SYDNEY — Australia's Parliament defeated legislation to set up a greenhouse gas emissions trading system on Wednesday, throwing a central plank of the government's plans to combat global warming into disarray. The Senate, where Prime Minister Kevin Rudd's government does not hold a majority, rejected his administration's proposal for Australia to become one of the first countries to install a so-called cap-and-trade system to slash the amount of heat-trapping pollution that industries pump into the air. The 41-33 vote followed a tumultuous debate in which the conservative main opposition party at first agreed to support a version of the government's bill, then dramatically dumped its leader and switched sides after bitter divisions erupted within the party. The new leader, Tony Abbott, said Australia should not adopt an emissions trading system before the rest of the world. "The right time, if ever, to have an ETS is if and when it becomes part of the international trading system and that is not going to happen prior to its adoption in America," he told reporters after the vote.