The idea is that by using new technology, the coal plants will sharply reduce the amount of sooty particles spewed into the air, as well as gases such as sulphur dioxide and nitrous oxide.
But critics say the technology has no effect on the emissions of carbon dioxide, a gas blamed for raising global temperatures.
Under optimal current conditions, coal produces more than twice as much carbon dioxide per unit of electricity as natural gas.
For coal to be clean and green, the industry needs technology which can capture and store carbon, to reduce emissions.
But solving that problem will take global coordination and billions of dollars in investment.
'Figuring out carbon capture is really critical - it may not work in the end - and if it is not viable, the situation with respect to climate change is far more dire,' said Mr Jeffrey Sachs, director of the Earth Institute at Columbia University.
Then there is the problem of storing the carbon. A large leak of underground carbon could be as dangerous as a leak of nuclear fuel, critics say.
NEW YORK TIMES