Unknown to most people except those with an interest in solar science, the sun is about to shut down. Well, not completely – we’ll still have plenty of sunlight and heat, but the small dark blotches on the sun’s surface called sunspots, visible in the figure below, are on the verge of disappearing. According to some climate scientists, this heralds a prolonged cold stretch of maybe 35 years starting in 2020, despite global warming.
How could that happen? Because sunspots, which are caused by magnetic turbulence in the sun’s interior, signal subtle changes in solar output or activity – changes that can have a significant effect on the earth’s climate. Together with the sun’s heat and light, the monthly or yearly number of sunspots goes up and down during the approximately 11-year solar cycle. For several decades now, the maximum number of sunspots seen in a cycle has been declining.
The last time sunspots disappeared altogether was during the so-called Maunder Minimum, a 70-year cool period in the 17th and 18th centuries forming part of the Little Ice Age, and illustrated in the next figure showing the sunspot number over time. The Maunder Minimum from approximately 1645 to 1710 was the most recent occurrence of what are known as grand solar minima, or periods of very low solar activity, that recur every 350 to 400 years. So we’re due for another minimum.
Northumbria University’s Valentina Zharkova, a researcher who’s published several papers on sunspots and grand solar minima, has linked the minima to a drastic falloff in the sun’s internal magnetic field. The roughly 70% downswing in magnetic field from its average value is part of a 350- to 400-year cycle arising from regular variations in behavior of the very hot plasma powering our sun.
In between grand solar minima come grand solar maxima, when the magnetic field and number of sunspots reach their highest values. The most recent (“modern”) grand solar maximum, even though slightly lopsided, is represented by the blue peaks in the figure above. The figure below shows Zharkova’s calculated magnitude of the magnetic field from 1975 to 2040, which is seen to diminish as the minimum approaches.
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