An ideological chasm separates the environmental policies of the two candidates, with President Bush favoring more use of domestic coal and oil to cut dependence on Middle East oil while Kerry seeks a shift to clean energy like solar or wind power by 2020.
On global warming, Kerry wins fans abroad by pledging to rejoin international efforts to curb emissions of heat-trapping gases by the United States, the world's top polluter, even though he rules out signing up for the U.N.'s Kyoto protocol.
Bush angered U.S. allies by abandoning Kyoto in 2001.
But U.S. lawmakers, fearful of extra costs when oil is at $50 a barrel, might well constrain Kerry if he won on Nov. 2 as they did ex-President Bill Clinton, whose administration signed up for Kyoto in 1997 but never got it ratified.
"The problem is not Bush or Kerry, the problem is the Senate," said Dutch State Secretary for the Environment Pieter van Geel, whose country holds the rotating presidency of the European Union. "We still have almost the same Senate."
"On global warming and other global issues I don't see much difference between Kerry and Bush," added Sunita Narain, director of the Center for Science and Environment in New Delhi. "There'll be a nuance change."
But even nuances may be welcome news to supporters of the 126-nation Kyoto pact, who see targets for curbing emissions of carbon dioxide from cars, factories and power plants by 2012 as a first step in battling global warming.
"Kerry would engage with other countries about what would come after 2012 in a way that the Bush administration wouldn't," said Eileen Claussen, head of the Pew Center on Global Climate Change. She said the environment came far behind Iraq, terror and the economy in voter priorities.
The Republican president has derided Kyoto as too costly and says it is unfair because it exempts rapidly industrializing countries like China and India. "It's one of those deals where, in order to be popular in the halls of Europe, you sign a treaty," he said.
Kerry says Bush should have tried to renegotiate a "flawed" Kyoto rather than ditching it. Kyoto is set to enter into force in the next few weeks with Russian backing.
Kyoto aims to cut developed nations' emissions by 5.2 percent below 1990 levels by 2008-2012. Many scientists say storms, rising sea levels and desertification may be the biggest threat to life on the planet in the coming centuries, justifying trillions of dollars in spending to crack down.
Some say Russia could spur U.S. action.
"We have completely new momentum in the debate," said European Environment Commissioner Margot Wallstrom of Russia's imminent ratification. "This will continue to raise the debate level in the U.S."
Russian ratification would push Kyoto over the threshold of 55 percent of developed nations' emissions needed to enter into force. Kyoto will reach 61 percent with Russia's 17 percent.
"It's not as black as it seems. There is some hope for a tougher U.S. climate policy whoever wins," said Paal Prestrud of the Center for International Climate and Environmental Research in Oslo. "There's no doubt there will be better chances with Kerry than with Bush."
BUSH BACKS HYDROGEN
Bush's global warming policies seek to keep growth in carbon dioxide emissions sharply below the rate of economic growth by 2012 - but it falls short of Kyoto's demand for caps.
Bush recently got the worst "F" rating for his environmental record from the U.S. League of Conservation Voters. On a different scale, it gave Kerry a high 92 percent. "Bush has rewarded Big Oil and he wrongly walked away from Kyoto," said spokesman Mark Sokolove.
Both Bush and Kerry want to improve energy security by cutting dependence on foreign oil suppliers like Saudi Arabia, which meet about 65 percent of demand.
Both want more conservation and drilling in some offshore Gulf of Mexico fields. Bush also wants new drilling in the Arctic National Wildlife Refuge in Alaska, which Kerry opposes.
Bush has pushed for a $1.2 billion plan to run cars on hydrogen. Kerry wants the United States to get 20 percent of its electricity from alternative sources like solar and wind by 2020, up from one percent now, excluding hydropower.