http://www.ocregister.com/ocregister/sc ... 643955.php
Global warming on Mars
Causes of planet's heating believed to be different from those on Earth.
By DAVID PERLMAN
San Francisco Chronicle
Global warming has hit Mars, but the shifting winds and swirling dust that scientists theorize power climate changes there bear no relation to the heat-trapping gases that concern the people of Earth.
Researchers studying images of the Martian surface taken by generations of orbiting spacecraft have found that the planet's most prominent features have darkened and lightened in recent decades, altering the way sunlight reflects from its sandy soils, its rocky heights and its deep craters.
The result, say the scientists, is that average global ground temperatures on Mars have risen by more than 1.5 degrees Fahrenheit during the past two decades, while the surface air temperature has risen by a little more than a degree in the same period.
That level of climate change, extended over a century, is well within the ballpark of the 5 degree warming trend on Earth forecast by the International Panel on Climate Change for the end of this century.
A report on Mars's warming was published Thursday in the journal Nature by Lori Fenton, a planetary geologist with the SETI Institute's Carl Sagan Center in Mountain View, Robert M. Haberle, a climate model expert at NASA's Ames Research Center, and Paul Geissler, a Mars specialist at the U.S. Geological Survey in Flagstaff, Ariz.
On Earth, Fenton says, the recent decades of increasing global temperatures have been caused by increased emissions of industrial heat-trapping gases like carbon dioxide and methane, while on Mars, it's the darkening of many surface regions that allows the sun to warm the planet.
"Albedo" is the term for a planet's ability to reflect sunlight, and Mars' overall albedo has decreased since it was first measured from 1976 to 1978 by infrared detectors aboard the two orbiting Viking spacecraft whose landers searched for Martian life.
More than 20 years later, infrared heat detectors aboard the orbiting Mars Global Surveyor measured the planet's albedo and found it had darkened significantly.
The cause, according to Fenton, is a combination of high winds that periodically scour bright sand and dust from many rocky surface regions, fierce "dust devils" similar to those that whip desert sands on Earth, and truly major dust storms like the one in 2001 that literally wrapped itself around the planet before subsiding.
The causes of global warming on Mars – still not entirely understood, Fenton said – are not only far different from those on Earth, but so are the temperatures.
According to Fenton and her colleagues, the global average ground temperature on Mars measured by Viking's instruments was about 97 degrees below zero. When Mars Global Surveyor took measurements 22 years later, it had heated to 95 degrees below zero.
Whether warming persists depends on where and how the winds whirl the sands around and change the planet's albedo from bright to dark or back again, Fenton said.