Connie Hedegaard, who is a key mediator in the talks to find a successor to the Kyoto Treaty, said western nations must agree to pay to help poorer countries cut emissions.

However, this will not be enough to get a deal at a United Nations climate conference in Copenhagen in December, or to solve the problem of global warming.

"We must have all major emerging economies on board," she told the Offshore Europe oil conference on Tuesday, adding it remained "open" whether China and India would agree to curbs.

Scientists say industrialized nations are largely to blame for the increase in CO2 in the atmosphere but developing nations are expected to be major contributors in the future.

China has already nudged ahead of the United States to become the world's largest emitter of carbon dioxide,

increasing the pressure on China to limit future emissions.

"We will have to have a deviation from business as usual by China," Hedegaard said.

China needs to identify a date by which its emissions would start to fall, the minister said, adding this date should not be too distant. "The sooner the better," she said.

Climate change is expected to be on the agenda of the G20 meeting of the leaders of the world's largest economies in Pittsburgh later this month.

Hopes for progress at Pittsburgh were dented last weekend by the refusal of China and India to even debate measures to tackle global warming at the G20 finance ministers meeting in London.

Hedegaard said she hoped leaders of rich nations would agree at Pittsburgh to provide "upfront" financing to tackle climate change.

In recent months, developed nations have increasingly spoken of using market mechanisms such as "cap and trade" programs, whereby polluters pay to emit CO2, to meet the bill of tackling climate change.

Governments like these plans as they shift the bill away from state coffers to the private sector -- companies and individuals.

Emerging nations are suspicious rich that countries are using these mechanisms to avoid paying the full amount needed to tackle climate change.