Total solar irradiance (TSI), essentially a measure of the amount of light the Sun puts out, varies with the 11-year sunspot cycle and influences Earth's climate, especially when TSI is notably higher or lower than its average values. It had been thought that TSI was especially low during a period known as the Little Ice Age, which began in the late 17th century, coinciding with a period of unusually low sunspot activity known as the Maunder Minimum. However, Schrijver et al. now suggest that TSI during that period may not have been as low as previously thought. They analyze direct measurements of solar magnetic activity during the recent 2008-2009 period of low sunspot activity, which they argue was similar to the activity level during the Maunder Minimum.
They find that even when there were no sunspots, the Sun had a baseline level of magnetic activity. This baseline had not been taken into account in previous estimates of TSI during the Maunder Minimum, which were based solely on sunspot numbers. Therefore, the authors suggest that earlier estimates of the TSI during the Maunder Minimum were too low. The researchers argue that the Maunder Minimum probably had levels of magnetic activity and TSI similar to 2008-2009 values, and therefore factors other than low solar irradiance resulting from low sunspot activity must have contributed to the Little Ice Age.
Source: Geophysical Research Letters, doi:10.1029/2011GL046658, 2011 http://dx.doi.org/10.1029/2011GL046658
Title: The minimal solar activity in 2008-2009 and its implications for long-term climate modeling
Authors: C. J. Schrijver: Lockheed Martin Advanced Technology Center, Palo Alto, California, USA; W. C. Livingston: National Solar Observatory, Tucson, Arizona, USA; T. N. Woods: Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, Colorado, USA; R. A. Mewaldt: Space Radiations Laboratory, California Institute of Technology, Pasadena, California, USA.
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