WASHINGTON - Environmentalists and some Democrats on Friday seized on the United Nations' finding that climate change would probably increase certain extreme weather events, using it as ammo in their continuing battle with conservative Republicans who doubt the existence of global warming.

"It's not too late to act," Frances Beinecke, president of the Natural Resources Defense Council, an environmental group, said in a statement responding to the report.

Extreme weather has become climate advocates' latest rallying cry. They point to a record-breaking year in 2011 for weather disasters with damages of $1 billion or more each. But they caution that rising population and wealth may at least partly explain why damages have increased over time.

"I've been a meteorologist 30 years, and I've never seen a year that comes close to 2011 for the number of astounding extreme weather events," said Jeff Masters, co-founder of the Weather Underground.

Republicans, many of whom have expressed skepticism or outright denial of the scientific consensus on climate change, have passed a number of measures in the House opposing policies to address global warming. They claim actions to reduce greenhouse-gas emissions would weaken an already struggling economy.

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