While the Obama administration has laid out a goal that would sharply reduce greenhouse-gas emissions, legislation remains stalled in the Senate. The Environmental Protection Agency has signaled that it might not wait for Congress and instead move ahead with its own regulations in the coming months. Here's a rundown so far of EPA's actions:
Last April, the EPA found that greenhouse gases contribute to air pollution and therefore endanger public health. The "endangerment finding", as it's called, allows the EPA to regulate six gases, including carbon dioxide, and provide footing to issue regulations under the Clean Air Act.
Any EPA regulations of carbon emissions wouldn't be nearly as comprehensive as one passed by Congress. Also, any emissions regulations without the backing of Congress would generate a wave of legal challenges.
President Obama has long called for tougher fuel-economy standards for all cars and light trucks sold in the United States, and in September the White House made that proposal official. Vehicles would have to achieve 35.5 miles per gallon by 2016, saving 1.8 billion barrels of oil and reducing greenhouse gas emissions by 950 million metric tons.
According to EPA Administrator Lisa Jackson, automakers will know sometime in March the specifics on fuel-economy standards that would affect vehicles built for the 2012 model year.
In January, the EPA required large emitters of heat-trapping emissions to collect greenhouse-gas data. The information from those reports will be released in 2011 publicly. Businesses that emit at least 25,000 metric tons of greenhouse gases per year would have to participate, which is expected to encompass about 10,000 facilities.