World talks on climate change struggled to overcome a rift on the future of the Kyoto Protocol with only two days left on the clock to bridge the gap.
Sharpening the sense of division in Durban, Canada declared that, for it, Kyoto was now history.
It confirmed it would not renew pledges after the landmark pact's first roster of carbon curbs expires at the end of 2012.
"We have long said we will not take on a second commitment under the Kyoto Protocol. We will not obstruct or discourage those that do, but Kyoto for Canada is in the past," Canadian Environment Minister Peter Kent said.
Kent's slapdown of a treaty viewed as iconic by poorer countries hit the nerve point of the talks, which have until late Friday to avoid the second bustup in two years.
The conference is taking place under the 194-nation UN Framework Convention on Climate Change (UNFCCC), which has struggled for nearly two decades to roll back what scientists say is a dire threat for mankind.
NATIONS WON'T RENEW VOWS
Several key nations beside Canada, including Japan and Russia, have said they will not renew their Kyoto vows, which are legally binding.
They say to do so would be senseless so long as emerging giants and the United States, which has refused to ratify Kyoto, are not bound by the treaty's constraints.
"For Canada, the Kyoto Protocol is not where the solution lies," Kent said.
"It is an agreement that covers fewer than 30 percent of global emissions, by some estimates 15 percent or less. It's an approach that does not lead to a more comprehensive engagement of key parties who need to be actively a part of a global agreement."
So far, however, only Europe, which accounts for barely 11 percent of global CO2 emissions, has shown any enthusiasm for renewing its Kyoto vows.
And even then there is a condition: all the world's major emitters -- including the United States and China -- must agree in principle to conclude a binding climate pact by 2015 and implement it by 2020.
"Even if other countries are not ready, we are ready to commit to the second commitment period of the Kyoto Protocol and we do this in order to preserve what it took us so many years to build up," said European Climate Commissioner Connie Hedegaard.
"But we must be reassured that others would join us in a new legally-binding framework after the second commitment period and we must also know when they will do that."
But none of the big polluters has bought in to Europe's "roadmap" idea.
US CALLS FOR VOLUNTARY APPROACH
The United States, for its part, is calling for countries to implement a looser, voluntary approach that was born in the stormy final hours of the 2009 Copenhagen Summit.
For developing countries, Kyoto is a touchstone of cooperation between rich and poor, and UN Secretary General Ban Ki-moon on Tuesday pleaded with the talks to keep the treaty alive.
Brazil, South Africa, India and China have described a second commitment period as "a must," a position loudly supported on Wednesday by the poorest countries and vulnerable small-island states.
South Africa, as host, gathered a group of countries into an informal huddle known as an indaba, out of which four options emerged for tackling carbon emissions in the medium and longer-term.
PROGRESS ON OTHER ISSUES
Despite the row over Kyoto, other issues have made progress or have a good chance of doing so, said delegates.
They include the design of a "Green Climate Fund" that by 2020 would help channel up to 100 billion dollars a year to help poor countries tackle worsening flood, drought, rising seas and storms.
There is also optimism that the conference would give the green light to a levy on carbon emissions from shipping, which until now has been excluded from international curbs. Part of the tax would be channelled into the climate fund.
