The Democrats' leading environmental messenger, Al Gore, is declaring that President Barack Obama has failed to lead on the issue of global warming.

In a 7,000-word essay posted online Wednesday by Rolling Stone magazine, Gore says the president hasn't stood up for "bold action" on the problem and has done little to move the country forward since he replaced 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. The scientific case has only gotten stronger since, Gore argues, but Obama has not used it to force significant change.

"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."

Gore does credit Obama's political appointees with making hundreds of changes that have helped move the country "forward slightly" on the climate issue, but says the president "has simply not made the case for action." He is the second Clinton administration official this month to express disappointment with Obama on environmental issues. Former Interior Secretary Bruce Babbitt, in a speech in early June, said Obama had yet to take up the "mantle of land and water conservation...in a significant way."

Gore's comments mark a turnaround for the nation's most prominent global warming advocate, 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 to pass a global warming bill in 2009 that would have set the first-ever limits on the pollution blamed for global warming, a bill that 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.

It was a reference to Denmark talks at which 193 nations met to draft a global treaty to reduce greenhouse gases. The 1997 Kyoto Protocol, which the U.S. signed onto when Gore was vice president, but the Senate refused to ratify, expires in 2012.

Gore declined a request for an interview.

Bush pulled out of Kyoto altogether. He also refused to control heat-trapping pollution even after the Supreme Court said the government had the authority to move ahead on it 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."

Referring to the climate-change skeptics 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 hurt the economy. For Obama, the biggest risk is that some environmental voters may not go to the polls.

"It is one of many issues where Obama is going to have problems with his progressive base," said Glenn Hurowitz, a senior fellow at the Center for International Policy, who has been critical of Obama's environmental and energy policies.

"Gore's telling the world what most environmentalists know in their hearts _ that Obama is not our friend, and he hasn't lived up to his promises," Hurowitz said.

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."

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Online:

Rolling Stone essay: http://tinyurl.com/3uz2jpx