Officials gather in Copenhagen this week for an international climate summit, but business leaders are focusing even more on Washington, where the Obama administration is expected as early as Monday to formally declare carbon dioxide a dangerous pollutant.

An "endangerment" finding by the Environmental Protection Agency could pave the way for the government to require businesses that emit carbon dioxide and five other greenhouse gases to make costly changes in machinery to reduce emissions -- even if Congress doesn't pass pending climate-change legislation. EPA action to regulate emissions could affect the U.S. economy more directly, and more quickly, than any global deal inked in the Danish capital, where no binding agreement is expected.

Many business groups are opposed to EPA efforts to curb a gas as ubiquitous as carbon dioxide.