Australia's plan to become one of the first nations with a carbon trading system to cut greenhouse gas emissions was dealt a blow Tuesday when the main opposition party chose a leader who vowed to vote it down.

A tumultuous day in politics also means the country could also be one step closer to early elections, with policy differences over global warming placing it as a central issue of the coming campaign.

Debate in the Senate on the government's plans for an emissions trading system continued Tuesday as the conservative Liberal party ejected one leader from the post and elected another. A final vote could come at almost any time.

The conservatives split bitterly and publicly in the past week over the bill, culminating in Tuesday's leadership challenge. Right-leaning Tony Abbott won the vote, ousting Malcolm Turnbull, who had struck a deal with the government to support the bill.

Abbott said his party would now move to defer the bill until after next week's U.N. global summit on climate change in Copenhagen, and possibly longer. If the bill is not deferred, the opposition would vote against it this week in the Senate, he said. The government lacks a majority in the Senate, and the bill will almost certainly fail if the Liberals vote against it.

If the bill is defeated, Prime Minister Kevin Rudd is handed a trigger to call an election at any time under constitutional rules meant to be the ultimate resolution to any deadlocks between Australia's two houses of Parliament.

Rudd is unlikely to call elections immediately, for reasons including that political campaigning during the Christmas-New Year holiday season is considered out of bounds. In any case, elections are due sometime in 2010, and opinion polls consistently show Rudd is so popular that _ barring major stumbles _ he would probably win whenever they are held.

Rudd wants the legislation passed before the Copenhagen summit to help portray him as a world leader on tackling climate change.

Australia is a small greenhouse gas polluter in global terms, but one of the worst per capita because it relies heavily for its electricity on its abundant reserves of coal, which also make it the world's largest exporter of the polluting fuel. As the driest continent after Antarctica, it is also considered one of the most vulnerable countries to climate change.

The European Union has a carbon trading system, as do some U.S. states. Canada and New Zealand are among countries considering them.