[extropy-chat] Martian warming
thespike at satx.rr.com
Thu Apr 5 20:18:14 UTC 2007
Global warming rapidly heating Mars
Thursday, 5 April 2007
PARIS: Climate change could be warming Mars four
times faster than Earth due to a mutually
reinforcing interplay of wind-swept dust and
changes in reflected heat from the Sun.
Scientists have long observed a perplexing
correlation on Mars between the darkening or
lightening of swathes of its surface and the
planet's fluctuating temperatures; which range
from -87°C to -5°C depending on the season and the location.
The explanation may lie in the dirt, according to a report published today.
Glistening Martian dust lying on the ground
reflects the Sun's light - and its heat - back
into space, a phenomenon called albedo. But when
this reddish dust is churned up by violent winds,
the storm-ravaged surface loses its reflective
qualities and more of the Sun's heat is absorbed
into the atmosphere, causing temperatures to rise.
The study, published today by the British journal
Nature, shows for the first time that these
variations not only result from the storms but
help cause them too. It also suggests that
short-term climate change is currently occurring
on Mars and at a much faster rate than on Earth.
The report's authors, led by planetary scientist
Lori Fenton, with U.S. space agency NASA's Ames
Research Centre in California, describe the
phenomenon as a "positive feedback" system. In
other words, a vicious circle, in which changes
in albedo strengthen the winds, which in turn
kick up more dust and further add to the warming.
In the same way, if a snow-covered area on Earth
warms and the snow melts, the reflected light
decreases and more solar radiation is absorbed,
causing local temperatures to increase. If new
snow falls, a cooling cycle starts.
On Mars, there have been an unusual number of
massive, planet-darkening storms over the last 30
years, and computer models indicate that surface
air temperatures on the Red Planet increased by
0.65°C from the 1970s to the 1990s. Residual ice
on the Martian south pole, the researchers note,
has steadily retreated over the last four years.
By comparison, the average temperature of Earth
increased by 0.75°C over the last century.
To measure the change in patterns of reflected
light, Fenton and her colleagues compared thermal
spectrometer images of Mars taken by NASA's
Viking mission in the late 1970s with similar
images gathered more than 20 years later by the
Global Surveyor. They then analysing the
correlation between albedo variations, the
presence of atmospheric dust and change in temperature.
Exactly what triggers the planet's so-called
"global dust storms" remains a mystery. But any
future research must now consider albedo
variations as one of the factors that drive
Martian climate change, they conclude.
Mars ... atmosphere is composed mostly of carbon dioxide.
The albedo of Earth, averaged across all its
different surfaces, is about 30 times greater
than that of Mars, which is far darker.
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