Some media reports and headlines recently suggested that the sun's present lack of activity could lead to another Little Ice Age, but many solar scientists say that's unlikely.
Yes, the sun has been quiet lately, with very little magnetic activity on its surface; strong activity would be signified by dark patches called sunspots. Until recently, this was to be expected: The sun goes through roughly 11-year cycles, and 2008 was a predicted trough of activity.
But so far, the sun hasn't seemed to pick up in activity as predicted ? sunspots were seen on only 12 of the first 90 days in 2009.
"This reluctance of the new cycle to start has me and others wondering if we might be headed toward a grand minimum where the sun stops producing spots for decades," said NASA solar physicist David Hathaway.
Still, Hathaway does not think this is going to lead to major global cooling, or anything that will significantly alter the trend toward global warming.
History as a guide
The previous grand minimum, called the Maunder Minimum, occurred between 1645 and 1715. The lull fell during a longer range (from about the 16th century to the mid-19th century) when certain areas on Earth experienced a dip in temperatures that became known as the "Little Ice Age."
This connection has prompted some to say we could be heading toward another mini Ice Age. But the science of all this ? how and how much changes in solar activity affect Earth's temperature ? remain largely unresolved.
And anyway, Earth's climate has bigger fish to fry these days, scientists say. The last Little Ice Age occurred before the Industrial Revolution, and may also have been influenced by volcanoes, which tend to lower temperatures.
This time around, Earth's atmosphere is packed with carbon dioxide and greenhouse gases produced by human activities. The warming effects of these heat-trapping gases will probably dwarf any slight cooling that occurs because of a lull in the solar cycle.
"I doubt a Little Ice Age given that we now have nearly twice as much carbon dioxide in the atmosphere than we did 200 years ago," Hathaway told SPACE.com. "I think that plays a larger role than what the sun does."
Judith Lean, a solar physicist at the U.S. Naval Research Laboratory in Washington, D.C., agreed. Even if we do enter a grand minimum of solar activity, it would likely cool the atmosphere only slightly, she said.
"It's possible that there would be some regions that cool more, but globally we wouldn?t expect cooling of more than a few tenths of a degree," Lean said. "And that would be an order of magnitude less than the effects we expect because of global warming, where we're talking about warming of 1 to 4 degrees."
Earth-sun connection poorly understood
In general, the connection between solar activity and temperatures on Earth is not firmly established. There is good evidence that solar activity does affect climate: When the sun is more active, surface temperatures on Earth tend to be slightly warmer, and when the sun is inactive, Earth tends to be cooler.
However, the strength of this effect and the reasons for it are not well understood. The explanation is not simply that the sun is brighter during periods of high activity and cooler when the sun is quiet.
It's more likely that changes in solar activity release different kinds of energetic particles toward the Earth, which then influence the chemistry of Earth's atmosphere and affect the climate. With certainty, scientists know that when the sun is active, it can kick up space storms capable of knocking out satellites and even disabling power grids on Earth. In fact some researchers think the next predicted solar activity peak, in 2012, could be one of the strongest ever, potentially kicking up storms that could bring modern technology to its knees.
So no matter what the sun does over the next few years, it will be very interesting to scientists.
"The solar community is very excited about the sun's behavior right now," Lean said in a phone interview. "It's a fascinating time to be working in this area."
- Gallery: The Wild and Stormy Sun
- Vote: The Best Images of the Sun
- Video - How Space Storms Wreak Havoc on Earth