In the long-running battle for the nation’s energy soul between green power and fossil fuels, victories are taken in measure. Despite their emergent success in recent years, renewables still have a long way to go to become the predominant power source.

Short of such a monumental tipping point, proponents celebrate other less dramatic, yet no less significant, indications that the historic advantage enjoyed by traditional power sources is slowly being chipped away. Such a milestone took place in February, when the Sierra Club announced the 100th coal-fired power plant is planned for retirement since January 2010.

By announcing its plans for retirement on that day, the Crawford Coal plant in Chicago earned the distinction of becoming the 100th coal plant to do so. Eight other plants in Chicago, Ohio and Pennsylvania also announced plans for retirement, which totals nearly one-fifth of the nation’s current fleet of coal-fired plants.

The environmental organization credited its “Beyond Coal” campaign for helping to raise awareness, increase community activism and ratchet up the pressure on the issue of coal-fired plants and the pollution they generate, which led to this important milestone. It also credited the campaign with helping to scuttle another 166 new coal plants nationwide, which have been proposed since 2002.

While the announcement can be taken as a sure sign that the times are changing for coal, it will be a long time, if ever, before this power source—which produces more than 40 percent of the United States’ energy—will be reduced to a minor role. Even the Sierra Club offers tacit admission of this. The ambitious yet realistic goal of the “Beyond Coal” campaign is to retire one-third of the nation’s coal plants by 2020.