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."
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