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The Unusually Quiet Sun finally gets some attention

Larry Kummer, Editor

Solar cycle 24 has yet to decisively start, and many metrics show solar activity at unusually low levels.  This potentially important story has begun to get some attention from the media.

  1. “‘Still Sun’ baffling astronomers“, BBC, 21 April 2009
  2. “Sun ‘at its quietest for 100 years’“, Press Association (a newswire), 21 April 2009
  3. “Has the sun gone in? Earth’s closest star ‘dimmest it’s been for a century’“, Daily Mail, 21 April 2009
  4. “A Quiet Sun Doesn’t Happen Overnight“, Charles Osgood, CBS, 21 April 2009
  5. (update) “The missing sunspots: Is this the big chill?“, The Independent, 27 April 2009 — “Scientists are baffled by what they’re seeing on the Sun’s surface – nothing at all. And this lack of activity could have a major impact on global warming.”

It’s a little flurry of stories, all careful to avoid mentioning the strong evidence about the Sun’s influence on Earth’s climate (although the mechanism for this remains unclear).  Perhaps the best summary I’ve seen is this, from NASA’s Earth Observatory page — “The Sun’s Chilly Impact on Earth“, 6 December 2001. Excerpt:

During the coldest part of the Little Ice Age, from 1645 to 1715, there is believed to have been a decrease in the total energy output from the Sun, as indicated by little or no sunspot activity. Known as the Maunder Minimum, astronomers of the time observed only about 50 sunspots for a 30-year period as opposed to a more typical 40-50,000 spots. The Sun normally shows signs of variability, such as its eleven-year sunspot cycle. Within that time, it goes from a minimum to a maximum period of activity represented by a peak in sunspots and flare activity.

Beginning in 1611, Galileo Galilei made drawings of lower sunspot activity before the Maunder Minimum. Records of sunspot activity during the Minimum from other astronomers confirm the lower number of sunspots over the70 year event.

During those periods of low solar activity, levels of the Sun’s ultraviolet radiation decrease, and can significantly impact ozone formation in the stratosphere. “The changes in ozone that we modeled were key in producing the enhanced response,” Shindell said. “The changes in the upper atmosphere then feed down to the surface climate.”

Between the mid-1600s and the early 1700s the Earth’s surface temperatures in the Northern Hemisphere appear to have been at or near their lowest values of the last millennium. European winter temperatures over that time period were reduced by 1.8 to 2.7 degrees Fahrenheit (1-1.5 Celsius). This cool down is evident through derived temperature readings from tree rings and ice cores, and in historical temperature records, as gathered by the University of Massachusetts-Amherst and the University of Virginia.

Solar cycle 24, the next 11 year cycle (they vary in length), has gotten off to a slow start.  There is growing concern about this.  For more information about this see these posts on the FM site about the solar cycle (esp the last one).  If solar activity does not pick up soon, we will see a lot more articles about this.

  1. Worrying about the Sun and climate change: cycle 24 is late, 10 July 2008
  2. Update: is Solar Cycle 24 late (a cooling cycle, with famines, etc)?, 15 july 2008
  3. Solar Cycle 24 is still late, perhaps signalling cool weather ahead, 2 September 2008
  4. Update on solar cycle 24 – and a possible period of global cooling, 1 October 2008
  5. This week’s report on the news in climate science, 7 December 2008
  6. Weekend reading recommenations about climate change, 13 December 2008
  7. An important new article about climate change, 29 December 2008
  8. About the recent conference ”Solar Activity during the onset of Solar Cycle 24″, 3 January 2009
  9. NASA: Sun undergoing a “deep solar minimum”, 13 April 2009

To see a small slice of the scientific literature about the Sun’s influence on Earth’s climate, see section 4 — The Solar Cycle — on the FM reference page Science & nature – studies & reports.

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