Sun & Climate Change News


Sun Oddly Quiet -- Hints at Next "Little Ice Age"?


Anne Minard

for National Geographic News

May 4, 2009

A prolonged lull in solar activity has astrophysicists glued to their telescopes waiting to see what the sun will do next—and how Earth's climate might respond.

The sun is the least active it's been in decades and the dimmest in a hundred years. The lull is causing some scientists to recall the Little Ice Age, an unusual cold spell in Europe and North America, which lasted from about 1300 to 1850.

The coldest period of the Little Ice Age, between 1645 and 1715, has been linked to a deep dip in solar storms known as the Maunder Minimum.

During that time, access to Greenland was largely cut off by ice, and canals in Holland routinely froze solid. Glaciers in the Alps engulfed whole villages, and sea ice increased so much that no open water flowed around Iceland in the year 1695.

But researchers are on guard against their concerns about a new cold snap being misinterpreted.

"[Global warming] skeptics tend to leap forward," said Mike Lockwood, a solar terrestrial physicist at the University of Southampton in the U.K. (Get the facts about global warming.)

He and other researchers are therefore engaged in what they call "preemptive denial" of a solar minimum leading to global cooling.

Even if the current solar lull is the beginning of a prolonged quiet, the scientists say, the star's effects on climate will pale in contrast with the influence of human-made greenhouse gases such as carbon dioxide (CO2).

"I think you have to bear in mind that the CO2 is a good 50 to 60 percent higher than normal, whereas the decline in solar output is a few hundredths of one percent down," Lockwood said. "I think that helps keep it in perspective."

Even so, Lockwood added, small variations in the sun's brightness are more powerful than changes in greenhouse gas

contributions. For example, a 50 percent variation in solar brightness would mean the end of life on Earth.

(Related: "Don't Blame Sun for Global Warming, Study Says.")

Local Cooling

For hundreds of years scientists have used the number of observable sunspots to trace the sun's roughly 11-year cycles of activity.

Sunspots, which can be visible without a telescope, are dark regions that indicate intense magnetic activity on the sun's surface. Such solar storms send bursts of charged particles hurtling toward Earth that can spark auroras, disrupt satellites, and even knock out electrical grids.

In the current cycle, 2008 was supposed to have been the low point, and this year the sunspot numbers should have begun to climb.

But of the first 90 days of 2009, 78 have been sunspot free. Researchers also say the sun is the dimmest it's been in a hundred years.

The Maunder Minimum corresponded to a profound lull in sunspots—astronomers at the time recorded just 50 in a 30-year period.

If the sun again sinks into a similar depression, at least one preliminary model has suggested that cool spots could crop up in regions of Europe, the United States, and Siberia.

During the previous event, though, many parts of the world were not affected at all, said Jeffrey Hall, an astronomer and associate director at Lowell Observatory in Flagstaff, Arizona.

"Even a grand minimum like that was not having a global effect," he said.

Wild Cards and Uncertainties

Changes in the sun's activity can affect Earth in other ways, too.

For example, ultraviolet (UV) light from the sun is not bottoming out the same way it did during the past few visual minima.

"The visible light doesn't vary that much, but UV varies 20 percent, [and] x-rays can vary by a factor of ten," Hall said. "What we don't understand so well is the impact of that differing spectral irradiance."

Solar UV light, for example, affects mostly the upper layers of Earth's atmosphere, where the effects are not as noticeable to humans. But some researchers suspect those effects could trickle down into the lower layers, where weather happens.

In general, recent research has been building a case that the sun has a slightly bigger influence on Earth's climate than most theories have predicted.

Atmospheric wild cards, such as UV radiation, could be part of the explanation, said the University of Southampton's Lockwood.

In the meantime, he and other experts caution against relying on future solar lulls to help mitigate global warming.

"There are many uncertainties," said Jose Abreu, a doctoral candidate at the Swiss government's research institute Eawag.

