Al Gore has a major campaign under way — to change policies on global warming.

The 2000 Democratic presidential nominee has hired longtime political associate Roy Neel to aid in his effort to raise awareness about global warming, a problem Gore calls "a planetary emergency."

Gore's movie and book about the issue, both called "An Inconvenient Truth," are set for widespread release in May.

"He's taking an increasingly high-profile role in working on the climate change issue," Gore spokesman Michael Feldman said.

Gore repeatedly has brushed aside talk of another presidential bid, telling a Tennessee audience last month, "I'm not planning to be a candidate again. I haven't reached a stage in my life where I'm willing to say I will never consider something like this."

A payment of $40,000 to a Democratic polling firm stirred political talk, but pollster Mark Penn said it was settlement of a 2000 account.

Gore has warned about the dangers of global warming for years, arguing that without dramatic changes in the emission of greenhouse gases, the planet is likely to experience a dramatic increase in violent storms, infectious disease, deadly heat waves and rising sea levels that will force the evacuation of low-lying cities.

He plans to hold a training session in Nashville this summer on how to deliver the message on climate change.

The New York Daily News first reported on Gore's hiring of Neel on Tuesday.

Gore's campaign will pit him against an old adversary: President Bush.

Bush acknowledges global warming is a real problem, but he believes more uncertainty exists about the degree to which humans play a part — mainly through fossil fuel burning — than most scientists do.

He reversed a 2000 campaign pledge to regulate carbon dioxide, the chief global warming pollutant, and withdrew the United States from the Kyoto climate treaty, saying it would harm the U.S. economy and unfairly excluded fast-growing developing countries. Gore is a strong supporter of the Kyoto treaty.