ClimateWire: Only a few years ago, two coal-rich countries, the United States and Australia, both stood accused of hampering global efforts to tackle climate change. Now Australia is struggling to construct a carbon trading system to curb greenhouse gas emissions, and America may not be far behind. In a series of talks in the United States this week, Australian Climate Minister Penny Wong said her country has been hammering out tough decisions over how broad-based the scheme should be, how much of …