It's encouraging that President Obama has declared his commitment to a "national conversation" on climate change just as 2012 is confirmed as the hottest year on record in U.S. history, and among the hottest 10 years in the modern global temperature record.

Solving what England's Stern Commission called "the greatest market failure of all time" -- allowing the fossil fuels industry to use the atmosphere as a free sewer for carbon waste that alters the climate -- must inform the energy and tax policy debates of the next three years, with the president committed to resolving it in favor of the health of the planet.

Before that conversation begins, let's review energy issues the last election settled. For although climate change was shamefully not raised by debate moderators, the election became a clear referendum on energy policy -- and green energy won.

In the debates, Mitt Romney made clear his priority was to quickly approve the Keystone XL Pipeline to move dirty Canadian tar sands oil to Gulf ports. Obama was wisely mute. Now it is Obama's time to speak up, cancel the pipeline by presidential order and use his State of the Union address to tell Americans why. This export pipeline will provide few long-term jobs, and may well raise oil prices. Far more important, canceling it would be the beginning of the end of the oil industry's political and economic hegemony.

Subsidies to the oil industry must end. This issue was fully vetted in the campaign, and Obama won, in spite of at least $136 million of direct oil industry attack ads.

Subsidies for noncarbon energy, especially wind, have already been renewed, another victory. Romney lost Iowa, where wind power is well-established, in part by opposing such subsidies, which Obama supported.

Finally, Obama and Romney agreed that the federal government should expand research into next-generation energy, the kind that is already bearing fruit in new storage battery technology soon to be commercialized from MIT laboratories, research partially funded by Obama's Department of Energy. The president has a mandate to increase funding for such research.

The major climate policy not addressed in the campaign was a carbon tax or cap-and-trade regime. Here is where the "national conversation" is essential. Obama certainly supported the cap-and-trade bill that died in the Senate early in his first term, and has expressed doubts about the carbon tax. Romney endorsed neither.

Some environmentalists are critical of the president for his apparent passivity on carbon solutions. But gridlock politics requires just this conversation. The costs of carbon taxes or cap-and-trade will be broad, with impacts greater on some sectors than others, and tens of thousands of workers in the coal and oil industries need to prepare for the mostly coal- and oil-free world a stable climate demands. That transition will be wrenching, and the impacts need to be mitigated as much as possible.

In the climate wars, President Obama must be our Roosevelt, rallying the nation and the world to the cause of saving the future. For all of us now know that a rising sea level is no cheap laugh, and that the record heat and drought of the last year is no statistical blip but a crippling trend. Crops withered in the fields; 75 million acres of western forests have died; acidification of the oceans has begun to damage shellfish production. The symptoms of a planet reeling from carbon sickness, a form of cancer, are all around us.

President Obama -- it is time for you to lead this war for all of us. You did not ask for the wars in Iraq and Afghanistan, one ended, the other ending, nor for the recession, which you defeated. Nor did you ask for the carbon war. But you understand it. History demands that you be not only America's first black president, but America's first green president.

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James P. Lenfestey is a former Star Tribune editorial writer.