An international treaty on climate change won't be enough to avert a dangerous rise in global temperatures, according to the head of the UN Environment Program, who also said that countries need to make voluntary reductions to their emissions.
Meanwhile, U.N. chief Ban Ki-Moon said an all-encompassing climate deal "may be beyond our reach" for now.
Ban spoke at the UN climate conference in Durban, South Africa, where a coalition of influential environmental groups have launched a scathing attack on the American negotiating team, accusing them of blocking progress and demanding that they change their stance or leave the conference.
We have a report from the BBC's Mike Williams in Durban.
This program aired on December 6, 2011.