A couple years back, scientists were predicting that the next peak in solar activity would be among the strongest in modern times. Now they say it could be the weakest since 1928.

However, big Earth-threatening solar storms could still kick up at any time, the researchers cautioned today.

The solar cycle runs about 11 years. At the low point, which is now, sunspots and solar flares are rare for months and months. During the peak, sunspots, flares and solar storms are common.

The spots are dark areas of magnetic activity that suppress energy below. When the energy is unleashed, it's like a cork coming off a bottle of Champagne. But rather than bubbly, the sun emits flares of charged particles called coronal mass ejections that race to Earth. Within a day or two, a strong solar storm can slam into our planet's defense system – the protective magnetic field. Big storms overwhelm the field, leak in, and can knock out satellites and even trip power grids on Earth's surface.

The latest forecast, from the NOAA's Space Weather Prediction Center (our Weather Service for the cosmos), sees a mild peak that should come in about May, 2013.

(In 2007, they had predicted a peak for late 2011 or mid-2012.)

Why the change?

The sun has been very, very quiet lately. This unusually long, deep lull in sunspots forced the revision, the panel stated. Some have even raised the possibility that the quiescence could lead to a Little Ice Age, as the sun pumps less energy our way. Scientists say that's very unlikely.

But the forecasters note that big individual storms can strike before, during or after any cycle's peak, even if it is weak.

"As with hurricanes, whether a cycle is active or weak refers to the number of storms, but everyone needs to remember it only takes one powerful storm to cause huge problems," said NOAA scientist Doug Biesecker, who chairs the panel. "The strongest solar storm on record occurred in 1859 during another below-average cycle."

The 1859 storm shorted out telegraph wires, causing fires in North America and Europe. It produced northern lights (the auroras that ring the North Pole) so bright that people are said to have read newspapers by their light at night.

Things are a lot different than 1859, of course. Modern communication systems are vulnerable to solar storms, and we are far more reliant on them for everything from heat to water to 911 calls.

A recent report by the National Academy of Sciences found that if a storm that severe occurred nowadays, it could cause up to $2 trillion in initial damages by crippling communications on Earth and fueling chaos among residents and even governments in a scenario that would require four to 10 years for recovery. For comparison, hurricane Katrina inflicted somewhere between $80 billion and $125 billion in damage.

The new forecast was prepared by an international panel of experts, funded by NASA and led by NOAA.

The panel predicts Solar Cycle 24 will peak in May 2013 with 90 sunspots per day on average. If it proves true, Solar Cycle 24 would be the weakest cycle since number 16, which peaked at 78 daily sunspots in 1928, and ninth weakest since the 1750s, when reliable recordkeeping began.

But as today's turnabout illustrates, forecasting sunspots, overall solar activity and even specific storms is all a science in its infancy. And more so than with terrestrial weather and climate predictions, figuring out what the sun will do three years from now is, researchers admit, tricky business.

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