"We don't know the sensitivity of the climate to changes in solar intensity. In my opinion, I wouldn't play with things I don't know."


© 1996-2008 National Geographic Society. All rights reserved.


Don't Blame Sun for Global Warming, Study Says


Brian Handwerk

for National Geographic News

September 13, 2006

Sunspots alter the amount of energy Earth gets from the sun, but not enough to impact global climate change, a new study suggests.

The sun's role in global warming has long been a matter of debate and is likely to remain a contentious topic.

Solar astronomer Peter Foukal of Heliophysics, Inc., in Nahant, Massachusetts, points out that scientists have pondered the link between the sun and Earth's climate since the time of Galileo, the famous 17th-century astronomer.

"There has been an intuitive perception that the sun's variable degree of brightness—the coming and going of sunspots for instance—might have an impact on climate," Foukal said.

Foukal is lead author of a review paper on sunspot intensity appearing in tomorrow's issue of the journal Nature.

He says that most climate models—including ones used by the Intergovernmental Panel on Climate Change—already incorporate the effects of the sun's waxing and waning power on Earth's weather (related images: our stormy star).

But, Foukal said, "this paper says that that particular mechanism [sunspots], which is most intuitive, is probably not having an impact."

Sunspot Impact Simply Too Small

Sunspots are magnetic disturbances that appear as cooler, dark patches on the sun's surface. The number of spots cycles over time, reaching a peak every 11 years.

The spots' impact on the sun's total energy output is easy to see.

"As it turns out, most of the sun's power output is in the visible range—what we see as brightness," said Henk Spruit, study co-author from the Max Planck Institute for Astrophysics in Garching, Germany.

"The sun's brightness varies only because of the blemishes that are also visible directly on pictures: the dark patches called sunspots and the minute bright points called faculae. In terms of brightness changes, in large part, what you see is what you get."

The sun's energy output varies slightly as sunspots wax and wane on the star's surface.

But sunspot-driven changes to the sun's power are simply too small to account for the climatic changes observed in historical data from the 17th century to the present, research suggests.

The difference in brightness between the high point of a sunspot cycle and its low point is less than 0.1 percent of the sun's total output.

"If you run that back in time to the 17th century using sunspot records, you'll find that this amplitude variance is negligible for climate," Foukal said.

The researchers obtained accurate daily sunspot measurements dating as far back as 1874 from institutions such as the Mount Wilson Observatory near Pasadena, California, and the Royal Observatory in Greenwich, England.

Older records exist all the way back to when the telescope was invented in the 17th century, though the data become increasingly patchy with age (see a related graphic of how the Hubble Space Telescope works).

The team also derived the sun's historic strength by looking at the presence or absence of isotopes, such as beryllium 10, in ice samples from Greenland and Antarctic that reflect the past contents of Earth's atmosphere.

(Related news: "Climate-Change Forecast? Ask the Antarctic Ice" [November 2004].)

Such isotopes are formed when cosmic radiation penetrates the atmosphere.

In periods of high activity, a brighter sun emits more magnetic and plasmatic particles that shield Earth from the galaxy's rays, resulting in fewer isotopes.

Measuring the historical record of such isotopes from ice yields useful, though debatable, estimates of the sun's past power on Earth.

"If you see that these isotopes were low for 50 or 100 years, it's a darn good bet that the sun was more active then," Foukal said.

Sun Not Off the Hook for Warming

The authors and other experts are quick to point out that more complicated solar mechanisms could possibly be driving climate change in ways we don't yet understand.

Climate change carries such high stakes that even more unlikely possibilities may capture scientific attention.

"There are numerous studies that find a correlation [between solar variation and Earth climate]," said Sami Solanki of the Max Planck Institute for Solar System Research in Lindau, Germany.

"These authors have looked at the simplest mechanism, and they find that this mechanism does not produce the same level of change that has been observed," he continued.

"This could be suggesting that there are other mechanisms acting for the way that the sun influences climate."

