Global warming: What happens if the sun loses its spots?
Solar physicists increasingly say we could be entering a 'grand solar minimum' of no sunspot activity, the last one of which coincided with the Little Ice Age. Climate scientists are looking at how that could impact global warming.
What would happen to global warming if the sun quit producing sunspots for a few decades?Skip to next paragraph
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The question is of more than passing interest to climate scientists as they ponder the prospect that the sun may be about to enter such a period.
The coming flip of the sun's magnetic field in a few months marks the peak of the current sunspot cycle – one that has produced the fewest sunspots in at least 100 years, and perhaps the last 200 years.
Peering at trends – or in some cases, the lack of them – in the sun's behavior during the run-up to the current cycle's peak, some solar physicists increasingly are considering the possibility that the sun may be on the verge of a "grand solar minimum," comparable to a 70-year period running from the early 17th century into the early 18th century, when the sun produced no sunspots at all.
That period, known as the Maunder Minimum, coincided with the Little Ice Age, when the climate in the Northern Hemisphere cooled significantly.
In the most detailed look yet at the impact a similar event might have on global warming, researchers from the US and Australia have concluded that a 50-year grand minimum in sunspot activity likely would reduce global average temperatures during the period by a few tenths of a degree Celsius, but that the warming trend would resume once solar activity returns to normal.
"What if we went into another Maunder Minimum? Would that actually stop global warming"? asks Gerald Meehl, a researcher at the National Center for Atmospheric Research in Boulder, Colo., who led the team that conducted the study. "The short answer is: No. It slows it down for a while. But the minute the sunspots come back and the solar output goes back up, the temperature pops back up" close to where it would have been if the sun spots hadn't taken a powder, and the warming trend resumes.
The notion that the sun could be heading for a grand minimum hit the headlines two years ago, when three research teams using independent measures suggested that the next sunspot cycle's activity could be substantially lower than the current cycle's.
One sign: A fairly steady decline in the strength of the spots' magnetic fields over a 13-year-period. If the trend is to continue, scientists said, they anticipated a spotless sun by around 2022.
"We still see a decrease in the sunspot magnetic fields," says Matt Penn, a researcher with the National Solar Observatory in Tucson, who took part in the study. "The results are consistent with what we presented in 2011. It seems the trend is continuing along that line" leading to a cut-off in sunspot production.
More recently, research has suggested that the strength of the suns' magnetic field during one solar minimum – when the field is at its strongest – is a harbinger of the size of the peak for the next sunspot maximum. Over the past three sunspot cycles, those fields at solar minimum have been getting weaker, with the weakest appearing during the most recent minimum.