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P. Foukal, L. Milano (CRI, Inc.)
We use recently digitized, archived Ca K images obtained between 1905-present, to measure variations in the area of quiet chromospheric network at the 9 solar activity minima between 1911 and 1996. We find only a marginally significant increase, an order of magnitude smaller than required to provide an increase in total irradiance even comparable in magnitude to the small 0.1% increase observed radiometrically during cycles 21 and 22. Our results cast doubt on the hypothesis that an irradiance decrease caused by disappearance of the magnetic network during the Maunder Minimum could influence global warming since the 17th century. Together with recent findings from stellar photometry and solar radiometry, this result calls into question previous evidence for a significant long-term component of irradiance change beyond the small 11-year modulation measured by space-borne pyrheliometers.