Slowing the buildup of greenhouse gases responsible for warming the planet is one of the biggest challenges the United States and President Barack Obama face. The effects of rising global temperatures are widespread and costly: more severe storms, rising seas, species extinctions, and changes in weather patterns that will alter food production and the spread of disease.
Politically, the stakes are huge.
Any policy to reduce heat-trapping pollution will inevitably target the main sources of Americans' energy: the coal burned by power plants for electricity and the oil that is refined to run automobiles.
Those industries have powerful protectors in both parties in Congress who will fight any additional regulations handed down by the administration that could contribute to Americans paying more for electricity and gas at the pump. There's also the lingering question of how much the U.S. can do to solve the problem alone, without other countries taking aggressive steps to curb their own pollution.
"My plan will continue to reduce the carbon pollution that is heating our planet, because climate change is not a hoax. More droughts and floods and wildfires are not a joke." Obama at the Democratic National Convention, Sept. 6, 2012.
"I urge this Congress to pursue a bipartisan, market-based solution to climate change. … But if Congress won't act soon to protect future generations, I will. I will direct my Cabinet to come up with executive actions we can take, now and in the future, to reduce pollution, prepare our communities for the consequences of climate change, and speed the transition to more sustainable sources of energy." Obama in his State of the Union speech, Feb. 12, 2013.
Obama has shown he doesn't need Congress to take action against climate change.
In his first term, he struck a deal with automakers to double fuel economy standards. After failing to pass a climate bill through a Democratic-controlled Congress, he proposed rules to control heat-trapping pollution from future power plants.
The president's chances of going through Congress are no better the second time around.
While some liberal Democrats have proposed legislation to tax emissions of carbon dioxide, the chief greenhouse gas, Republicans controlling the House have pledged to block any and all efforts to price carbon pollution. Democrats from states with coal and oil probably will be stumbling blocks.
Obama has more tools he can tap to deal with the problem. The big question is how aggressive he will be and how he will balance expanding domestic energy production with his climate goals.
On the one hand, he says he supports an "all of the above" energy plan that uses all of the nation's energy resources. But should he proceed with regulations to control pollution from existing coal-fired power plants, the single largest source of carbon pollution, those regulations probably will contribute to shuttering facilities already struggling to compete with cheap natural gas.
Also looming is a decision whether to grant a permit to the Keystone XL oil pipeline, which would transport carbon-laden tar sands oil from Canada to Texas.
While the pipeline project is a better alternative from a carbon pollution standpoint than shipping the oil by rail, the emissions created by harvesting tar sands, processing them into oil and eventually burning it in automobiles in the U.S. and abroad will contribute to global warming.
Obama also supports the natural gas drilling boom brought about by hydraulic fracturing, but that boom is also responsible for releasing methane, a potent greenhouse gas.
Obama is likely to take more steps to reduce the pollution blamed for climate change. But those actions probably will not be of the scale needed to help much in slowing the heating of the planet.