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As the United Nations climate change talks in Cancún lurch slowly toward an uncertain conclusion, the World Bank is stepping in to help developing countries set up pollution credit markets to help pay for clean development programs.

Robert B. Zoellick, the World Bank president, will appear before delegates here on Wednesday to announce the creation of a multimillion-dollar program to create trading mechanisms to stimulate clean energy projects and to slow the destruction of tropical forests, one of the primary sources of global warming emissions. He will also be announcing new World Bank programs to help island nations that are acutely vulnerable to rising seas and other climate-related threats to increase their access to renewable energy sources.

He said that the dangers of a changing climate were moving at a faster pace than the international negotiations aimed at controlling them and that the most threatened nations could not afford to wait.

“We know that the poorest countries will suffer the earliest and the most from climate change,” Mr. Zoellick said in a statement. “They will bear the brunt of changing weather patterns, water shortages, and rising sea levels even though they are the least equipped to deal with them.”

He added: “We also know that, while these countries would like to see a comprehensive global accord on climate change, they are not waiting for one. They are acting now and acting differently to shift from being climate vulnerable to being climate smart.”

Mr. Zoellick served as United States trade representative and deputy secretary of state in the George W. Bush administration before becoming World Bank president in 2007.

The list of countries that will take part in the carbon market initiative was not announced, but they are expected to include China, Mexico, Indonesia and Chile. Other countries were expected to join as more funds become available, bank officials said.

The European Union already has a carbon market, known as the Emissions Trading System, which barters pollution credits for European industries for climate-friendly projects, mainly in the developing world. Legislation to create a similar national trading system in the United States stalled in Congress this year.

Such programs are controversial because they have been at times poorly monitored and the price for carbon credits has fluctuated wildly. Many poorer nations also complain that their natural resources have been turned into commodities traded on exchanges in wealthy countries.

“Carbon markets are an irreparably flawed means of addressing climate change,” Karen Orenstein of the environmental group Friends of the Earth told Reuters. “They are unreliable and subject to fraud, and they open the door to offset loopholes that undermine environmental integrity.”

The World Bank hopes to devote as much as $100 million to provide technical support and other aid to help developing countries establish carbon exchanges and other ways of raising private funds to help reduce emissions and adapt to climate changes.