Earlier today, the U.S. Environmental Protection Agency released its annual report on the nation's greenhouse gas emissions.

The data is for 2011.

The good news: Emissions decreased 1.6 percent that year, compared to 2010. Since 2005, they have declined 6.9 percent.

But many environmental groups remain dismayed by what they see as a slow pace of declines.

And, as the Washington Post reported on Saturday, the Environmental Protection Agency needs more time and will not meet its one-year deadline to impose the first-ever greenhouse gas limits on new power plants.

The EPA credited reduced emissions from electricity generation, improvements in fuel efficiency in vehicles with reductions in miles traveled, and year-to-year changes in the prevailing weather.

From the agency: "Greenhouse gases are the primary driver of climate change, which can lead to hotter, longer heat waves that threaten the health of the sick, poor or elderly; increases in ground-level ozone pollution linked to asthma and other respiratory illnesses; as well as other threats to the health and welfare of Americans."

Electricitry generation remains the largest source of GHG emissions — 33 percent of all emissions. Transportation accounts for 28 percent of emissions, industry for 20 percent. Next are commercial and residential, at a combined 11 percent, and agriculture at 8 percent.

Union of Concerned Scientists senior climate economist Rachel Cleetus told the Post that limiting greenhouse gas emissions from existing power plants "is one of the most important things the administration can do to cut global warming emissions."

She said groups want to hear — and soon — what the new timeline is. "Missing the deadline is one thing," Cleetus said, "but if we hear dead silence, that will be truly troubling."

Jeffrey Holmstead, a partner at the law firm Bracewell & Guiliani who represents utilities, wrote in an e-mail to the Post that the EPA is trying to figure out whether to revamp a previous rule, or start from scratch. that he was not surprised by the EPA's decision. "The big problem they face is that the Clean Air Act just wasn't designed to deal with greenhouse gas emissions," he said.