Reading the Latest Solar Tea Leaves (or There Goes the Sun?)

by Bill Chameides | October 20th, 2011
posted by Erica Rowell (Editor)

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Will a dimming of our shining star be the deux ex machina that saves us from global warming?

I know I’ve posed this question before, but it’s time to revisit it, as some new info is hot off the presses. But first a recap.

Solar cycles come and go every 11 years or so. At the height of a cycle the Sun grows lots of sunspots and sends a bit more energy out into the cosmos — and, to our great fortune, to our planet Earth. At the nadir of a cycle, there are fewer sunspots and a bit less energy. And all solar cycles are not created equal — some are stronger or more active with more sunspots and more energy radiated; some are less active, with fewer sunspots and less energy.

The past 90 years have been known as a “grand solar maximum” because the cycles have been unusually strong. (See chart below.) But all good things come to an end and so it seems inevitable that this grand maximum won’t last forever — or else it would hardly be grand, right? The question is when will the grand maximum end? The answer, it turns out, may be right now with the current solar cycle 24 (in the jargon of solar scientists, it is the 24th cycle since 1749 when solar cycles began to be recorded).

We’ve been in what’s called a “grand solar maximum” for about the past 90 years, thanks to strong solar cycles. That may be changing. Click on graphic for larger image. (Source: NASA)

A Wicked Solar Minimum

The first signs that things might be changing came with the transition from cycle 23 to 24 in 2008/09. (Officially, cycle 23 ended December 2008 while cycle 24 began on January 2008. I know that doesn’t seem possible, but cycles typically overlap for about a year or so — if you had to undergo a magnetic pole reversal you’d understand.) During any transition from one cycle to the next, solar activity is depressed. But this most recent transition was a doozie. Sunspot numbers scraped along at or near zero for close to two years — 2008 had 266 spot-free days and 2009 had 260.

In 2010 solar cycle 24 finally got going — but with more of a whimper than a roar and it’s been a pretty paltry cycle since. The solar cycles of recent history have typically peaked with an averaged annual sunspot number ranging from about 120 to 150. According to the National Oceanic and Atmospheric Administration (which has the largest estimate), the maximum sunspot number for cycle 24 is predicted to peak at a number of only about 90 sometime in May 2013.

What That May Portend

Last week Matt Owens of the University of Reading in England and colleagues published a paper in the journal Geophysical Research Letters that adds fuel to the fire, or lack of fire, with two bold predictions:

  • Cycle 24 will be even weaker than previously predicted with the maximum sunspot number peaking at only 65-75 in mid- or late 2012.
  • The weakness of cycle 24 may not be an isolated event but the harbinger of a new regime of very low solar activity. How low? Pretty low. The authors state that “parameters during the current solar cycle … are following trajectories consistent with a rapid descent into Maunder minimum conditions (within about 40 years).” The Maunder Minimum, you will recall, occurred in the 17th and early 18th centuries when records indicate a virtual absence of any sunspots over a period of 70 years.

This latter prediction was accompanied by an important caveat that is based on an extrapolation from “past experience.” Other studies have shown that the weakness in a single cycle cannot always be used to predict the characteristics of subsequent cycles. A case in point was the dip in solar activity in the transition between cycles 19 and 20 that turned out to be a blip rather than a flip from the grand solar maximum. (See this graphic.)

And Whither Global Warming

Still, even the possibility that we are headed to a modern Maunder Minimum has got to raise some eyebrows. After all, the Maunder Minimum coincided with the so-called Mini Ice Age. Could a new Maunder Minimum cancel out greenhouse warming? Perhaps even lead to cooling instead of warming global temperatures? I wouldn’t go so far as to say it’s beyond the realm of possibility, but, as I wrote last year, model simulations suggest that even should we descend into a Maunder-like period, it probably won’t be sufficient to counter present day warming.

Many years ago when I was living in Atlanta, the hometown Braves were down by a bunch of runs in the early innings of the final game of a playoff series. The announcer asked the color commentator if he had any advice for Braves fans. He said, yes, pray for rain. It didn’t and the Braves lost.

In the case of global warming, we could I suppose pray for a new Maunder Minimum and hope it will suffice. Probably not the best advice.

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