In an interview with AFP, Hedegaard said the European Union set the example for both Washington and Beijing when it pledged last Friday to cut EU emissions by at least 40 percent by 2030 compared with 1990 levels.

"We can do that in Europe because it's in our own interests but that in itself cannot solve the climate change issue," she said.

"The American have to come forward with something ambitious, something tangible and something concrete," Hedegaard added.

"I believe that only the moment that the Americans have done so, then the Chinese will come forward," she said.

China and the United States are the world's biggest emitters of greenhouse gases which are blamed for global warming.

The United States must not only set a more ambitious target than it did in Copenhagen in 2009 -- when it pledged to reduce emissions by 3.6 percent by 2020 from 1990 levels -- but actually stick to it, Hedegaard said.

"They are not even on track to reach the 3.6 percent that they pledged in Copenhagen. Last year their emissions increased, not decreased," she said.

Europe, on the other hand, is cutting its emissions and sticking to its more ambitious pledge to reduce emissions by 20 percent by 2020 from 1990 levels, she argued.

The EU wanted to agree on the 2030 targets ahead of a summit in Paris in November and December 2015, where it is hoped the world will agree to a new series of the Kyoto climate accords which run until 2020.

The European Union accounts for 11 percent of the world's greenhouse gas emissions, compared to 16 percent for the United States and 29 percent for China.

Hedegaard still hoped that US President Barack Obama will deliver when Washington is expected to put its proposal to fight climate change on the table early next year.

Obama, who made the battle against climate change a core promise of his 2008 election campaign, has been stymied at the federal level by opposition from lawmakers.

In early June he announced a major initiative that aims to cut by 30 percent carbon emissions from power plants by 2030 from 2005 levels.

The EU climate commissioner, who gave one of the last interviews before she leaves her job on October 31, expects a surprise from China.

Leaders from Beijing announced during the climate change summit in New York last month that the "Chinese were now analysing when they could peak their emissions, and how can we do it as soon as possible," she said.

To do it by 2030 would be too late but a much earlier "peaking year" would "be a very important gift from China to the whole world," she said.

"They are now really serious on that," she added. But Hedegaard, who fought fellow commissioners and member states to get the 2030 climate targets, is realistic, recalling that EU commitments for the Copenhagen summit in 2009 did not prevent its collapse and acknowledging that the same risk hovers over the Paris conference in 2015.

She worries that the French government will seek to minimise expectations to avoid paying the political price of failure.

"When something gets difficult the solution is lower the ambitions, but this is not a game, this is something quite serious," she said.

"The success criteria for Paris should be to make an agreement that makes it credible and likely that the world will stay below the (temperature gain of) two degrees Celcius. Nothing more, nothing less."

Scientists say the planet is currently on a path to see temperatures rise by perhaps four degrees to five degrees Celcius before the end of the century if nothing is down.