A little more than five years after envisioning the year of his election as “the moment when the rise of the oceans began to slow and our planet began to heal,” U.S. President Barack Obama is pushing for policies to address the threat of climate change.

In a speech scheduled for Tuesday afternoon at Georgetown University, the president will likely not touch on the controversial Keystone XL pipeline that has become a flashpoint for environmentalists. However, early talking points from the speech circulating among the press point toward one substantial proposal that's cheering many climate scientists and environmental advocates: a plan to limit carbon emissions from existing power plants.

"That is a major development, and it will go some way to stemming our growing carbon emissions, and the impact they are having on our climate," Pennsylvania State University climate scientist Michael Mann wrote in an email.

Currently, there are no federal regulations capping greenhouse gas output by power plants, which account for more than one-third of U.S. carbon emissions, according to Angela Anderson, director of the climate and energy program, for the advocacy group Union of Concerned Scientists.

“They’re the last big source to be regulated,” Anderson said in a phone interview. “The administration has already moved on reducing emissions from cars and trucks. This is the next step.”

The U.S. Environmental Protection Agency already proposed standards to limit carbon emissions from new power plants in March 2012. Now, in the wake of the president’s speech, the EPA will unveil its proposal of standards for existing power plants by June 2014, and finalize the rules by June 2015, according to the Hill, which quoted an unnamed administration official. Other officials told the Hill that the White House will offer a modified version of the EPA’s proposed standards for new plants later this year.

Overall, the advance details of Obama's proposed climate plan show the president is relying more on executive actions than trying to push bills through Congress.

"Ultimately, we need a comprehensive energy [and] climate policy that prices the emission of carbon into the atmosphere," Mann says. "But given that we have an intransigent congress (the House Science committee is led by someone who doesn't even accept the reality of climate change), the president is forced to turn to executive actions."

Federal regulations already limit emissions of other pollutants from power plants – mercury, ozone-depleting chlorofluorocarbons, and the sulfur dioxide emissions that can lead to acid rain, to name a few. Whether or not the EPA had standing to regulate carbon emissions was a legal controversy for some time, but the Supreme Court held in 2007 in Massachusetts v. EPA that greenhouse gases are indeed, pollutants, and subject to the Clean Air Act.

There are no details as of yet how standards for existing power plants might work, but looking at the EPA’s proposed rules for new plants could prove illustrative. Under those rules, a power plant can use any fossil fuel to generate electricity, but carbon emissions are limited to a figure tied to the plant’s output – 1,000 pounds of carbon dioxide per megawatt-hour. Meeting such standards is already easier for natural gas plants, which emit an average of 850 pounds of carbon dioxide per megawatt-hour. But plants that run on coal or petroleum coke emit an average of around 1,800 pounds of carbon dioxide per mega-watt hour, will need new technology to cope with emissions caps.

The oil industry has been practicing carbon capture for decades, and even injects waste carbon dioxide back into the ground to breathe life back into aging wells. Pumping carbon dioxide underground also sequesters it instead of releasing it into the atmosphere.

However, such carbon capturing technologies “have not been used at the commercial scale with power plants,” Anderson says. “So one thing you might see [in Obama’s speech] is investment in pilot projects for carbon capture and storage.”

The coal industry is already wincing at the prospect of new regulations. Stocks in U.S. coal companies tumbled on Tuesday morning, and advocacy groups issued fierce warnings about the impact of new regulations on the economy.

“Coal power plants generate more electricity and create and sustain more jobs than any other energy source,” National Mining Association president Hal Quinn said in a statement Tuesday. “So policies that shut off coal energy damage the nation's job and economic engine, while also raising costs to American consumers.”

The president’s speech isn't the only climate issue on deck in Washington this week. On Monday, the U.S. Supreme Court said it would review an appellate court’s decision to strike down the Cross-State Air Pollution Rule, which addresses pollution that crosses state lines.

But even if Obama’s power plant policies take effect, will the resulting reduction in emissions mitigate or even reverse the effects of climate change? Most scientists say time will tell whether the seas will truly halt their rise. The goal of reducing carbon emissions by 17 percent by 2020 was appropriate enough when Obama announced it in 2009, Anderson says, but many scientists are concerned that deeper emissions cuts may be needed to try and turn back the tide -- noting 17 percent reductions may be admirable, but not enough.

“We hope his plan puts us on the path to reach and exceed that goal,” she said.

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