Solar cycles and climate

Yesterday, the solar boffins at the American Astronomical Society’s Solar Physics meeting announced that we may be seeing evidence that the Sun is entering a “quiet phase” of low activity and sunspot counts. The intertubes are atwitter with this news because of the association of no sunspots in the Maunder Minimum with the coldest part of the Little Ice Age.

Well. We have one observational data point, and the Maunder Minimum came after the LIA had already started, and during the same period several large volcanic eruptions put haze in the atmosphere, which leads to cooling effects, so the case is far from proved. We do have some speculation, due to the correlation of a quiet Sun and a cold Earth.

In defense of the speculation, there is a plausible physical mechanism given by Dr. Henrik Svensmark; a quiet Sun has a lower strength interplanetary magnetic field, a decrease in the solar magnetic field should result in more cosmic rays reaching the Earth, a higher cosmic ray flux should produce more ionization in the atmosphere, the increased ionization may lead to more cloud formation, more cloud coverage will certainly reflect solar energy back into space, and less solar energy reaching the ground means less IR radiation trapped near the surface due to greenhouse effects. But. That is a long chain of effects, and it hasn’t been clearly demonstrated AFAIK. For more info, see The Chilling Stars.

I hope we don’t find out the hard way that low sunspot numbers means a cold Earth, because a colder climate is Bad News, with slower growing plants and a reduced growing season. Food supplies are already quite tight in the world. Who knows, we may all have to leave the Hummer idling in the driveway overnight!

[Update] I seem to recall, but can’t find after a quick Google search, that someone examined paintings made during the Marunder Minimum and found lots and lots of cloudy days depicted in the outdoor scenes. I’ll try and find the reference later, but if anyone knows, please leave it in a comment! My Google-fu is weak today.


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