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Where Have All the Sunspots Gone?
Reference
Livingston, W. and Penn, M. 2009. Are sunspots different during this solar minimum? EOS, Transactions, American Geophysical Union 90: 257-258.

Background
The authors write that "sunspots are dark regions on the solar disk with magnetic field strengths greater than 1500 gauss," and that "the 11-year sunspot cycle is actually a 22-year cycle in the solar magnetic field, with sunspots showing the same hemispheric magnetic polarity on alternate 11-year cycles."

What was done
Livingston and Penn report what has been known for quite some time now, i.e., that "something is unusual about the current sunspot cycle," and that is, as they describe it, that "the current solar minimum has been unusually long." More specifically, they state that "with more than 670 days without sunspots through June 2009, the number of spotless days has not been equaled since 1933." In addition, they say "the solar wind is reported to be in a uniquely low energy state since space measurements began nearly 40 years ago," citing the work of Fisk and Zhao (2009); and in light of this unique set of observations, they proceed to enlighten us about some important related matters.

What was learned
First of all, they report that data they analyzed some four years ago (Penn and Livingston, 2006) showed that the magnetic field strengths of sunspots "were decreasing with time, independent of the sunspot cycle," and that "a simple linear extrapolation of those data suggested that sunspots might completely vanish by 2015." And now, with four more years of data in hand, they report that "the predicted cycle-independent dearth in sunspot numbers has proven accurate," with sunspots still on track to totally disappear in four to five years.

What it means
The two researchers openly wonder whether their findings represent "an omen of long-term sunspot decline, analogous to the Maunder Minimum," the period from 1645-1715 "when through several 11-year periods the sun displayed few if any sunspots," the reason for their curiosity, of course, being that "models of the sun's irradiance suggest that the solar energy input to the earth decreased during that time and that this change in solar activity could explain the low temperatures recorded in Europe during the Little Ice Age (Lean et al., 1992)." Since the answer to their question should become apparent before too long (about the time of the next U.S. Presidential Election), it might be wise to wait to see what the answer actually is before enacting legislation to attempt to stop CO2-induced global warming that might well be needed to forestall another "Little Ice Age," the cold of which (which was the most severe of the current interglacial) would likely prove much more deadly that the bit of extra heat we may -- or may not! -- otherwise experience.

References
Fisk, L.A. and Zhao, L. 2009. The heliospheric magnetic field and the solar wind during the solar cycle. In: Gopalswamy, N. and Webb, D.F., Eds. Universal Heliophysical Processes: Proceedings of the International Astronomical Union 257: 109-120 (Cambridge University Press, New York, New York, USA).

Lean, J., Skumanich, A. and White, O. 1992. Estimating the sun's radiative output during the Maunder Minimum. Geophysical Research Letters 19: 1591-1594.

Penn, M.J. and Livingston, W. 2006. Temporal changes in sunspot umbral magnetic fields and temperatures. Astrophysical Journal 649: L45-L48.

Reviewed 26 August 2009