His warning cast doubt on a Chinese proposal to ask the world's rich nations to devote up to 1 percent of their total economic worth to pay for cleaner expansion in the poor world.

"It is undeniable that the financial crisis will have an impact on the climate change negotiations," said Yvo de Boer, who heads the U.N. Climate Change Secretariat.

More than 190 nations have agreed to seek a new U.N. treaty by the end of 2009 to try to cut greenhouse gases from human activity and slow rising temperatures bringing more heatwaves, droughts, more powerful storms and rising sea levels.

"If we go to citizens under the current circumstances...and say 'I'm increasing your tax burden in order to pay for climate policy', that might not go down very well," he told Reuters.

The solution, he said, was to directly target the polluters as a source of revenue to help developing countries.

Speaking ahead of a major conference on climate technology transfer in Beijing, de Boer warned the rich world that under a roadmap for a climate deal to replace the current Kyoto Protocol, they had to create revenue to help developing nations fund greener growth.

The plan agreed in Bali last year committed poor countries to curbing emissions if rich governments helped with technology so they did not have to sacrifice economic growth.

De Boer said the developed world has focused on commitments to cut emissions as part of the pact to be finalized at a high-level meeting in Copenhagen next year but not paid sufficient attention to technology transfer.

He praised China's leadership in negotiations over recent years, and its effort to firm up demands for technology.

"This is a great opportunity for the country that has put so much emphasis on this issue to really focus the debate on how technology transfer can be part of the long-term climate change response...(and) create the institutional arrangements that will finally make this rather elusive concept find a practical base."

De Boer said while the financial crisis threatened global efforts to tackle global warming it could also give impetus to talks aimed at forging a new climate-change pact.

The crisis has also highlighted the benefits of a trading system, currently favored by most rich nations, that sets pollution limits but allows companies to buy and sell quotas to meet their targets.

The auction of credits to pollute could fund cleaner development in poor nations, he said

"This offers the opportunity to generate resources for international co-operation from within the climate change regime...without having to go to finance ministers them to raise income taxes or other taxes to generate that revenue."

A flat carbon tax would be more efficient than the current system, but far more complicated to implement, he said.