Anthony Watt’s at WUWT discussed a new report issued by the National Research Council (NRC), “The Effects of Solar Variability on Earth’s Climate,” lays out some of the surprisingly complex ways that solar activity can make itself felt on our planet.
This the part of the report that mentions grand minimums.
Much has been made of the probable connection between the Maunder Minimum, a 70-year deficit of sunspots in the late 17th-early 18th century, and the coldest part of the Little Ice Age, during which Europe and North America were subjected to bitterly cold winters. The mechanism for that regional cooling could have been a drop in the sun’s EUV output; this is, however, speculative.
The yearly averaged sunspot number for a period of 400 years (1610-2010). SOURCE: Courtesy of NASA Marshall Space Flight Center.
Dan Lubin of the Scripps Institution of Oceanography pointed out the value of looking at sun-like stars elsewhere in the Milky Way to determine the frequency of similar grand minima. “Early estimates of grand minimum frequency in solar-type stars ranged from 10% to 30%, implying the sun’s influence could be overpowering. More recent studies using data from Hipparcos (a European Space Agency astrometry satellite) and properly accounting for the metallicity of the stars, place the estimate in the range of less than 3%.” This is not a large number, but it is significant.
Indeed, the sun could be on the threshold of a mini-Maunder event right now. Ongoing Solar Cycle 24 is the weakest in more than 50 years. Moreover, there is (controversial) evidence of a long-term weakening trend in the magnetic field strength of sunspots. Matt Penn and William Livingston of the National Solar Observatory predict that by the time Solar Cycle 25 arrives, magnetic fields on the sun will be so weak that few if any sunspots will be formed. Independent lines of research involving helioseismology and surface polar fields tend to support their conclusion. (Note: Penn and Livingston were not participants at the NRC workshop.)
“If the sun really is entering an unfamiliar phase of the solar cycle, then we must redouble our efforts to understand the sun-climate link,” notes Lika Guhathakurta of NASA’s Living with a Star Program, which helped fund the NRC study. “The report offers some good ideas for how to get started.”
The full report, “The Effects of Solar Variability on Earth’s Climate,” is available from the National Academies Press at http://www.nap.edu/catalog.php?record_id=13519.
Author: Dr. Tony Phillips | http://science.nasa.gov/science-news/science-at-nasa/2013/08jan_sunclimate/
Quiet sun = cold planet.