Is the Solar Cycle Broken?
The Sun's 11-year solar cycles have been weakening since 1990. Is the Sun entering a grand-minimum? The last one coincided with "the little ice age" which lasted 500 years.
Solar cycle (SC) 24 started in 2008. SC 25 is expected to start 11 years later, in 2019. But the number of sunspots has been decreasing in recent cycles. SC 22 reached a peak of over 150 sunspots in 1990. SC 23 peaked in 2001 with about 125 while our last cycle, SC 24, peaked with about 75 in 2014. Active regions (AR) 2719 and 2720 pictured above are just rounding the Sun's descending limb. If their polarity is opposite those of SC 24 they may herald the start of SC 25. Solar physicists are watching SC 25 for signs that the decrease in sunspots is continuing. If the Sun is entering an extended period of quiet, a "grand-minimum, that could significantly impact Earth's climate. The Maunder Minimum was a period from 1645 to 1715 during which sunspots were exceedingly rare and global temperatures plummeted. This occurred during a longer period of unusual cold from about 1300 to 1850 known as "the little ice age". Cooling, if it occurs, is not expected to be as severe, but could delay the man-made effects of global warming, at least for awhile.
With thanks to Mindy Weisberger at Live Science