Solar Variability: Striking a Balance with Climate Change

May 08, 2008
Solar Variability: Striking a Balance with Climate Change
The sun radiates huge amounts of electromagnetic energy in all directions. Earth is only one small recipient of the sun´s energy; the sun´s rays extend far out into the solar system, illuminating all the other planets. Credit: NASA

The sun has powered almost everything on Earth since life began, including its climate. The sun also delivers an annual and seasonal impact, changing the character of each hemisphere as Earth's orientation shifts through the year. Since the Industrial Revolution, however, new forces have begun to exert significant influence on Earth's climate.

"For the last 20 to 30 years, we believe greenhouse gases have been the dominant influence on recent climate change," said Robert Cahalan, climatologist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

For the past three decades NASA scientists have investigated the unique relationship between the sun and Earth. Using space-based tools, like the Solar Radiation and Climate Experiment (SORCE), they have studied how much solar energy illuminates Earth, and explored what happens to that energy once it penetrates the atmosphere. The amount of energy that reaches Earth's outer atmosphere is called the total solar irradiance. Total solar irradiance is variable over many different timescales, ranging from seconds to centuries due to changes in solar activity.

The sun goes through roughly an 11-year cycle of activity, from stormy to quiet and back again. Solar activity often occurs near sunspots, dark regions on the sun caused by concentrated magnetic fields. The solar irradiance measurement is much higher during solar maximum, when sunspot cycle and solar activity is high, versus solar minimum, when the sun is quiet and there are usually no sunspots.

"The fluctuations in the solar cycle impacts Earth's global temperature by about 0.1 degree Celsius, slightly hotter during solar maximum and cooler during solar minimum," said Thomas Woods, solar scientist at the University of Colorado in Boulder. "The sun is currently at its minimum, and the next solar maximum is expected in 2012."

Using SORCE, scientists have learned that about 1,361 watts per square meter of solar energy reaches Earth's outermost atmosphere during the sun's quietest period. But when the sun is active, 1.3 watts per square meter (0.1 percent) more energy reaches Earth. "This TSI measurement is very important to climate models that are trying to assess Earth-based forces on climate change," said Cahalan.

Over the past century, Earth's average temperature has increased by approximately 0.6 degrees Celsius (1.1 degrees Fahrenheit). Solar heating accounts for about 0.15 C, or 25 percent, of this change, according to computer modeling results published by NASA Goddard Institute for Space Studies researcher David Rind in 2004. Earth's climate depends on the delicate balance between incoming solar radiation, outgoing thermal radiation and the composition of Earth's atmosphere. Even small changes in these parameters can affect climate. Around 30 percent of the solar energy that strikes Earth is reflected back into space. Clouds, atmospheric aerosols, snow, ice, sand, ocean surface and even rooftops play a role in deflecting the incoming rays. The remaining 70 percent of solar energy is absorbed by land, ocean, and atmosphere.

"Greenhouse gases block about 40 percent of outgoing thermal radiation that emanates from Earth," Woods said. The resulting imbalance between incoming solar radiation and outgoing thermal radiation will likely cause Earth to heat up over the next century, accelerating the melting polar ice caps, causing sea levels to rise and increasing the probability of more violent global weather patterns.

Non-Human Influences on Climate Change

Before the Industrial Age, the sun and volcanic eruptions were the major influences on Earth's climate change. Earth warmed and cooled in cycles. Major cool periods were ice ages, with the most recent ending about 11,000 years ago.

"Right now, we are in between major ice ages, in a period that has been called the Holocene,” said Cahalan. “Over recent decades, however, we have moved into a human-dominated climate that some have termed the Anthropocene. The major change in Earth's climate is now really dominated by human activity, which has never happened before."

The sun is relatively calm compared to other stars. "We don't know what the sun is going to do a hundred years from now," said Doug Rabin, a solar physicist at Goddard. "It could be considerably more active and therefore have more influence on Earth's climate."

Or, it could be calmer, creating a cooler climate on Earth similar to what happened in the late 17th century. Almost no sunspots were observed on the sun's surface during the period from 1650 to 1715. This extended absence of solar activity may have been partly responsible for the Little Ice Age in Europe and may reflect cyclic or irregular changes in the sun's output over hundreds of years. During this period, winters in Europe were longer and colder by about 1 C than they are today.

