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Sun Flatlining Into Grand Minimum, Says Solar Physicist
Who can argue with a sudden outbreak of the “polar vortex” phenomenon; unprecedented winter drought in California; and summer temperatures so torrid Down Under that even play at the Australian Open was briefly halted?
Is any of this connected to the sun’s drastically diminished recent sunspot cycles?
Weather isn’t climate, but circumstantial evidence indicates our sun may be entering a grand minimum of sunspot activity, not unlike the Maunder Minimum that some climatologists think caused record low winter temperatures in Northern Europe during the latter half of the 17th century.
“My opinion is that we are heading into a Maunder Minimum,” said Mark Giampapa, a solar physicist at the National Solar Observatory (NSO) in Tucson, Arizona. “I’m seeing a continuation in the decline of the sun’s mean magnetic field strengths and a weakening of the polar magnetic fields and subsurface flows.”
Theoretical details of how sunspots are actually produced continue to be debated. But one popular idea is that they are generated as the result of concentrated and twisted solar magnetic fields blocking internal convection in the outer third of the sun’s interior. This, in turn, gives the sunspots their dark appearance, since on average they are 2000 degrees cooler than the surrounding solar plasma.
Even though the solar magnetic fields are thought to be triggered by the sun’s own internal “differential rotation” — or the fact that the sun’s equator rotates more rapidly at the poles than its equator — once these fields start twisting and turning, some theorists think their interaction at the sun’s photosphere (or surface) plays a crucial role in sunspot creation.
But David Hathaway, a solar physicist at NASA Marshall Space Flight Center in Huntsville, says it’s the actual strength of such magnetic field at the end of a given maximum 11-year sunspot cycle that are thought to act as bellwethers for the size and strength of the next solar maximum.
“At the end of a sunspot cycle about all you have left are magnetic fields at the solar poles,” said Hathaway. “We’re at the sunspot maximum of Cycle 24. It’s the smallest sunspot cycle in 100 years and the third in a trend of diminishing sunspot cycles. So, Cycle 25 could likely be smaller than Cycle 24.”
Another indicator pointing to an imminent grand minimum is that the current solar cycle shows some signs of hemispheric asymmetry, says Steve Tobias, an applied mathematician at the University of Leeds in the U.K.
“When the field is about to enter a minimum or is leaving a minimum,” said Tobias, “we see more sunspots in one solar hemisphere than the other.”
Yet during the 1645 — 1715 Maunder Minimum itself, sunspots basically disappeared and as documented in paintings from the era, Northern Europe suffered unusually cold winter temperatures.
Such minima are thought to be a part of the normal life of a sunlike star, however. And from recent surveys of several solar analogues in the open stellar cluster M67, Giampapa and colleagues see indications that such grand minima take place up to 15 percent of the time.
Hathaway says that the observed effects of the sunspot cycle in radioisotopes; in ice cores; and in tree rings indicate that some 10 to 15 percent of the time the sun is in “something like a Maunder Minimum.”
“If we’re entering a Maunder Minimum, it will persist until the 2080s,” said Giampapa, who points out that if such a minimum’s primary effect is cooling, it could wreak havoc by curtailing agricultural growing seasons which, for instance, could lead to lower wheat production in breadbasket economies.
But Giampapa says it could also mean a global excursion from the mean, resulting in local climate extremes in terms of both anomalous temperatures and precipitation.
Could a Maunder Minimum mitigate a warming climate?
Not likely, says Hathaway.
Although the rise of global temperatures seen in “the last decade or so seems to have currently leveled off,” says Hathaway, he notes that even a Maunder Minimum would still not be enough to counter the warming effects of anthropogenic climate change.
If anything, a Maunder Minimum may simply make existing weather and short term climate even more unusual and difficult to predict.