Update: Reading Solar Tea Leavesby Bill Chameides | April 5th, 2010
posted by Erica Rowell (Editor)
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During the current solar cycle the Sun has seen very few sunspots — those visible dark dots on the star's surface that indicate intense magnetic activity and lowered solar output. Could this current minimum provide a preview of the coming solar cycles?
The Sun’s latest minimum is one for the record books. What does it portend?
The Sun is a force front and center in any discussion about climate change — and its possible role in global warming has been the subject of many a post here at TheGreenGrok (for a sampling, see Global Warming and Predictions of an Impending Ice Age: Sunspots, Solar Cycle 24: Ho Hum or Gee Whiz?, Update: The Sun’s Spots Are Back … Sort Of, Galactic Cosmic Rays and Climate: Forbush Puts Kibosh on Theory.)
Is the Sun responsible for the warming over the past few decades? Satellite data say no. See the posts above and this.
But what about the future? Could the Sun, for example, suddenly enter a cool period that would counter the warming from carbon dioxide and other greenhouse gases? Kind of a solar deus ex machina swooping down and saving us from climate catastrophe.
Now, this is an interesting question and one that we know too little about to answer authoritatively, especially since we’re talking about the future. Nevertheless, predictions are one of the things scientists like to do, so why not try to predict the Sun’s future. Here’s where things get really interesting … and quiet.
Does a Quiet Sun Speak Volumes?
The Sun is currently pulling itself out of a minimum in its 11-year solar cycle, transitioning from cycle 23 to cycle 24. From a climate point of view, solar cycles turn out to be a relatively small deal resulting in a temperature variation on the Earth from minimum to maximum of only about 0.2 degrees Celsius or 0.4 degrees Fahrenheit. For more info check this previous post.
Much to most solar scientists’ surprise, the cycle 23-24 minimum turned out to be a doozie, with almost 800 so-called spotless days (i.e., days without any sunspots at all, meaning there’s not much solar activity). According to solar physicist David Hathaway of the Marshall Space Flight Center, we are now seeing one of the “quietest Sun[s] we’ve seen in almost a century.”
It seems logical to expect that a long and deep solar minimum is a harbinger of a weak solar cycle, and maybe even an extended, multi-cycle period of low solar output too. Perhaps even something like the Maunder Minimum, when for about 500-600 years the Sun went with little or no sunspots and temperatures were quite low, so low in fact that the period is referred to as the Little Ice Age. If correct, maybe, some argue, we should forget global warming and worry about global cooling, another Little Ice Age to come (see here, here, here, here, and even here).
A recent paper suggests that even if the Sun enters a cool phase, it is unlikely to significantly counteract global warming. But maybe the authors of that paper underestimated the strength of the still hypothetical coming solar minimum. What then?
Does Current Solar Minimum Indicate More to Come?
Before we get too carried way, maybe we all should re-examine the premise. Can we use the strength of the cycle 23-24 solar minimum to predict the strength of the coming solar cycle? This is the question Mausumi Dikpati of the National Center for Atmospheric Research and colleagues asked themselves.
To answer it, they analyzed data from the previous 23 solar cycles. They published their findings last week in the journal Geophysical Research Letters. And their answer is no. They found, on the basis of the historical solar-cycle record, that the length and strength of a minimum cannot be used to predict the strength of the ensuing solar cycle.
The authors conclude that “the current long minimum at the end of cycle 23 does not necessarily portend a weaker cycle 24 than 23. The rise of cycle 24 is underway and we all must wait to see the peak of cycle 24 to see” whether it will be a strong or weak cycle.
If you’ll forgive me for mixing my culinary metaphors, you can read all the tea leaves you want, but the proof is — or will be — in the pudding.filed under: carbon dioxide, climate change, faculty, global warming, Planetary Watch
and: climate science, Little Ice Age, Maunder Minimum, solar activity, solar cycle, solar minimum, Sun, sunspots