When it comes to global warming, the Bush administration puts its faith in volunteerism and new energy technologies to scale back the American Everest of heat-trapping gases. But government studies say the results are at best uncertain.
One thing is not: Each year, the mountain of "greenhouse" gases emitted by the US grows bigger.
While the rest of the developed world requires -- but isn't always achieving -- mandatory cuts in carbon dioxide and other emissions, the country adding the most gases to the atmosphere is deadlocked in a debate over how to deal with it.
Individual states, meanwhile, are taking the lead.
Voluntary programs emphasized by President George W. Bush since 2002 are claimed to be sparing the atmosphere 270 million tonnes of carbon dioxide a year, or 4 percent of US emissions.
But the US government doesn't know -- and often can't verify -- whether the reductions reported by 230 US companies are real.
"It's difficult to prove," said Paul McArdle, who manages the Energy Department's voluntary reporting system. "It's my sense that some of these are real reductions."
What's more, McArdle acknowledged, companies can increase their emissions overall but still claim cutbacks -- by counting as reductions such steps as replacing old lighting, using more efficient vehicles or planting trees.
In a review last April, Congress' Government Accountability Office questioned Washington's ability to monitor these voluntary efforts.
"Determining the reductions attributable to each program will be challenging," it said.
Carbon dioxide from burning coal, oil and other fossil fuels is the biggest of the greenhouse gases, so called because they create a heat-trapping blanket when released into the atmosphere. Others are methane, nitrous oxide and synthetic gases.
The atmosphere holds more carbon dioxide now than it has for hundreds of thousands of years, and the Earth's surface warmed an average 0.5oC over the past century.
As a first step, the White House talks of reducing the "intensity" of US carbon pollution -- not shrinking emissions overall, but reducing the carbon dioxide emitted per unit of economic growth.
"Our objective is to significantly slow the growth of greenhouse gas emissions and, as the science justifies, stop it and then reverse it," said James Connaughton, chairman of the White House Council on Environmental Quality.
"We're making good progress. It's reasonably ambitious, but it still provides for reasonable human welfare," he said.
Now, the US is spending US$3 billion each year researching technologies to cut global warming and US$2 billion on climate research.
In a program called the Asia-Pacific Partnership, Bush is also working with Australia, China, India, Japan and South Korea -- producers of half the world's greenhouse gases -- to attract private money for cleaner energy technologies.
Connaughton calls that joint effort a major breakthrough.
Senator Jim Jeffords, an independent, calls it an "excuse for further delay."
Bush envisions using more hydrogen powered vehicles, electricity from renewable energy sources and clean coal technology.
The Energy Department's technology program has helped build 34,000 new energy-efficient homes and it plans to create "bioenergy" research centers and to advance research into hydrogen fuel and fusion energy.