Coal is the most carbon intensive fossil fuel and so is normally the focus of climate change concern. Yet, oil is America's biggest source of carbon pollution.
By itself, oil accounts for 42% of America's energy related carbon emissions, while coal is responsible for 32%. America's economy and way of life is much more dependent on oil and coal, unlike China which gets an incredible 70% of its total energy from coal.
Indeed, burning oil is responsible for 2.25 billion tons of the America's 5.29 billion tons of carbon pollution.
http://www.eia.gov/totalenergy/data/monthly/pdf/sec12_3.pdf. By comparison, coal burning emitted 1.66 billion tons of carbon during 2012.
Though both carbon pollution from coal and oil in the USA have been declining in recent years, the declines in carbon pollution from coal have been much bigger and faster. As a result of the bigger declines in coal's carbon pollution, the spread in carbon pollution totals of coal and oil has been growing. For many years, oil would account for 300 million to 400 million more tons of carbon pollution per year than coal. By last year, oil, however, accounted for 600 million more tons of carbon emissions.
Natural gas explains why coal emissions dropped more rapidly than oil's during 2012. At this point, natural gas is a powerful competitor to coal for power generation but a weak competitor to oil for transportation market share. Gas is displacing oil in heating and industrial uses, but its gains in transportation barely move the needle on oil demand.
Until either gas, electricity or biofuels become powerful substitutes for oil in transportation, oil will remain America's largest source of carbon emissions.