At the global climate change conference in Copenhagen in December, President Obama pledged to cut United States emissions from 2005 levels by 17 percent by 2020 — if he could get Congress to pass climate and energy legislation.

The task proved impossible even with Democratic majorities in both houses of Congress. But now, any legislative progress on the issue will depend on the cooperation of the new Republican majority in the House of Representatives and the incoming majority leader, presumed to be John Boehner of Ohio.

Mr. Boehner fought bitterly against the cap-and-trade bill passed last year by the House, and on one memorable occasion appeared to scoff at the idea that climate change was anything to be concerned about.

“The idea that carbon dioxide is a carcinogen that is harmful to our environment is almost comical,” Mr. Boehner told ABC News in an April 2009 interview. “Every time we exhale, we exhale carbon dioxide. Every cow in the world, you know, when they do what they do, you’ve got more carbon dioxide.”

As some science writers quickly pointed out, Mr. Boehner’s statements did not hew to the basics of climate science. Human respiration, for instance, does produce carbon dioxide — about two pounds per person per day. But this carbon dioxide was originally taken out of the air by plants before being consumed by humans, either directly or in the form of meat, so no net addition of carbon dioxide to the atmosphere is created.

By contrast, the combustion of fossil fuels by humans since the Industrial Revolution has increased atmospheric carbon dioxide concentrations by about 40 percent, to a level substantially higher than at any other time in the last 800,000 years.

Climate scientists also do not claim that carbon dioxide is a carcinogen, or cancer-causing substance. Rather, their concern is that carbon dioxide and other greenhouse gases will trap heat in the form of sunlight, raising global temperatures to potentially dangerous levels.

As for cows, their flatulence is composed mainly of methane (a greenhouse gas, to be sure), not carbon dioxide.

In an interview in with NPR in January 2009, Mr. Boehner seemed to take a somewhat more conciliatory view of climate science, more in line with the moderate wing of his party.

“I think most members think that the climate change is a serious issue that needs to be addressed,” he said. “The question is, how do you address it?”

The American Energy Act, an energy plan introduced by House Republicans last year, offers some clues to Mr. Boehner’s latest thinking. It calls for expanding domestic oil and gas drilling and nuclear power and would subsidize some clean energy development, but makes no provisions for curbing carbon dioxide emissions.

The bill would have also curtailed environmental reviews of energy projects and put restrictions on environmental lawsuits.

Mr. Boehner has often called this an “all of the above” energy strategy.

“The House Republicans’ American Energy Act –- not the Democrats’ national energy tax –- is the fastest route to a cleaner environment, lower energy costs and more American jobs,” he said in introducing that bill.