New energy: climate change and sustainability shape a new era

HURRYING ACROSS THE BRIDGE

It will also be necessary to consider all of those smokestacks gushing coal exhaust into the sky. Americans may want to kick their coal habit soonest – even before they're off the other fossil fuels.

Compared with oil and natural gas, coal releases up to twice as much carbon per unit of energy produced. And although coal tends to be seen as old-fashioned fuel – the stuff that powered Charles Dickens's London – its use continues to grow.

The US still derives 50 percent of its electricity from coal, and China doubled its use of coal-fired power plants from 2000 to 2007, building roughly one new plant per week, according to estimates provided in recent reports by the Massachusetts Institute of Technology and the US Department of Energy.

The good news is that many coal-fired power plants could be retrofitted to burn natural gas. It involves removing heavy machinery that pulverizes coal into dust, and replacing steam turbines with massive gas turbines. It is no small expense – but utilities sometimes do this anyway for purely profit motives when gas prices are low.

Swapping coal for gas on a large scale could cut carbon emissions by hundreds of millions of tons as the world moves toward renewables.

"Natural gas is the logical bridge [fuel]," says Joseph Pratt, an energy historian at the University of Houston. "We might want to hurry across that bridge," he adds. "Even hurrying is two generations, I'm afraid."

Hurrying will require compromises.

Electricity produced from wind or solar can power many homes and factories as is, but the world's automobiles, cargo ships, and airplanes rely on liquid fuels – gasoline, kerosene, and diesel. Ramping up mass transit and building a fleet of electric ships and autos will take decades.

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