Ever since the late 1980s, James Rogers has been beating the drum for green energy as an answer to global warming, putting him in the vanguard of climate-change activists. But what’s most remarkable is that Rogers happens to be the CEO of Duke Energy Corp., the huge electric and gas utility that ranks among the U.S.’s biggest emitters of carbon dioxide.

Moreover, that dubious distinction is one the Charlotte, North Carolina, utility won’t be relinquishing any time soon. It is the only power company in the U.S. that is simultaneously building two coal-burning plants, which are due to come online in 2012. And coal, although it is both abundant and cheap, is a notorious pollutant compared with natural gas or nuclear power.

What explains the apparent paradox between Rogers’s green persona and Duke’s seemingly retrograde strategy? A self-proclaimed pragmatist, he argues that a climate-friendly future will require a 40-year forced march. So how do new coal plants fit into this scenario?

Rogers frames the history of power generation as one big cleanup effort. “When people were burning coal and wood in the fireplace and using kerosene lights, going to electricity automatically cleaned up the cities,” he points out. Then the Clean Air Acts and subsequent amendments got utilities to clean up power plants. Now that coal plants built in the 1970s and ’80s are reaching the end of their lives, Rogers says, the U.S. will have to build fewer but more-efficient coal and other types of power plants to carry consumers into the brave new world of alternative energy sources that he envisions arriving around 2050. (The coal plants under construction by Duke are efficient enough to qualify for a combined $258.5 million in clean-coal tax credits.)

In the meantime, Duke Energy must serve a big and growing marketplace. It supplies electricity to 4 million retail customers in the Carolinas and the Midwest, and distributes natural gas in Ohio and Kentucky. Duke’s commercial unit operates power plants for municipalities, other utilities and industrial facilities. Its international division runs plants in Latin America. In addition, Duke has a portfolio of renewable-energy ventures — wind, solar and biomass — that now supply roughly 1,000 megawatts of the company’s nearly 40,000 megawatts. In all, some 40 percent of Duke’s power comes from noncarbon-producing sources, including water and nuclear energy.