NASA
A solar eruption. Solar weather can affect the climate on Earth as the sun goes through its 11-year solar weather cycle.
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updated 10/7/2010 2:56:14 PM ET 2010-10-07T18:56:14

As the ultimate source of all the energy on Earth, the sun has an inextricable hand in driving our planet's climate and atmosphere. But a new look at the sun's connection to Earth's climate has returned some surprising results.

The study finds that during the most recent lull in the sun's weather cycle, the amount of energy that reached Earth increased, instead of decreasing as predicted. The planet may have experienced a slight warming effect as well, researchers said.

Breaking down the radiation

The study, led by Joanna Haigh, a professor of atmospheric physics at the Imperial College London,analyzed the types of radiation that reach Earth from the sun, and the various effects they have on our planet's atmosphere.

Haigh and her colleagues used satellite measurements taken from 2004 to 2007, the declining phase of the latest 11-year solar weather cycle.

As the sun becomes less active, it typically releases less energy in the form of radiation. Previously, this was understood as a decrease in the total amount of radiation that reaches the top of the Earth's atmosphere.

In examining solar emissions during this declining phase, however, the researchers found that a large decrease in ultraviolet radiation was roughly compensated for, by an increase in visible radiation.

"Visible radiation is the only kind that, in any substantial quality, gets to the Earth's surface and heats the lower atmosphere," Haigh told SPACE.com. "We found that as the sun's activity declined from 2004 to 2007, more of this radiation was entering into the lower atmosphere."

Ultraviolet radiation is largely absorbed in the stratosphere, where it combines with ozone molecules to form what is known as stratospheric ozone. As stratospheric ozone depletes, more UV radiation is able to pass through to the Earth's surface.

Visible radiation, on the other hand, more readily penetrates into the Earth's lower atmosphere. So, if more visible radiation reaches the Earth's surface, the heating of our planet's lower atmosphere results in a warming of the climate.

"In just over three years of observation, we conclude that the visible radiation was going to be warming the planet as the solar activity declined," Haigh said.

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This may seem counterintuitive, and the researchers are careful to note that their findings cannot be generalized without more extensive study of these processes. Furthermore, they said, their observations were made over a relatively short period of time during a potentially anomalous solar cycle.

Their research is detailed in the Oct. 7 issue of the journal Nature.

Understanding the solar cycle

An extremely long stretch of low solar activity in recent years has baffled scientists, and the expected minimum of solar activity between 2008 and 2009 was unusually quiet.

The ebb and flow of the sun's magnetic activity, and the amount of energy it puts out, make up the solar cycle. Typically, a cycle lasts about 11 years, taking roughly 5.5 years to move from a solar minimum to a solar maximum.

The total energy that reaches Earth from the sun varies by only 0.1 percent across the solar cycle, and atmospheric physicists and meteorologists have struggled to link such a small variation to the ups and downs of Earth's natural weather and climate patterns.

"In the past, it was thought that the changes were too small to do anything," Haigh said. "People knew there was a UV component that was heating the stratosphere, but it was thought to be unimportant to the climate."

The findings of this new study, however, could be a step toward piecing together the puzzle.

"The sun has been behaving very strangely over the past few years," Haigh said. "We need to know more about how strange it is before we extrapolate the findings to other periods of time. But it does suggest that our previous understanding of how the sun affects the Earth's climate may be in need of revision."

It doesn't end there

There is more work to be done, Haigh said.

Now that the sun has presumably awoken from its solar minimum, scientists are keen to observe the star as it ramps up its activity.

"It'll be very interesting," Haigh said. "If the visible radiation starts to decline as solar activity goes up, that would be very, very interesting."

These types of studies will be an important part of the discourse on climate change. Being able to gauge the influence of solar activity on our climate and atmosphere will be crucial to the ongoing debate, Haigh said.

"It's quite clear that we have to understand what the sun does to our climate and how much more or less solar activity affects the atmosphere," she said. "We need to work out the solar component of climate change."

"This is not at all to suggest that the sun is causing climate change, but I do think we need to accurately know what the sun is doing, so that we can better assess the human component."

