The television ad shows John McCain, the Republican presidential nominee, in scenic desert landscapes as he talks about the dangers of global warming. "We have an obligation to future generations to take action and fix it," he says.
Striving to appeal to moderate voters, McCain has frequently highlighted his bipartisan proposal to clamp down on greenhouse gas emissions.
But by naming Sarah Palin as his running mate, McCain has aligned himself with a Republican whose record as governor of Alaska has drawn scorn from environmentalists, most notably for her denial that humans are causing climate change.
That, combined with McCain's call for opening new stretches of coastline to oil drilling, risks undercutting his standing on the environment.
Global warming has been one of the main issues McCain has used to put distance between himself and his party's tarnished brand. In pursuit of that goal, he and Palin also have cast themselves in recent days as reformers who would shake up Washington.
In a time of war and economic troubles, the environment ranks low on the list of voter priorities. But it carries symbolic value and offers McCain a way to suggest that he would break with the unpopular Bush administration. Given the scant contrasts between McCain and President Bush on Iraq and the economy, anything that helps the Arizona senator distinguish himself could prove crucial.
"The environment is important to many of the groups of people that McCain has to make some progress with -- especially to many independents," said pollster Andrew Kohut, president of the nonpartisan Pew Research Center for the People & the Press.
Doug Holtz-Eakin, a senior McCain policy advisor, said that neither Palin's presence on the ticket nor McCain's shift on oil drilling would harm his standing as a champion of the environment. Environmentalists who criticize McCain "don't represent the entire spectrum" of opinion, he said, and others recognize that coal, nuclear power, gas and oil must be part of any "thoughtful approach" to global warming.
The major environmental groups, however, favor Illinois Sen. Barack Obama over McCain. The League of Conservation Voters gives the Democratic presidential nominee a lifetime score of 86% on environmental votes. McCain's score is 24%.
Nonetheless, environmentalists have cheered McCain for backing a cap on carbon emissions that contribute to global warming, a position not shared by many in his party. They have also applauded him for opposing oil drilling in the Arctic National Wildlife Refuge, a longtime goal of Bush and other Republicans, including Palin.
"To his credit, we've always said that John McCain was better on the environment than George Bush, but that's an incredibly low bar because Bush was the most anti-environment president we've ever seen," said Gene Karpinski, president of the League of Conservation Voters.
The McCain campaign's focus on global warming follows a tradition of Republicans brandishing their environmental credentials to gain support among Democrats and independents. Gov. Arnold Schwarzenegger made California's law limiting greenhouse gas emissions a centerpiece of his reelection campaign two years ago.
Jim Douglas, the Republican governor of left-leaning Vermont, took on Bush in his 2004 reelection bid. "We backed legal action against the federal government when they wouldn't protect our air and water," Douglas told Vermont TV viewers in an ad.
But in June, McCain dropped his support for the federal ban on new offshore oil drilling. His sudden reversal, in a speech to cheering energy executives in Houston, set off a fierce backlash among environmentalists.
"We have a card-carrying member of the oil wing of the Republican Party," said Carl D. Pope, executive director of the Sierra Club. "There's nothing left of his independence."
McCain's decision to focus on drilling as a key to lower gasoline prices ("Drill, baby, drill," supporters chanted at the Republican convention last week in St. Paul, Minn.) has intensified the anger among environmentalists.
They have ridiculed McCain ads that tout coastal drilling in tandem with renewable power from wind turbines. In the Senate, they note, McCain has voted repeatedly against renewable energy bills. Pope, for one, called the ads "cynical and manipulative."
But the political imperative for McCain was to demonstrate that he would take action against gas prices that had soared above $4 per gallon. A Pew survey in June showed a rise in voter support for expanded energy exploration, including in the Alaska wildlife refuge.
Voters "don't want to hear about magic unicorn-powered cars or future, down-the-line, hydrogen-powered vehicles," said Rick Wilson, a Republican strategist behind the Vermont TV ad. "They want to know how you're going to cut the price of gas at the pump."
The shift in public opinion helps explain the new willingness even of Democrats, Obama among them, to consider lifting the offshore drilling ban.