By Alister Doyle and Gerard Wynn

POZNAN, Poland, Dec 11 (Reuters) - The world must avoid backsliding in the fight against global warming and work out a "Green New Deal" to solve twin climate and economic crises, U.N. Secretary-General Ban Ki-moon said on Thursday.

"We must re-commit ourselves to the urgency of our cause," Ban told about 100 environment ministers at Dec. 1-12 U.N. talks in Poland working on details of a new treaty to fight global warming. The talks are overshadowed by worries about recession.

Ban urged leadership in fighting warming from President-elect Barack Obama and from the European Union, which is holding a summit in Brussels on Thursday trying to break deadlock on a plan to axe greenhouse gas emissions by 2020.

"There can be no backsliding on our commitments to a future of low-carbon emissions," he said. Nations agreed last year to work out a new pact by the end of 2009 to succeed the Kyoto Protocol for fighting global warming.

"Yes, the economic crisis is serious. Yet when it comes to climate change, the stakes are far higher. The climate crisis affects our potential prosperity and peoples' lives, both now and far into the future," he said.

He urged a "Green New Deal" inspired by the 1930s "New Deal" by U.S. President Franklin Roosevelt, which ended the 1930s depression.

"Together, we face two crises: climate change and the global economy, he said. "But these crises present us with a great opportunity -- an opportunity to address both challenges simultaneously," he said.

He said that managing the financial crisis would need a "massive stimulus". "A big part of that spending should be an investment -- an investment in a green future," he said.

"We need a Green New Deal," he said.

LEADERSHIP

"What we need, today, is leadership," he said, singling out the United States and the EU.

"The decisions currently being made by European leaders in Brussels are (of) great consequence for the whole world," he said. The EU is seeking to work out details of its plan to cut emissions by 20 percent below 1990 levels by 2020.

And he said that he was encouraged by Obama's "plan to put alternative energy, environmentalism and climate change at the very centre of America's definition of national security, economic recovery and prosperity."

The U.N. talks are reviewing progress towards a new deal to be agreed in Copenhagen next year. A main sticking point is details of a new fund to help poor countries adapt to the impacts of rising seas, droughts, floods and heatwaves.

-- For Reuters latest environment blogs click on: http://blogs.reuters.com/environment/ (Editing by Charles Dick)

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