Earth is not the only planet in the solar system showing the effects of global warming, according to a study published on Wednesday.
A rise in wind-swept dust on Mars is causing more heat from sunlight to be absorbed by the planet's surface, leading to rising temperatures, according to a study published in the British journal Nature.
Surface air temperatures increased by 0.65 degrees C over a 20-year period, the authors said, based on computer models comparing changes in the planet's surface brightness. Light-coloured dust lying on the surface of the planet usually reflects the sun's light back into space in a process called albedo. But high winds can churn up this dust and expose the planet's darker soil to the sun's rays.
On Mars, one of the key factors in planetary warming is the change caused by the darkening of its surface, according to the team led by NASA planetary scientist Lori Fenton. Fenton and her colleagues collected data from two sources: an albedo map from the 1970s produced by an infrared thermal mapper onboard NASA's Viking probe and a more recent map from 1999-2000 taken by a sensor aboard the Mars Global Surveyor probe.
The researchers found that the darker soil absorbs more light and traps heat in the atmosphere, which in turn causes more turbulence that creates more wind storms. This "positive feedback loop" is similar to a predicted cycle expected to affect Earth's glaciers: higher temperatures will melt glaciers, which will in turn reduce the amount of reflective ice, trapping more heat and leading to even higher temperatures.
"Results indicate enhanced wind stress in recently darkened areas and decreased wind stress in brightened areas, producing a positive feedback system in which the albedo changes strengthen the winds that generate the changes," the authors say in the study. But the process and causes of planetary warming on Mars share little in common with Earth.
Mars has a much thinner atmosphere, lacks Earth's cloud cover and doesn't have either vegetation or active volcanoes to release greenhouse gases that might trap heat and warm the planet. Mars also doesn't have any of the man-made factors that a UN-led report on climate change (which was backed by 2,000 climate scientists from 113 countries) said in February were "very likely" behind rises in Earth's average annual temperatures.
By comparison, the dust storm initiation process responsible for and caused by rising temperatures is a phenomenon unique to Mars, the researchers write. The rise in temperature also wouldn't help make the planet any more livable for humans. Although midsummer temperatures on the planet can reach 26 C, they can also drop to a numbing -111 C.