Dust blamed for warming on Mars

energy

[is this a factor for warming on earth ...?!]


The walls of many pits in the "Swiss cheese" structure of the ice on Mars's southern polar cap retreated by 1 to 3 metres over a recent Martian year, suggesting the planet has been warming up (Image: NASA/JPL/MSSS)

Scientists have been puzzling over the cause of dramatic global warming on Mars, which has made parts of the south polar ice cap disappear in recent years. The answer, it seems, is blowing in the wind: the planet's famous reddish dust.
Using global circulation models similar to those used to analyse Earth's changing climate, a team led by Lori Fenton of NASA's Ames Research Center in California, US, found that Mars seems to have warmed by about 0.65° Celsius in the three decades since the Viking mission first provided detailed mapping of the whole planet.
That warming can be explained entirely by the scouring away of light-coloured dust from darker areas of the surface, causing an increase in the absorption of solar radiation.
This effect is greatly amplified by positive feedback: The warmer ground causes stronger winds, which in turn scour away more of the light dust and lead to greater warming.
Team member Paul Geissler, a planetary geologist at the US Geological Survey in Flagstaff, Arizona, says the mechanism can account for the rapid warming that has been seen in the disappearing polar caps, which are turning directly from solid to vapour at a rapid rate (watch an animation showing Mars's south polar cap change from 1999 to 2005).
Global dust storm
The overall distribution of dark and light areas on Mars has clearly changed since Viking (watch an animation of the surface reflectivity changes over the entire planet). The new modelling shows that the heating produced by those changes is "the same order of magnitude" as that required for the rapid removal of the polar ice, Geissler says.
At some point, the model predicts the winds will build up so much they will trigger a global dust storm, redistributing the light dust over most of the surface and starting the process over again.
While the dust redistribution may be unique to Mars, Earth may have analogous feedback processes that can amplify changes in surface reflectivity – in this case, mostly based on changes in sea ice and snow cover.
But although some scientists argue that the global warming on Mars shows there must be some external cause to Earth's warming – such as a change in solar output rather than human-caused increases in greenhouse gases – Geissler says the new research undercuts that argument. "What our work shows is that the warming on Mars that we know has been going on for some time has a local cause [on Mars]," he told New Scientist.
The new work could have a significant impact on understanding past changes in the Martian climate. "This is the first attempt to quantify the impact of these surface changes," Geissler said. From now on, "when we study Mars' climate, we need to keep track of the surface [reflectivity] and its interaction with climate."
Journal reference: Nature (vol 446, p 646)