President Obama told leaders at the United Nations summit on climate change that "nobody can stand on the sidelines on this issue," insisting that an "ambitious" agreement is needed to protect the world from environmental dangers. (AP)

The Obama administration appears to be losing ground in its efforts to cut U.S. emissions of greenhouse gases, according to new government figures that show pollution levels rising again after several years of gradual decline.

Data released Friday by the Energy Department show American factories and power plants putting more carbon dioxide into the atmosphere during the first six months of 2014 compared with the same period in each of the past two years. The figures confirm a reversal first seen in 2013, when the trend of steadily falling emissions abruptly halted.

The higher emissions are primarily a reflection of a rebounding economy, as American businesses burned more gas and oil to meet higher demand. But the shift also underscores the challenge confronting the Obama administration as it seeks to honor a pledge to sharply cut U.S. emissions of greenhouse gases by the end of the decade.

The release of the new emissions figures comes just three days after President Obama stood before a United Nations climate summit to highlight U.S. progress in reducing levels of carbon dioxide and other gases blamed for warming the planet.

“The United States has reduced our total carbon pollution by more than any other nation on Earth, but we have to do more,” the president told world leaders at U.N. headquarters in New York.

Administration officials said the increase was not particularly surprising given the improving economy, and some pointed to one of the report’s bright spots: Even as the economy expanded, carbon emissions from automobiles have remained essentially flat, as more Americans switched to fuel-efficient cars and trucks.

Some also cited another encouraging trend in the report: Big jumps in the use of alternative and renewable energy. Solar, wind and hydropower were up more than 7 percent compared with two years ago, according to the report, and renewable sources now account for nearly 12 percent of the country’s domestic energy production.

Environmental Protection Agency Administrator Gina McCarthy, while declining to comment specifically on the new Energy Department figures, predicted faster reductions in carbon emissions in the near future because of shifting attitudes among many of the country’s top corporations and investment houses. Driving the change, she said, is the growing appeal of alternative energy as a business investment, as well as concerns about the impacts of global warming on corporate profits.

“Companies like General Mills and Coca-Cola see climate change as a threat to commerce,” McCarthy said Thursday at a forum on the economic impacts of global warming. “Paying more for soda and cereal means less cash to buy other things. That chokes economies and stunts job growth. The bottom line is: We don’t act despite the economy, we act because of it.”

The Obama administration has taken a number of steps to lower U.S. greenhouse-gas emissions, including tougher fuel-efficiency standards for automobiles and proposed new regulations limiting carbon emissions from power plants. The White House has promised to lower U.S. carbon emissions by 2020 to a level 17 percent below where they stood in 2005.

“America will meet that target,” Obama told the U.N. gathering. “And by early next year, we will put forward our next emission target, reflecting our confidence in the ability of our technological entrepreneurs and scientific innovators to lead the way.”

The Energy Department data, a routine snapshot of U.S. energy consumption by the department’s Energy Information Administration, show higher pollution levels from all major classes of fossil fuels, including petroleum, natural gas and coal. Trend lines were up in nearly all industrial sectors, as factories, retail stores and utility plants all consumed more fuel compared with previous years.

American homeowners also contributed to rising pollution levels, the report showed, as households used more electricity, natural gas and fuel oil in a year that brought record-breaking cold to the East Coast and Midwest, and extreme heat and drought in the western third of the country. Across the nation, carbon emissions for the first six months of the year were nearly 3 percent higher than during the same period last year, and about 6 percent higher than in 2012.

The return of higher carbon emissions was viewed by environmental groups as a setback, given the administration’s commitment to addressing the causes of climate change.

“The growth in U.S. CO2 emissions is clear wake-up call,” said Ken Bosson, director of the SUN DAY Campaign, the Maryland-based nonprofit organization that promotes the use of renewable energy. “Much more needs to be done to accelerate the continued growth of renewable energy sources, as well as improved energy efficiency if the nation is to successfully address climate change.”