Age: The single biggest contributor to global warming is also one of Australia’s biggest money earners. So can Australia wean itself off coal? And what would the implications be if it did? “COAL,” says mining union chief Tony Maher, the hint of a smirk in his voice, ”is vegetable matter. It’s organic. It’s not toxic, it’s not radioactive. It has a waste problem. And that waste is carbon dioxide.” Maher’s 20,000 members rely for their jobs on digging up coal. But he knows that …