Australia's opposition Liberal Party has elected a new leader, amid a searing row over the government's carbon trading laws.
Tony Abbott was chosen to replace Malcolm Turnbull at a Canberra meeting.
Mr Turnbull had backed Prime Minister Kevin Rudd's emissions trading scheme (ETS), but Mr Abbott opposes it.
The government needs the support of the Liberals to pass the legislation in the Senate. The Liberal revolt throws Mr Rudd's plans into turmoil.
Mr Rudd had wanted the legislation to pass the Senate - where his party does not have a majority - by the start of the Copenhagen climate change summit next week.
Last week he secured Mr Turnbull's support for the bill, prompting the angry reaction from some Liberal lawmakers that triggered the leadership challenge.
Climate centrepiece
Mr Abbott won the final vote against Mr Turnbull by 42 votes to 41. A third challenger, Joe Hockey, was eliminated in first-round voting.
Minutes after his victory, Mr Abbott told a news conference that he would fight the ETS bill.
“ Many moderate Liberals are terrified. Malcolm Turnbull had warned that his once-dominant party would face an electoral catastrophe if it appeared before the electorate as the party of climate-change scepticism ”
Nick Bryant, BBC News, Sydney
"We will seek to refer the legislation to [a Senate] committee for further scrutiny. If we cannot get the support for that course of action we will oppose the legislation in the Senate this week," he said.
"I think on something of this magnitude, it is much more important to get it right than to rush it," he added.
The government's immediate hopes of passing the bill now rest on the possibility of some opposition lawmakers rebelling and voting with it.
But if the Senate fails to back the scheme - as now looks likely - Mr Rudd could call a snap election, correspondents say.
Opinion polls suggest he would win such an election and could then pass his climate legislation in a joint sitting of parliament.
But, says the BBC's Nick Bryant in Sydney, the issue is complicated by the onset of the southern summer, when political hostilities tend to be put on hold.
The ETS, aimed at reducing Australia's carbon footprint, is the centrepiece of the government's environmental strategy.
Mr Rudd wants to cut Australia's carbon emissions by up to 25% from 2000 levels by 2020.
But some opposition politicians question the scientific case for global warming and the energy lobby says the move would damage Australia's economy.
Australia has the highest per capita carbon emissions among developed nations and coal is its biggest export.
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/asia-pacific/8387653.stm