As Republicans head toward a showdown in the presidential primary race, the two main protagonists have something in common: They both reject anthropogenic climate change.

Mitt Romney did a policy about-face in October last year when he said: "My view is that we don't know what's causing climate change on this planet. And the idea of spending trillions and trillions of dollars to try to reduce CO2 emissions is not the right course for us." This was after he had told a New Hampshire audience four months earlier that global warming was man-made and that reducing greenhouse gases was important.

Rick Santorum, for his part, has been consistently unapologetic about his climate skepticism. "The apostles of this pseudo-religion believe that America and its people are the source of the Earth's temperature. I do not," he wrote last week. He claimed to be the only Republican candidate not to have bowed to "this liberal orthodoxy."

So as March temperatures are forecast to reach more than 80 degrees Fahrenheit in some parts of the U.S. next week, well above average for this season, it's timely to consider a government study from a nation that has the most to lose from rising global temperatures. Australia -- the world's driest inhabited continent, whose two-decade economic expansion can be largely attributed to the mining of fossil fuels -- has just released its review of greenhouse gases. The results leave little wiggle room for climate skeptics.

Greenhouse gases have risen to their highest level since modern humans evolved and emissions from human activity were increasingly affecting the country's temperatures. "Multiple lines of evidence show that global warming continues and that human activities are mainly responsible," said the State of the Climate 2012 report from the CSIRO, the national science agency, and the Bureau of Meteorology. Carbon dioxide in the atmosphere was measured at 390 parts per million last year, it said, the highest level in 800,000 years.

This is a grim warning from the CSIRO, which was accused in the Australian press of having compromising ties to the coal industry as recently as two years ago. If those claims were true, the agency has just done an about-face as impressive as the former Massachusetts governor's.

When Romney or Santorum turns to the climate debate during the general election campaign against President Barack Obama this year, he will be thinking about the next four years. Maybe that's the main reason voters shouldn't believe a word they're saying.

(David Henry is an editor for Bloomberg View.)

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