POZNAN, Poland – U.N. Secretary-General Ban Ki-moon on Thursday warned the world against backsliding in the fight against climate change as it battles financial crisis, calling for a renewed sense of urgency in facing "the defining challenge of our era."

Ban spoke as some 145 environment ministers and other top officials gathered to help push forward efforts to secure agreement next year on a new worldwide treaty to cut greenhouse gas emissions, which would take effect in 2013.

"The economic crisis is serious; yet when it comes to climate change, the stakes are far higher," Ban told the conference. "The climate crisis affects our potential prosperity and our people's lives, both now and far into the future."

"There can be no backsliding on our commitments to a future of low carbon emissions," he said, telling ministers who are meeting Thursday and Friday that "we must recommit ourselves to the urgency of our cause."

Ban said that managing the financial crisis requires a massive global stimulus and "a big part of that spending" should be directed at fighting global warming. "We need a Green New Deal," he said.

Scientists say the potential consequences of climate change include a potential meltdown of Greenland or Antarctic ice that could raise sea levels by several yards (meters), and a worsening shortage of water for millions of people by mid-century.

The prime minister of Tuvalu, whose island nation is threatened by extinction if the Pacific Ocean rises, told ministers that "our future is in your hands."

"It is our belief that Tuvalu, as a nation, has a right to exist forever," Apisai Ielemia said. "We are a proud nation of people with a unique culture which cannot be relocated somewhere else."

"We are looking to the United States to step out of the dark ages of inaction and become a leading light on climate change," Ielemia said.

Ban called for leadership from the U.S. and said he found the emphasis of President-elect Barack Obama on climate change encouraging.

On Wednesday, delegates at the 12-day U.N. conference, which concludes Friday, agreed on a series of goals to be included in a new treaty, but failed to make a real commitment to reduce the amount of carbon emissions — simply reaffirming aims similar to those they agreed last year in Bali, Indonesia.

They resolved to spell out specific emissions commitments for industrial countries, raise large-scale funds to help poor countries adapt to their changing climate, and create institutions to channel those funds.

A key committee at the conference cited scientific studies saying industrial countries must cut carbon emissions by 25 percent to 40 percent by 2020 to contain global warming to safe levels. But it did not adopt that target, leaving the issue for talks next year.

The top U.N. climate change official, Yvo de Boer, said ministers must now provide "clear political guidance and show resolve."

Ban said rich countries "must set ambitious long-term goals" and said developing countries will need "robust financial and technological support" to limit their emissions growth.

"Today we need a global solidarity on climate change, the defining challenge of our era," he said.

He called for leadership from the European Union, whose leaders were meeting in Brussels on Thursday to figure out how to fulfill their emission-cutting targets.

The new agreement, which is supposed to be concluded next December in Copenhagen, Denmark, would replace the Kyoto Protocol, which expires in 2012.