Mars in global warming debate
* Leigh Dayton, Science writer
* April 05, 2007
CLIMATE change sceptics have seized on news that Mars is heating up to back their claim that humans are not causing Earthly global warming.
The research comes from US planetary scientists, who suggest the Red Planet warmed by about 0.65C from the 1970s to the 1990s, similar to Earth's 0.6C average temperature rise during the 20th century.
"It could be coincidental or it might be the needle in the haystack," said climatologist William Kininmonth, former head of the National Climate Centre in Melbourne.
"It's an interesting observation, as it's the same time period as Earth's temperature has been warming."
Mr Kininmonth said the research, published in the journal Nature, showed there was enough natural climate variability to account for global warming on Earth.
Not so, claimed Neville Nicholls, a climate scientist at Monash University in Melbourne.
"The paper is interesting but it hasn't got anything to do with the question of human impact on global warming on Earth," Dr Nicholls said.
"It's not an excuse to argue that humans are not causing global warming on Earth."
The research was done by a team led by Lori Fenton of the NASA Ames Research Centre at Moffett Field, California.
They used a computer model based on those devised to study global warming on Earth, adding Martian features such as a cold, airless surface and a shifting south polar ice cap while subtracting Earth's oceans and atmosphere.
Dr Fenton's group found that annual variation in the solar radiation reflected from the surface of Mars -- its "albedo" -- contributed to the warming by causing more blowing dust.
Over the past 30 years, the dust swept clean large swaths of the planet's surface, reducing reflected radiation.
The result was a "positive feedback loop" between dust, wind, albedo and temperature.
"It's a nice piece of work," said UNSW climate scientist Andy Pitman. "But there are no implications for Earth."
Professor Pitman was lead author of the climate modelling section of the Intergovernmental Panel on Climate Change report released in February.
Professor Pitman disputed Associate Professor Franks's claim that changes in Earth's albedo had a bigger influence on climate than greenhouse gases such as carbon dioxide.
"Albedo is included in climate models," Professor Pitman said. "It can have a local effect but cannot explain the observed warming record."
The Nature paper comes on the eve of the second report from the fourth IPCC review, set to be released tomorrow night.