The sun is heading into an unusual and extended hibernation, scientists predict. Around 2020, sunspots may disappear for years, maybe decades.
But scientists say it is nothing to worry about. Solar storm activity has little to do with life-giving light and warmth from the sun. The effects from a calmer sun are mostly good. There'd be fewer disruptions of satellites and power systems. And it might mean a little less increase in global warming.
It's happened before, but not for a couple centuries.
"The solar cycle is maybe going into hiatus, sort of like a summertime TV show," said National Solar Observatory associate director Frank Hill, the lead author of a scientific presentation at a solar physics conference in New Mexico.
Scientists don't know why the sun is going quiet. But all the signs are there.
Hill and colleagues based their prediction on three changes in the sun spotted by scientific teams: Weakening sunspots, fewer streams spewing from the poles of the sun's corona and a disappearing solar jet stream.
Those three cues show, "there's a good possibility that the sun could be going into some sort of state from which it takes a long time to recover," said Richard Altrock, an astrophysicist at the Air Force Research Laboratory and study co-author.
The prediction is specifically aimed at the solar cycle starting in 2020. Experts say the sun has already been unusually quiet for about four years with few sunspots _ higher magnetic areas that appear as dark spots.
The enormous magnetic field of the sun dictates the solar cycle, which includes sunspots, solar wind and ejection of fast-moving particles that sometimes hit Earth. Every 22 years, the sun's magnetic field switches north and south, creating an 11-year sunspot cycle. At peak times, like 2001, there are sunspots every day and more frequent solar flares and storms that could disrupt satellites.
Earlier this month, David Hathaway, NASA's top solar storm scientist, predicted that the current cycle, which started around 2009, will be the weakest in a century. Hathaway is not part of Tuesday's prediction.
Altrock also thinks the current cycle won't have much solar activity. He tracks streamers from the solar corona, the sun's outer atmosphere seen during eclipses. The streamers normally get busy around the sun's poles a few years before peak solar storm activity. That "rush to the poles" would have happened by now, but it hasn't and there's no sign of it yet. That also means the cycle after that is uncertain, he said.
Matt Penn of the National Solar Observatory, another study co-author, said sunspot magnetic fields have been steadily decreasing in strength since 1998. If they continue on the current pace, their magnetic fields will be too weak to become spots as of 2022 or so, he said.
Jet streams on the sun's surface and below are also early indicators of solar storm activity, and they haven't formed yet for the 2020 cycle. That indicates that there will be little or delayed activity in that cycle, said Hill, who tracks jet streams.
"People shouldn't be scared of this," said David McComas, a scientist at the Southwest Research Institute in San Antonio, who wasn't part of the team. "This is about the magnetic field and the ionized gas coming out of the sun. It's a reduction in that, not the light and the heat."
There are questions about what this means for Earth's climate. Three times in the past the regular 11-year solar cycle has gone on an extended vacation _ at the same time as cool periods on Earth.
Skeptics of man-made global warming from the burning of fossil fuels have often pointed to solar radiation as a possible cause of a warming Earth, but they are in the minority among scientists. The Earth has warmed as solar activity has decreased.
Andrew Weaver, a climate scientist at the University of Victoria, said there could be small temperature effects, but they are far weaker than the strength of man-made global warming from carbon dioxide and methane. He noted that in 2010, when solar activity was mostly absent, Earth tied for its hottest year in more than a century of record-keeping.
Hill and colleagues wouldn't discuss the effects of a quiet sun on temperature or global warming.
"If our predictions are true, we'll have a wonderful experiment that will determine whether the sun has any effect on global warming," Hill said.