© 2013 Space.com. All rights reserved. More from Space.com.

Photos: Month in space: September 2010

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  1. Martian sea of sand

    Near Mars' north pole, the landscape is dominated by sand dunes forming a massive erg, or sand sea, much like parts of the Sahara Desert on Earth. In parts of the erg, sand is abundant and covers the entire surface. Here, near the edge, sand is in shorter supply and the dunes are separated by areas of lighter-toned soil. This color-coded image from NASA's Mars Reconnaissance Orbiter was captured in July and published on Sept. 1. (NASA /JPL/ University of Arizona) Back to slideshow navigation
  2. Dance of the galaxies

    NGC 5426 and NGC 5427 are two spiral galaxies of similar sizes engaged in a dramatic dance. It is not certain that this interaction will end in a collision and ultimately a merging of the two galaxies, although the galaxies have already been affected. Together known as Arp 271, this dance will last for tens of millions of years. This image, released Aug. 30, was taken with the EFOSC instrument attached to the New Technology Telescope at the European Southern Observatory's La Silla facility in Chile. (ESO) Back to slideshow navigation
  3. Crazy cones on Mars

    These Martian volcanic cones are similar in size and shape to cones found in Iceland, where hot lava has run over wet ground. The heat from the lava boils the water, which bursts through the lava flow. These steam-driven exploding bubbles of lava throw chunks of molten and solid lava into the air. A long series of such explosions is needed to build up one of the large cones. This image, released Sept. 1, was taken by a high-resolution camera on NASA's Mars Reconnaissance Orbiter. (NASA via AP) Back to slideshow navigation
  4. Creating Curiosity

    Engineers work on the Curiosity rover at NASA's Jet Propulsion Laboratory in Pasadena, Calif., on Sept. 16. Curiosity, also known as the Mars Science Laboratory, is due to be launched to the Red Planet from Cape Canaveral Air Force Station in Florida in late 2011. (Jae C. Hong / AP) Back to slideshow navigation
  5. Igor the Terrible

    A photo taken from the International Space Station on Sept. 15 shows Hurricane Igor whirling through the Atlantic Ocean hundreds of miles below. In the foreground you can see a Russian spacecraft docked to the space station. (NASA via AFP - Getty Images) Back to slideshow navigation
  6. Dodging a bullet

    An extreme ultraviolet image from NASA's Solar Dynamics Observatory shows an exceptionally heavy plasma eruption on the surface of the sun on Sept. 8. Not to worry, though: The resulting blast of electrically charged particles missed Earth. (NASA/SDA via EPA) Back to slideshow navigation
  7. Bull's-eye on the moon

    A color-coded topographic map based on data from NASA's Lunar Reconnaissance Orbiter shows the 580-mile-wide Mare Orientale, the largest young impact basin on the moon. This basin formed when a projectile hit the moon about 3.8 billion years ago and penetrated deeply into the lunar crust, ejecting huge amounts of material. The image was released Sept. 16 to coincide with the publication of scientific papers about LRO's mission. (NASA / Goddard / MIT / Brown) Back to slideshow navigation
  8. Two flashes from Jupiter

    A fleeting bright dot on each of these images of Jupiter marks a small comet or asteroid burning up in the atmosphere. The image on the left was taken on June 3 by Australian amateur astronomer Anthony Wesley, with a fireball appearing on the right side. The image on the right was taken by Japanese amateur astronomer Masayuki Tachikawa on Aug. 20, with a fireball appearing at upper right. In a report published Sept. 9, NASA said neither event left a lasting mark on the planet. (NASA via Reuters) Back to slideshow navigation
  9. Spiral in space

    A picture from the Hubble Space Telescope, published Sept. 7, shows an unusual spiral nebula around the star LL Pegasi, 3,000 light-years from Earth. Astronomers say the spiral shape was created by material swirling out from one of the stars in a binary-star system. (ESA / NASA) Back to slideshow navigation
  10. Bootprint on Mars?

