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EARTH'S CLIMATE (extended slates)

LIBRARY #: G04-028

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RELEASE DATE: 05/27/04

PRODUCER: LIZ SMITH 301-286-1540

URL(S): http://www.gsfc.nasa.gov/topstory/2004/0528earthshine.html


The Moon is an unlikely place to study climate change on Earth, but researchers are now looking to the Moon's dark side for answers. Sunlight reflecting off Earth can bounce onto the Moon causing what scientists call Earthshine. Leonardo DaVinci first explained the origin of Earthshine and 500 years later it has become an important tool in the measurement of Earth's global climate change.

Combined observations of Earthshine and satellite cloud data suggest that Earth bounced less sunlight into space in the 1980s and 1990s. Though not fully understood, the shifts may be a natural variability in cloud cover. This apparent change, if confirmed, is comparable to taking the effects of greenhouse gas warming since 1850 and doubling them. Surprisingly, this trend reversed in the last three years. Earth now appears to be reflecting more light towards space.
The study appears in the May 28, 2004 issue of the journal SCIENCE. This work was funded by NASA's Living with a Star Program.

ITEM 1: Earth's Albedo Crucial as Link to Climate Change Understanding

Viewed from space, Earth reflects quite a bit of light. Without this reflection, called albedo, these photographs would not be possible. If Earth absorbed all of the Sun's light, it would appear very dark if at all. Shifts in the intensity of Earth's albedo from day to day, and decade to decade, offer clues to mysteries surrounding Earth's changing climate.

Image 1: The entire Earth as seen from the Galileo mission.

Image 2: The Moon is an ideal place to view Earth's reflectance, where light from the Earth brightens the dark side in the form of Earthshine. This view of Earth from the Moon was taken during the Apollo 17 mission of 1972.
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ITEM 2: Cloud Cover Plays a Key Role in Climate Change

Clouds are Earth's natural blanket like your comforter that keeps you warm at night by trapping your body heat under the covers. Clouds floating above trap the Sun's light as heat, helping to maintain a regular temperature range for the Earth. However, a portion of the sunlight reaching the planet bounces off the tops of clouds and gets reflected back into space, contributing to Earth's albedo, or reflectance. Measuring this albedo can tell researchers about our changing climate. The Geostationary Operational Environmental Satellite (GOES) satellites captured these dramatic images of the atmospheric water vapor that makes up clouds over the Western Hemisphere.

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ITEM 3: Earthshine Highlights the Dark Side of the Moon

Only about two-thirds of the sunlight that reaches Earth actually makes it to our planet's surface. The rest bounces off reflective surfaces into space. A portion of this reflected light falls on the dark side of the Moon, causing what we call Earthshine. NASA-funded researchers at the Big Bear Solar Observatory (BBSO) compare this Earthshine found on the Moon's dark side to the reflection from sunlight on the Moon's bright side to study the earth's global climate change by measuring changes in the earth's albedo, or total reflectance.

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ITEM 4: Researchers Look to the Moon's Dark Side to Measure Albedo

This composite image of the Moon's dark and light sides suggests that the Sun isn't the only light source illuminating our closest neighbor. Researchers placed a blocking filter over the brightly lit quarter Moon to reveal the ghostly glow of the dark side, also known as Earthshine. The light side's Moonshine glows typically about 10,000 times brighter than the Earthshine. NASA funded researchers now look to the dark side of the Moon to study global climate change by measuring the result of Earth's reflectance on it, or what they call Earthshine.

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ITEM 5: Clouds Play a Role in Climate Change

Only about 70% of the solar energy that reaches Earth is absorbed, while the other 30% is reflected by the atmosphere, aerosols, oceans, continents, and clouds. Clouds account for about 20-24% of the total reflection. Similar to how a person wearing a white shirt stays cooler in the summer than a person wearing a black shirt, the vast area of cloud cover around the world reflects large amounts of solar radiation falling on the planet's surface. Clouds floating above can also act as a blanket, trapping that solar radiation as valuable heat. Through these processes, clouds help maintain a regular temperature regime for Earth. How much cloud cover there is can greatly affect the temperature on Earth's surface and have a major impact on Earth's climate.

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ITEM 6: Satellites Measure the Global Albedo

The Moderate Resolution Imaging Spectroradiometer (MODIS), on NASA's Terra and Aqua satellites, routinely measures how much solar radiation is reflected by Earth's surface. This detailed albedo information should help to greatly improve weather and forecast models as well as our understanding of longer-term climate trends.

The sequence begins with a true-color portrait of the planet and dissolves into MODIS albedo measurements. Red areas represent the brightest, most reflective regions; yellows and greens are intermediate values; and blues and violets show relatively dark surfaces. Black indicates no data available and no albedo data are provided over the oceans.

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ITEM 7: Clouds B-Roll

Clouds play a larger role in our lives than inspiring daydreams and dropping an unexpected shower. Clouds blanket our planet and help regulate Earth's temperature. They are a cornerstone of our climate from day to day and decade to decade. Without clouds, Earth would be a very different place.

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ITEM 8: Moon B-Roll

The Moon lies 238,751 miles from Earth. It is the only extraterrestrial body to have been visited by humans. The Soviet spacecraft Luna 2 first visited the Moon in 1959, but the first landing was on July 20, 1969. Do you remember where you were? The last visit was in December 1972. The spacecraft Clementine extensively mapped the Moon in the summer of 1994 and was followed by Lunar Prospector in 1999.

Image 1: Although no Earthshine is visible during a Full Moon, plenty of the Sun's light is reflected off the lunar surface, called Moonshine. Photograph Courtesy of Lick Observatory

Image 2 and 3: The Earth reflects enough of the Sun's light back into space that the Moon's dark side is lighter than we often think it is. These images capture this ghostly glow that researchers call Earthshine.

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