AFP - The true cost of fighting climate change will top 300 billion dollars and developed countries may balk at footing the bill, Guyana's Prime Minister Bharrat Jagdeo said Saturday.

Leading economists have calculated that "the cost of action and mitigation would be about one percent of the global economy," he told journalists. "This is one percent of the GDP of a 30-trillion-dollar global economy," he estimated.

"If resources of that magnitude were available then you'd be able to take serious mitigation action immediately."

Jagdeo was talking after a second day of Commonwealth talks that adopted a landmark declaration on climate change saying it was "essential" to reach a legally binding accord at global talks in Copenhagen in the coming days.

The Commonwealth also backed a special fund of 10-billion-dollars a year for the next three years to help small nations bear the costs of implementing the necessary changes to cut greenhouse gas emissions.

"I think the European Union will meet its share of the 10 billion dollars," Jagdeo said.

"But when we start talking about the larger sums of money... that is the one percent of GDP, we are going to have a serious pushback on the part of the developed world."