Solar ultraviolet (UV) rays are one possibility, though that theory creates its own challenges.

"UV is only a small fraction of total solar output, so you'd need a strong amplification mechanism in the Earth's atmosphere," study co-author Spruit said.

Magnetized plasma flares known as solar wind could also impact Earth's climate. Solar wind influences galactic rays and may in turn affect atmospheric phenomena on Earth, such as cloud cover.

Such complex interactions are poorly understood but could be crucial to unlocking Earth's climatic puzzle.

"I think the main question," the Max Planck Institute's Solanki said, "is, How does the sun [in general] act on climate? What are the processes that are going on in the Earth's atmosphere?"


© 1996-2008 National Geographic Society. All rights reserved.

NOAA Predictions for Cycle 24

May 8, 2009: A new active period of Earth-threatening solar storms will be the weakest since 1928 and its peak is still four years away, after a slow start last December, predicts an international panel of experts led by NOAA's Space Weather Prediction Center. Even so, Earth could get hit by a devastating solar storm at any time, with potential damages from the most severe level of storm exceeding $1 trillion. NASA funds the prediction panel.

Solar storms are eruptions of energy and matter that escape from the sun and may head toward Earth, where even a weak storm can damage satellites and power grids, disrupting communications, the electric power supply and GPS. A single strong blast of solar wind can threaten national security, transportation, financial services and other essential functions.

The panel predicts the upcoming Solar Cycle 24 will peak in May 2013 with a daily sunspot number of 90. If the prediction proves true, Solar Cycle 24 will be the weakest cycle since number 16, which peaked at 78 daily sunspots in 1928, and ninth weakest since the 1750s, when numbered cycles began.

The most common measure of a solar cycle’s intensity is the number of sunspots—Earth-sized blotches on the sun marking areas of heightened magnetic activity. The more sunspots there are, the more likely it is that solar storms will occur, but a major storm can occur at any time.

"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 expensive problems," said NOAA scientist Doug Biesecker, who chairs the panel. "The strongest solar storm on record occurred in 1859 during another below-average cycle similar to the one we are predicting."

The 1859 storm shorted out telegraph wires, causing fires in North America and Europe, sent readings of Earth's magnetic field soaring, and produced northern lights so bright that people read newspapers by their light.

A recent report by the National Academy of Sciences found that if a storm that severe occurred today, it could cause $1-2 trillion in damages the first year and require four to ten years for recovery, compared to $80-125 billion that resulted from Hurricane Katrina.

The panel also predicted that the lowest sunspot number between cycles—or solar minimum—occurred in December 2008, marking the end of Cycle 23 and the start of Cycle 24. If the December prediction holds up, at 12 years and seven months Solar Cycle 23 will be the longest since 1823 and the third longest since 1755. Solar cycles span 11 years on average, from minimum to minimum.

An unusually long, deep lull in sunspots led the panel to revise its 2007 prediction that the next cycle of solar storms would start in March 2008 and peak in late 2011 or mid-2012. The persistence of a quiet sun since the last prediction has led the panel to a consensus that the next cycle will be "moderately weak."

NOAA's Space Weather Prediction Center (SWPC) is the nation's first alert of solar activity and its effects on Earth. The Center's space weather experts issue outlooks for the next 11-year solar cycle and warn of storms occurring on the Sun that could impact Earth. SWPC is also the world warning agency for the International Space Environment Service, a consortium of 12 member nations.

As the world economy becomes more reliant on satellite-based communications and interlinked power grids, interest in solar activity has grown dramatically. In 2008 alone, SWPC acquired 1,700 new subscription customers for warnings, alerts, reports, and other products. Among the new customers are emergency managers, airlines, state transportation departments, oil companies, and nuclear power stations. SWPC's customers reside in 150 countries.

"Our customer growth reflects today’s reality that all sectors of society are highly dependent on advanced, space-based technologies," said SWPC director Tom Bogdan. "Today every hiccup from the sun aimed at Earth has potential consequences."