The UN’s top environmental official is warning a global climate summit in Bali is in danger of collapse over the Bush administration’s objection to a firm commitment on cutting emissions of greenhouse gases. Earlier today, UN climate chief Yvo de Boer warned the talks could fall like a “house of cards” if negotiations continue apace. European Union ministers are warning they may boycott a US-backed climate summit next month unless the administration changes its stance. The White House is opposing a measure calling on industrialized nations to cut emissions by up to 40 percent by the year 2020. The proposed emissions cut matches the figure recommended by scientists as necessary to curb global warming. The US has opposed several other measures, including providing financial assistance to developing nations affected by climate change. On Wednesday, UN Secretary-General Ban Ki-moon urged negotiators to reach an agreement.

UN Secretary-General Ban Ki-moon: “Now, finally, we are gathered together in Bali to address the defining challenge of our age. We gather because the time for equivocation is over. The science is clear: climate change is happening, the impact is real, the time to act is now.”

The Bali summit is being convened to negotiate a successor to the Kyoto Protocol, which expires in 2012. The United States is the world’s largest emitter of greenhouse gases and the only major industrial nation to have rejected Kyoto. Australia became the latest nation to back the accords this month, when new Prime Minister Kevin Rudd personally delivered his ratification to the Bali talks.