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May 27, 2004
Scientists Look at Moon to Shed Light
on Earth’s Climate
According to a new NASA-funded study,
insights into Earth’s climate may come from
an unlikely place: the moon.
Scientists looked at the ghostly glow of light
reflected from Earth onto the moon’s dark
side. During the 1980s and 1990s, Earth bounced
less sunlight out to space. The trend reversed
during the past three years, as the Earth appears
to reflect more light toward space.
Though not fully understood, the shifts may
indicate a natural variability of clouds, which
can reflect the sun’s heat and light away
from Earth. The apparent change in the amount of
sunlight reaching Earth in the 1980s and 1990s is
comparable to taking the effects of greenhouse
gas warming since 1850 and doubling them.
Increased reflectance since 2001 suggests change
of a similar magnitude in the opposite
direction.
Researchers from the New Jersey Institute of
Technology (NJIT), Newark, N.J., and California
Institute of Technology (Caltech), Pasadena,
Calif., combined NASA cloud data from satellites
with records of Earth’s reflectance off the
moon, called earthshine. The study, funded by
NASA’s Living With a Star Program, appears
May 28 in the journal Science.
“Using a phenomenon first explained by
Leonardo DaVinci, we can provide valuable data on
the overall reflectance of the Earth, and
indirectly, on global cloud cover,” said
Phil Goode, a physicist at NJIT, one of the
paper’s authors. He is director of Big Bear
Solar Observatory (BBSO), Big Bear City, Calif.
“Our method has the advantage of being very
precise, and light reflected by large portions of
Earth can be observed simultaneously,” he
said.
Recent news reports suggested sunshine
reaching Earth declined from the late 1950s to
the early 1990s. This new study suggests the
opposite. Earth’s surface may have been
sunnier, or less cloudy, in the 1980s and 1990s.
BBSO has conducted precision earthshine
observations since 1994. Regular observations
began in late 1997.
The research team improved upon an old method
for monitoring earthshine. They compared
earthshine measurements from 1999 to mid-2001
with overlapping satellite observations of global
cloud properties. The cloud satellite record from
1983 to 2001 came from the NASA-managed
International Satellite Cloud Climatology
Project. By matching these two records, the
researchers used the cloud data to extend the
record and construct a substitute measure of
Earth’s albedo, the fraction of light
reflected by a body or surface.
The data showed a steady decrease in
Earth’s albedo from 1984 to 2000. Between
1995 and 1996, Earth dimmed even more sharply.
The data were consistent with satellite
measurements of changing global properties. From
1997 to 2000, Earth continued to dim. The
researchers suggest, during this time period, the
decreases in Earth’s reflectance may be
related to an observed accelerated increase in
mean global surface temperatures. From 2001 to
2003, Earth brightened to pre-1995 values. The
researchers attributed the brightening to changes
in cloud properties.
“At the moment, the cause of these
variations is not known, but they imply large
shifts in Earth’s radiative budget,”
said co-author Steven Koonin, a Caltech
physicist. “Continued observations and
modelling efforts will be necessary to learn
their implications for climate.”
The research offers evidence Earth’s
average albedo varies considerably from year to
year, and from decade to decade. “Our most
likely contribution to the global warming debate
is to emphasize the role of clouds in climate
change must be accounted for, illustrating that
we still lack the detailed understanding of our
present and past climate system to confidently
model future changes,” said Enric Palle, a
postdoctoral associate at NJIT, lead author of
the paper. Pilar Montan~es-Rodriguez, a
postdoctoral associate at NJIT, is another
co-author.
“Even as the scientific community
acknowledges the likelihood of human impact on
climate, it must better document and understand
climate changes,” Koonin said. “Our
ongoing earthshine measurements will be an
important part of that process.”
BBSO, operated by NJIT, is partially supported
by NASA. NASA’s Living with a Star Program
develops the scientific understanding necessary
to effectively address those aspects of the
connected sun-Earth system that directly affect
life and society.
For information and images about this research
on the Internet, visit:
http://www.gsfc.nasa.gov/topstory/2004/0528earthshine.html
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Contacts:
Gretchen Cook-Anderson
Headquarters, Washington
Phone: 202/358-0836
Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, Md.
Phone: 607/273-2561
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A Different Perspective on Climate
Change
By reversing their point of reference,
researchers change their perspective on climate
change. This image was made possible by
Earth’s albedo. If a portion of the
Sun’s light was not reflected back into
space, this photograph could not have been taken.
Credit: NASA
Cloud Cover Plays a Key Role in Climate
Change
Clouds are Earth’s natural blanket.
Clouds trap the Sun’s light, helping to
maintain a regular temperature range for the
Earth; however, some sunlight bounces off the
tops of clouds and is reflected back into space.
The Geostationary Operational Environmental
Satellite (GOES) satellites captured these images
of atmospheric water vapor, which make up
clouds.
Credit: NASA
Researchers Look at Moon for Climate
Answers
This composite image of the dark side’s
Earthshine (left of image) and bright
side’s Moonshine (right of image)
illustrates what scientists are looking at.
Researchers used a blocking filter to dim the
Moonshine crescent, typically about 10,000 times
brighter than Earthshine.
Credit: BBSO/NJIT
NASA Satellites Study Earth’s
Reflectance From Space
The MODIS instrument, flying aboard
NASA’s Terra and Aqua satellites, measures
how much solar radiation is reflected by the
Earth’s surface over the entire planet.
Areas colored red show the most reflective
regions; yellows and greens are intermediate
values; and blues and violets show relatively
dark surfaces. White indicates no data were
available, and no albedo data are provided over
the oceans. This image was produced using data
composited from April 7-22, 2002. Credit: Crystal
Schaaf, Boston University
High-Resolution
Image
The Manned Earthshine
Network
This map shows the locations of observatories
in the present Earthshine Telescope Network. The
telescopes are located at Big Bear Solar
Observatory, California (USA), Crimea
Astronomical Observatory, Crimea (Ukraine), and
Yunnan Astronomical Observatory in Yunnan
(China). Credit: BBSO/NJIT
The Robotic Earthshine
Network
This map shows the varied locations of the
future robotic Earthshine Telescope Network. The
tentative placements of the telescopes are at Big
Bear Solar Observatory (USA), Hawaii (USA), West
Australia, China, Kazakhstan, Crimea (Ukraine),
Canary Islands (Spain) and Chile. Credit:
BBSO/NJIT
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