A dangerously obese man, serious about his New Year's resolution to lose weight, would not begin the year by buying $7 billion worth of fat-producing candy. Nor would any nation serious about reducing greenhouse gases approve construction of a $7 billion pipeline that would facilitate the consumption of 900,000 gallons a day of tar sand oil, spewing greenhouse emissions into the atmosphere.

On this New Year's Day 2013, America is that dangerously obese man.

And President Barack Obama is poised to make the long-delayed decision on whether to bulk up or slim down. The candy is the Keystone XL project, a proposed 1,700-mile pipeline across the United States that would transport extra-dirty crude oil mined from the tar sands of Canada's northern Alberta province to U.S. refineries on the Gulf of Mexico.

A go-ahead for the pipeline from the Obama administration would tell the world that the United States, like the glutton who can't control his appetite, is not serious about addressing climate change. A rejection would send the opposite message. It says that the United States will not continue to stand idly on the sidelines as the polar ice caps melt, coastal regions sink and extreme weather events – droughts, hurricanes, wildfires and tornadoes – intensify.

Keystone XL has been portrayed as a classic contest between jobs and the environment. That's just not true. Supporters' claims that the pipeline will create hundreds of thousands of new jobs are a gross exaggeration. A U.S. State Department review concluded that the pipeline would produce only 5,000 to 6,000 new jobs and that the vast majority of those would be temporary construction jobs, lasting two years at most.

Once built, the pipeline would support a scant 50 permanent jobs in the United States, a study from Cornell University's Global Labor Institute estimated.

Meanwhile the environmental and health risks posed by tar sands oil extraction, transport and use are incalculable. Oil from tar sands contains significantly more sulfur, nitrogen, nickel and carbon than conventional oil sources, making it more harmful to human health and the environment.

The usual methods of extraction, either through strip mining or by pumping steam underground to melt out the bitumen – a thick, tarlike form of petroleum – requires the use of vast amounts of water and energy and creates large lakes of toxic waste. The underground pipeline across the American heartland poses a serious risk to important aquifers that irrigate croplands and supply drinking water for millions of Americans.

Finally, if approved, the Keystone XL pipeline further cements America's dependence on fossil fuels that are warming the planet through a buildup of carbon emissions in the atmosphere. It delays the urgent need to shift to non-polluting renewable energies, to build more sustainable communities and energy-efficient cars and appliances.

America can't keep putting off its commitment to be a leader in combating global climate change. Obama can't keep putting off pledges to lead in that international effort.

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