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WASHINGTON -- Former U.S. Vice President Al Gore is going where few environmentalists -- and fellow Democrats -- have gone before: criticizing President Barack Obama's record on global warming.

In a 7,000-word essay for Rolling Stone magazine that will be published Friday, Gore says Obama has failed to stand up for "bold action" on global warming and has made little progress on the problem since the days of Republican President George W. Bush. Bush infuriated environmentalists by resisting mandatory controls on the pollution blamed for climate change, despite overwhelming scientific evidence that the burning of fossil fuels is responsible.

While Gore credits Obama's political appointees with making hundreds of changes that have helped move the country "forward slightly" on the climate issue, and acknowledges Obama has been dealing with many other problems, he says the president "has simply not made the case for action."

"President Obama has never presented to the American people the magnitude of the climate crisis," Gore says. "He has not defended the science against the ongoing withering and dishonest attacks. Nor has he provided a presidential venue for the scientific community ... to bring the reality of the science before the public."

The comments mark a turnaround for the nation's most prominent advocate for action on global warming, whose work on the climate problem has earned him a Nobel Prize and was adapted into an Oscar-winning documentary.

Gore toasted Obama's inauguration with a "green" ball. He helped the White House press the House of Representatives to pass a global warming bill in 2009 that would have set the first-ever limits on the pollution blamed for global warming. It died in the Democratic-controlled Senate. Gore also advised Obama before the president participated in international climate negotiations in 2009. Obama's last-minute appearance in Copenhagen helped salvage a nonbinding deal to reduce greenhouse gases.

In the essay, Gore calls the Copenhagen result a "rhetorical agreement" that provided cover for the administration's inability to commit to enforceable targets for global warming pollution. Without legislation, Obama couldn't follow through on his promises to cut emissions.

"During the final years of the Bush-Cheney administration, the rest of the world was waiting for a new president who would aggressively tackle the climate crisis, and when it became clear that there would be no real change from the Bush era, the agenda at Copenhagen changed from `How do we complete this historic breakthrough?' to `How can we paper over this embarrassing disappointment?"' Gore writes, referring to the talks, where 193 nations met to draft a new global treaty to reduce greenhouse gases. The 1997 Kyoto Protocol, in which the U.S. never participated and Gore helped to broker, expires in 2012.

Gore declined an Associated Press request for an interview.

Bush pulled out of Kyoto and refused to control heat-trapping pollution even after the Supreme Court said the government had the authority to move forward forcefully on this front and federal scientists determined that increasing concentrations of greenhouse gases posed dangers to human health.

Obama, by contrast, has tightened fuel economy standards to reduce global warming pollution from automobiles, included billions of dollars for climate-friendly projects in the economic stimulus package and started controlling emissions under existing law.

As recently as April, at a Democratic fundraiser in San Francisco, Obama said he was "not finished when it comes to energy."

Mentioning the climate deniers in Congress, Obama said, "Unless we are able to move forward in a serious way on clean energy, we're putting our children and grandchildren at risk."

Regardless of views such as Gore's, environmental voters may see little choice in the 2012 election. Those in the Republican field so far either deny global warming is a man-made problem altogether or say actions to address it would harm the economy. For Obama, the biggest risk is that some environmental voters may not turn out.

In his essay, Gore notes his comments could weaken Obama at a time when he already is under attack from Republicans.

"Even writing an article like this one carries risks," Gore says. "Opponents of the president will excerpt the criticism and strip it of context."

Bowing to political resistance from Republicans and some in his own party, Obama abandoned an effort and a campaign pledge to enact legislation that would put the first-ever limit on greenhouse gases.

In November, after Republicans took control of the House, Obama said in a news conference there were other ways to tackle global warming that wouldn't require new legislation.

"His election was accompanied by intense hope that many things in need of change would change," Gore writes. "Some things have, but others have not. Climate policy, unfortunately, falls into the second category."