The tectonic plates of global politics shifted in Copenhagen last week, and it was tiny Tuvalu that exposed the rift. For more than a decade, developing countries have maintained an uneasy united front at climate conferences, one resolved to force the big polluters of the West to cut their emissions and to defend the innocence of developing countries.

The rift that was exposed last Wednesday has profound geopolitical significance. Third World solidarity — indeed, the idea of the Third World itself — dates from the Bandung conference in 1955, a meeting of Asian and African nations aimed at resisting colonialism and neo-colonialism.

At every climate conference, the G77  — or more usually G77 plus China — has been the developing country bloc that faced up to the big powers of the United States, Europe and Japan. But is has always been an awkward alliance, combining nations mired in poverty with those industrialising rapidly, and nations rich in oil with those dependent on imports.

Frequently, the G77 was represented by oil-exporting nations, such as Saudi Arabia, bent not on defending the interests of the South but on protecting oil revenues by sabotaging any agreement to cut emissions.

On Wednesday, Tuvalu finally broke the veneer of solidarity. Speaking for the most vulnerable countries — the small island states and the mainly African least-developed countries — Tuvalu called for the creation of a contact group to discuss a Copenhagen Protocol, which would require large developing country emitters to take on legally binding emission reductions.

The move was blocked on the floor of the plenary by China, India and Saudi Arabia, the developing nations that would be most affected.  But Tuvalu would not be cowed and, in a tactic that shocked the conference, moved that proceedings be suspended.

The intransigence of the big developing countries had come up against the desperation of the least-developed nations. The stridency of the vulnerable is new to international climate talks; they understand that Copenhagen really is the last chance to head off the unthinkable.

Morally, there is a world of difference between calls by the United States for China, India and the like to take on binding emission cuts and calls for the same from Tuvalu, the Maldives and Bangladesh. China is now caught in a pincer, but one of its own making, because with economic power comes responsibility. China was a significant player at Bandung, but in recent years it has begun to look more and more like a colonial power, especially in Africa with its huge investments in resources.

If Tuvalu, with the population of a small Australian suburb, is at the sharp point of the fracturing of one of the three blocs that defined post-war geo-politics, the man who has precipitated it is an unassuming Australian. Ian Fry has, for a decade, been Tuvalu’s lead negotiator. Previously a Greenpeace employee, he lives quietly in Queanbeyan when not travelling to climate conferences.

It was Fry who last Wednesday refused to bow to the Chinese juggernaut and called for the conference to be suspended. It was an act that required a deep knowledge of how these conferences work, a measure of courage and a steely determination not to let the moment pass. He put it very simply: “Tuvalu is one of the most vulnerable countries in the world to climate change, and our future rests on the outcome of this meeting.” It was an heroic act.

For 50 years, the Third World remained united in the face of a common threat, the influence of the United States and, to a lesser extent, the Soviet Union. But for least-developed countries a greater enemy has now emerged, the threat to their survival posed by global warming, and they are no longer willing to subsume their demand that all the world’s polluters curb their activities beneath the imperative of maintaining the appearance of G77 unity.

They know that the US and China are locked in a struggle in which one will not move without the other, a struggle that is an environmental version of the mutually assured destruction of the Cold War era.

If the Copenhagen conference has announced the end of the Third World, it has also exposed the unbridgeable divide within the First World. The US position, we can now see, was not an artifact of the Bush presidency and the ascendancy of the neo-cons in Washington, but is deeply embedded in the American political system.

The characterisation of global warming by conservatives as a left-wing scam is uniquely American (although it has been imported by those temporarily in charge of the Liberal Party in Australia). Indeed, even before Kyoto, American conservatives were just as likely to attack global warming as a European plot to achieve world governance. (In Australia, the earliest documents of the Lavoisier Group promote this bizarre notion.)

Never has the Atlantic appeared so wide. The weird conspiracy theories of the neo-cons and sceptics are nowhere to be heard in the Bella Centre, but the entire conference is being held hostage by them because of their influence in the United States’ Senate, the spectre present in every back-room here.

Every move made by US lead negotiator Todd Stern is conditioned by the numbers in the Senate, and its ability to block any treaty will be the ball chained to the leg of Barack Obama when he walks into the conference arena on Friday.

Everyone will swoon before the Obama magic, except for the hard-heads of the Chinese delegation. And they are the only ones who count if a breakthrough is to be had.