The coming Solar grand minimum isn't a 400 year cycle per say. It's something that happens every 400 years. Not like the solar output goes up and down like a sine wave with a 400 year period. Scientists are starting to talk about 2050 and expect the total solar output to be 7% less than average. The last mini ice age lasted 75 years. The Baltic sea froze over.
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The Sun is getting cooler and dimmer, but scientists aren’t worried – BGR
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