Since then, there seems to have been on average a slow increase in solar activity. Unless we find a way to reduce the amount of greenhouse gases we put into the atmosphere, such as carbon dioxide from fossil fuel burning, the solar influence is not expected to dominate climate change. But the solar variations are expected to continue to modulate both warming and cooling trends at the level of 0.1 to 0.2 degrees Celsius (0.18 to 0.26 Fahrenheit) over many years.

Future Measurements of Solar Variability

For three decades, a suite of NASA and European Space Agency satellites have provided scientists with critical measurements of total solar irradiance. The Total Irradiance Monitor, also known as the TIM instrument, was launched in 2003 as part of the NASA’s SORCE mission, and provides irradiance measurements with state-of-the-art accuracy. TIM has been rebuilt as part of the Glory mission, scheduled to launch in 2009. Glory's TIM instrument will continue an uninterrupted 30-year record of solar irradiance measurements and will help researchers better understand the sun's direct and indirect effects on climate. Glory will also collect data on aerosols, one of the least understood pieces of the climate puzzle.

Source: by Rani Gran, NASA's Goddard Space Flight Center

Explore further: Europe sat-nav launch glitch linked to frozen pipe

add to favorites email to friend print save as pdf

Related Stories

NASA launches RapidScat wind watcher to Space Station

Sep 22, 2014

A new NASA mission that will boost global monitoring of ocean winds for improved weather forecasting and climate studies is among about 5,000 pounds (2,270 kilograms) of NASA science investigations and cargo ...

'Hot Jupiters' provoke their own host suns to wobble

Sep 11, 2014

Blame the "hot Jupiters." These large, gaseous exoplanets (planets outside our solar system) can make their suns wobble when they wend their way through their own solar systems to snuggle up against their ...

Researchers measure ozone-depleting bromine

Sep 10, 2014

How much does bromine affect stratospheric ozone? Answering this question is the primary objective of measurements by a multi-instrument gondola carried by a high-altitude balloon. The gondola accommodates ...

Recommended for you

Europe sat-nav launch glitch linked to frozen pipe

11 hours ago

A frozen fuel pipe in the upper stage of a Soyuz launcher likely caused the failure last month to place two European navigation satellites in orbit, a source close to the inquiry said Wednesday.

Cyanide ice in Titan's atmosphere

13 hours ago

Gigantic polar clouds of hydrogen cyanide roughly four times the area of the UK are part of the impressive atmospheric diversity of Titan, the largest moon of Saturn, a new study led by Leiden Observatory, ...

Video: Alleged meteor caught on Russian dash cam (again)

17 hours ago

Thanks to the ubiquity of dashboard-mounted video cameras in Russia yet another bright object has been spotted lighting up the sky over Siberia, this time a "meteor-like object" seen on the evening of Saturday, Sept. 27.

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

mikiwud
3.7 / 5 (6) May 09, 2008
"greenhouse gases block about 40% of out going thermal radiation" is not strictly correct.Molecules of various gases aborb thermal radiation on a narrow wave length (different for each gas),the radiate some of this back in all directions at a different wave length to which it absorbed it.This decreases as the ppm increase,i.e the law of diminishing returns.If Solar radiation is constant the max radiation at any specific wave length is thus limited. Therefore there is a point when there is no more radiation at that wave length to be absorbed to be radiated.There could be no runaway green house effect as the scaremongers say (although this article does not suggest this one way or the other).
The also ignore the possible indirect effect of Solar variation (sun spots) on cloud formation which has a large effect on climate.

At least the did not blame CO2 directly,but most readers would assume it as being the only greenhouse gas.
Rick69
3 / 5 (8) May 09, 2008
I wonder how much confidence in NASA scientists Christa McAuliffe's family has?
marjon
not rated yet Aug 04, 2008
"For the last 20 to 30 years, we believe greenhouse gases have been the dominant influence on recent climate change," said Robert Cahalan, climatologist at NASA%u2019s Goddard Space Flight Center in Greenbelt, Md.

After 30 years they still can't prove it?