Sunday, April 8, 2007

Earth's warming and evidence from Mars

I just read (via Peter Gordon []) that yesterday's LA Times reported global warming on Mars. As Peter writes this is uncomfortable evidence for those that deny that humans contribute but a fraction to changes in temperatures on earth.

Clue to Mars' warming is seen

The planet's darkening surface could account for its temperature rise, scientists report.

Global warming on Mars? It turns out you don't need belching smokestacks and city-choking traffic to heat up a planet. Changes in surface reflectivity may also do the trick, according to research published Thursday in the journal Nature.The research team, composed of scientists from NASA's Ames Research Center in Northern California and the U.S. Geological Survey, compared images of Mars taken by the Viking missions in the 1970s to pictures taken a quarter century later by Mars Global Surveyor.The surface was noticeably darker in the new pictures, said Lori Fenton, a planetary geologist at the Carl Sagan Center in Mountain View, Calif., who worked with Ames scientists on the project. Plugging in a climate model developed at Ames, the research team said the changes in surface reflectivity could account for a 1 degree Fahrenheit rise in the surface temperature of the planet. "That's a significant amount," said Rich Zurek, lead Mars scientist at the Jet Propulsion Laboratoryin La CaƱada Flintridge, who was not involved in the research. The scientists believe the changes in surface reflectivity —known as albedo — are caused by wind-driven dust storms that occasionally sweep the entire Martian surface. The storms fill the air and cover the surface with fine grains that are more reflective than the bedrock. Several big storms preceded the visit of Vikings 1 and 2 in 1975, Fenton said. Comparatively, there was less heavy wind and, consequently, more light-absorbing bedrock in the picture taken by Mars Global Surveyor in 2000. If Mars is getting hotter, that could explain one finding that has puzzled planetary scientists since it was discovered several years ago: the loss of carbon dioxide ice at Mars' south pole. The CO2 ice forms a cap on top of water ice that ranges from several feet to several hundred feet in thickness. Each of the last few years, scientists have seen holes develop in the CO2 layer late in the Martian summer. So does all this mean Mars is undergoing a new round of climate change like the one that dried up its ancient lakes and drove its waterunderground? Fenton is unsure. What's going on at the south pole "is an indication of at least regional temperature change," she said.