which serves as a long term proxy of solar activity. Note the present day is on the left-hand side of this figure.
Changes in several different parameters of solar activity associated with the last three solar cycles.

This figure summarizes the 400 years of regular sunspot number observations. Since ~1749, continuous monthly averages of sunspot activity have been available and are shown here as reported by the Solar Influences Data Analysis Center, World Data Center for the Sunspot Index, at the Royal Observatory of Belgium. These figure are based on an average of measurements from many different observatories around the world. Prior to 1749, sporadic observations of sunspots are available. These were compiled and placed on consistent monthly framework by Hoyt & Schatten (1998a, 1998b).

The most prominent feature of this graph is the ~11 year solar magnetic cycle which is associated with the natural waxing and waning of solar activity.

On longer time scales, the sun has also shown considerable variability, including the long Maunder Minimum when almost no sunspots were observed, the less severe Dalton Minimum, and increased sunspot activity during the last fifty years, known as the Modern Maximum. The causes for these variations are not well understood, but because sunspots and associated faculae affect the brightness of the sun, solar luminosity is lower during periods of low sunspot activity. It is widely believed that the low solar activity during the Maunder Minimum and earlier periods may be among the principle causes of the Little Ice Age. Similarly, the Modern Maximum is partly responsible for global warming, especially the temperature increases between 1900 and 1950. Residual warming due to the sustained high level of activity since 1950 is believed responsible for 16 to 36% of recent warming (Stott et al. 2003).


This figure was prepared by Robert A. Rohde.

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  • Hoyt, D. V., and K. H. Schatten (1998a). "Group sunspot numbers: A new solar activity reconstruction. Part 1.". Solar Physics 179: 189-219. 
  • Hoyt, D. V., and K. H. Schatten (1998b). "Group sunspot numbers: A new solar activity reconstruction. Part 2.". Solar Physics 181: 491-512. 
  • [abstract] [full text] Stott, Peter A.; Gareth S. Jones and John F. B. Mitchell (15 December 2003). "Do Models Underestimate the Solar Contribution to Recent Climate Change". Journal of Climate 16: 4079-4093. 

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