Former Vice President Al Gore on Monday called for immediate action to stop global warming, calling the phenomenon a "climate crisis" that demands attention from American leaders.

Gore, a Democrat who narrowly lost the 2000 presidential race to George W. Bush, decried the lack of action on global warming by politicians across the ideological spectrum.

"When we make big mistakes in America, it is usually because the people have not been given an honest accounting of the choices before us," Gore said in an hour-long speech at New York University Law School. "It also is often because too many members of both parties who knew better did not have the courage to do better."

But he implicitly criticized the Bush administration, which has been accused of editing official scientific studies to downplay the impact of global warming and asking scientists at federal agencies to refrain from speaking out on the phenomenon.

Future generations, Gore said, "deserve better than the spectacle of censorship of the best scientific evidence about the truth of our situation and harassment of honest scientists who are trying to warn us about the looming catastrophe."

"Each passing day brings yet more evidence that we are now facing a planetary emergency, a climate crisis that demands immediate attention," Gore said.

While the administration has acknowledged the effects of global warming on the environment, President Bush has rejected mandatory controls on carbon dioxide, the chief gas blamed for the phenomenon. He also has kept the country out of the Kyoto treaty, which called for mandatory reductions of greenhouse gases among the signing nations. He has said the pact would harm the U.S. economy.

A White House spokesman declined Monday to comment on Gore's remarks.

Said Republican National Committee spokesman Aaron McLear: "Under the president's tenure, the air and water have gotten cleaner while we have implemented pro-growth strategies that have created almost 6 million jobs in the past three years."

Gore has brought considerable attention to the global warming phenomenon since last spring, when his documentary film, "An Inconvenient Truth," was released to wide critical praise. The movie has become one of the highest-grossing documentaries, while a companion book on the topic has become a best-seller.

The resulting wave of publicity has raised questions about whether Gore intends to run for president again in 2008. While he has said he doesn't intend to be a candidate, he hasn't ruled out a run.

In his speech, Gore framed the pursuit of renewable energy as an economic and national security issue for the United States, besides being an environmental imperative. But he also said the challenge of global climate change offered opportunities for innovation and investment.

"We can change this by inventing and manufacturing new solutions to stop global warming right here in America," he said, adding that venture capitalists are eager to put money behind effective technologies to cut greenhouse gases.