AFP - Getty Images
The sun unleashes a powerful solar flare from the right side of its disk on June 7, as seen in this image from NASA's Solar Dynamics Observatory. Scientists say the sun is heading toward a peak in its activity cycle in 2013 or so, but may enter a period of hibernation afterward.
By Alan Boyle, Science Editor, NBC News
Last updated 3:15 p.m. ET
The latest long-range space forecast predicts a prolonged drop in solar activity after the next peak — and scientists say that might cool down temperatures here on Earth, or at least slow down the warming trend a bit.
Scientists have studied sunspots and the sun's 11-year activity cycle for 400 years, and they're getting increasingly savvy about spotting the harbingers of "space weather" years in advance, just as meteorologists can figure out what's coming after the next storm.
Storms from the sun are expected to build to a peak in 2013 or so, but after that, the long-range indicators are pointing to an extended period of low activity — or even hibernation.
"This is important because the solar cycle causes space weather ... and may contribute to climate change," Frank Hill, associate director of the National Solar Observatory's Solar Synoptic Network, told journalists today.
In the past, such periods have coincided with lower-than-expected temperatures on Earth. The most famous example is the Maunder Minimum, a 70-year period with virtually no sunspots from 1645 to 1715. Average temperatures in Europe sank so low during that period that it came to be known as "the Little Ice Age."
The linkage between solar activity and climate change is still a matter of scientific debate. And even if there is a link, it's not clear how solar-caused global cooling might interact with industrial global warming due to greenhouse-gas emissions. Climate scientists say the swings in solar activity that they've studied so far have had little or no impact on temperatures or other climate indicators — and they don't expect to see a big impact even if the sun goes quiet for a decade or longer.
But if today's forecast is correct, solar physicists and climatologists will have a golden opportunity to find out for sure.
Hill said scientists had "no way of predicting" how long the hibernation period might last. "It may very well last as long as the Maunder Minimum ... if it occurs," he said.
Hill and other experts on solar activity announced the long-range forecast today at the annual meeting of the American Astronomical Society's Solar Physics Division, being conducted this week at New Mexico State University in Las Cruces, N.M.
How do they know?
The forecast is based on three indicators thought to be tied to long-range solar activity, the comparative rise and fall of sunspots over the activity cycle, as well as the brightness of those sunspots; patterns in the sun's internal "jet stream" of superheated plasma; and the pace of migration in the sun's magnetic field toward the poles, as seen in the sun's corona.
An unusually low number of sunspots have been observed during the current cycle, and the spots are fainter than average. Scientists say they have seen no sign of a characteristic east-west flow of internal plasma, which usually sets the stage for future increases in activity. And the magnetic "rush to the poles" appears to be slowing down.
All these signs suggest that the current solar cycle, Cycle 24, "may be the last one for quite some time," Hill said. The next upswing in solar storms, Cycle 25, may be "very much delayed ... very weak, or may not happen at all."
Beyond the climate effect, solar activity is known to have a significant potential impact on satellite operations, electric power grids and even exposure to radiation at high-altitudes. Solar storms can disrupt satellite signals or air-traffic navigation systems. In 1989, a solar outburst caused a widespread power outage in Quebec. And particularly strong solar flares have forced astronauts to take shelter in shielded areas of the space shuttle or the International Space Station.
Some observers have worried about the possibility of a massive geomagnetic super-storm like the one that swept over Earth in 1859, known as the "Carrington event." For those folks, the news that the sun appears to be settling down, coupled with indications that the 2013 solar maximum is not expected to be unusually strong, should be reassuring.
About that ice age ...
Hill and two other solar physicists involved in formulating the forecast, NSO researcher Matt Penn and Richard Altrock of the U.S. Air Force's coronal research program, said there was not yet enough data to firm up a climate connection to solar activity. But they and other scientists have noted that historic lulls in sunspots, such as the Maunder Minimum and another solar minimum between 1790 and 1830, coincided with cooler temperatures.
Gavin Schmidt, a climatologist at NASA's Goddard Institute for Space Studies and one of the founders of the RealClimate blog, said the effects of solar activity on climate over the past 30 years have been "at the margin of what we can detect."
"They are detectable in the high atmosphere, but when you get down to the surface, there is so much other stuff going on that it's been really hard to get a clean signal," he told me.
One of the reasons why so little is known about solar effects on climate is that the sun's highs and lows have been within such a narrow range in recent history.
"If we were to see a return to what's called Maunder Minimum conditions in the next 50 years or so, that would be interesting," Schmidt said. "I think we'd learn a lot about solar physics and solar variability. ... It's going to be scientifically very exciting if all this pans out."
Even then, however, he estimated that the effect of greenhouse-gas emissions would be on the order of 10 times as great. "What you might see over a 20- to 30-year period is a slight slowdown in the pace of warming," Schmidt said. "In terms of how we should think about climate change prediction in the future, reducing emissions and so on, it really wouldn't make much of a difference."
But what about the Little Ice Age in the 1600s, when Swiss Alpine villages were reported destroyed by encroaching glaciers? Schmidt said that period also coincided with an upswing in volcanic emissions, which are known more definitely to contribute to global cooling.
"Parsing out how much of that was solar, how much of that was volcanic and how much of that was just noise ... that's tricky," Schmidt said.
Will this latest forecast be used to argue that we don't need to worry about global warming? Or will the effect of solar hibernation (if it even occurs) turn out to be a blip at best? Feel free to weigh in with your comments below.
More on solar weather:
The studies presented at this week's SPD meeting in Las Cruces include "Large-Scale Zonal Flows During the Solar Minimum — Where Is Cycle 25?" by Frank Hill, R. Howe, R. Komm, J. Christensen-Dalsgaard, T.P. Larson, J. Schou and M.J. Thompson; "A Decade of Diminishing Sunspot Vigor" by W.C. Livingston, M. Penn and L. Svalgard; and "Whither Goes Cycle 24? A View From the Fe XIV Corona" by R.C. Altrock.
You can connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. Also, give a look to "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.
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