[extropy-chat] Martian warming

[Damien Broderick]

Global warming rapidly heating Mars

Thursday, 5 April 2007
Agençe France-Presse
http://www.cosmosmagazine.com/node/1148

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.