    Orcus Patera is an enigmatic elliptical depression near Mars' equator, in the eastern hemisphere of the planet. Located between the volcanoes of Elysium Mons and Olympus Mons, its formation remains a mystery. The favored theory is that the feature was created when a comet or asteroid hit the Red Planet at a shallow angle. This picture of Orcus Patera, released Aug. 27, was taken by the European Space Agency's Mars Express orbiter. (ESA) Back to slideshow navigation
  11. NASA's six-legged robot

    The All-Terrain Hex-Limbed Extra-Terrestrial Explorer, or ATHLETE, is a prototype heavy-lift utility vehicle designed to support future human exploration of extraterrestrial surfaces. ATHLETE got a chance to flex its limbs on Sept. 15 in northern Arizona during NASA's Desert RATS field tests. (Robyn Beck / AFP - Getty Images) Back to slideshow navigation
  12. Practicing for Mars

    Geologists Jacob Bleacher and Jim Rice take a close look at a rock formation in northern Arizona before collecting samples on Sept. 5. The geologists took part in NASA's Desert RATS exercise, which is aimed at trying out the equipment and procedures that could come into play during a mission to Mars or other interplanetary destinations. The "RATS" in the name stands for "Research and Technology Studies." (NASA Desert RATS) Back to slideshow navigation
  13. Ice sculptures in space

    Clouds of gas and dust in the Carina Nebula are sculpted into bizarre shapes by stellar radiation, as seen in this image captured by the Hubble Space Telescope and unveiled on Sept. 16. The Hubble team compares the pillars to "cosmic ice sculptures." (NASA, ESA, and the Hubble Heritage Project) Back to slideshow navigation
  14. New York at night

    New York City is ablaze in an image sent by NASA astronaut Doug Wheelock from the International Space Station on Aug. 28. "The City That Never Sleeps," he wrote in a Twitter tweet. "New York, New York on a clear summer night." (Doug Wheelock / NASA via AP) Back to slideshow navigation
  15. Shooting a laser at the sky

    This image, released on Sept. 6, shows a laser beam shooting up from the European Southern Observatory’s Paranal Observatory in Chile. The laser beam is used as a guide for the observatory's adaptive-optics system, which compensates for unsteadiness in the atmosphere to produce sharper astronomical images. (Y. Beletsky / ESO) Back to slideshow navigation
  16. Thar she blows!

    A solid rocket motor that could be used on future NASA launch vehicles is tested Aug. 31 at ATK Aerospace Systems' test site in Promontory, Utah. The rocket motor burned for just over two minutes during the successful static test, producing about 3.6 million pounds of thrust. (ATK) Back to slideshow navigation
  17. The road ahead

    NASA's Opportunity rover looks across a series of sand ripples and bedrock outcrops toward the rim of Endeavour Crater on the horizon on Sept. 6. Opportunity has just crossed the halfway mark in its trip from Victoria Crater to Endeavour. The rover headed out from Victoria in September 2008. (NASA / JPL-Caltech) Back to slideshow navigation
  18. Saturn and its children

    Four of Saturn's moons join the planet for a well-balanced portrait, released by the Cassini orbiter's imaging team on Sept. 10. Saturn's largest moon, Titan, is at lower left. Tethys is at upper right. Two much smaller moons, Pandora and Epimetheus, are barely visible near the rings. (NASA/JPL/Space Science Institute) Back to slideshow navigation
  19. Moon and Earthglow

    A crescent moon is just about to set below Earth's glowing horizon in a picture taken Sept. 4 from the International Space Station. The glow is sunlight scattered by Earth's atmosphere. (NASA via Reuters) Back to slideshow navigation
  20. Twilight of the shuttle

    Photographers gather early on the morning of Sept. 21 to take pictures of the space shuttle Discovery, just after its arrival at the launch pad. Discovery is scheduled to embark on the shuttle fleet's penultimate mission on Nov. 1. The final shuttle flight, involving Endeavour, is set for launch in February - although there's a chance that one additional mission will be flown. (Scott Audette / Reuters) Back to slideshow navigation
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